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Tse G, Wong ST, Tse V, Lee YT, Lin HY, Yeo JM. Cardiac dynamics: Alternans and arrhythmogenesis. J Arrhythm 2016; 32:411-417. [PMID: 27761166 PMCID: PMC5063258 DOI: 10.1016/j.joa.2016.02.009] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Revised: 01/28/2016] [Accepted: 02/22/2016] [Indexed: 12/23/2022] Open
Abstract
Pre-existing heterogeneities present in cardiac tissue are essential for maintaining the normal electrical and mechanical functions of the heart. Exacerbation of such heterogeneities or the emergence of dynamic factors can produce repolarization alternans, which are beat-to-beat alternations in the action potential time course. Traditionally, this was explained by restitution, but additional factors, such as cardiac memory, calcium handling dynamics, refractory period restitution, and mechano-electric feedback, are increasingly recognized as the underlying causes. The aim of this article is to review the mechanisms that generate cardiac repolarization alternans and convert spatially concordant alternans to the more arrhythmogenic spatially discordant alternans. This is followed by a discussion on how alternans generate arrhythmias in a number of clinical scenarios, and concluded by an outline of future therapeutic targets for anti-arrhythmic therapy.
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Affiliation(s)
- Gary Tse
- School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong
| | - Sheung Ting Wong
- Faculty of Medicine, Imperial College London, SW7 2AZ London, UK
| | - Vivian Tse
- Department of Physiology, McGill University, Canada
| | - Yee Ting Lee
- School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong
| | - Hiu Yu Lin
- School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong
| | - Jie Ming Yeo
- Faculty of Medicine, Imperial College London, SW7 2AZ London, UK
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Burattini L, Man S, Fioretti S, Di Nardo F, Swenne CA. Heart Rate-Dependent Hysteresis of T-Wave Alternans in Primary Prevention ICD Patients. Ann Noninvasive Electrocardiol 2015; 21:460-9. [PMID: 26671620 DOI: 10.1111/anec.12330] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND T-wave alternans (TWA) is usually performed at accelerated heart rates (HR) during exercise, while recovery TWA is typically not analyzed. Consequently, it is still unknown if TWA shows a HR-dependent hysteresis or not. Thus, the aim of the present study was to investigate TWA dependency on HR during both the exercise and recovery phases of an ergometer test, and to evaluate if recovery TWA may contribute to identify subjects at increased risk of arrhythmic events. METHODS Our HR adaptive match filter was used to identify TWA from electrocardiographic recordings acquired during a bicycle ergometer test in 266 patients with implanted cardio-defibrillator. During the 4-year follow-up, 76 patients developed tachycardia or ventricular fibrillation (ICD_Cases) and 190 did not (ICD_Controls). RESULTS TWA was statistically lower during exercise than recovery for HRs between 75 and 110 bpm (16-21 μV vs 20-27 μV; P < 0.05), and reverse for HRs between 120 and 130 bpm (41-51 μV vs 28 μV; P < 0.05). ICD_Cases and ICD_Controls showed significantly different TWA at 80 bpm (20 μV vs 15 μV; P < 0.05) and 140 bpm (15 μV vs 22 μV; P < 0.05) during exercise, and at 90 bpm (38 μV vs 21 μV; P < 0.05) and 95 bpm (33-24 μV vs 28 μV; P < 0.05) during recovery. CONCLUSIONS TWA shows a HR-dependent hysteresis and there is a different behavior of TWA in ICD_Cases and ICD_Controls groups. Consequently, beside exercise TWA also recovery TWA may contribute to identify subjects at increased risk of arrhythmic events.
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Affiliation(s)
- Laura Burattini
- Department of Information Engineering, Polytechnic University of Marche, Ancona, Italy
| | - Sumche Man
- Department of Cardiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Sandro Fioretti
- Department of Information Engineering, Polytechnic University of Marche, Ancona, Italy
| | - Francesco Di Nardo
- Department of Information Engineering, Polytechnic University of Marche, Ancona, Italy
| | - Cees A Swenne
- Department of Cardiology, Leiden University Medical Center, Leiden, The Netherlands
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Puntmann VO. An Interplay Between Left Ventricular Wall Thickness and T-Wave Alternans in Patients With Hypertrophic Cardiomyopathy in Predicting Ventricular Tachyarrythmic Events:. Circ J 2010. [DOI: 10.1253/circj.cj-10-0560] [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: 11/09/2022]
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Garzón A, Grigoriev RO, Fenton FH. Model-based control of cardiac alternans on a ring. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 80:021932. [PMID: 19792176 DOI: 10.1103/physreve.80.021932] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2008] [Revised: 05/11/2009] [Indexed: 05/08/2023]
Abstract
Cardiac alternans, a beat-to-beat alternation of cardiac electrical dynamics, and ventricular tachycardia, generally associated with a spiral wave of electrical activity, have been identified as frequent precursors of the life-threatening spatiotemporally chaotic electrical state of ventricular fibrillation (VF). Schemes for the elimination of alternans and the stabilization of spiral waves through the injection of weak external currents have been proposed as methods to prevent VF but have not performed at the level required for clinical implementation. In this paper we propose a control method based on linear-quadratic regulator (LQR) control. Unlike most previously proposed approaches, our method incorporates information from the underlying model to increase efficiency. We use a one-dimensional ringlike geometry, with a single control electrode, to compare the performance of our method with that of two other approaches, quasi-instantaneous suppression of unstable modes (QISUM) and time-delay autosynchronization (TDAS). We find that QISUM fails to suppress alternans due to conduction block. Although both TDAS and LQR succeed in suppressing alternans, LQR is able to suppress the alternans faster and using a much weaker control current. Our results highlight the benefits of a model-based control approach despite its inherent complexity compared with nonmodel-based control such as TDAS.
