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Yang J, Luo J, Li K, Li D, Lv T, Liu F, Liu Y, She F, He R, Zhang P. T-Wave Alternans Measured by 24-Hour Ambulatory Recordings Rather Than Exercise Stress Tests as a Risk Stratification Marker in Patients With Long QT Syndrome. J Am Heart Assoc 2024; 13:e033619. [PMID: 38979841 PMCID: PMC11292749 DOI: 10.1161/jaha.123.033619] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Accepted: 06/06/2024] [Indexed: 07/10/2024]
Abstract
BACKGROUND Few small-sample studies have quantified the T-wave alternans (TWA) value by 24-hour ambulatory recordings or exercise stress tests in patients with long QT syndrome (LQTS). The cutoff point of TWA ≥47 μV was based on patients with myocardial infarction. In our study, we aimed to (1) evaluate the association of TWA with life-threatening arrhythmic events (LAEs); (2) compare the predictive model of LAEs according to the TWA value measured by 24-hour ambulatory recordings and exercise stress tests; and (3) propose a cutoff point for the high risk of LAEs in patients with LQTS. METHODS AND RESULTS The study cohort included 110 patients with LQTS referred to our hospital, and the primary outcome was LAEs. Thirty-one patients with LQTS (31/110 [28.2%]) developed LAEs during the following 24 (12-47) months. Peak TWA value quantified from 12 leads by 24-hour ambulatory recordings in patients with LQTS with LAEs (LQTS-LAEs group) was significantly higher than LQTS without LAEs (LQTS-non-LAEs group) (64.0 [42.0-86.0] μV versus 43.0 [36.0-53.0] μV; P<0.01). There was no statistical difference in TWA value measured by exercise stress tests between the 2 groups (69.0 [54.5-127.5] μV versus 68.5 [53.3-99.8] μV; P=0.871). The new cutoff point of the peak TWA value measured by 24-hour ambulatory recordings was 55.5 μV, with a sensitivity of 75.0% and a specificity of 78.6%. A univariate Cox regression analysis revealed that TWA value ≥55.5 μV was a strong predictor of LAEs (hazard ratio [HR], 4.5 [2.1-9.6]; P<0.001]. A multivariate Cox regression analysis indicated that TWA value ≥55.5 μV remained significant (HR, 2.7 [1.1-6.8]; P=0.034). CONCLUSIONS Peak TWA measured by 24-hour ambulatory recordings was a more favorable risk stratification marker than exercise stress tests for patients with LQTS.
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Affiliation(s)
- Jing Yang
- Department of CardiologyBeijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua UniversityBeijingChina
| | - Jiangying Luo
- Department of CardiologyBeijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua UniversityBeijingChina
| | - Kun Li
- Department of CardiologyBeijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua UniversityBeijingChina
| | - Dan Li
- Department of CardiologyBeijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua UniversityBeijingChina
| | - Tingting Lv
- Department of CardiologyBeijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua UniversityBeijingChina
| | - Fulan Liu
- Department of CardiologyBeijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua UniversityBeijingChina
| | - Yuanwei Liu
- Department of CardiologyBeijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua UniversityBeijingChina
| | - Fei She
- Department of CardiologyBeijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua UniversityBeijingChina
| | - Rong He
- Department of CardiologyBeijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua UniversityBeijingChina
| | - Ping Zhang
- Department of CardiologyBeijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua UniversityBeijingChina
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2
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Abrahams T, Davies B, Laksman Z, Sy RW, Postema PG, Wilde AAM, Krahn AD, Han HC. Provocation testing in congenital long QT syndrome: A practical guide. Heart Rhythm 2023; 20:1570-1582. [PMID: 37481219 DOI: 10.1016/j.hrthm.2023.07.059] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/18/2023] [Revised: 07/01/2023] [Accepted: 07/14/2023] [Indexed: 07/24/2023]
Abstract
Congenital long QT syndrome (LQTS) is a hereditary cardiac channelopathy with an estimated prevalence of 1 in 2500. A prolonged resting QT interval corrected for heart rate (QTc interval) remains a key diagnostic component; however, the QTc value may be normal in up to 40% of patients with genotype-positive LQTS and borderline in a further 30%. Provocation of QTc prolongation and T-wave changes may be pivotal to unmasking the diagnosis and useful in predicting genotype. LQTS provocation testing involves assessment of repolarization during and after exercise, in response to changes in heart rate or autonomic tone, with patients with LQTS exhibiting a maladaptive repolarization response. We review the utility and strengths and limitations of 4 forms of provocation testing-stand-up test, exercise stress test, epinephrine challenge, and mental stress test-in diagnosing LQTS and provide some practical guidance for performing provocation testing. Ultimately, exercise testing, when feasible, is the most useful form of provocation testing when considering diagnostic sensitivity and specificity.
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Affiliation(s)
- Timothy Abrahams
- Victorian Heart Institute & Monash Health Heart, Victorian Heart Hospital, Monash University, Melbourne, Victoria, Australia
| | - Brianna Davies
- Center for Cardiovascular Innovation, Division of Cardiology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Zachary Laksman
- Center for Cardiovascular Innovation, Division of Cardiology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Raymond W Sy
- Faculty of Medicine and Health, The University of Sydney, Sydney, New South Wales, Australia
| | - Pieter G Postema
- Department of Cardiology, Amsterdam UMC location University of Amsterdam, Amsterdam, The Netherlands; Heart Failure & Arrhythmias, Amsterdam Cardiovascular Sciences, Amsterdam, The Netherlands; European Reference Network for Rare, Low Prevalence and Complex Diseases of the Heart (ERN GUARD-Heart), Academic Medical Center, Amsterdam, The Netherlands
| | - Arthur A M Wilde
- Department of Cardiology, Amsterdam UMC location University of Amsterdam, Amsterdam, The Netherlands; Heart Failure & Arrhythmias, Amsterdam Cardiovascular Sciences, Amsterdam, The Netherlands; European Reference Network for Rare, Low Prevalence and Complex Diseases of the Heart (ERN GUARD-Heart), Academic Medical Center, Amsterdam, The Netherlands
| | - Andrew D Krahn
- Center for Cardiovascular Innovation, Division of Cardiology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Hui-Chen Han
- Victorian Heart Institute & Monash Health Heart, Victorian Heart Hospital, Monash University, Melbourne, Victoria, Australia.
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Abstract
Cardiac alternans arises from dynamical instabilities in the electrical and calcium cycling systems of the heart, and often precedes ventricular arrhythmias and sudden cardiac death. In this review, we integrate clinical observations with theory and experiment to paint a holistic portrait of cardiac alternans: the underlying mechanisms, arrhythmic manifestations and electrocardiographic signatures. We first summarize the cellular and tissue mechanisms of alternans that have been demonstrated both theoretically and experimentally, including 3 voltage-driven and 2 calcium-driven alternans mechanisms. Based on experimental and simulation results, we describe their relevance to mechanisms of arrhythmogenesis under different disease conditions, and their link to electrocardiographic characteristics of alternans observed in patients. Our major conclusion is that alternans is not only a predictor, but also a causal mechanism of potentially lethal ventricular and atrial arrhythmias across the full spectrum of arrhythmia mechanisms that culminate in functional reentry, although less important for anatomic reentry and focal arrhythmias.
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Affiliation(s)
- Zhilin Qu
- Departments of Medicine (Cardiology), Physiology, and Computational Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA
| | - James N. Weiss
- Departments of Medicine (Cardiology), Physiology, and Computational Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA
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Qi D, Li W, Quan XQ, Gao Y, Wang J, Guo L, Zhao W, Liu T, Gao C, Yan GX. Alternating Early Afterdepolarizations Underlying Bradycardia-Dependent Macroscopic T Wave and Discordant Mechanical Alternans. Circ Arrhythm Electrophysiol 2023; 16:e011453. [PMID: 36595630 DOI: 10.1161/circep.122.011453] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
BACKGROUND Macroscopic T wave alternans (macro-TWA) often heralds the onset of Torsades de Pointes in patients with QT prolongation. However, the mechanisms underlying macro-TWA remain unclear. We examined the cellular and ionic basis for macro-TWA in rabbits with left ventricular hypertrophy (LVH). METHODS The renovascular hypertension model was used to induce LVH in rabbits. Action potentials were simultaneously recorded from epicardium and endocardium together with a transmural ECG and isometric contractility in arterially perfused left ventricular wedges. Late sodium current (INa-L) was recorded in single-isolated left ventricular myocytes with the whole cell patch-clamp technique. RESULTS Macro-TWA and accompanied mechanical alternans occurred spontaneously in 8 of 33 LVH rabbits (P<0.05, versus 0/15 in controls) and were induced by an INa-L enhancer ATX-II at 1 to 3 nM in additional 7. Macro-TWA and mechanical alternans occurred discordantly, that is, that longer QT interval and larger T wave were associated with weaker isometric contvractility. Alternating early afterdepolarizations in the endocardium caused macro-TWA in 12 of 15 LVH rabbits and, therefore, early afterdepolarization-dependent R-from-T extrasystoles and Torsades de Pointes always originated from the beats with longer QT and larger T wave during macro-TWA. INa-L density was significantly larger in LVH myocytes than that of control myocytes. Macro-TWA, mechanical alternans, R-from-T extrasystoles, and Torsades de Pointes were all abolished by INa-L blocker ranolazine or mexiletine. CONCLUSIONS LVH enhances INa-L density and promotes alternating early afterdepolarizations in the left ventricular endocardium that manifest as macro-TWA with discordant mechanical alternans. INa-L blockade abolishes macro-TWA, mechanical alternans, early afterdepolarization-dependent R-from-T extrasystoles, and Torsades de Pointes.
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Affiliation(s)
- Datun Qi
- Zhengzhou University People's Hospital and Central China Fuwai Hospital, Zhengzhou, China (D.Q., C.G., G.-X.Y.).,Lankenau Institute for Medical Research, Wynnewood, PA (D.Q., X.-Q.Q., Y.G., J.W., W.Z., G.-X.Y.)
| | - Wei Li
- Department of Cardiology, Xinhua Hospital, Shanghai, China (W.L.)
| | - Xiao-Qing Quan
- Lankenau Institute for Medical Research, Wynnewood, PA (D.Q., X.-Q.Q., Y.G., J.W., W.Z., G.-X.Y.)
| | - Yuan Gao
- Lankenau Institute for Medical Research, Wynnewood, PA (D.Q., X.-Q.Q., Y.G., J.W., W.Z., G.-X.Y.).,Henan University of Traditional Chinese Medicine, Zhengzhou, China (Y.G.)
| | - Jianyong Wang
- Lankenau Institute for Medical Research, Wynnewood, PA (D.Q., X.-Q.Q., Y.G., J.W., W.Z., G.-X.Y.).,TEDA International Cardiovascular Hospital, Tianjin, China (J.W.)
| | | | - Wenping Zhao
- Lankenau Institute for Medical Research, Wynnewood, PA (D.Q., X.-Q.Q., Y.G., J.W., W.Z., G.-X.Y.).,Affiliated Hospital of Hebei University, Baoding, China (W.Z.)
| | - Tong Liu
- Department of Cardiology, Second Hospital of Tianjin Medical University, China (T.L.)
| | - Chuanyu Gao
- Zhengzhou University People's Hospital and Central China Fuwai Hospital, Zhengzhou, China (D.Q., C.G., G.-X.Y.)
| | - Gan-Xin Yan
- Zhengzhou University People's Hospital and Central China Fuwai Hospital, Zhengzhou, China (D.Q., C.G., G.-X.Y.).,Lankenau Institute for Medical Research, Wynnewood, PA (D.Q., X.-Q.Q., Y.G., J.W., W.Z., G.-X.Y.).,Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, PA (G.-X.Y.)
