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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: 0] [Impact Index Per Article: 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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2
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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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Harvey A, Curnier D, Dodin P, Abadir S, Jacquemet V, Caru M. OUP accepted manuscript. Eur J Prev Cardiol 2022; 29:1633-1677. [PMID: 35537006 DOI: 10.1093/eurjpc/zwac081] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Revised: 04/15/2022] [Accepted: 04/18/2022] [Indexed: 11/13/2022]
Abstract
Current exercise recommendations make it difficult for long QT syndrome (LQTS) patients to adopt a physically active and/or athletic lifestyle. The purpose of this review is to summarize the current evidence, identify knowledge gaps, and discuss research perspectives in the field of exercise and LQTS. The first aim is to document the influence of exercise training, exercise stress, and postural change interventions on ventricular repolarization in LQTS patients, while the second aim is to describe electrophysiological measurements used to study the above. Studies examining the effects of exercise on congenital or acquired LQTS in human subjects of all ages were included. Systematic searches were performed on 1 October 2021, through PubMed (NLM), Ovid Medline, Ovid All EBM Reviews, Ovid Embase, and ISI Web of Science, and limited to articles written in English or French. A total of 1986 LQTS patients and 2560 controls were included in the 49 studies. Studies were mainly case-control studies (n = 41) and examined exercise stress and/or postural change interventions (n = 48). One study used a 3-month exercise training program. Results suggest that LQTS patients have subtype-specific repolarization responses to sympathetic stress. Measurement methods and quality were found to be very heterogeneous, which makes inter-study comparisons difficult. In the absence of randomized controlled trials, the current recommendations may have long-term risks for LQTS patients who are discouraged from performing physical activity, rendering its associated health benefits out of range. Future research should focus on discovering the most appropriate levels of exercise training that promote ventricular repolarization normalization in LQTS.
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Affiliation(s)
- Audrey Harvey
- Laboratory of Pathophysiology of EXercise (LPEX), School of Kinesiology and Physical Activity Sciences, Faculty of Medicine, University of Montreal, Montreal, Canada
- Sainte-Justine University Health Center, Research Center, Montreal, Canada
| | - Daniel Curnier
- Laboratory of Pathophysiology of EXercise (LPEX), School of Kinesiology and Physical Activity Sciences, Faculty of Medicine, University of Montreal, Montreal, Canada
- Sainte-Justine University Health Center, Research Center, Montreal, Canada
| | - Philippe Dodin
- Sainte-Justine University Health Center, Research Center, Montreal, Canada
| | - Sylvia Abadir
- Department of Pediatric Cardiology, Sainte-Justine University Health Center, Montreal, Canada
| | - Vincent Jacquemet
- Department of Pharmacology and Physiology, Faculty of Medicine, University of Montreal, Montreal, Canada
| | - Maxime Caru
- Sainte-Justine University Health Center, Research Center, Montreal, Canada
- Department of Pediatrics, Pennsylvania State University College of Medicine, Hershey, PA, USA
- Department of Public Health Sciences, Pennsylvania State University College of Medicine, Hershey, PA, USA
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4
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Melgar Quicaño LA, Chipa Ccasani F. [Congenital long QT syndrome]. ARCHIVOS PERUANOS DE CARDIOLOGIA Y CIRUGIA CARDIOVASCULAR 2021; 2:49-57. [PMID: 37727265 PMCID: PMC10506569 DOI: 10.47487/apcyccv.v2i1.125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Accepted: 03/17/2021] [Indexed: 09/21/2023]
Abstract
Congenital long QT syndrome (LQTS) represents a group of heart diseases of genetic origin characterized by prolongation of the QT interval and an abnormal T wave on the electrocardiogram (ECG). They can have a dominant or recessive expression, the latter associated with sensorineural deafness. In both cases, its clinical presentation is associated with recurrent syncope and sudden death as a consequence of ventricular tachycardia, specifically Torsades de Pointes. Currently they are classified according to the specific genetic defect, being able to compromise around 16 genes and almost 2000 mutations. It should be suspected in individuals with related symptoms, electrocardiographic findings, and family history. Management is based on the reduction or elimination of symptoms, and concomitantly the prevention of sudden death (SD), in those children with congenital deafness, the management requires the application of the otolaryngologist specialist's own measures. The cardiovascular management implies the modification of lifestyles, mainly the prohibition of competitive sports, including swimming, avoiding exposure to loud sounds or triggers. The medications used include beta-blockers, and more rarely flecainide, ranozaline, and verapamil; invasive management consists of the implantation of a cardioverter defibrillator or even left sympathetic denervation, each with its own risks and benefits. In any of the cases, we must avoid the circumstances that increase the QT interval, as well as carry out the appropriate analysis of the benefits and risks of each possible invasive measure.
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Affiliation(s)
| | - Fredy Chipa Ccasani
- Instituto Nacional de Salud del Niño, San Borja. Lima, PerúInstituto Nacional de Salud del NiñoLimaPerú
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5
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Siontis KC, Wen S, Asirvatham SJ. Cardiac memory for the clinical electrophysiologist. J Cardiovasc Electrophysiol 2019; 30:2140-2143. [DOI: 10.1111/jce.14134] [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: 08/08/2019] [Accepted: 08/08/2019] [Indexed: 11/30/2022]
Affiliation(s)
| | - Songnan Wen
- Department of Cardiovascular DiseasesMayo ClinicRochester Minnesota
| | - Samuel J. Asirvatham
- Department of Cardiovascular DiseasesMayo ClinicRochester Minnesota
- Department of Pediatrics and Adolescent MedicineMayo ClinicRochester Minnesota
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6
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Atanasovska T, Smith R, Graff C, Tran CT, Melgaard J, Kanters JK, Petersen AC, Tobin A, Kjeldsen KP, McKenna MJ. Protection against severe hypokalemia but impaired cardiac repolarization after intense rowing exercise in healthy humans receiving salbutamol. J Appl Physiol (1985) 2018; 125:624-633. [PMID: 29745804 DOI: 10.1152/japplphysiol.00680.2017] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Intense exercise induces pronounced hyperkalemia, followed by transient hypokalemia in recovery. We investigated whether the β2 agonist salbutamol attenuated the exercise hyperkalemia and exacerbated the postexercise hypokalemia, and whether hypokalemia was associated with impaired cardiac repolarization (QT hysteresis). Eleven healthy adults participated in a randomized, counterbalanced, double-blind trial receiving either 1,000 µg salbutamol (SAL) or placebo (PLAC) by inhalation. Arterial plasma potassium concentration ([K+]a) was measured at rest, during 3 min of intense rowing exercise, and during 60 min of recovery. QT hysteresis was calculated from ECG ( n = 8). [K+]a increased above baseline during exercise (rest, 3.72 ± 0.7 vs. end-exercise, 6.81 ± 1.4 mM, P < 0.001, mean ± SD) and decreased rapidly during early recovery to below baseline; restoration was incomplete at 60 min postexercise ( P < 0.05). [K+]a was less during SAL than PLAC (4.39 ± 0.13 vs. 4.73 ± 0.19 mM, pooled across all times, P = 0.001, treatment main effect). [K+]a was lower after SAL than PLAC, from 2 min preexercise until 2.5 min during exercise, and at 50 and 60 min postexercise ( P < 0.05). The postexercise decline in [K+]a was correlated with QT hysteresis ( r = 0.343, n = 112, pooled data, P = 0.001). Therefore, the decrease in [K+]a from end-exercise by ~4 mM was associated with reduced QT hysteresis by ~75 ms. Although salbutamol lowered [K+]a during exercise, no additive hypokalemic effects occurred in early recovery, suggesting there may be a protective mechanism against severe or prolonged hypokalemia after exercise when treated by salbutamol. This is important because postexercise hypokalemia impaired cardiac repolarization, which could potentially trigger arrhythmias and sudden cardiac death in susceptible individuals with preexisting hypokalemia and/or heart disease. NEW & NOTEWORTHY Intense rowing exercise induced a marked increase in arterial potassium, followed by a pronounced decline to hypokalemic levels. The β2 agonist salbutamol lowered potassium during exercise and late recovery but not during early postexercise, suggesting a protective effect against severe hypokalemia. The decreased potassium in recovery was associated with impaired cardiac QT hysteresis, suggesting a link between postexercise potassium and the heart, with implications for increased risk of cardiac arrhythmias and, potentially, sudden cardiac death.