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Affiliation(s)
- Alejandro Garzón
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, USA
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Abstract
T-wave alterans (TWA) measures alternate-beat fluctuations in the ECG T-wave, and has been used to predict the risk for life-threatening ventricular arrhythmias in various clinical populations. This work reviews the traditional literature linking repolarization alternans in cellular and tissue-level studies, with clinical studies that TWA can successfully add to existing clinical risk factors in predicting ventricular arrhythmias. We conclude by providing an evidence-based framework integrating TWA with other risk factors to stratify risk for sudden cardiac arrest.
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Affiliation(s)
- Sanjiv M Narayan
- University of California and VA Medical Center, La Jolla, CA, USA.
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Narayan SM, Cox V, Patel M. RESPONSE: LETTER TO THE EDITOR. Pacing Clin Electrophysiol 2007. [DOI: 10.1111/j.1540-8159.2007.00915.x] [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: 11/28/2022]
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Narayan SM, Drinan DD, Lackey RP, Edman CF. Acute volume overload elevates T-wave alternans magnitude. J Appl Physiol (1985) 2007; 102:1462-8. [PMID: 17158246 DOI: 10.1152/japplphysiol.00965.2006] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The objective of this study was to determine whether acute volume loading elevates T-wave alternans (TWA) in dogs with structurally normal hearts. TWA predicts sudden cardiac arrest in patients with left ventricular dysfunction and congestive heart failure. However, volume load and ventricular stretch may themselves precipitate arrhythmias. It is unclear to what extent volume load causes TWA. In six male mongrel dogs [25.8 kg (SD 4.2)] under general anesthesia, we measured TWA during progressive atrial pacing to 160 beats/min. Pacing was performed at baseline, at the midpoint and peak of a saline infusion designed to induce acute CHF, and then during diuresis. Dog 1 was hypothermic throughout the protocol and excluded from analysis. For dogs 2– 6, 102 ml/kg (SD 30) were infused over 315 min (SD 50), causing pulmonary capillary wedge pressure to rise from 9.6 (SD 3.5) to 21.2 mmHg (SD 1.6) ( P < 0.01), and heart rate variability to fall ( P < 0.01). TWA magnitude (Valt) rose in all dogs with volume load ( P < 0.001). Compared with baseline, TWA at peak infusion had higher magnitude [Valt 3.4 (SD 1.95) vs. 0.5 μV (SD 0.35); P = 0.011] and occurred at lower heart rates [128 (SD 6) vs. 151 beats/min (SD 12); P = 0.008]. Net volume load was linearly related to Valt ( P < 0.01), with each 10 ml/kg net volume load increasing Valt by 0.23 μV. Acute volume overload elevates TWA in normal canine hearts. Although dramatic, however, this effect may contribute clinically to abnormal TWA only in patients with marked volume overload. Future studies should examine the interaction of fluid overload, myocardial disease, and arrhythmia susceptibility.
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Cox V, Patel M, Kim J, Liu T, Sivaraman G, Narayan SM. Predicting Arrhythmia-Free Survival Using Spectral and Modified-Moving Average Analyses of T-Wave Alternans. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2007; 30:352-8. [PMID: 17367354 DOI: 10.1111/j.1540-8159.2007.00675.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND T-wave alternans (TWA) is a promising electrocardiogram (ECG) predictor of sudden cardiac arrest, yet needs specialized recordings for conventional spectral analysis. Modified moving average (MMA) analysis is a new approach that can measure TWA from routine ECGs, thus widening its applicability. However, MMA-TWA has not been calibrated against spectral TWA nor outcome in high risk patients. We hypothesized that spectral and MMA-TWA would both predict arrhythmia-free survival on long-term prospective follow-up. METHODS AND RESULTS In 41 patients with left ventricular systolic dysfunction (ejection fraction 31 +/- 13%), we studied TWA simultaneously using spectral and MMA during pacing (< 110 beats/min). MMA amplified TWA over spectral analyses (13.0 +/- 8.28 microV vs 1.96 +/- 5.15 microV, P < 0.001). On 542 +/- 311 days' follow-up, from clinic visits, telephonic interviews, and device interrogations, there were 11 deaths or sustained ventricular arrhythmias ('events'). Positive spectral TWA (>or=1.9 microV) identified patients with from those without events (P = 0.02). Receiver-operating characteristics for MMA-TWA showed that the cutpoint >or= 10.75 microV was optimal for the combined endpoint. Kaplan-Meier analysis using this MMA-TWA cutpoint trended to predict events (P = 0.06), while MMA combined with spectral TWA identified events (P = 0.01). CONCLUSIONS MMA amplifies TWA compared to traditional spectral analyses, but both likely reflect similar pathophysiology. Validation in larger populations will enable MMA-TWA to be widely applied to stratify risk for sudden cardiac arrest.