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5
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Krahn AD, Laksman Z, Sy RW, Postema PG, Ackerman MJ, Wilde AAM, Han HC. Congenital Long QT Syndrome. JACC Clin Electrophysiol 2022; 8:687-706. [PMID: 35589186 DOI: 10.1016/j.jacep.2022.02.017] [Citation(s) in RCA: 27] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Revised: 02/16/2022] [Accepted: 02/16/2022] [Indexed: 12/14/2022]
Abstract
Congenital long QT syndrome (LQTS) encompasses a group of heritable conditions that are associated with cardiac repolarization dysfunction. Since its initial description in 1957, our understanding of LQTS has increased dramatically. The prevalence of LQTS is estimated to be ∼1:2,000, with a slight female predominance. The diagnosis of LQTS is based on clinical, electrocardiogram, and genetic factors. Risk stratification of patients with LQTS aims to identify those who are at increased risk of cardiac arrest or sudden cardiac death. Factors including age, sex, QTc interval, and genetic background all contribute to current risk stratification paradigms. The management of LQTS involves conservative measures such as the avoidance of QT-prolonging drugs, pharmacologic measures with nonselective β-blockers, and interventional approaches such as device therapy or left cardiac sympathetic denervation. In general, most forms of exercise are considered safe in adequately treated patients, and implantable cardioverter-defibrillator therapy is reserved for those at the highest risk. This review summarizes our current understanding of LQTS and provides clinicians with a practical approach to diagnosis and management.
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Affiliation(s)
- Andrew D Krahn
- Center for Cardiovascular Innovation, Heart Rhythm Services, Division of Cardiology, University of British Columbia, Vancouver, BC, Canada.
| | - Zachary Laksman
- Center for Cardiovascular Innovation, Heart Rhythm Services, Division of Cardiology, University of British Columbia, Vancouver, BC, Canada
| | - Raymond W Sy
- Faculty of Medicine and Health, The University of Sydney, Sydney, New South Wales, Australia
| | - Pieter G Postema
- Department of Clinical and Experimental Cardiology, Heart Center, Amsterdam University Medical Centers, Amsterdam, the Netherlands
| | - Michael J Ackerman
- Department of Cardiovascular Medicine, Division of Heart Rhythm Services, Windland Smith Rice Genetic Heart Rhythm Clinic, Mayo Clinic, Rochester, Minnesota, USA; Department of Pediatric and Adolescent Medicine, Division of Pediatric Cardiology, Mayo Clinic, Rochester, Minnesota, USA; Departments of Molecular Pharmacology and Experimental Therapeutics, Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, Minnesota, USA
| | - Arthur A M Wilde
- Department of Clinical and Experimental Cardiology, Heart Center, Amsterdam University Medical Centers, Amsterdam, the Netherlands; European Reference Network for Rare and Low Prevalence Complex Diseases of the Heart (ERN GUARD-Heart), Academic University Medical Center, Amsterdam, the Netherlands
| | - Hui-Chen Han
- Center for Cardiovascular Innovation, Heart Rhythm Services, Division of Cardiology, University of British Columbia, Vancouver, BC, Canada; Victorian Heart Institute, Monash University, Clayton, VIC, Australia
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6
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Ola O, Gharacholou SM, Del-Carpio Munoz F. Massive Discordant T-Wave Alternans and Imminent Torsades de Pointes: The "Elephant in the Room". JAMA Intern Med 2021; 181:1393-1395. [PMID: 34459879 DOI: 10.1001/jamainternmed.2021.4021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Affiliation(s)
- Olatunde Ola
- Division of Hospital Medicine, Mayo Clinic Health System, La Crosse, Wisconsin.,Center for Clinical and Translational Science, Mayo Clinic Graduate School of Biomedical Sciences, Rochester, Minnesota
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7
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Munshi F, Fontaine JM. Application of Electromechanical Window Negativity as an Arrhythmia Risk Correlate in Acquired Long QT Syndrome. JACC Case Rep 2021; 3:1427-1433. [PMID: 34557686 PMCID: PMC8446257 DOI: 10.1016/j.jaccas.2021.07.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2021] [Revised: 07/08/2021] [Accepted: 07/15/2021] [Indexed: 11/03/2022]
Abstract
Long QT syndrome is a congenital or acquired condition associated with life-threatening cardiac arrhythmias. Risk stratification measures are paramount to providing life-saving therapy. We present a case of a 30-year-old man with syncope and polymorphic ventricular tachycardia from drug-induced QTc prolongation. Electromechanical window negativity correlated with arrhythmia risk and risk predictors. (Level of Difficulty: Advanced.).
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Affiliation(s)
- Farhan Munshi
- Cardiology Division, Electrophysiology Section, University of Pittsburgh Medical Center, Williamsport Campus, Williamsport, Pennsylvania, USA
| | - John M Fontaine
- Cardiology Division, Electrophysiology Section, University of Pittsburgh Medical Center, Williamsport Campus, Williamsport, Pennsylvania, USA
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8
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Hornyik T, Rieder M, Castiglione A, Major P, Baczko I, Brunner M, Koren G, Odening KE. Transgenic rabbit models for cardiac disease research. Br J Pharmacol 2021; 179:938-957. [PMID: 33822374 DOI: 10.1111/bph.15484] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Revised: 02/23/2021] [Accepted: 03/11/2021] [Indexed: 12/20/2022] Open
Abstract
To study the pathophysiology of human cardiac diseases and to develop novel treatment strategies, complex interactions of cardiac cells on cellular, tissue and on level of the whole heart need to be considered. As in vitro cell-based models do not depict the complexity of the human heart, animal models are used to obtain insights that can be translated to human diseases. Mice are the most commonly used animals in cardiac research. However, differences in electrophysiological and mechanical cardiac function and a different composition of electrical and contractile proteins limit the transferability of the knowledge gained. Moreover, the small heart size and fast heart rate are major disadvantages. In contrast to rodents, electrophysiological, mechanical and structural cardiac characteristics of rabbits resemble the human heart more closely, making them particularly suitable as an animal model for cardiac disease research. In this review, various methodological approaches for the generation of transgenic rabbits for cardiac disease research, such as pronuclear microinjection, the sleeping beauty transposon system and novel genome-editing methods (ZFN and CRISPR/Cas9)will be discussed. In the second section, we will introduce the different currently available transgenic rabbit models for monogenic cardiac diseases (such as long QT syndrome, short-QT syndrome and hypertrophic cardiomyopathy) in detail, especially in regard to their utility to increase the understanding of pathophysiological disease mechanisms and novel treatment options.
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Affiliation(s)
- Tibor Hornyik
- Translational Cardiology, Department of Cardiology, Inselspital, Bern University Hospital, and Institute of Physiology, University of Bern, Bern, Switzerland.,Department of Cardiology and Angiology I, University Heart Center, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Marina Rieder
- Translational Cardiology, Department of Cardiology, Inselspital, Bern University Hospital, and Institute of Physiology, University of Bern, Bern, Switzerland
| | - Alessandro Castiglione
- Translational Cardiology, Department of Cardiology, Inselspital, Bern University Hospital, and Institute of Physiology, University of Bern, Bern, Switzerland
| | - Peter Major
- Institute for Genetics and Biotechnology, Hungarian University of Agriculture and Life Sciences, Gödöllő, Hungary
| | - Istvan Baczko
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Szeged, Hungary
| | - Michael Brunner
- Department of Cardiology and Angiology I, University Heart Center, Faculty of Medicine, University of Freiburg, Freiburg, Germany.,Department of Cardiology and Medical Intensive Care, St. Josefskrankenhaus, Freiburg, Germany
| | - Gideon Koren
- Cardiovascular Research Center, Division of Cardiology, Rhode Island Hospital, Alpert Medical School of Brown University, Providence, Rhode Island, USA
| | - Katja E Odening
- Translational Cardiology, Department of Cardiology, Inselspital, Bern University Hospital, and Institute of Physiology, University of Bern, Bern, Switzerland.,Department of Cardiology and Angiology I, University Heart Center, Faculty of Medicine, University of Freiburg, Freiburg, Germany
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9
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Karadeniz C. Importance of electrocardiographic markers in predicting cardiac events in children. Biomark Med 2020; 14:1679-1689. [PMID: 33336595 DOI: 10.2217/bmm-2020-0391] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
ECG is a common diagnostic tool in medical practice. Sudden cardiac death (SCD) is a rare but devastating event. The most common cause of SCD in the young is a primary arrhythmic event, which is often produced by malignant ventricular arrhythmia. Several electrocardiographic markers for ventricular repolarization and depolarization have been proposed to predict this arrhythmic risk and SCD in children. Although many of these parameters can easily be used in clinical practice, some of them need specific techniques for interpretation. In this review, we summarized the current knowledge regarding the clinical importance and the ability of these ECG parameters to predict adverse cardiac events in the pediatric population.
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Affiliation(s)
- Cem Karadeniz
- Department of Pediatric Cardiology, Pediatric Arrhythmia & Electrophysiology, School of Medicine, Kâtip Celebi University, Izmir, Turkey
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10
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Huang C, Song Z, Di Z, Qu Z. Stability of spatially discordant repolarization alternans in cardiac tissue. CHAOS (WOODBURY, N.Y.) 2020; 30:123141. [PMID: 33380024 PMCID: PMC7928074 DOI: 10.1063/5.0029209] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Accepted: 11/18/2020] [Indexed: 06/02/2023]
Abstract
Cardiac alternans, a period-2 behavior of excitation and contraction of the heart, is a precursor of ventricular arrhythmias and sudden cardiac death. One form of alternans is repolarization or action potential duration alternans. In cardiac tissue, repolarization alternans can be spatially in-phase, called spatially concordant alternans, or spatially out-of-phase, called spatially discordant alternans (SDA). In SDA, the border between two out-of-phase regions is called a node in a one-dimensional cable or a nodal line in a two-dimensional tissue. In this study, we investigate the stability and dynamics of the nodes and nodal lines of repolarization alternans driven by voltage instabilities. We use amplitude equation and coupled map lattice models to derive theoretical results, which are compared with simulation results from the ionic model. Both conduction velocity restitution induced SDA and non-conduction velocity restitution induced SDA are investigated. We show that the stability and dynamics of the SDA nodes or nodal lines are determined by the balance of the tensions generated by conduction velocity restitution, convection due to action potential propagation, curvature of the nodal lines, and repolarization and coupling heterogeneities. Our study provides mechanistic insights into the different SDA behaviors observed in experiments.