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Affiliation(s)
- Tania Atanasovska
- Institute for Health and Sport, Victoria University , Melbourne, Victoria , Australia
| | - Robert Smith
- Institute for Health and Sport, Victoria University , Melbourne, Victoria , Australia.,Department of Anaesthesia, Western Hospital , Melbourne, Victoria , Australia
| | - Claus Graff
- Department of Health Science and Technology, Faculty of Medicine, Aalborg University , Aalborg , Denmark
| | - Cao T Tran
- Division of Cardiology, John Hopkins University School of Medicine , Baltimore, Maryland
| | - Jacob Melgaard
- Department of Health Science and Technology, Faculty of Medicine, Aalborg University , Aalborg , Denmark
| | - Jørgen K Kanters
- Laboratory of Experimental Cardiology, Department of Biomedical Sciences, Copenhagen University , Copenhagen , Denmark
| | - Aaron C Petersen
- Institute for Health and Sport, Victoria University , Melbourne, Victoria , Australia
| | - Antony Tobin
- Intensive Care Unit, St. Vincent Hospital , Melbourne, Victoria , Australia
| | - Keld P Kjeldsen
- Department of Health Science and Technology, Faculty of Medicine, Aalborg University , Aalborg , Denmark.,Medical Department, Copenhagen University Hospital (Holbæk Hospital), Holbæk, Denmark.,Institute of Clinical Medicine, Faculty of Medicine, Copenhagen University , Copenhagen , Denmark
| | - Michael J McKenna
- Institute for Health and Sport, Victoria University , Melbourne, Victoria , Australia
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7
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8
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Gravel H, Jacquemet V, Dahdah N, Curnier D. Clinical applications of QT/RR hysteresis assessment: A systematic review. Ann Noninvasive Electrocardiol 2017; 23. [PMID: 29083088 DOI: 10.1111/anec.12514] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 09/17/2017] [Indexed: 12/15/2022] Open
Abstract
BACKGROUND QT/RR hysteresis (QT-hys) is an index of the time accommodation of ventricular repolarization to heart rate changes. This report comprehensively reviews studies addressing QT-hys as a biomarker of medical conditions. METHODS This is a secondary analysis of data from a recent systematic review pertaining to methods of assessment of QT-hys. Articles included in the former review were filtered in order to select original articles investigating the association of QT-hys with medical conditions in humans. RESULTS Nineteen articles fulfilled our inclusion criteria. Given the heterogeneity of the methods and investigated conditions, no pooled analysis of data could be implemented. QT-hys was mostly studied as a risk marker of severe arrhythmias, as a predictor of the long QT syndrome (LQTS) phenotypes and genotypes and as a marker of exercise-induced ischemia. An increased QT-hys appears to be implicated in arrhythmogenesis, although the evidence in this regard relies on few human studies. An augmented QT-hys was reported in the LQTS, predominantly in the LQT2 genotype, but conflicting results were obtained between studies using different methods of assessment. In addition, QT-hys appears to be a useful marker of stress-induced myocardial ischemia in patients suspected of coronary artery disease. CONCLUSIONS QT-hys evaluation has potential clinical utility in at least some clinical conditions. Further studies of the clinical validity of QT-hys assessment are warranted, particularly condition specific studies based on QT-hys evaluation methods that provide separate estimates of QT-hys and QT/RR dependency.
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Affiliation(s)
- Hugo Gravel
- Department of Kinesiology, University of Montreal, Montreal, QC, Canada
| | - Vincent Jacquemet
- Department of Pharmacology and Physiology, Faculty of Medicine, University of Montreal, Montreal, QC, Canada
| | - Nagib Dahdah
- Division of Pediatric Cardiology and CHU Ste-Justine Research Center, CHU Ste-Justine, Montreal, QC, Canada
| | - Daniel Curnier
- Department of Kinesiology, University of Montreal, Montreal, QC, Canada
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9
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Jacquemet V, Gravel H, Curnier D, Vinet A. Theoretical and experimental comparison of lag-based and time-based exponential moving average models of QT hysteresis. Physiol Meas 2017; 38:1885-1905. [PMID: 28885987 DOI: 10.1088/1361-6579/aa8b59] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE In the electrocardiogram, adaptation of the QT interval to variations in heart rate is not instantaneous. Quantification of this hysteresis phenomenon relies on mathematical models describing the relation between the RR and QT time series. These models reproduce hysteresis through an effective RR interval computed as a linear combination of the history of past RR intervals. This filter depends on a time constant parameter that may be used as a biomarker. APPROACH The most common hysteresis model is based on an autoregressive filter with an impulse response that decreases exponentially with the beat number (lag-based model). Recognizing that the QT time series is unevenly spaced, we propose two exponential moving average filters (time-based models) to define the effective RR interval: one with an impulse response that decreases exponentially with time in seconds, and one with a step response that relaxes exponentially with time in seconds. These two filters are neither linear nor time-invariant. Recurrence formulas are derived to enable efficient implementation. MAIN RESULTS Application to clinical signals recorded during tilt table test, exercise and 24 h Holter demonstrates that the three models perform similarly in terms of goodness-of-fit. When comparing the hysteresis time constant in two conditions with different heart rates, however, the time-based models are shown to reduce the bias on the hysteresis time constant caused by heart rate acceleration and deceleration. SIGNIFICANCE Time-based models should be considered when intergroup differences in both heart rate and QT hysteresis are expected.
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Affiliation(s)
- Vincent Jacquemet
- Département de Pharmacologie et Physiologie, Institut de Génie Biomédical, Université de Montréal, Montréal, Canada. Hôpital du Sacré-Coeur de Montréal, Centre de Recherche, Montréal, Canada
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10
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Gravel H, Curnier D, Dahdah N, Jacquemet V. Categorization and theoretical comparison of quantitative methods for assessing QT/RR hysteresis. Ann Noninvasive Electrocardiol 2017; 22. [PMID: 28510313 DOI: 10.1111/anec.12463] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/14/2017] [Accepted: 03/27/2017] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND In the human electrocardiogram, there is a lag of adaptation of the QT interval to heart rate changes, usually termed QT/RR hysteresis (QT-hys). Subject-specific quantifiers of QT-hys have been proposed as potential biomarkers, but there is no consensus on the choice of the quantifier. METHODS A comprehensive literature search was conducted to identify original articles reporting quantifiers of repolarization hysteresis from the surface ECG in humans. RESULTS Sixty articles fulfilled our inclusion criteria. Reported biomarkers were grouped under four categories. A simple mathematical model of QT/RR loop was used to illustrate differences between the methods. Category I quantifiers use direct measurement of QT time course of adaptation. They are limited to conditions where RR intervals are under strict control. Category IIa and IIb quantifiers compare QT responses during consecutive heart rate acceleration and deceleration. They are relevant when a QT/RR loop is observed, typically during exercise and recovery, but are not robust to protocol variations. Category III quantifiers evaluate the optimum RR memory in dynamic QT/RR relationship modeling. They estimate an intrinsic memory parameter independent from the nature of RR changes, but their reliability remains to be confirmed when multiple memory parameters are estimated. Promising approaches include the differentiation of short-term and long-term memory and adaptive estimation of memory parameters. CONCLUSION Model-based approaches to QT-hys assessment appear to be the most versatile, as they allow separate quantification of QT/RR dependency and QT-hys, and can be applied to a wide range of experimental settings.
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Affiliation(s)
- Hugo Gravel
- Department of Kinesiology, University of Montreal, Montréal, QC, Canada
| | - Daniel Curnier
- Department of Kinesiology, University of Montreal, Montréal, QC, Canada
| | - Nagib Dahdah
- Division of Pediatric Cardiology and CHU Ste-Justine Research Center, CHU Ste-Justine, Montréal, QC, Canada
| | - Vincent Jacquemet
- Department of Pharmacology and Physiology, Faculty of Medicine, University of Montreal, Montréal, QC, Canada
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Hurtado-Sierra D, Rivera-Rodríguez L. Anomalía de Ebstein y síndrome de QT largo congénito. A propósito de un caso. ARCHIVOS DE CARDIOLOGIA DE MEXICO 2017; 87:178-180. [DOI: 10.1016/j.acmx.2016.04.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2015] [Revised: 04/21/2016] [Accepted: 04/22/2016] [Indexed: 11/24/2022] Open
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Schilling JM, Horikawa YT, Zemljic-Harpf AE, Vincent KP, Tyan L, Yu JK, McCulloch AD, Balijepalli RC, Patel HH, Roth DM. Electrophysiology and metabolism of caveolin-3-overexpressing mice. Basic Res Cardiol 2016; 111:28. [PMID: 27023865 DOI: 10.1007/s00395-016-0542-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Accepted: 02/17/2016] [Indexed: 10/22/2022]
Abstract
Caveolin-3 (Cav-3) plays a critical role in organizing signaling molecules and ion channels involved in cardiac conduction and metabolism. Mutations in Cav-3 are implicated in cardiac conduction abnormalities and myopathies. Additionally, cardiac-specific overexpression of Cav-3 (Cav-3 OE) is protective against ischemic and hypertensive injury, suggesting a potential role for Cav-3 in basal cardiac electrophysiology and metabolism involved in stress adaptation. We hypothesized that overexpression of Cav-3 may alter baseline cardiac conduction and metabolism. We examined: (1) ECG telemetry recordings at baseline and during pharmacological interventions, (2) ion channels involved in cardiac conduction with immunoblotting and computational modeling, and (3) baseline metabolism in Cav-3 OE and transgene-negative littermate control mice. Cav-3 OE mice had decreased heart rates, prolonged PR intervals, and shortened QTc intervals with no difference in activity compared to control mice. Dobutamine or propranolol did not cause significant changes between experimental groups in maximal (dobutamine) or minimal (propranolol) heart rate. Cav-3 OE mice had an overall lower chronotropic response to atropine. The expression of Kv1.4 and Kv4.3 channels, Nav1.5 channels, and connexin 43 were increased in Cav-3 OE mice. A computational model integrating the immunoblotting results indicated shortened action potential duration in Cav-3 OE mice linking the change in channel expression to the observed electrophysiology phenotype. Metabolic profiling showed no gross differences in VO2, VCO2, respiratory exchange ratio, heat generation, and feeding or drinking. In conclusion, Cav-3 OE mice have changes in ECG intervals, heart rates, and cardiac ion channel expression. These findings give novel mechanistic insights into previously reported Cav-3 dependent cardioprotection.
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Affiliation(s)
- Jan M Schilling
- Veterans Affairs San Diego Healthcare System, San Diego, CA, USA.,Department of Anesthesiology, University of California San Diego, La Jolla, CA, USA
| | - Yousuke T Horikawa
- Department of Pediatrics, University of California San Diego, La Jolla, CA, USA.,Department of Pediatrics, Sharp Rees-Stealy Medical Group, San Diego, CA, USA
| | - Alice E Zemljic-Harpf
- Veterans Affairs San Diego Healthcare System, San Diego, CA, USA.,Department of Anesthesiology, University of California San Diego, La Jolla, CA, USA
| | - Kevin P Vincent
- Department of Bioengineering, University of California San Diego, La Jolla, CA, USA
| | - Leonid Tyan
- Department of Medicine, Cellular and Molecular Arrhythmia Research Program, University of Wisconsin, Madison, WI, USA
| | - Judith K Yu
- Department of Anesthesiology, University of California San Diego, La Jolla, CA, USA
| | - Andrew D McCulloch
- Department of Bioengineering, University of California San Diego, La Jolla, CA, USA.,Department of Medicine, University of California San Diego, La Jolla, CA, USA
| | - Ravi C Balijepalli
- Department of Medicine, Cellular and Molecular Arrhythmia Research Program, University of Wisconsin, Madison, WI, USA
| | - Hemal H Patel
- Veterans Affairs San Diego Healthcare System, San Diego, CA, USA.,Department of Anesthesiology, University of California San Diego, La Jolla, CA, USA
| | - David M Roth
- Veterans Affairs San Diego Healthcare System, San Diego, CA, USA. .,Department of Anesthesiology, University of California San Diego, La Jolla, CA, USA.
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13
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Cheung CC, Laksman ZWM, Mellor G, Sanatani S, Krahn AD. Exercise and Inherited Arrhythmias. Can J Cardiol 2016; 32:452-8. [PMID: 26927864 DOI: 10.1016/j.cjca.2016.01.007] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Revised: 12/29/2015] [Accepted: 01/06/2016] [Indexed: 01/11/2023] Open
Abstract
Sudden cardiac death (SCD) in an apparently healthy individual is a tragedy that prompts a series of investigations to identify the cause of death and to prevent SCD in potentially at-risk family members. Several inherited channelopathies and cardiomyopathies, including long QT syndrome (LQTS), catecholaminergic polymorphic ventricular cardiomyopathy (CPVT), hypertrophic cardiomyopathy (HCM), and arrhythmogenic right ventricular cardiomyopathy (ARVC) are associated with exercise-related SCD. Exercise restriction has been a historical mainstay of therapy for these conditions. Syncope and cardiac arrest occur during exercise in LQTS and CPVT because of ventricular arrhythmias, which are managed with β-blockade and exercise restriction. Exercise may provoke hemodynamic or ischemic changes in HCM, leading to ventricular arrhythmias. ARVC is a disease of the desmosome, whose underlying disease process is accelerated by exercise. On this basis, expert consensus has erred on the side of caution, recommending rigorous exercise restriction for all inherited arrhythmias. With time, as familiarity with inherited arrhythmia conditions has increased and patients with milder forms of disease are diagnosed, practitioners have questioned the historical rigorous restrictions advocated for all. This change has been driven by the fact that these are often children and young adults who wish to lead active lives. Recent evidence suggests a lower risk of exercise-related arrhythmias in treated patients than was previously assumed, including those with previous symptoms managed with an implantable cardioverter-defibrillator. In this review, we emphasize shared decision making, monitored medical therapy, individual and team awareness of precautions and emergency response measures, and a more permissive approach to recreational and competitive exercise.