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Affiliation(s)
| | - Zhen Song
- Department of Medicine, University of California, Los Angeles, California 90095, USA
| | - Zengru Di
- Department of Systems Science, Beijing Normal University, Beijing 100875, China
| | - Zhilin Qu
- Author to whom correspondence should be addressed:
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11
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Huang C, Song Z, Landaw J, Qu Z. Spatially Discordant Repolarization Alternans in the Absence of Conduction Velocity Restitution. Biophys J 2020; 118:2574-2587. [PMID: 32101718 DOI: 10.1016/j.bpj.2020.02.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 01/21/2020] [Accepted: 02/06/2020] [Indexed: 01/20/2023] Open
Abstract
Spatially discordant alternans (SDA) of action potential duration (APD) has been widely observed in cardiac tissue and is linked to cardiac arrhythmogenesis. Theoretical studies have shown that conduction velocity restitution (CVR) is required for the formation of SDA. However, this theory is not completely supported by experiments, indicating that other mechanisms may exist. In this study, we carried out computer simulations using mathematical models of action potentials to investigate the mechanisms of SDA in cardiac tissue. We show that when CVR is present and engaged, such as fast pacing from one side of the tissue, the spatial pattern of APD in the tissue undergoes either spatially concordant alternans or SDA, independent of initial conditions or tissue heterogeneities. When CVR is not engaged, such as simultaneous pacing of the whole tissue or under normal/slow heart rates, the spatial pattern of APD in the tissue can have multiple solutions, including spatially concordant alternans and different SDA patterns, depending on heterogeneous initial conditions or pre-existing repolarization heterogeneities. In homogeneous tissue, curved nodal lines are not stable, which either evolve into straight lines or disappear. However, in heterogeneous itssue, curved nodal lines can be stable, depending on their initial locations and shapes relative to the structure of the heterogeneity. Therefore, CVR-induced SDA and non-CVR-induced SDA exhibit different dynamical properties, which may be responsible for the different SDA properties observed in experimental studies and arrhythmogenesis in different clinical settings.
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Affiliation(s)
- Chunli Huang
- Department of Medicine, University of California, Los Angeles, Los Angeles, California; Department of Systems Science, Beijing Normal University, Beijing, China
| | - Zhen Song
- Department of Medicine, University of California, Los Angeles, Los Angeles, California
| | - Julian Landaw
- Department of Medicine, University of California, Los Angeles, Los Angeles, California
| | - Zhilin Qu
- Department of Medicine, University of California, Los Angeles, Los Angeles, California; Department of Computational Medicine, University of California, Los Angeles, Los Angeles, California.
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12
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Marcantoni I, Sbrollini A, Agostinelli G, Surace FC, Colaneri M, Morettini M, Pozzi M, Burattini L. T-Wave Alternans in Nonpathological Preterm Infants. Ann Noninvasive Electrocardiol 2020; 25:e12745. [PMID: 31986237 PMCID: PMC7358874 DOI: 10.1111/anec.12745] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/03/2019] [Revised: 12/17/2019] [Accepted: 12/30/2019] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND Sudden infant death syndrome is more frequent in preterm infants (PTI) than term infants and may be due to cardiac repolarization instability, which may manifest as T-wave alternans (TWA) on the electrocardiogram (ECG). Therefore, the aim of the present work was to analyze TWA in nonpathological PTI and to open an issue on its physiological interpretation. METHODS Clinical population consisted of ten nonpathological PTI (gestational age ranging from 29 3 7 to 34 2 7 weeks; birth weight ranging from 0.84 to 2.10 kg) from whom ECG recordings were obtained ("Preterm infant cardio-respiratory signals database" by Physionet). TWA was identified through the heart-rate adapting match filter method and characterized in terms of mean amplitude values (TWAA). TWA correlation with several other clinical and ECG features, among which gestational age-birth weight ratio, RR interval, heart-rate variability, and QT interval, was also performed. RESULTS TWA was variable among infants (TWAA = 26 ± 11 µV). Significant correlations were found between TWAA versus birth weight (ρ = -0.72, p = .02), TWAA versus gestational age-birth weight ratio (ρ = 0.76, p = .02) and TWAA versus heart-rate variability (ρ = -0.71, p = .02). CONCLUSIONS Our preliminary retrospective study suggests that nonpathological PTI show TWA of few tens of µV, the interpretation of which is still an open issue but could indicate a condition of cardiac risk possibly related to the low development status of the infant. Further investigations are needed to solve this issue.
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Affiliation(s)
- Ilaria Marcantoni
- Department of Information Engineering, Università Politecnica delle Marche, Ancona, Italy
| | - Agnese Sbrollini
- Department of Information Engineering, Università Politecnica delle Marche, Ancona, Italy
| | - Gloria Agostinelli
- Department of Information Engineering, Università Politecnica delle Marche, Ancona, Italy
| | - Francesca Chiara Surace
- Department of Paediatric and Congenital Cardiac Surgery and Cardiology, Ospedali Riuniti, Ancona, Italy
| | - Massimo Colaneri
- Department of Paediatric and Congenital Cardiac Surgery and Cardiology, Ospedali Riuniti, Ancona, Italy
| | - Micaela Morettini
- Department of Information Engineering, Università Politecnica delle Marche, Ancona, Italy
| | - Marco Pozzi
- Department of Paediatric and Congenital Cardiac Surgery and Cardiology, Ospedali Riuniti, Ancona, Italy
| | - Laura Burattini
- Department of Information Engineering, Università Politecnica delle Marche, Ancona, Italy
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Liu MB, Vandersickel N, Panfilov AV, Qu Z. R-From-T as a Common Mechanism of Arrhythmia Initiation in Long QT Syndromes. Circ Arrhythm Electrophysiol 2019; 12:e007571. [PMID: 31838916 PMCID: PMC6924944 DOI: 10.1161/circep.119.007571] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Accepted: 09/24/2019] [Indexed: 02/07/2023]
Abstract
BACKGROUND Long QT syndromes (LQTS) arise from many genetic and nongenetic causes with certain characteristic ECG features preceding polymorphic ventricular tachyarrhythmias (PVTs). However, how the many molecular causes result in these characteristic ECG patterns and how these patterns are mechanistically linked to the spontaneous initiation of PVT remain poorly understood. METHODS Anatomic human ventricle and simplified tissue models were used to investigate the mechanisms of spontaneous initiation of PVT in LQTS. RESULTS Spontaneous initiation of PVT was elicited by gradually ramping up ICa,L to simulate the initial phase of a sympathetic surge or by changing the heart rate, reproducing the different genotype-dependent clinical ECG features. In LQTS type 2 (LQT2) and LQTS type 3 (LQT3), T-wave alternans was observed followed by premature ventricular complexes (PVCs). Compensatory pauses occurred resulting in short-long-short sequences. As ICa,L increased further, PVT episodes occurred, always preceded by a short-long-short sequence. However, in LQTS type 1 (LQT1), once a PVC occurred, it always immediately led to an episode of PVT. Arrhythmias in LQT2 and LQT3 were bradycardia dependent, whereas those in LQT1 were not. In all 3 genotypes, PVCs always originated spontaneously from the steep repolarization gradient region and manifested on ECG as R-on-T. We call this mechanism R-from-T, to distinguish it from the classic explanation of R-on-T arrhythmogenesis in which an exogenous PVC coincidentally encounters a repolarizing region. In R-from-T, the PVC and the T wave are causally related, where steep repolarization gradients combined with enhanced ICa,L lead to PVCs emerging from the T wave. Since enhanced ICa,L was required for R-from-T to occur, suppressing window ICa,L effectively prevented arrhythmias in all 3 genotypes. CONCLUSIONS Despite the complex molecular causes, these results suggest that R-from-T is likely a common mechanism for PVT initiation in LQTS. Targeting ICa,L properties, such as suppressing window ICa,L or preventing excessive ICa,L increase, could be an effective unified therapy for arrhythmia prevention in LQTS.
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Affiliation(s)
- Michael B. Liu
- Department of Medicine (M.B.L., Z.Q.), University of California, Los Angeles
| | - Nele Vandersickel
- Department of Physics and Astronomy, Ghent University, Belgium (N.V., A.V.P.)
| | - Alexander V. Panfilov
- Department of Physics and Astronomy, Ghent University, Belgium (N.V., A.V.P.)
- Laboratory of Computational Biology and Medicine, Ural Federal University, Ekaterinburg, Russia (A.V.P.)
| | - Zhilin Qu
- Department of Medicine (M.B.L., Z.Q.), University of California, Los Angeles
- Department of Biomathematics (Z.Q.), University of California, Los Angeles
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14
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Brüggemann B, Djajadisastra I, Duncker D, Eitel C, Fink T, Grimm W, Heeger C, Israel CW, Müller-Leisse J, Sheta MK, Sinha AM, Tilz RR, Veltmann C, Vogler J, Zormpas C. [Canalopathies, arrhythmogenic right ventricular cardiomyopathy and artefacts]. Herzschrittmacherther Elektrophysiol 2019; 30:51-71. [PMID: 30825043 DOI: 10.1007/s00399-019-0611-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2018] [Accepted: 01/29/2019] [Indexed: 06/09/2023]
Affiliation(s)
- B Brüggemann
- Medizinische Klinik II/Kardiologie, Angiologie und Intensivmedizin, Universitätsklinikum Schleswig-Holstein, Campus Lübeck, Ratzeburger Allee 160, Haus 40, 23538, Lübeck, Deutschland
| | - I Djajadisastra
- Abteilung Rhythmologie, Klinik für Innere Medizin I, St.-Johannes-Hospital Dortmund, Johannesstr. 9-17, 44137, Dortmund, Deutschland.
| | - D Duncker
- Rhythmologie und Elektrophysiologie, Klinik für Kardiologie und Angiologie, Medizinische Hochschule Hannover, Carl-Neuberg-Str. 1, 30625, Hannover, Deutschland.
| | - C Eitel
- Medizinische Klinik II/Kardiologie, Angiologie und Intensivmedizin, Universitätsklinikum Schleswig-Holstein, Campus Lübeck, Ratzeburger Allee 160, Haus 40, 23538, Lübeck, Deutschland
| | - T Fink
- Medizinische Klinik II/Kardiologie, Angiologie und Intensivmedizin, Universitätsklinikum Schleswig-Holstein, Campus Lübeck, Ratzeburger Allee 160, Haus 40, 23538, Lübeck, Deutschland
| | - W Grimm
- Universititätsklinik Marburg, Klinik für Innere Medizin - Kardiologie, Angiologie und Intensivmedizin, UKGM Gießen und Marburg, Standort Marburg, Baldingerstraße, 35033, Marburg, Deutschland.