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Affiliation(s)
- Christopher C Cheung
- Division of Cardiology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Zachary W M Laksman
- Division of Cardiology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Gregory Mellor
- Division of Cardiology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Shubhayan Sanatani
- Children's Heart Centre, BC Children's Hospital, Vancouver, British Columbia, Canada
| | - Andrew D Krahn
- Division of Cardiology, University of British Columbia, Vancouver, British Columbia, Canada.
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Swenne CA. Mechanisms of exercise-recovery hysteresis in the ECG: ISCE 2015 paper. J Electrocardiol 2015; 48:1006-9. [PMID: 26336871 DOI: 10.1016/j.jelectrocard.2015.08.016] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2015] [Indexed: 10/23/2022]
Abstract
This paper gives an overview of multiple factors, like the mechanisms governing rate adaptation of ventricular action potentials and autonomic mechanisms, which play a role in the genesis of exercise-recovery hysteresis in the ECG. It also discusses the possible association between exercise-recovery ECG hysteresis and arrhythmogeneity.
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Affiliation(s)
- Cees A Swenne
- Cardiology Department, Leiden University Medical Center, Leiden, the Netherlands.
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Zhang Y, Bao M, Dai M, Zhong H, Li Y, Tan T. QT hysteresis index improves the power of treadmill exercise test in the screening of coronary artery disease. Circ J 2014; 78:2942-9. [PMID: 25311775 DOI: 10.1253/circj.cj-14-0697] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND QT hysteresis phenomenon exists in healthy subjects, and is more exaggerated in patients with coronary artery disease (CAD) and long QT syndrome. The purpose of this study was to establish an appropriate method to evaluate the magnitude of QT hysteresis, and assess the value of QT hysteresis index in the treadmill exercise test (TET) in predicting CAD. METHODS AND RESULTS: A total of 138 subjects with suspected CAD and referred for TET and selective coronary angiography (SCA) were divided into positive (n=77) and negative (n=61) SCA groups. Dynamic ECG were recorded during TET. QT/RR curves were constructed and QTp (Q-Tpeak) and QTe (Q-Tend) hysteresis indices were calculated for each subject. SYNTAX score in the positive SCA group was determined. The QTp and QTe hysteresis indices in the positive SCA group were significantly higher than in the negative SCA group. The combination of QTe hysteresis index and conventional TET criteria had the highest sensitivity and negative predictive value according to receiver operating characteristic curve, and was an independent predictor on multivariate logistic regression. QT hysteresis indices significantly correlated with SYNTAX score in the positive SCA group. CONCLUSIONS QTe hysteresis index enhances the specificity of predicting CAD in TET. It improves the diagnostic value of TET for CAD significantly when combined with conventional criteria and is associated with the severity of CAD.
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Affiliation(s)
- Yijie Zhang
- Department of Cardiology, Wuhan University, Renmin Hospital
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Bennett MT, Gula LJ, Klein GJ, Skanes AC, Yee R, Leong-Sit P, Chattha I, Sy R, Jones DL, Krahn AD. Effect of beta-blockers on QT dynamics in the long QT syndrome: measuring the benefit. ACTA ACUST UNITED AC 2014; 16:1847-51. [DOI: 10.1093/europace/euu086] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Fossa AA, Zhou M, Brennan N, Round P, Ford J. Use of continuous ECG for improvements in assessing the standing response as a positive control for QT prolongation. Ann Noninvasive Electrocardiol 2013; 19:82-9. [PMID: 24460808 DOI: 10.1111/anec.12079] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
BACKGROUND Standing invoked change in QT interval has been identified as a promising autonomic maneuver for the assessment of QT/QTc prolongation in patients with underlying heart abnormalities or as a positive control in healthy volunteers for drug studies. Criticism for its more widespread use is the high variability in reported results and the need for a more standardized methodology with defined normal ranges. METHODS Forty healthy male subjects underwent continuous ECG collection on the day before dosing in a double-blind, placebo-controlled, randomized, single ascending dose trial. A brisk supine to standing (3 minutes) response was conducted at three time points. Results were grouped by treatment cohort or assessed as a pooled group at each time point. Maximum time and median change from baseline (ΔTmax QTcF, ΔQTcF) were calculated for each individual over sequential 30-second periods staggered by 5 seconds. RESULTS Maximum ΔQTcF at all time points and in all groups was significant (i.e., the lower bound of 90% CI was > 5 milliseconds) which is the ICH E14 regulatory requirement for a positive control. Variability of the time to maximum response was also reduced 9-fold by the third time period. CONCLUSIONS Standing invoked ΔQTcF can be utilized to validate the sensitivity of a study for assessment of the QT interval effect of drugs in early development. The methodology may be used to further improve its diagnostic use of long QT syndromes by reducing the variability and allowing adequate definition of normal limits.
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Tran CT, Bundgaard H, Ladefoged SD, Haunsø S, Kjeldsen K. Potassium dynamics are attenuated in hyperkalemia and a determinant of QT adaptation in exercising hemodialysis patients. J Appl Physiol (1985) 2013; 115:498-504. [PMID: 23722704 DOI: 10.1152/japplphysiol.01019.2012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Disturbances in plasma potassium concentration (pK) are well known risk factors for the development of cardiac arrhythmia. The aims of the present study were to evaluate the effect of hemodialysis on exercise pK dynamics and QT hysteresis, and whether QT hysteresis is associated with the pK decrease following exercise. Twenty-two end-stage renal disease patients exercised on a cycle ergometer with incremental work load before and after hemodialysis. ECG was recorded and pK was measured during exercise and recovery. During exercise, pK increased from 5.1 ± 0.2 to 6.1 ± 0.2 mM (mean ± SE; P < 0.0001) before hemodialysis and from 3.8 ± 0.1 to 5.1 ± 0.1 mM (P < 0.0001) after hemodialysis. After 2 min of recovery, pK had decreased to 5.0 ± 0.2 mM and 4.1 ± 0.1 mM (P < 0.0001) before and after hemodialysis, respectively. pK increase during exercise was accentuated after hemodialysis. The pK increase was negatively linearly correlated with pK before exercise (β = -0.21, R(2) = 0.23, P = 0.001). QT hysteresis was negatively linearly correlated with the decrease in pK during recovery (β = -28 ms/mM, R(2) = 0.36, P = 0.006). Thus, during recovery, low pK was associated with relatively longer QT interval. In conclusion, new major findings are an accentuated increase in pK during exercise after hemodialysis, an attenuated increase in pK in hyperkalemia, and an association between pK and QT interval adaptation during recovery. The acute pK shift after exercise may modulate QT interval adaptation and trigger cardiac arrhythmias.
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Affiliation(s)
- Cao Thach Tran
- Laboratory for Molecular Cardiology, The Heart Centre, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark.
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El síndrome de QT largo: una breve revisión del diagnóstico electrocardiográfico incluyendo la prueba de Viskin. ARCHIVOS DE CARDIOLOGIA DE MEXICO 2012; 82:243-7. [DOI: 10.1016/j.acmx.2012.06.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Accepted: 06/08/2012] [Indexed: 11/22/2022] Open
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Pelchovitz DJ, Ng J, Chicos AB, Bergner DW, Goldberger JJ. QT-RR hysteresis is caused by differential autonomic states during exercise and recovery. Am J Physiol Heart Circ Physiol 2012; 302:H2567-73. [PMID: 22542617 DOI: 10.1152/ajpheart.00041.2012] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
QT-RR hysteresis is characterized by longer QT intervals at a given RR interval while heart rates are increasing during exercise and shorter QT intervals at the same RR interval while heart rates are decreasing during recovery. It has been attributed to a lagging QT response to different directional changes in RR interval during exercise and recovery. Twenty control subjects (8 males, age 51 ± 6 yr), 16 subjects with type 2 diabetes (12 males, age 56 ± 8 yr), 71 subjects with coronary artery disease (CAD) and preserved left ventricular ejection fraction (LVEF) (≥50%) (51 males, age 59 ± 12 yr), and 17 CAD subjects with depressed LVEF (<50%) (13 males, age 57 ± 10 yr) underwent two 16-min exercise tests followed by recovery. In session 2, parasympathetic blockade with atropine (0.04 mg/kg) was achieved at end exercise. QT-RR hysteresis was quantified as: 1) the area bounded by the QT-RR relationships for exercise and recovery in the range of the minimum RR interval at peak exercise to the minimum RR interval + 100 ms and 2) the difference in QT interval duration between exercise and recovery at the minimum RR interval achieved during peak exercise plus 50 ms (ΔQT). The effect of parasympathetic blockade was assessed by substituting the QT-RR relationship after parasympathetic blockade. QT-RR hysteresis was positive in all groups at baseline and reversed by parasympathetic blockade (P < 0.01). We conclude that QT-RR hysteresis is not caused by different directional changes in RR interval during exercise and recovery. Instead, it is predominantly mediated by differential autonomic nervous system effects as the heart rate increases during exercise vs. as it decreases during recovery.
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Affiliation(s)
- Daniel J Pelchovitz
- Division of Cardiology, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611, USA
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LIAN JIE, MUESSIG DIRK, LANG VOLKER. Risk Assessment of R-on-T Event Based on Modeled QT-RR Relationship. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2011; 34:700-8. [DOI: 10.1111/j.1540-8159.2011.03058.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Chattha IS, Sy RW, Yee R, Gula LJ, Skanes AC, Klein GJ, Bennett MT, Krahn AD. Utility of the recovery electrocardiogram after exercise: a novel indicator for the diagnosis and genotyping of long QT syndrome? Heart Rhythm 2010; 7:906-11. [DOI: 10.1016/j.hrthm.2010.03.006] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/21/2010] [Accepted: 03/03/2010] [Indexed: 11/28/2022]
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GRAY CHRISTOPHER, GULA LORNEJ, KLEIN GEORGEJ, SKANES ALLANC, YEE RAYMOND, SY RAYMOND, SALISBURY BENJAMINA, WONG JORGE, CHATTHA ISHVINDER, SUBBIAH RAJESHN, KRAHN ANDREWD. Expression of a Common LQT1 Mutation in Five Apparently Unrelated Families in a Regional Inherited Arrhythmia Clinic. J Cardiovasc Electrophysiol 2010; 21:296-300. [DOI: 10.1111/j.1540-8167.2009.01626.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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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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Open-loop, clockwise QT-RR hysteresis immediately before the onset of torsades de pointes in type 2 long QT syndrome. J Electrocardiol 2010; 43:261-3. [PMID: 20079908 DOI: 10.1016/j.jelectrocard.2009.12.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2009] [Indexed: 11/23/2022]
Abstract
Delay of QT interval adaptation to sudden heart rate change causes hysteresis in dynamic QT-RR relationship. We analyzed QT-RR plotting during and after exercise in a patient with genetically identified type 2 long QT syndrome before and after starting oral propranolol. Blunted QT shortening by exercise and augmented postexercise QT prolongation resulted in an open-loop, clockwise QT-RR hysteresis immediately before the onset of torsades de pointes before propranolol. However, this hysteresis was eliminated by propranolol. QT-RR analysis provided insight into the mechanisms of the onset of torsades de pointes at least in this case of type 2 long QT syndrome.
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Wong JA, Gula LJ, Klein GJ, Yee R, Skanes AC, Krahn AD. Utility of treadmill testing in identification and genotype prediction in long-QT syndrome. Circ Arrhythm Electrophysiol 2010; 3:120-5. [PMID: 20071715 DOI: 10.1161/circep.109.907865] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND The clinical diagnosis of long-QT syndrome (LQTS) remains challenging when ECG abnormalities are borderline or intermittent. Despite issues with access, cost, and heterogeneity of LQTS mutations, genetic testing remains the diagnostic gold standard for diagnosis of LQTS. We sought to develop a provocative testing strategy to unmask the LQTS phenotype and relate this to the results of genetic testing. METHODS AND RESULTS From 1995 to 2008, 159 consecutive patients with suspected LQTS underwent provocative testing that consisted of a modified Bruce protocol treadmill exercise test, with ECGs recorded supine at rest, immediately on standing, and at 1-minute intervals during exercise, at peak exercise, and at 1-minute intervals during the recovery phase. Similar testing was carried out on a stationary bike in a gradual and burst exercise fashion. LQTS was confirmed with genotyping in all 95 affected LQTS patients and excluded with negative family screening in 64 control subjects. Patients were studied before and after initiation of beta-blockers. Of 159 patients, 50 had an LQT1 mutation and 45 had an LQT2 mutation. In the LQTS group, 44.3% of patients had a normal-to-borderline resting QTc interval. LQTS patients exhibited a greater prolongation in QTc with postural change than unaffected patients (LQT1: 40 ms [IQR, 42]; LQT2: 35 ms [IQR, 46]; and LQTS-negative: 21 ms [IQR, 37]; P=0.029). During exercise, LQT1 patients had marked QTc prolongation compared with LQT2 and LQTS-negative patients (LQT1: 65 ms [60], LQT2: 3 ms [46], LQTS negative: 5 ms [41]; P<0.0001). QT hysteresis was more pronounced in patients with LQT2 mutations compared with LQT1 and LQT-negative patients (LQT2: 40 ms [10], LQT1: 15 ms [40]; LQTS-negative: 20 ms [20]; P<0.001). beta-Blockade normalized the QTc changes seen with standing and QT hysteresis. CONCLUSIONS The presence and genotype of LQTS can be predicted by a combination of postural and exercise changes in the QT/RR relationship. beta-Blockade normalized these changes. Routine exercise testing is useful in predicting and directing genetic testing in LQTS.
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Affiliation(s)
- Jorge A Wong
- Arrhythmia Service, Division of Cardiology, University of Western Ontario, London, Ontario, Canada
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Abstract
PURPOSE To measure the corrected QT cardiac repolarization time before and during epileptic seizures. METHODS Thirty-nine video-EEG/ECG/SAO(2) (electroencephalography/electrocardiography/oxygen saturation) telemetry patients were included in this prospective study. Epileptic seizures were identified both clinically and electrographically. RR intervals and associated QT intervals were measured 5 min prior to the onset of the identified seizure. Consecutive RR and associated QT intervals were then measured from the seizure onset until the seizure had ended and the EEG had resumed its preseizure trace. Averaged RR and QT intervals over nine consecutive beats were applied to Bazett's, Hodge's, Fridericia's, and Framingham's formulas to compare the corrected QT values before and during the seizures. RESULTS A total of 156 seizures had corrected QT analysis performed. Nine generalized tonic-clonic seizures (5 patients), 34 absences (6 patients), 12 tonic seizures (6 patients), 27 temporal lobe seizures (14 patients), 58 frontal lobe seizures (4 patients), and 16 subclinical seizures (4 patients). All formulae reported a statistically significant difference in corrected QT (p < 0.001) during total seizure data compared to total preseizure values. According to Bazett's formula, 21 seizures (nine patients) transiently increased their corrected QT beyond normal limits, with a maximum corrected QT of 512 ms during a right temporal lobe seizure. CONCLUSION Significant lengthening of corrected QT cardiac repolarization time occurred during some epileptic seizures in this study. Prolonged corrected QT may have a role in sudden unexplained death in epilepsy (SUDEP).