| | - C Heeger
- Medizinische Klinik II/Kardiologie, Angiologie und Intensivmedizin, Universitätsklinikum Schleswig-Holstein, Campus Lübeck, Ratzeburger Allee 160, Haus 40, 23538, Lübeck, Deutschland
| | - C W Israel
- Klinik für Innere Medizin - Kardiologie, Diabetologie & Nephrologie, Ev. Klinikum Bethel, Burgsteig 13, 33617, Bielefeld, Deutschland.
| | - J Müller-Leisse
- Rhythmologie und Elektrophysiologie, Klinik für Kardiologie und Angiologie, Medizinische Hochschule Hannover, Carl-Neuberg-Str. 1, 30625, Hannover, Deutschland
| | - M K Sheta
- Klinik für Kardiologie, Nephrologie, Pneumologie und Internistische Intensivmedizin, Sana Klinikum Hof GmbH, 95032, Eppenreuther Str. 9, Hof, Deutschland
| | - A M Sinha
- Klinik für Kardiologie, Nephrologie, Pneumologie und Internistische Intensivmedizin, Sana Klinikum Hof GmbH, 95032, Eppenreuther Str. 9, Hof, Deutschland.
| | - R R Tilz
- Medizinische Klinik II/Kardiologie, Angiologie und Intensivmedizin, Universitätsklinikum Schleswig-Holstein, Campus Lübeck, Ratzeburger Allee 160, Haus 40, 23538, Lübeck, Deutschland.
| | - C Veltmann
- Rhythmologie und Elektrophysiologie, Klinik für Kardiologie und Angiologie, Medizinische Hochschule Hannover, Carl-Neuberg-Str. 1, 30625, Hannover, Deutschland
| | - J Vogler
- Medizinische Klinik II/Kardiologie, Angiologie und Intensivmedizin, Universitätsklinikum Schleswig-Holstein, Campus Lübeck, Ratzeburger Allee 160, Haus 40, 23538, Lübeck, Deutschland
| | - C Zormpas
- Rhythmologie und Elektrophysiologie, Klinik für Kardiologie und Angiologie, Medizinische Hochschule Hannover, Carl-Neuberg-Str. 1, 30625, Hannover, Deutschland
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15
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Tse G, Gong M, Meng L, Wong CW, Bazoukis G, Chan MTV, Wong MCS, Letsas KP, Baranchuk A, Yan GX, Liu T, Wu WKK. Predictive Value of T peak - T end Indices for Adverse Outcomes in Acquired QT Prolongation: A Meta-Analysis. Front Physiol 2018; 9:1226. [PMID: 30233403 PMCID: PMC6129769 DOI: 10.3389/fphys.2018.01226] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Accepted: 08/14/2018] [Indexed: 01/13/2023] Open
Abstract
Background: Acquired QT interval prolongation has been linked with malignant ventricular arrhythmias, such as torsade de pointes, in turn predisposing to sudden cardiac death. Increased dispersion of repolarization has been identified as a pro-arrhythmic factor and can be observed as longer Tpeak - Tend interval and higher Tpeak - Tend/QT ratio on the electrocardiogram. However, the values of these repolarization indices for predicting adverse outcomes in this context have not been systematically evaluated. Method: PubMed, Embase and Cochrane Library databases were searched until 14th February 2018, identifying 232 studies. Results: Five studies on acquired QT prolongation met the inclusion criteria and 308 subjects with drug-induced LQTS patients (mean age: 66 ± 18 years old; 46% male) were included in this meta-analysis. Tpeak - Tend intervals were longer [mean difference [MD]: 76 ms, standard error [SE]: 26 ms, P = 0.003; I2 = 98%] and Tpeak - Tend/QT ratios were higher (MD: 0.14, SE: 0.03, P = 0.000; I2 = 29%) in patients with torsade de pointes compared to those without these events. Conclusion: Tpeak - Tend interval and Tpeak - Tend/QT ratio were higher in patients with acquired QT prolongation suffering from torsade de pointes compared to those who did not. These repolarization indices may provide additional predictive value for identifying high-risk individuals.
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Affiliation(s)
- Gary Tse
- Department of Medicine and Therapeutics, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, Hong Kong.,Li Ka Shing Institute of Health Sciences, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, Hong Kong
| | - Mengqi Gong
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical University, Tianjin, Hong Kong
| | - Lei Meng
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical University, Tianjin, Hong Kong
| | - Cheuk W Wong
- Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, Hong Kong
| | - George Bazoukis
- Laboratory of Cardiac Electrophysiology, Second Department of Cardiology, Evangelismos General Hospital of Athens, Athens, Greece
| | - Matthew T V Chan
- Department of Anaesthesia and Intensive Care, Chinese University of Hong Kong, Hong Kong, Hong Kong
| | - Martin C S Wong
- JC School of Public Health and Primary Care, Chinese University of Hong Kong, Hong Kong, Hong Kong
| | - Konstantinos P Letsas
- Laboratory of Cardiac Electrophysiology, Second Department of Cardiology, Evangelismos General Hospital of Athens, Athens, Greece
| | - Adrian Baranchuk
- Division of Cardiology, Kingston General Hospital, Queen's University, Kingston, ON, Canada
| | - Gan-Xin Yan
- Lankenau Institute for Medical Research and Lankenau Medical Center, Wynnewood, PA, United States.,Beijing Anzhen Hospital, Capital Medical University, Beijing, China
| | - Tong Liu
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical University, Tianjin, Hong Kong
| | - William K K Wu
- Department of Anaesthesia and Intensive Care, Chinese University of Hong Kong, Hong Kong, Hong Kong
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16
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Lane CM, Bos JM, Rohatgi RK, Ackerman MJ. Beyond the length and look of repolarization: Defining the non-QTc electrocardiographic profiles of patients with congenital long QT syndrome. Heart Rhythm 2018; 15:1413-1419. [DOI: 10.1016/j.hrthm.2018.04.033] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Indexed: 10/17/2022]
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17
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Liu W, Kim TY, Huang X, Liu MB, Koren G, Choi BR, Qu Z. Mechanisms linking T-wave alternans to spontaneous initiation of ventricular arrhythmias in rabbit models of long QT syndrome. J Physiol 2018; 596:1341-1355. [PMID: 29377142 DOI: 10.1113/jp275492] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Accepted: 01/23/2018] [Indexed: 01/23/2023] Open
Abstract
KEY POINTS T-wave alternans (TWA) and T-wave lability (TWL) are precursors of ventricular arrhythmias in long QT syndrome; however, the mechanistic link remains to be clarified. Computer simulations show that action potential duration (APD) prolongation and slowed heart rates promote APD alternans and chaos, manifesting as TWA and TWL, respectively. Regional APD alternans and chaos can exacerbate pre-existing or induce de novo APD dispersion, which combines with enhanced ICa,L to result in premature ventricular complexes (PVCs) originating from the APD gradient region. These PVCs can directly degenerate into re-entrant arrhythmias without the need for an additional tissue substrate or further exacerbate the APD dispersion to cause spontaneous initiation of ventricular arrhythmias. Experiments conducted in transgenic long QT rabbits show that PVC alternans occurs at slow heart rates, preceding spontaneous intuition of ventricular arrhythmias. ABSTRACT T-wave alternans (TWA) and irregular beat-to-beat T-wave variability or T-wave lability (TWL), the ECG manifestations of action potential duration (APD) alternans and variability, are precursors of ventricular arrhythmias in long QT syndromes. TWA and TWL in patients tend to occur at normal heart rates and are usually potentiated by bradycardia. Whether or how TWA and TWL at normal or slow heart rates are causally linked to arrhythmogenesis remains unknown. In the present study, we used computer simulations and experiments of a transgenic rabbit model of long QT syndrome to investigate the underlying mechanisms. Computer simulations showed that APD prolongation and slowed heart rates caused early afterdepolarization-mediated APD alternans and chaos, manifesting as TWA and TWL, respectively. Regional APD alternans and chaos exacerbated pre-existing APD dispersion and, in addition, APD chaos could also induce APD dispersion de novo via chaos desynchronization. Increased APD dispersion, combined with substantially enhanced ICa,L , resulted in a tissue-scale dynamical instability that gave rise to the spontaneous occurrence of unidirectionally propagating premature ventricular complexes (PVCs) originating from the APD gradient region. These PVCs could directly degenerate into re-entrant arrhythmias without the need for an additional tissue substrate or could block the following sinus beat to result in a longer RR interval, which further exacerbated the APD dispersion giving rise to the spontaneous occurrence of ventricular arrhythmias. Slow heart rate-induced PVC alternans was observed in experiments of transgenic LQT2 rabbits under isoproterenol, which was associated with increased APD dispersion and spontaneous occurrence of ventricular arrhythmias, in agreement with the theoretical predictions.
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Affiliation(s)
- Weiqing Liu
- Department of Medicine, University of California, Los Angeles, California, USA.,School of Science, Jiangxi University of Science and Technology, Ganzhou, China
| | - Tae Yun Kim
- Cardiovascular Research Center, Division of Cardiology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA
| | - Xiaodong Huang
- Department of Medicine, University of California, Los Angeles, California, USA.,Department of Physics, South China University of Technology, Guangzhou, China
| | - Michael B Liu
- Department of Medicine, University of California, Los Angeles, California, USA
| | - Gideon Koren
- Cardiovascular Research Center, Division of Cardiology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA
| | - Bum-Rak Choi
- Cardiovascular Research Center, Division of Cardiology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA
| | - Zhilin Qu
- Department of Medicine, University of California, Los Angeles, California, USA.,Department of Biomathematics, University of California, Los Angeles, California, USA
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18
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T-wave Alternans and Long QT Syndrome. Anesthesiology 2018; 127:567. [PMID: 28346324 DOI: 10.1097/aln.0000000000001618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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19
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Abstract
Long QT syndrome (LQTS) is a congenital disorder characterized by prolongation of QT interval in the electrocardiogram (ECG) and a propensity to develop ventricular arrhythmias, which may lead to syncope, cardiac arrest or sudden death. T-wave alternans (TWA), a phenomenon of beat-to-beat variability in the repolarization phase of the ventricles, has been closely associated with an increased risk of ventricular tachyarrhythmic events (VTE) and sudden cardiac death (SCD).
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Affiliation(s)
- Siddharth Narayan Gadage
- Department of Cardiology, Division of Pediatric Cardiology, Ruby Hall Clinic, Pune, Maharashtra, India
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20
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Tunca Sahin G, Ergul Y. A case report: Is mexiletine usage effective in the shortening of QTC interval and improving the T-wave alternans in Timothy syndrome? Ann Noninvasive Electrocardiol 2017; 23:e12522. [PMID: 29194862 DOI: 10.1111/anec.12522] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Accepted: 10/14/2017] [Indexed: 01/12/2023] Open
Abstract
Timothy syndrome (TS) is a multisystemic disease that occurs because of a mutation in CACN1C gene and is characterized by prolonged QT interval. Mexiletine is a Class 1B antiarrhythmic drug that causes the disappearance of T-wave alternans by shortening QTc and peak-to-end of the T wave. It may block the development of torsades de pointes in a prolonged QT. This study presented the case of a patient diagnosed with TS and had a cardiac arrest history, prolonged QT, and T-wave alternans. After mexiletine treatment, the QTc interval shortened and T-wave alternans disappeared. Such a case has rarely been seen in the literature, and hence considered rare. This case presentation was of particular importance because it highlighted the use of mexiletine besides an initial beta-blocker treatment in the cases with TS.
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Affiliation(s)
- Gulhan Tunca Sahin
- Department of Pediatric Cardiology, Istanbul Mehmet Akif Ersoy Thoracic and Cardiovascular Surgery Education and Research Hospital, Istanbul Saglik Bilimleri University, Istanbul, Turkey
| | - Yakup Ergul
- Department of Pediatric Cardiology, Istanbul Mehmet Akif Ersoy Thoracic and Cardiovascular Surgery Education and Research Hospital, Istanbul Saglik Bilimleri University, Istanbul, Turkey
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21
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Uzelac I, Ji YC, Hornung D, Schröder-Scheteling J, Luther S, Gray RA, Cherry EM, Fenton FH. Simultaneous Quantification of Spatially Discordant Alternans in Voltage and Intracellular Calcium in Langendorff-Perfused Rabbit Hearts and Inconsistencies with Models of Cardiac Action Potentials and Ca Transients. Front Physiol 2017; 8:819. [PMID: 29104543 PMCID: PMC5655020 DOI: 10.3389/fphys.2017.00819] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Accepted: 10/05/2017] [Indexed: 02/03/2023] Open
Abstract
Rationale: Discordant alternans, a phenomenon in which the action potential duration (APDs) and/or intracellular calcium transient durations (CaDs) in different spatial regions of cardiac tissue are out of phase, present a dynamical instability for complex spatial dispersion that can be associated with long-QT syndrome (LQTS) and the initiation of reentrant arrhythmias. Because the use of numerical simulations to investigate arrhythmic effects, such as acquired LQTS by drugs is beginning to be studied by the FDA, it is crucial to validate mathematical models that may be used during this process. Objective: In this study, we characterized with high spatio-temporal resolution the development of discordant alternans patterns in transmembrane voltage (Vm) and intracellular calcium concentration ([Cai]+2) as a function of pacing period in rabbit hearts. Then we compared the dynamics to that of the latest state-of-the-art model for ventricular action potentials and calcium transients to better understand the underlying mechanisms of discordant alternans and compared the experimental data to the mathematical models representing Vm and [Cai]+2 dynamics. Methods and Results: We performed simultaneous dual optical mapping imaging of Vm and [Cai]+2 in Langendorff-perfused rabbit hearts with higher spatial resolutions compared with previous studies. The rabbit hearts developed discordant alternans through decreased pacing period protocols and we quantified the presence of multiple nodal points along the direction of wave propagation, both in APD and CaD, and compared these findings with results from theoretical models. In experiments, the nodal lines of CaD alternans have a steeper slope than those of APD alternans, but not as steep as predicted by numerical simulations in rabbit models. We further quantified several additional discrepancies between models and experiments. Conclusions: Alternans in CaD have nodal lines that are about an order of magnitude steeper compared to those of APD alternans. Current action potential models lack the necessary coupling between voltage and calcium compared to experiments and fail to reproduce some key dynamics such as, voltage amplitude alternans, smooth development of calcium alternans in time, conduction velocity and the steepness of the nodal lines of APD and CaD.
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Affiliation(s)
- Ilija Uzelac
- School of Physics, Georgia Institute of Technology, Atlanta, GA, United States
| | - Yanyan C. Ji
- School of Physics, Georgia Institute of Technology, Atlanta, GA, United States
| | - Daniel Hornung
- Max Planck Institute for Dynamics and Self-Organization, Gottingen, Germany
| | | | - Stefan Luther
- Max Planck Institute for Dynamics and Self-Organization, Gottingen, Germany
| | - Richard A. Gray
- Center for Device and Radiological Health, Food and Drug Administration, Silver Spring, MD, United States
| | - Elizabeth M. Cherry
- School of Mathematical Sciences, Rochester Institute of Technology, Rochester, NY, United States
| | - Flavio H. Fenton
- School of Physics, Georgia Institute of Technology, Atlanta, GA, United States
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22
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Es-Salah-Lamoureux Z, Jouni M, Malak OA, Belbachir N, Al Sayed ZR, Gandon-Renard M, Lamirault G, Gauthier C, Baró I, Charpentier F, Zibara K, Lemarchand P, Beaumelle B, Gaborit N, Loussouarn G. HIV-Tat induces a decrease in I Kr and I Ks via reduction in phosphatidylinositol-(4,5)-bisphosphate availability. J Mol Cell Cardiol 2016; 99:1-13. [DOI: 10.1016/j.yjmcc.2016.08.022] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Revised: 08/23/2016] [Accepted: 08/29/2016] [Indexed: 02/07/2023]
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23
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Abstract
In this review article, we will explore some of the contemporary methods for predicting sudden cardiac death (SCD). These include experimental methods yet to be adopted in the clinical setting, and methods that have been extrapolated from observational data in those with a history of SCD. We will discuss how these relate to the different aetiologies and disease processes. We will also explore how these may be used in the clinical setting to decide on management.
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Affiliation(s)
- Elijah Behr
- Cardiovascular Research Unit, St George’s University of London, London, UK
| | - Bode Ensam
- Cardiovascular Research Unit, St George’s University of London, London, UK
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24
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Lang CN, Koren G, Odening KE. Transgenic rabbit models to investigate the cardiac ion channel disease long QT syndrome. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2016; 121:142-56. [PMID: 27210307 DOI: 10.1016/j.pbiomolbio.2016.05.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2016] [Accepted: 05/01/2016] [Indexed: 12/13/2022]
Abstract
Long QT syndrome (LQTS) is a rare inherited channelopathy caused mainly by different mutations in genes encoding for cardiac K(+) or Na(+) channels, but can also be caused by commonly used ion-channel-blocking and QT-prolonging drugs, thus affecting a much larger population. To develop novel diagnostic and therapeutic strategies to improve the clinical management of these patients, a thorough understanding of the pathophysiological mechanisms of arrhythmogenesis and potential pharmacological targets is needed. Drug-induced and genetic animal models of various species have been generated and have been instrumental for identifying pro-arrhythmic triggers and important characteristics of the arrhythmogenic substrate in LQTS. However, due to species differences in features of cardiac electrical function, these different models do not entirely recapitulate all aspects of the human disease. In this review, we summarize advantages and shortcomings of different drug-induced and genetically mediated LQTS animal models - focusing on mouse and rabbit models since these represent the most commonly used small animal models for LQTS that can be subjected to genetic manipulation. In particular, we highlight the different aspects of arrhythmogenic mechanisms, pro-arrhythmic triggering factors, anti-arrhythmic agents, and electro-mechanical dysfunction investigated in transgenic LQTS rabbit models and their translational application for the clinical management of LQTS patients in detail. Transgenic LQTS rabbits have been instrumental to increase our understanding of the role of spatial and temporal dispersion of repolarization to provide an arrhythmogenic substrate, genotype-differences in the mechanisms for early afterdepolarization formation and arrhythmia maintenance, mechanisms of hormonal modification of arrhythmogenesis and regional heterogeneities in electro-mechanical dysfunction in LQTS.
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Affiliation(s)
- C N Lang
- Department of Cardiology and Angiology I, University Heart Center Freiburg, Medical Center - University of Freiburg, Germany; Faculty of Medicine, University of Freiburg, Germany
| | - G Koren
- Cardiovascular Research Center, Division of Cardiology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, RI, USA
| | - K E Odening
- Department of Cardiology and Angiology I, University Heart Center Freiburg, Medical Center - University of Freiburg, Germany; Faculty of Medicine, University of Freiburg, Germany.
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25
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Affiliation(s)
- Andrew M Davis
- From the Department of Cardiology, Royal Children's Hospital, Melbourne, Victoria, Australia; Department of Pediatrics, University of Melbourne, Melbourne, Victoria, Australia; and the Murdoch Children's Research Institute, Melbourne, Victoria, Australia.
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26
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Takasugi N, Goto H, Takasugi M, Verrier RL, Kuwahara T, Kubota T, Toyoshi H, Nakashima T, Kawasaki M, Nishigaki K, Minatoguchi S. Prevalence of Microvolt T-Wave Alternans in Patients With Long QT Syndrome and Its Association With Torsade de Pointes. Circ Arrhythm Electrophysiol 2016; 9:e003206. [DOI: 10.1161/circep.115.003206] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Nobuhiro Takasugi
- From the Gifu University Hospital, Gifu, Japan (N.T., T.K., H.T., T.N., M.K., K.N., S.M.); Gifu Prefectural General Medical Center, Gifu, Japan (H.G., T.K.); Matsunami General Hospital, Gifu, Japan (M.T.); and Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA (R.L.V.)
| | - Hiroko Goto
- From the Gifu University Hospital, Gifu, Japan (N.T., T.K., H.T., T.N., M.K., K.N., S.M.); Gifu Prefectural General Medical Center, Gifu, Japan (H.G., T.K.); Matsunami General Hospital, Gifu, Japan (M.T.); and Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA (R.L.V.)
| | - Mieko Takasugi
- From the Gifu University Hospital, Gifu, Japan (N.T., T.K., H.T., T.N., M.K., K.N., S.M.); Gifu Prefectural General Medical Center, Gifu, Japan (H.G., T.K.); Matsunami General Hospital, Gifu, Japan (M.T.); and Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA (R.L.V.)
| | - Richard L. Verrier
- From the Gifu University Hospital, Gifu, Japan (N.T., T.K., H.T., T.N., M.K., K.N., S.M.); Gifu Prefectural General Medical Center, Gifu, Japan (H.G., T.K.); Matsunami General Hospital, Gifu, Japan (M.T.); and Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA (R.L.V.)
| | - Takashi Kuwahara
- From the Gifu University Hospital, Gifu, Japan (N.T., T.K., H.T., T.N., M.K., K.N., S.M.); Gifu Prefectural General Medical Center, Gifu, Japan (H.G., T.K.); Matsunami General Hospital, Gifu, Japan (M.T.); and Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA (R.L.V.)
| | - Tomoki Kubota
- From the Gifu University Hospital, Gifu, Japan (N.T., T.K., H.T., T.N., M.K., K.N., S.M.); Gifu Prefectural General Medical Center, Gifu, Japan (H.G., T.K.); Matsunami General Hospital, Gifu, Japan (M.T.); and Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA (R.L.V.)
| | - Hiroyuki Toyoshi
- From the Gifu University Hospital, Gifu, Japan (N.T., T.K., H.T., T.N., M.K., K.N., S.M.); Gifu Prefectural General Medical Center, Gifu, Japan (H.G., T.K.); Matsunami General Hospital, Gifu, Japan (M.T.); and Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA (R.L.V.)
| | - Takashi Nakashima
- From the Gifu University Hospital, Gifu, Japan (N.T., T.K., H.T., T.N., M.K., K.N., S.M.); Gifu Prefectural General Medical Center, Gifu, Japan (H.G., T.K.); Matsunami General Hospital, Gifu, Japan (M.T.); and Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA (R.L.V.)
| | - Masanori Kawasaki
- From the Gifu University Hospital, Gifu, Japan (N.T., T.K., H.T., T.N., M.K., K.N., S.M.); Gifu Prefectural General Medical Center, Gifu, Japan (H.G., T.K.); Matsunami General Hospital, Gifu, Japan (M.T.); and Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA (R.L.V.)
| | - Kazuhiko Nishigaki
- From the Gifu University Hospital, Gifu, Japan (N.T., T.K., H.T., T.N., M.K., K.N., S.M.); Gifu Prefectural General Medical Center, Gifu, Japan (H.G., T.K.); Matsunami General Hospital, Gifu, Japan (M.T.); and Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA (R.L.V.)
| | - Shinya Minatoguchi
- From the Gifu University Hospital, Gifu, Japan (N.T., T.K., H.T., T.N., M.K., K.N., S.M.); Gifu Prefectural General Medical Center, Gifu, Japan (H.G., T.K.); Matsunami General Hospital, Gifu, Japan (M.T.); and Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA (R.L.V.)