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Affiliation(s)
- Ruth Brotherstone
- Department of Clinical Neurophysiology, Western General Hospital, Edinburgh, United Kingdom.
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Cardiac regulation and electrocardiographic factors contributing to the measurement of repolarization variability. J Electrocardiol 2009; 42:494-9. [PMID: 19716566 DOI: 10.1016/j.jelectrocard.2009.06.019] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2009] [Indexed: 11/22/2022]
Abstract
Cellular and macroelectrical instability within the heart ventricles during repolarization is described as a potential triggering mechanism of life-threatening arrhythmias. Although this phenomenon was observed in animal and in vitro studies, significant efforts have been put into the design of computerized technologies to quantify very subtle variations of the repolarization signal from the surface electrocardiograms. These technologies aim at capturing repolarization instability of ventricular repolarization while controlling for the normal variability. Currently, the methods have focused on the autonomic regulation of the heart rate as a primary confounding factor (such as in the QT variability index). However, there are other factors that can influence the measurements of beat-to beat variability of the repolarization segment. Among them, the amplitude of the repolarization signal, the selected lead, and the heart vector orientation are very important and too often neglected in clinical investigations. We will discuss these factors and provocatively describe why they should be cautiously considered to avoid erroneous measurements of repolarization instability.
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Kannankeril PJ, Harris PA, Norris KJ, Warsy I, Smith PD, Roden DM. Rate-independent QT shortening during exercise in healthy subjects: terminal repolarization does not shorten with exercise. J Cardiovasc Electrophysiol 2008; 19:1284-8. [PMID: 18665873 DOI: 10.1111/j.1540-8167.2008.01266.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
INTRODUCTION QT interval for a given heart rate differs between exercise and recovery (QT hysteresis) due to slow QT adaptation to changes in heart rate. We hypothesized that QT hysteresis is evident within stages of exercise and investigated which component of the QT contributes to hysteresis. METHODS AND RESULTS Nineteen healthy volunteers performed a staged exercise test (four stages, 3 min each). Continuous telemetry was analyzed with software to compare QT intervals in a rate-independent fashion. QRST complexes during each minute were sorted by RR interval, and complexes in bins of 20 ms width were signal-averaged. QT and QTp (onset of QRS to peak T wave) were measured, and terminal QT calculated (peak to end of T wave, Tpe = QT - QTp). QT, QTp, and Tpe at the same heart rate were compared between the first and last minute of each stage. QT shortened from the first to last minute of exercise in each stage (Stage I: 358 +/- 30 to 346 +/- 25 ms, P < 0.001; Stage II: 342 +/- 27 to 331 +/- 24 ms, P = 0.003; Stage III: 329 +/- 21 to 322 +/- 18 ms, P = 0.03; Stage IV: 313 +/- 22 to 303 +/- 23 ms, P = 0.005). QTp also shortened in each stage, while Tpe was unchanged. CONCLUSION QT hysteresis occurs during exercise in normals, and the major determinant is shortening of the first component of the T wave. Terminal repolarization (peak to end of T wave), a surrogate for transmural dispersion of repolarization, does not shorten significantly with exercise.
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Affiliation(s)
- Prince J Kannankeril
- Oates Institute for Experimental Therapeutics, Clinical Research Center, Department of Biomedical Informatics, Vanderbilt University Medical Center, Nashville, Tennessee 37232-9119, USA.
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The impact of varying autonomic states on the dynamic beat-to-beat QT-RR and QT-TQ interval relationships. Br J Pharmacol 2008; 154:1508-15. [PMID: 18663381 DOI: 10.1038/bjp.2008.123] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The beat-to-beat dynamicity of the QT-RR interval relationship is difficult to assess with the use of traditional correction factors (QTc) and changes in QTc do not accurately reflect or quantify arrhythmogenic risk. Further, the interpretation of arrhythmogenic risk is influenced by autonomic state. To visualize the QT-RR interval dynamics under varying conditions of autonomic state from impaired repolarization, we have developed a system to sequentially plot the beat-to-beat confluence of ECG data or 'clouds' obtained from conscious dogs and humans. To represent the non-uniformity of the clouds, a bootstrap sampling method that computes the mathematical centre of the uncorrected beat-to-beat QT value (QTbtb) and defines the upper and lower 95% confidence bounds is used. The same method can also be used to examine heterogeneity, hysteresis (both acceleration and deceleration) and restitution (beat-to-beat QT-TQ interval relationship). Impaired repolarization with the combination of E-4031 and L-768,673 (inhibitor of IKs current) increased heterogeneity of restitution at rest 55-91%; increased hysteresis during heart rate acceleration after isoproterenol challenge by approximately 40-60%; and dramatically diminished the minimum TQ boundary by 72% to only 28 ms. Impaired repolarization alters restitution during normal sinus rhythm and increases hysteresis/heterogeneity during heart rate acceleration following sympathetic stimulation. These findings are supported by similar clinical observations in LQT1 and LQT2 syndromes. Therefore, the assessment of the dynamic QT-RR and QT-TQ interval relationships through quantification of heterogeneity, hysteresis and restitution may allow a more accurate non-invasive evaluation of the conditions leading to cardiac arrhythmia.
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Fossa AA, Wisialowski T, Crimin K, Wolfgang E, Couderc JP, Hinterseer M, Kaab S, Zareba W, Badilini F, Sarapa N. Analyses of dynamic beat-to-beat QT-TQ interval (ECG restitution) changes in humans under normal sinus rhythm and prior to an event of torsades de pointes during QT prolongation caused by sotalol. Ann Noninvasive Electrocardiol 2008; 12:338-48. [PMID: 17970959 DOI: 10.1111/j.1542-474x.2007.00183.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND Restitution through intracardiac pacing has been used to assess arrhythmia vulnerability. We examined whether analyses of sequential beat-to-beat QT and TQ interval measures can be used to quantify ECG restitution changes under normal sinus rhythm. METHODS The QT, R-R and TQ intervals were examined 22.5 hour Holter monitoring before and after oral sotalol in normal male and female volunteers. Additionally, comparisons were made to those observed in the time-matched dataset prior to torsades de pointes in a heart diseased patient that received a single dose of sotalol. RESULTS Sotalol increased QT, R-R and TQ intervals 71, 101, and 125 ms after 160 mg (n = 38) and 194, 235, and 135 ms after 320 mg (n = 19) during maximum plasma concentrations, respectively. The percentage of beats with a QT/TQ ratio >1 was reduced 25% over the entire 22.5 hours after sotalol and the lower TQ interval boundary (5th quantile) was increased 22-30%. In contrast, 99% of the beats prior to torsades de pointes had a QT/TQ ratio > 1 and the median TQ interval was below the lower 98% confidence bounds of normals before and after sotalol. CONCLUSIONS ECG restitution changes are quantifiable under varying states (nocturnally, beta-adrenergic blockade, QT prolongation) in healthy subjects.
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Affiliation(s)
- Anthony A Fossa
- Pfizer Global Research and Development, Groton, Connecticut 06340, USA.
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Abstract
Congenital long QT syndrome (LQTS) is one of the most common cardiac channelopathies and is characterized by prolonged ventricular repolarization and life-threatening arrhythmias. The mortality is high among untreated patients. The identification of several LQTS genes has had a major impact on the management strategy for both patients and family members. An impressive genotype-phenotype correlation has been noted and genotype identification has enabled genotype specific therapies. Beta blockers continue to be the primary treatment for prevention of life threatening arrhythmias in the majority of patients. Other therapeutic options include pacemakers, implantable cardioverter defibrillators, left cardiac sympathetic denervation, sodium channel blocking medications and lifestyle modification.