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Perspective: a dynamics-based classification of ventricular arrhythmias. J Mol Cell Cardiol 2015; 82:136-52. [PMID: 25769672 DOI: 10.1016/j.yjmcc.2015.02.017] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Revised: 02/05/2015] [Accepted: 02/20/2015] [Indexed: 02/04/2023]
Abstract
Despite key advances in the clinical management of life-threatening ventricular arrhythmias, culminating with the development of implantable cardioverter-defibrillators and catheter ablation techniques, pharmacologic/biologic therapeutics have lagged behind. The fundamental issue is that biological targets are molecular factors. Diseases, however, represent emergent properties at the scale of the organism that result from dynamic interactions between multiple constantly changing molecular factors. For a pharmacologic/biologic therapy to be effective, it must target the dynamic processes that underlie the disease. Here we propose a classification of ventricular arrhythmias that is based on our current understanding of the dynamics occurring at the subcellular, cellular, tissue and organism scales, which cause arrhythmias by simultaneously generating arrhythmia triggers and exacerbating tissue vulnerability. The goal is to create a framework that systematically links these key dynamic factors together with fixed factors (structural and electrophysiological heterogeneity) synergistically promoting electrical dispersion and increased arrhythmia risk to molecular factors that can serve as biological targets. We classify ventricular arrhythmias into three primary dynamic categories related generally to unstable Ca cycling, reduced repolarization, and excess repolarization, respectively. The clinical syndromes, arrhythmia mechanisms, dynamic factors and what is known about their molecular counterparts are discussed. Based on this framework, we propose a computational-experimental strategy for exploring the links between molecular factors, fixed factors and dynamic factors that underlie life-threatening ventricular arrhythmias. The ultimate objective is to facilitate drug development by creating an in silico platform to evaluate and predict comprehensively how molecular interventions affect not only a single targeted arrhythmia, but all primary arrhythmia dynamics categories as well as normal cardiac excitation-contraction coupling.
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Schweigmann U, Biliczki P, Ramirez RJ, Marschall C, Takac I, Brandes RP, Kotzot D, Girmatsion Z, Hohnloser SH, Ehrlich JR. Elevated heart rate triggers action potential alternans and sudden death. translational study of a homozygous KCNH2 mutation. PLoS One 2014; 9:e103150. [PMID: 25140878 PMCID: PMC4139196 DOI: 10.1371/journal.pone.0103150] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2014] [Accepted: 06/27/2014] [Indexed: 01/08/2023] Open
Abstract
BACKGROUND Long QT syndrome (LQTS) leads to arrhythmic events and increased risk for sudden cardiac death (SCD). Homozygous KCNH2 mutations underlying LQTS-2 have previously been termed "human HERG knockout" and typically express severe phenotypes. We studied genotype-phenotype correlations of an LQTS type 2 mutation identified in the homozygous index patient from a consanguineous Turkish family after his brother died suddenly during febrile illness. METHODS AND RESULTS Clinical work-up, DNA sequencing, mutagenesis, cell culture, patch-clamp, in silico mathematical modelling, protein biochemistry, confocal microscopy were performed. Genetic analysis revealed a homozygous C-terminal KCNH2 mutation (p.R835Q) in the index patient (QTc ∼506 ms with notched T waves). Parents were I° cousins - both heterozygous for the mutation and clinically unremarkable (QTc ∼447 ms, father and ∼396 ms, mother). Heterologous expression of KCNH2-R835Q showed mildly reduced current amplitudes. Biophysical properties of ionic currents were also only nominally changed with slight acceleration of deactivation and more negative V50 in R835Q-currents. Protein biochemistry and confocal microscopy revealed similar expression patterns and trafficking of WT and R835Q, even at elevated temperature. In silico analysis demonstrated mildly prolonged ventricular action potential duration (APD) compared to WT at a cycle length of 1000 ms. At a cycle length of 350 ms M-cell APD remained stable in WT, but displayed APD alternans in R835Q. CONCLUSION Kv11.1 channels affected by the C-terminal R835Q mutation display mildly modified biophysical properties, but leads to M-cell APD alternans with elevated heart rate and could precipitate SCD under specific clinical circumstances associated with high heart rates.
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Affiliation(s)
| | - Peter Biliczki
- Division of Clinical Electrophysiology, Goethe University, Frankfurt, Germany
- Div. of Cardiology, Deutsche Klinik für Diagnostik, Wiesbaden, Germany
| | - Rafael J. Ramirez
- Center for Arrhythmia Research, University of Michigan, Ann Arbor, Michigan, United States of America
| | | | - Ina Takac
- Institute of Cardiovascular Physiology, Goethe University, Frankfurt, Germany
| | - Ralf P. Brandes
- Institute of Cardiovascular Physiology, Goethe University, Frankfurt, Germany
| | - Dieter Kotzot
- Section for Human Genetics, Innsbruck Medical University, Innsbruck, Austria
| | - Zenawit Girmatsion
- Division of Clinical Electrophysiology, Goethe University, Frankfurt, Germany
| | - Stefan H. Hohnloser
- Division of Clinical Electrophysiology, Goethe University, Frankfurt, Germany
| | - Joachim R. Ehrlich
- Division of Clinical Electrophysiology, Goethe University, Frankfurt, Germany
- Div. of Cardiology, Deutsche Klinik für Diagnostik, Wiesbaden, Germany
- * E-mail:
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Merchant FM, Sayadi O, Moazzami K, Puppala D, Armoundas AA. T-wave alternans as an arrhythmic risk stratifier: state of the art. Curr Cardiol Rep 2014; 15:398. [PMID: 23881581 DOI: 10.1007/s11886-013-0398-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Microvolt level T-wave alternans (MTWA), a phenomenon of beat-to-beat variability in the repolarization phase of the ventricles, has been closely associated with an increased risk of ventricular tachyarrhythmic events (VTE) and sudden cardiac death (SCD) during medium- and long-term follow-up. Recent observations also suggest that heightened MTWA magnitude may be closely associated with short-term risk of impending VTE. At the subcellular and cellular level, perturbations in calcium transport processes likely play a primary role in the genesis of alternans, which then secondarily lead to alternans of action potential morphology and duration (APD). As such, MTWA may play a role not only in risk stratification but also more fundamentally in the pathogenesis of VTE. In this paper, we outline recent advances in understanding the pathogenesis of MTWA and also the utility of T-wave alternans testing for clinical risk stratification. We also highlight emerging clinical applications for MTWA.
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Affiliation(s)
- Faisal M Merchant
- Cardiology Division, Emory University School of Medicine, Atlanta, GA, USA
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Bini S, Burattini L. Quantitative characterization of repolarization alternans in terms of amplitude and location: What information from different methods? Biomed Signal Process Control 2013. [DOI: 10.1016/j.bspc.2013.06.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Maury P, Extramiana F, Giustetto C, Cardin C, Rollin A, Duparc A, Mondoly P, Denjoy I, Delay M, Messali A, Leenhardt A, Marangoni D. Microvolt T-wave alternans in short QT syndrome. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2012; 35:1413-9. [PMID: 22897428 DOI: 10.1111/j.1540-8159.2012.03491.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
BACKGROUND T-wave alternans (TWA) is an accepted marker of risk for malignant ventricular arrhythmias, for which prognosis value has been established in different populations. Short QT syndrome (SQTS) is a very rare primary electrical disease carrying the risk of ventricular fibrillation. TWA in SQTS has not been evaluated yet. METHODS Thirteen patients with SQTS (QT = 308 ± 16 ms, QTc = 329 ± 10 ms, heart rate = 69 ± 8 beats/min) underwent microvolt TWA measurement using spectral analysis. TWA testing was performed using Heartwave II (Cambridge Heart™, Inc., Bedford, MA, USA) during bicycle exercice and classified as negative, positive, or indeterminate according to the published standards for clinical interpretation. RESULTS Twelve patients were male (mean age 23 ± 5 years). Five were asymptomatic, three presented with aborted sudden cardiac death, and five with unexplained syncope. Six patients belonged to two unrelated families, while familial cases of SQTS were present for two other patients. A familial history of sudden death (SD) was present for seven patients. Ventricular fibrillation was inducible in three patients. Four patients were implanted with an implantable cardioverter-defibrillator and one presented with polymorphic ventricular tachycardia during follow-up. TWA was negative in each but one patient (indeterminate). Maximal negative heart rate was 118 ± 12 beats/min. Patients with previous SD displayed significant shorter QT and higher resting heart rate compared to the remaining cases. CONCLUSIONS TWA testing is negative in 12 of 13 SQTS patients, even in the symptomatic or inducible ones. Measurement of TWA using conventional protocol and criteria for risk stratification in SQTS seems therefore useless.
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Affiliation(s)
- Philippe Maury
- University Hospital Rangueil, Toulouse, France University Hospital Bichat Paris, France.
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Burattini L, Man S, Burattini R, Swenne CA. Comparison of standard versus orthogonal ECG leads for T-wave alternans identification. Ann Noninvasive Electrocardiol 2012; 17:130-40. [PMID: 22537331 DOI: 10.1111/j.1542-474x.2012.00490.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
T-wave alternans (TWA), an electrophysiologic phenomenon associated with ventricular arrhythmias, is usually detected from selected ECG leads. TWA amplitude measured in the 12-standard and the 3-orthogonal (vectorcardiographic) leads were compared here to identify which lead system yields a more adequate detection of TWA as a noninvasive marker for cardiac vulnerability to ventricular arrhythmias. Our adaptive match filter (AMF) was applied to exercise ECG tracings from 58 patients with an implanted cardiac defibrillator, 29 of which had ventricular tachycardia or fibrillation during follow-up (cases), while the remaining 29 were used as controls. Two kinds of TWA indexes were considered, the single-lead indexes, defined as the mean TWA amplitude over each lead (MTWAA), and lead-system indexes, defined as the mean and the maximum MTWAA values over the standard leads and over the orthogonal leads. Significantly (P < 0.05) higher TWA in the cases versus controls was identified only occasionally by the single-lead indexes (odds ratio: 1.0-9.9, sensitivity: 24-76%, specificity: 76-86%), and consistently by the lead-system indexes (odds ratio: 4.5-8.3, sensitivity: 57-72%, specificity: 76%). The latter indexes also showed a significant correlation (0.65-0.83) between standard and orthogonal leads. Hence, when using the AMF, TWA should be detected in all leads of a system to compute the lead-system indexes, which provide a more reliable TWA identification than single-lead indexes, and a better discrimination of patients at increased risk of cardiac instability. The standard and the orthogonal leads can be considered equivalent for TWA identification, so that TWA analysis can be limited to one-lead system.
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Affiliation(s)
- Laura Burattini
- Department of Information Engineering, Polytechnic University of Marche, Ancona, Italy.
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Halamek J, Couderc JP, Jurak P, Vondra V, Zareba W, Viscor I, Leinveber P. Measure of the QT-RR dynamic coupling in patients with the long QT syndrome. Ann Noninvasive Electrocardiol 2012; 17:323-30. [PMID: 23094878 DOI: 10.1111/j.1542-474x.2012.00526.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
BACKGROUND The patients with the long QT syndrome type-1 (LQT-1) have an impaired adaptation of the QT interval to heart rate changes. Yet, the description of the dynamic QT-RR coupling in genotyped LQT-1 has never been thoroughly investigated. METHOD We propose a method to model the dynamic QT-RR coupling by defining a transfer function characterizing the relationship between a QT interval and its previous RR intervals measured from ambulatory Holter recordings. Three parameters are used to characterize the QT-RR coupling: a fast gain (Gain(F) ), a slow gain (Gain(L) ), and a time constant (τ). We investigated the values of these parameters across genders, and in genotyped LQT-1 patients with normal QTc interval duration (QTc < 470 ms). RESULTS The QT-RR dynamic profiles are significantly different between LQT-1 patients (97) and controls (154): LQT-1 have longer QTc interval (453 ± 35 vs. 384 ± 26 ms, P < 0.0001), and an increased dependency of the QT interval to previous RR changes revealed by a larger Gain(L) (0.22 ± 0.06 vs. 0.18 ± 0.07, P < 0.0001) and Gain(F) (0.05 ± 0.02 vs. 0.03 ± 0.01, P < 0.0001). Importantly, LQT-1 patients have a faster QT dynamic response to previous RR changes described by τ: 122 ± 44 vs. 172 ± 92 beats (P < 0.0001). This faster QT dynamic response of the QT-RR dynamic coupling remained in LQT-1 patients with QTc in a normal range (<430 ms). CONCLUSIONS The measurement of QT-RR dynamic coupling could be used in patients suspected to carry a concealed form of the LQT-1 syndrome, or to provide insights into the types of arrhythmogenic triggers a patient may be prone to.
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Affiliation(s)
- Josef Halamek
- Institute of Scientific Instruments, AS CR, Brno, Czech Republic.
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Spears DA, Suszko AM, Krahn AD, Selvaraj RJ, Ivanov J, Chauhan VS. Latent microvolt T-wave alternans in survivors of unexplained cardiac arrest unmasked by epinephrine challenge. Heart Rhythm 2012; 9:1076-82. [PMID: 22373794 DOI: 10.1016/j.hrthm.2012.02.026] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/29/2011] [Indexed: 12/01/2022]
Abstract
BACKGROUND The arrhythmogenic substrate in survivors of unexplained cardiac arrest (UCA) has not been defined. OBJECTIVES To test the hypothesis that patients with UCA have latent repolarization abnormalities, in particular T-wave alternans (TWA), which may be unmasked with epinephrine (EPI) challenge. METHODS We prospectively studied 10 UCA survivors (46 ± 9 years) and 11 first-degree relatives (FDRs) of sudden death victims (37 ± 14 years). Patients with UCA underwent standard clinical testing, which was normal. FDRs had normal clinical history and testing. All subjects underwent an EPI infusion (0.05, 0.1, and 0.2 μg/(kg·min), 5 minutes each dose) while recording continuous digital 12-lead electrocardiograms. Corrected QT interval and QT variability index were evaluated at each EPI dose. TWA magnitude (V(alt)) was assessed at each dose by using the spectral method. Positive (+) TWA at each dose was defined as V(alt) > 0 with k ≥ 3 in 1 or more 128-beat segment in ≥2 electrocardiogram leads. A novel metric, TWA burden, reflecting V(alt) integrated over time (s), was also evaluated for each EPI dose. RESULTS There was no difference between UCA survivors and FDRs with respect to heart rate, QT, corrected QT interval, or QT variability index at baseline or during EPI. At baseline, +TWA was similar between UCA survivors and FDRs (10% vs 0%; P = NS). During EPI, +TWA was more prevalent in UCA survivors than in FDRs (80% vs 18%; P = .009). TWA burden was greater in UCA survivors than in FDRs during EPI 0.1 (P = .039) and EPI 0.2 μg/(kg·min) (P = .009). CONCLUSIONS UCA survivors are more likely to demonstrate latent TWA compared with FDRs, which becomes manifest with EPI. This novel finding provides evidence for an arrhythmogenic substrate in UCA survivors.
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Affiliation(s)
- Danna A Spears
- Division of Cardiology, University Health Network, Toronto, Ontario, Canada
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Armoundas AA, Mela T, Merchant FM. On the estimation of T-wave alternans using the spectral fast fourier transform method. Heart Rhythm 2011; 9:449-56. [PMID: 22001706 DOI: 10.1016/j.hrthm.2011.10.013] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Accepted: 10/08/2011] [Indexed: 11/20/2022]
Abstract
BACKGROUND T-wave alternans (TWA) has been associated with increased vulnerability to ventricular tachyarrhythmias and sudden cardiac death. However, both random (white) noise and (patho)physiologic processes (ie, premature ventricular contractions and heart and respiration rates) may hamper TWA estimation and therefore lessen its clinical utility for risk stratification. OBJECTIVE To investigate the effect of random noise and certain (patho)physiologic processes on the estimation of TWA by using the fast Fourier transform method and to develop methods to overcome these potential sources of error. METHODS We used a combination of human electrocardiogram data and computer simulations to assess the effects of a premature ventricular contraction and random and colored noise on the accuracy of TWA estimation. RESULTS We quantitatively demonstrate that replacing a "bad" beat with an odd/even median beat is a more accurate approach than replacing it with the overall average or the overall median beat. We also show that phase resetting may have a significant effect on alternans estimation and that estimation of alternans by using frequencies >0.4922 cycles/beat in a 128-point fast Fourier transform provides the most accurate approach for estimating the alternans when phase resetting is likely to occur. In addition, our data demonstrate that the number of indeterminate TWA tests due to high levels of noise can be reduced when the alternans voltage exceeds a new higher threshold. Furthermore, the amplitude of random noise has a significant effect on alternans estimation and the alternans voltage threshold should be adjusted for noise levels >1.8 μV. Finally, we quantitatively demonstrate that colored noise may lead to a false-positive or a false-negative result. We propose methods to estimate the effect of these (patho)physiologic processes on the alternans estimation in order to determine whether a TWA test is likely to be a true positive or a true negative. CONCLUSION This study introduces novel methods to overcome potential sources of error in the estimation of TWA. These methods may improve the utility of TWA either for ambulatory monitoring or for clinical risk stratification for ventricular arrhythmias and sudden cardiac death.
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Affiliation(s)
- Antonis A Armoundas
- Cardiovascular Research Center, Division of Cardiology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02129, USA.
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Shu J, Yan GX. Instability of type 1 Brugada wave: A more sensitive ECG predictor of cardiac events? Heart Rhythm 2011; 8:1022-3. [DOI: 10.1016/j.hrthm.2011.03.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/28/2011] [Indexed: 11/24/2022]
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MAURIELLO DANIELA, JOHNSON JONATHANN, ACKERMAN MICHAELJ. Holter Monitoring in the Evaluation of Congenital Long QT Syndrome. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2011; 34:1100-4. [DOI: 10.1111/j.1540-8159.2011.03102.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Chen SF, Yabumoto K, Haywood LJ. Serious ups and downs. Am J Med 2010; 123:1094-6. [PMID: 20951367 DOI: 10.1016/j.amjmed.2010.07.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/07/2010] [Revised: 07/12/2010] [Accepted: 07/13/2010] [Indexed: 10/18/2022]
Affiliation(s)
- Shih-Fan Chen
- Division of Cardiovascular Medicine, Department of Medicine, Los Angeles County and University of Southern Medical Center, Los Angeles, USA
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Abstract
T-wave alternans, a manifestation of repolarization alternans at the cellular level, is associated with lethal cardiac arrhythmias and sudden cardiac death. At the cellular level, several mechanisms can produce repolarization alternans, including: (1) electrical restitution resulting from collective ion channel recovery, which usually occurs at fast heart rates but can also occur at normal heart rates when action potential is prolonged resulting in a short diastolic interval; (2) the transient outward current, which tends to occur at normal or slow heart rates; (3) the dynamics of early after depolarizations, which tends to occur during bradycardia; and (4) intracellular calcium cycling alternans through its interaction with membrane voltage. In this review, we summarize the cellular mechanisms of alternans arising from these different mechanisms, and discuss their roles in arrhythmogenesis in the setting of cardiac disease.
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Affiliation(s)
- Zhilin Qu
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, California, USA.
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Extramiana F, Tatar C, Maison-Blanche P, Denjoy I, Messali A, Dejode P, Iserin F, Leenhardt A. Beat-to-beat T-wave amplitude variability in the long QT syndrome. Europace 2010; 12:1302-7. [PMID: 20472689 DOI: 10.1093/europace/euq137] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
AIMS Long QT syndrome (LQTS) is a primary electrical disease characterized by QT prolongation and increased repolarization dispersion leading to T-wave amplitude beat-to-beat changes. We aimed to quantify beat-to-beat T-wave amplitude variability from ambulatory Holter recordings in genotyped LQTS patients. METHODS AND RESULTS Seventy genotyped LQTS patients (mean age 23 +/- 15 years, 42 males, 50% LQT1, 39% LQT2, and 11% LQT3) and 70 normal matched control subjects underwent a 24-h digital Holter recording. Using the Tvar software (Ela Medical, Sorin group), the beat-to-beat variance of the T-wave amplitude (TAV in microV) [corrected] was assessed on 50-ms consecutive clusters during three 1-h periods: one with around average diurnal heart rate (Day Fast), one nocturnal period (Night), and one diurnal period with around average nocturnal heart rate (Day Slow). TAV was increased in LQTS patients during the two diurnal periods but not at night (during the Day Fast period, mean TAV was 34 +/- 20 microV [corrected] in LQTS patients vs. 27 +/- 10 microV [corrected] in controls, P < 0.05). This effect depended on the genotype. In LQT1, TAV was larger when compared with controls for both Day Fast and Slow periods, but in LQT2 only Day Fast shows higher TAV. Oppositely, in LQT3 the TAV was higher than in the control group during the Day slow period (mean TAV = 34 +/- 20 vs. 25 +/- 8 microV [corrected] in controls, P < 0.05). CONCLUSION In genotyped LQTS patients beat-to-beat T-wave amplitude variability was increased when compared with control subjects. That pattern was modulated by circadian influences in a gene-dependent manner.