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Affiliation(s)
- Maully Shah
- The Cardiac Center, The Children's Hospital of Philadelphia, Philadelphia, USA
| | - Christopher Carter
- The Cardiac Center, The Children's Hospital of Philadelphia, Philadelphia, USA
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Identifying coronary artery flow reduction and ischemia using quasistationary QT/RR-interval hysteresis measurements. J Electrocardiol 2007; 40:S91-6. [DOI: 10.1016/j.jelectrocard.2007.05.024] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2007] [Accepted: 05/14/2007] [Indexed: 11/17/2022]
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Lauer MS, Pothier CE, Chernyak YB, Brunken R, Lieber M, Apperson-Hansen C, Starobin JM. Exercise-induced QT/R-R–interval hysteresis as a predictor of myocardial ischemia. J Electrocardiol 2006; 39:315-23. [PMID: 16777519 DOI: 10.1016/j.jelectrocard.2005.12.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2005] [Revised: 11/20/2005] [Accepted: 12/13/2005] [Indexed: 11/25/2022]
Abstract
OBJECTIVES Exercise-induced QT/RR hysteresis exists when, for a given R-R interval, the QT interval duration is shorter during recovery after exercise than during exercise. We sought to assess the association between QT/RR hysteresis and imaging evidence of myocardial ischemia. BACKGROUND Because ischemia induces cellular disturbances known to decrease membrane action potential duration, we hypothesized a correlation between QT/RR and myocardial ischemia. METHODS We digitally analyzed 4-second samples of QT duration and R-R-interval duration in 260 patients referred for treadmill exercise stress and rest single photon emission computed tomography myocardial perfusion imaging; a cool-down period was used after exercise. None of the patients were in atrial fibrillation or used digoxin, and none had marked baseline electrocardiographic abnormalities. Stress and rest myocardial perfusion images were analyzed visually and quantitatively to define the extent and severity of stress-induced ischemia. QT/RR hysteresis was calculated using a computerized algorithm. RESULTS There were 82 patients (32%) who manifested myocardial ischemia by single photon emission computed tomography myocardial perfusion imaging. The likelihood of ischemia increased with increasing QT/RR hysteresis, with prevalence according to quartiles of 20%, 30%, 26%, and 49% (P = .003 for trend). In analyses adjusting for ST-segment changes, exercise capacity, heart rate recovery, and other confounders, QT/RR hysteresis was independently predictive of presence of myocardial ischemia (adjusted odds ratio for 100-point increase of QT/RR hysteresis, 1.61; 95% confidence interval, 1.22-2.12; P = .0008). QT/RR hysteresis was also predictive of severe ischemia. CONCLUSION Exercise-induced QT/RR hysteresis is a strong and independent predictor of myocardial ischemia and provides additional information beyond that afforded by standard ST-segment measures.
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Affiliation(s)
- Michael S Lauer
- Department of Cardiovascular Medicine, Cleveland Clinic Foundation, OH 44195, USA.
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Lewis MJ, Short AL. Hysteresis of electrocardiographic depolarization–repolarization intervals during dynamic physical exercise and subsequent recovery. Physiol Meas 2006; 27:191-201. [PMID: 16400205 DOI: 10.1088/0967-3334/27/2/009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The post-exercise electrocardiographic QT interval is shortened relative to that at similar heart rates during exercise or pre-exercise rest. This lag in QT adaptation to the recovering heart rate is described as "hysteresis". No previous studies have quantified the influence of ECG electrode placement on hysteresis following physical exercise. Six males and six females of similar age, mass and aerobic fitness undertook progressive sub-maximal bicycle exercise. A three-channel ECG was recorded continuously during pre-exercise, exercise and recovery. Beat-to-beat NN (cardiac interval) and QT(a) interval (Q wave onset to T wave apex) data were measured for each sinus heart beat. QT(a)-NN hysteresis was calculated as the difference in QT(a) magnitude at identical heart rates during the rest/exercise and post-exercise recovery periods. There were some significant (p < 0.05) between-channel and between-gender differences in calculated hysteresis values. Hysteresis was generally greatest during the second or third minute post-exercise; ranges of means for all channels were 10.9 +/- 11.7 ms to 25.5 +/- 16.8 ms (males) and 19.1 +/- 10.3 ms to 28.4 +/- 3.0 ms (females). For males only, hysteresis values calculated using channel 1 between 1 and 3 min post-exercise were generally significantly (p < 0.05) different to those between 4 and 10 min. Similar trends were observed in females. QT(a)-NN hysteresis is significantly affected by the locations of the ECG electrodes used to record the surface ECG. These results emphasize the need for standardization of ECG electrode placement in future investigations.
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Affiliation(s)
- M J Lewis
- Department of Sports Science, University of Wales-Swansea, Singleton Park, Swansea SA2 8PP, UK.
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Walker BD, Krahn AD, Klein GJ, Skanes AC, Yee R. Burst bicycle exercise facilitates diagnosis of latent long QT syndrome. Am Heart J 2005; 150:1059-63. [PMID: 16290996 DOI: 10.1016/j.ahj.2005.02.041] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/23/2003] [Accepted: 02/15/2005] [Indexed: 01/08/2023]
Abstract
OBJECTIVES The aim of this study was to develop a diagnostic technique to detect latent long QT syndrome. BACKGROUND Asymptomatic patients with genetically diagnosed long QT syndrome (LQTS) may have a normal resting QT interval, yet remain at risk for cardiac events. We hypothesized that the QT response during a novel burst exercise protocol simulating clinical events might distinguish patients with "latent LQTS" from healthy subjects. METHODS A burst bicycle protocol was performed on 31 healthy subjects and 31 patients with LQTS (13 LQT2, 3 LQT1, 15 unknown genotype). The bicycle exercise protocol involved sudden maximal exertion against a fixed workload (200 W) for 1 minute. Digitized 12-lead eletrocardiograms were acquired every 10 seconds at baseline for 1 minute, during 1 minute of burst exercise, and for 5 minutes during recovery. Patients with LQTS were segregated according to whether the baseline QTc was normal (< or = 440 milliseconds, n = 13) or abnormal (> 440 milliseconds, n = 18). RESULTS During exercise, the QTc increased to a greater extent in the group with latent LQTS (DeltaQTc 98 +/- 36 milliseconds) in comparison with controls (DeltaQTc 65 +/- 19 milliseconds, P < .01) and those with baseline QTc prolongation (DeltaQTc 17 +/- 70 milliseconds, P < .01). In patients with a normal baseline QTc, a DeltaQTc > 85 milliseconds had a sensitivity of 85% and a specificity of 86% for LQTS (P = .0004). CONCLUSION Marked QTc prolongation during burst bicycle ergometry provides potentially diagnostic information for patients with normal baseline QTc and suspected LQTS.
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Affiliation(s)
- Bruce D Walker
- Division of Cardiology, University of Western Ontario, London, Ontario, Canada
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Fossa AA, Wisialowski T, Crimin K. QT Prolongation Modifies Dynamic Restitution and Hysteresis of the Beat-to-Beat QT-TQ Interval Relationship during Normal Sinus Rhythm under Varying States of Repolarization. J Pharmacol Exp Ther 2005; 316:498-506. [PMID: 16204470 DOI: 10.1124/jpet.105.095471] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The analysis of cardiac electrical restitution (the relationship between an action potential duration and its preceding diastolic interval) has been used to predict arrhythmia liability. However, the procedure to measure restitution is invasive and disrupts normal physiological autonomic balance. Dynamic analysis of sequential beat-to-beat ECG data was used to study restitution under normal sinus rhythm and to quantify changes in temporal hysteresis with heart rate acceleration/deceleration during QT prolongation. Congenital long QT (LQT) 1 and LQT2 syndromes during sympathetic stimulation were modeled because of their association with increased risk of ventricular arrhythmia. Temporal heterogeneity and hysteresis of restitution were examined in the conscious dog under varying conditions of delayed repolarization using either the selective inhibitors of the slowly activating delayed rectifier potassium current (R)-2-(4-trifluoromethyl)-N-[2-oxo-5-phenyl-1-(2,2,2-trifluoroethyl)-2,3-dihydro-1H-benzo[e][1,4]diazepin-3-yl]acetamide (L-768,673); the rapidly activating delayed rectifier potassium current (1-[2-(6-methyl-2-pyridyl)ethyl]-4-methyl-sulfonylaminobenzoyl)-piperidine (E-4031); or a combination of both at rest and during heart rate acceleration with sympathetic stimulation using isoproterenol challenges. Impaired repolarization with the combination of E-4031 and L-768,673 increased heterogeneity of restitution at rest 55 to 91%, increased hysteresis during heart rate acceleration after isoproterenol challenge by approximately 40 to 60%, and dramatically reduced the minimum TQ interval by 72% to only 28 ms. Impaired repolarization alters restitution during normal sinus rhythm and increases hysteresis/heterogeneity during heart rate acceleration following sympathetic stimulation. Thus, dynamic beat-to-beat measurements of restitution could lead to clinically applicable ECG obtained biomarkers for assessment of changes associated with arrhythmogenic risk.
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Affiliation(s)
- Anthony A Fossa
- Pfizer Global Research and Development, Groton, CT 06340, USA.
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Krahn AD, Gollob M, Yee R, Gula LJ, Skanes AC, Walker BD, Klein GJ. Diagnosis of unexplained cardiac arrest: role of adrenaline and procainamide infusion. Circulation 2005; 112:2228-34. [PMID: 16203906 DOI: 10.1161/circulationaha.105.552166] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
BACKGROUND Cardiac arrest with preserved left ventricular function may be caused by uncommon genetic conditions. Although these may be evident on the ECG, long-term monitoring or provocative testing is often necessary to unmask latent primary electrical disease. METHODS AND RESULTS Patients with unexplained cardiac arrest and no evident cardiac disease (normal left ventricular function, coronary arteries, and resting corrected QT) underwent pharmacological challenge with adrenaline and procainamide infusions to unmask subclinical primary electrical disease. Family members underwent noninvasive screening and directed provocative testing on the basis of findings in the proband. Eighteen patients (mean+/-SD age, 41+/-17 years; 11 female) with unexplained cardiac arrest were assessed. The final diagnosis was catecholaminergic ventricular tachycardia (CPVT) in 10 patients (56%), Brugada syndrome in 2 patients (11%), and unexplained (idiopathic ventricular fibrillation) in 6 patients (33%). Of 55 family members (mean+/-SD age, 27+/-17 years; 33 female), 9 additional affected family members were detected from 2 families, with a single Brugada syndrome patient and 8 CPVT patients. CONCLUSIONS Provocative testing with adrenaline and procainamide infusions is useful in unmasking the etiology of apparent unexplained cardiac arrest. This approach helps to diagnose primary electrical disease, such as CPVT and Brugada syndrome, and provides the opportunity for therapeutic intervention in identified, asymptomatic family members who harbor the same disease.
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Affiliation(s)
- Andrew D Krahn
- Division of Cardiology, University of Western Ontario, London, Canada.
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Abstract
Drug therapy can reduce the incidence of sudden death in many subgroups of patients. Patients who have long QT syndrome, in particular, benefit significantly from the use of beta-blockers and other antiarrhythmic agents. Although less useful, drug therapy has an important adjunctive role in patients who have conditions, such as hypertrophic cardiomyopathy and congestive heart failure. Proarrhythmia, which is a potentially dangerous side effect of drug therapy, needs to be watched for with special care in this group of high-risk patients.
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Affiliation(s)
- Seshadri Balaji
- Division of Cardiology, Oregon Health & Science University, 707 SW Gaines Road, Mailcode CDRC-P, Portland, OR 97239, USA.
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Pueyo E, Smetana P, Caminal P, de Luna AB, Malik M, Laguna P. Characterization of QT Interval Adaptation to RR Interval Changes and Its Use as a Risk-Stratifier of Arrhythmic Mortality in Amiodarone-Treated Survivors of Acute Myocardial Infarction. IEEE Trans Biomed Eng 2004; 51:1511-20. [PMID: 15376499 DOI: 10.1109/tbme.2004.828050] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
A new method is proposed to evaluate the dynamics of QT interval adaptation in response to heart rate (HR) changes. The method considers weighted averages of RR intervals (RR) preceding each cardiac beat to express RR interval history accounting for the influence on repolarization duration. A global optimization algorithm is used to determine the weight distribution leading to the lowest regression residual when curve fitting the [QT, RR1 data using a patient-specific regression model. From the optimum weight distribution, a memory lag L90 is estimated, expressing the delay in the QT adaptation to HR changes. On average, RR intervals of the past 150 beats (approximately 2.5 min) are required to model the QT response accurately. From a clinical point of view, the interval of the initial tens of seconds to one minute seems to be most important in the majority of cases. A measure of the optimum regression residual (r(opt)) has been calculated, discriminating between post-myocardial infarction patients at high and low risk of arrhythmic death while on treatment with amiodarone. A similar discrimination has been achieved with a variable expressing the character of QT lag behind the RR interval dynamics.
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Affiliation(s)
- Esther Pueyo
- Communications Technology Group (GTC), Aragón Institute for Engineering Research (13A), University of Zaragoza, 50018 Zaragoza, Spain.
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Khan IA, Gowda RM. Novel therapeutics for treatment of long-QT syndrome and torsade de pointes. Int J Cardiol 2004; 95:1-6. [PMID: 15159030 DOI: 10.1016/j.ijcard.2003.04.018] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/06/2002] [Revised: 04/04/2003] [Accepted: 04/13/2003] [Indexed: 11/15/2022]
Abstract
Long-QT syndrome is a clinically and genetically heterogeneous syndrome characterized by lengthening of the QT interval and increased dispersion of the ventricular repolarization on surface electrocardiogram and a propensity to malignant ventricular arrhythmias, torsade de pointes and ventricular fibrillation, which may lead to sudden cardiac death. Long-QT syndrome mostly affects adolescents and young adults with structurally and functionally normal hearts and is caused by aberrations in potassium and sodium ion channels. Standard therapies for long-QT syndrome include correction of the underlying cause, alleviation of the precipitating factors, magnesium sulfate, isoproterenol, antiadrenergic therapy (beta-adrenergic receptor blockers, left cervicothoracic sympathectomy), cardiac pacing, and implantable cardioverter defibrillator. The potential therapies include sodium channel blockers (mexiletine, flecainide, lidocaine, pentisomide, phenytoin), potassium, potassium channel activators (nicorandil, pinacidil, cromakalim), alpha-adrenergic receptor blockers, calcium channel blockers, atropine, and protein kinase inhibitors. The purpose of this review is to outline the established therapies and update the recent advances and potential future strategies in the treatment of long-QT syndrome and torsade de pointes.
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Affiliation(s)
- Ijaz A Khan
- Division of Cardiology, Creighton University School of Medicine, 3006 Webster Street, Omaha, NE 68131, USA.
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