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Affiliation(s)
- Fabrice Extramiana
- Cardiology Department, Lariboisière Hospital APHP, University Paris Diderot, Paré, France.
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Drew BJ, Ackerman MJ, Funk M, Gibler WB, Kligfield P, Menon V, Philippides GJ, Roden DM, Zareba W. Prevention of torsade de pointes in hospital settings: a scientific statement from the American Heart Association and the American College of Cardiology Foundation. J Am Coll Cardiol 2010; 55:934-47. [PMID: 20185054 DOI: 10.1016/j.jacc.2010.01.001] [Citation(s) in RCA: 278] [Impact Index Per Article: 19.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Farkas AS, Nattel S. Minimizing Repolarization-Related Proarrhythmic Risk in Drug Development and Clinical Practice. Drugs 2010; 70:573-603. [DOI: 10.2165/11535230-000000000-00000] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Drew BJ, Ackerman MJ, Funk M, Gibler WB, Kligfield P, Menon V, Philippides GJ, Roden DM, Zareba W. Prevention of torsade de pointes in hospital settings: a scientific statement from the American Heart Association and the American College of Cardiology Foundation. Circulation 2010; 121:1047-60. [PMID: 20142454 DOI: 10.1161/circulationaha.109.192704] [Citation(s) in RCA: 385] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Burattini L, Zareba W, Burattini R. Assessment of physiological amplitude, duration, and magnitude of ECG T-wave alternans. Ann Noninvasive Electrocardiol 2010; 14:366-74. [PMID: 19804514 DOI: 10.1111/j.1542-474x.2009.00326.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND An association between T-wave alternans (TWA) and malignant ventricular arrhythmias is generally recognized. Because relatively low levels of TWA have also been observed in healthy (H) subjects, the question arises as to whether these are ascribable to noise and artifacts, or can be given the relevance of a physiological phenomenon characterizing a preclinical condition. METHODS To answer this question, in the present study 20-minute not noisy, sinus ECG recordings, from 138 H-subjects and 148 coronary artery diseased (CAD) patients, were submitted to our adaptive match filter (AMF) procedure to identify and parameterize TWA in terms of duration (TWAD), amplitude (TWAA), and magnitude (TWAM, defined as the product of TWAD times TWAA). The 99.5th percentiles of mean values of TWAA, TWAD, and TWAM over 20-minute ECGs were used to define three threshold levels (THRD, THRA, and THRM), which allow discrimination of abnormal TWA levels. RESULTS Nonstationary TWA was found in all our H-subjects and CAD-patients. TWAD, TWAA, and TWAM levels were classified as being physiological in 99% of H-subjects and 87% of CAD-patients. A linear correlation (r =-0.52, P < 0.001) was found between TWAA and RR interval in the H-population. CONCLUSIONS Our results support the hypothesis of the existence of physiological TWA levels, which are to be considered in the effort to improve reliability of nonphysiological TWA levels discrimination.
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Affiliation(s)
- Laura Burattini
- Department of Biomedical, Electronics, and Telecommunication Engineering, Polytechnic University of Marche, 60131 Ancona, Italy.
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Howley LW, DI Maria M, Bailey A, Schaffer MS. Neonatal long QT syndrome type 3 predicted by positive lidocaine challenge. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2009; 33:377-9. [PMID: 19793370 DOI: 10.1111/j.1540-8159.2009.02550.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A female infant presented with bradycardia and an electrocardiogram demonstrating 2:1 atrioventricular depolarization, a prolonged QT interval, and T wave alternans. After propranolol therapy was initiated, a lidocaine challenge was performed with progressive shortening of the QT interval. This positive lidocaine challenge prompted clinical suspicion of long QT syndrome type 3 (LQT3) and early initiation of mexiletine therapy. Subsequent genetic testing confirmed the infant's diagnosis of LQT3.
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Affiliation(s)
- Lisa W Howley
- Section of Pediatric Cardiology University of Colorado, Denver, The Children's Hospital, Aurora, Colorado 80045, USA
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Burattini L, Bini S, Burattini R. Comparative analysis of methods for automatic detection and quantification of microvolt T-wave alternans. Med Eng Phys 2009; 31:1290-8. [PMID: 19758833 DOI: 10.1016/j.medengphy.2009.08.009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2009] [Revised: 06/24/2009] [Accepted: 08/22/2009] [Indexed: 10/20/2022]
Abstract
Microvolt T-wave alternans (TWA), consisting of every-other-beat changes in ECG T-wave morphology, is an index of susceptibility to malignant ventricular arrhythmias, requiring automatic techniques to be identified. Five of these, namely, fast-Fourier-transform spectral method (FFTSM), complex-demodulation method (CDM), modified-moving-average method (MMAM), Laplacian-likelihood-ratio method (LLRM) and adaptive-match-filter method (AMFM), were applied here to simulated and sample clinical data. The aim was to compare individual methods ability to properly identify stationary and time-varying TWA, avoiding false-positive detections. The MMAM provided false-positive TWA when applied to simulated ECGs affected by amplitude variability, but TWA. Stationary TWA was properly quantified by the MMAM and, occasionally, underestimated by all other methods. The AMFM properly identified time-varying TWA. By contrast, the FFTSM detected not-stationary TWA as stationary, the MMAM introduced a time-delay in the estimated TWA-amplitude signal, while the CDM and LLRM were reliable only in the presence of slow-varying TWA. Altogether, the AMFM accomplished the best compromise between the needs to avoid false-positive TWA and to detect and characterize true-positive TWA. Results of our simulation approach were useful to explain different TWA levels measured by each competing methods applied to sample Holter ECGs from healthy subjects and coronary artery disease patients.
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Affiliation(s)
- Laura Burattini
- Department of Biomedical, Electronics and Telecommunication Engineering, Polytechnic University of Marche, Ancona, Italy
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Ziv O, Morales E, Song YK, Peng X, Odening KE, Buxton AE, Karma A, Koren G, Choi BR. Origin of complex behaviour of spatially discordant alternans in a transgenic rabbit model of type 2 long QT syndrome. J Physiol 2009; 587:4661-80. [PMID: 19675070 DOI: 10.1113/jphysiol.2009.175018] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Enhanced dispersion of repolarization has been proposed as an important mechanism in long QT related arrhythmias. Dispersion can be dynamic and can be augmented with the occurrence of spatially out-of-phase action potential duration (APD) alternans (discordant alternans; DA). We investigated the role of tissue heterogeneity in generating DA using a novel transgenic rabbit model of type 2 long QT syndrome (LQT2). Littermate control (LMC) and LQT2 rabbit hearts (n = 5 for each) were retrogradely perfused and action potentials were mapped from the epicardial surface using di-4-ANEPPS and a high speed CMOS camera. Spatial dispersion (Delta APD and Delta slope of APD restitution) were both increased in LQT2 compared to LMC (Delta APD: 34 +/- 7 ms vs. 23 +/- 6 ms; Delta slope: 1.14 +/- 0.23 vs. 0.59 +/- 0.19). Onset of DA under a ramp stimulation protocol was seen at longer pacing cycle length (CL) in LQT2 compared to LMC hearts (206 +/- 24 ms vs. 156 +/- 5 ms). Nodal lines between regions with APD alternans out of phase from each other were correlated with conduction velocity (CV) alternation in LMC but not in LQT2 hearts. In LQT2 hearts, larger APD dispersion was associated with onset of DA at longer pacing CL. At shorter CLs, closer to ventricular fibrillation induction (VF), nodal lines in LQT2 (n = 2 out of 5) showed persistent complex beat-to-beat changes in nodal line formation of DA associated with competing contribution from CV restitution and tissue spatial heterogeneity, increasing vulnerability to conduction block. In conclusion, tissue heterogeneity plays a significant role in providing substrate for ventricular arrhythmia in LQT2 rabbits by facilitating DA onset and contributing to unstable nodal lines prone to reentry formation.
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Affiliation(s)
- Ohad Ziv
- Cardiovascular Research Center, Division of Cardiology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, RI 02903, USA
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Romero I, Grubb NR, Clegg GR, Robertson CE, Addison PS, Watson JN. T-wave alternans found in preventricular tachyarrhythmias in CCU patients using a wavelet transform-based methodology. IEEE Trans Biomed Eng 2009; 55:2658-65. [PMID: 18990637 DOI: 10.1109/tbme.2008.923912] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Ventricular tachyarrhythmias are potentially lethal cardiac pathologies and the commonest cause of sudden cardiac death. Efforts to predict the onset of such events are based on feature extraction from the surface ECG. T-wave alternans (TWAs) are considered a marker of abnormal ventricular function that may be associated with ventricular tachycardia (VT) and ventricular fibrillation. A novel TWA detection algorithm utilizing the continuous wavelet transform is described in this paper. Simulated ECGs containing artificial TWA were used to test the algorithm that achieved a sensitivity of 91.40% and a specificity of 94.00%. The algorithm was subsequently used to analyze the ECGs of eight patients prior to the onset of VT. Of these, the algorithm indicated that five patients exhibited TWA prior to the onset of the tachyarrhythmic events, while the remaining three patients did not exhibit identifiable TWA. Healthy individuals were also studied in which one short TWA episode was detected by the algorithm. However, closer visual inspection of the data revealed this to be a likely false positive result.
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Affiliation(s)
- Iñaki Romero
- Department of Medical Physics, German National Institute of Metrology, Berlin D-10587, Germany.
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Abstract
The hereditary Long QT syndrome (LQTS) is a genetic channelopathy with variable penetrance that is associated with increased propensity for polymorphic ventricular tachyarrhythmias and sudden cardiac death in young individuals with normal cardiac morphology. The diagnosis of this genetic disorder relies on a constellation of electrocardiographic, clinical, and genetic factors. Accumulating data from recent studies indicate that the clinical course of affected LQTS patients is time-dependent and age-specific, demonstrating important gender differences among age groups. Risk assessment should consider age-gender interactions, prior syncopal history, QT-interval duration, and genetic factors. Beta-blockers constitute the mainstay therapy for LQTS, while left cardiac sympathetic denervation and implantation of a cardioverter defibrillator should be considered in patients who remain symptomatic despite beta-blocker therapy. Current and ongoing studies are also evaluating genotype-specific therapies that may reduce the risk for life-threatening cardiac events in high-risk LQTS patients.
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