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Affiliation(s)
- Veronica Cox
- University of California and Veterans Affairs Medical Center, San Diego, California, USA
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Bao M, Zhang J, Huang C, Jiang H, Liu J, Zhao D. Abnormal Intracellular Calcium Handling Underlying T-Wave Alternans and Its Hysteresis. Cardiology 2006; 108:147-56. [PMID: 17085935 DOI: 10.1159/000096566] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/18/2005] [Accepted: 08/12/2006] [Indexed: 02/01/2023]
Abstract
AIMS To investigate the mechanism underlying T-wave alternans (TWA) and its hysteresis under ischemia conditions. METHODS Transmembrane action potential (AP) from endocardial, M, and epicardial cells and monophasic AP (MAP) from four epicardial sites were recorded in ventricular wedge preparation and in isolated intact rabbit heart, respectively. The AP/MAP duration (APD/ MAPD), effective refractory period (ERP), activation time, and APD/MAPD restitution were determined under control and ischemia conditions. The effects of ryanodine (0.01 and 1 micromol x l(-1)) on TWA, and the effects of low extracellular Ca2+ and 4-aminopyridine on its hysteresis were studied. RESULTS Ischemia shortened the APD/MAPD and effective refractory period of all recording sites symmetrically, except the APD of M cells, which shortened markedly. In the ischemia group, TWA was induced within a cycle length (CL) range from 160 to 250 ms, which corresponded to a diastolic interval region of 0-70 ms. In this diastolic interval region, the repolarization restitution curve was the steepest (slope > 1.0). All TWA were accompanied by repolarization alternations. Low concentration ryanodine (0.01 micromol x l(-1)) facilitated TWA, high concentration (1 micromol x l(-1)) abolished it. Alternans of calcium transient were observed in myocytes purfused with ischemia solution during rapid stimulation. Ryanodine (0.1 micromol x l(-1)) abolished alternans of calcium transient, and ryanodine (0.01 micromol x l(-1)) facilitated them. After 60 min pacing at a CL of 200 ms, TWA persisted until the initial several beats at a CL of 300 ms at which a TWA was exceptional. The suppression of hysteresis by low extracellular Ca2+ and 4-aminopyridine indicated an underlying role of the intracellular Ca2+ overload and transient outward current (I(to)). CONCLUSION TWA is principally due to repolarization alternans, which is secondary to steep APD/MAPD restitution, and relates to intracellular calcium cycling. Hysteresis relates to intracellular Ca2+ overload and I(to).
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Affiliation(s)
- Mingwei Bao
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, Hubei, China.
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Narayan SM, Smith JM, Cain ME. T-wave alternans using ventricular and atrial pacing. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2006; 28:1145; author reply 1145-6. [PMID: 16221281 DOI: 10.1111/j.1540-8159.2005.00232_1.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Narayan SM, Smith JM, Lindsay BD, Cain ME, Dávila-Román VG. Relation of T-wave alternans to regional left ventricular dysfunction and eccentric hypertrophy secondary to coronary heart disease. Am J Cardiol 2006; 97:775-80. [PMID: 16516574 DOI: 10.1016/j.amjcard.2005.09.127] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/02/2005] [Revised: 09/23/2005] [Accepted: 09/23/2005] [Indexed: 10/25/2022]
Abstract
Left ventricular (LV) hypertrophy and structural disease are associated with exaggerated repolarization dispersion and risk for cardiac arrest. We hypothesized that T-wave alternans (TWA) from the electrocardiogram, reflecting proarrhythmic repolarization dispersion, would increase with extent of eccentric LV hypertrophy and vary spatially with the distribution of myocardial scar. We studied 28 patients with coronary disease, systolic dysfunction, and nonsustained ventricular tachycardia. On echocardiography, 21 patients had wall motion abnormalities and 20 had LV hypertrophy (mass index > or =100 g/m(2)). TWA magnitude (voltage of alternation), which was computed spectrally during ventricular stimulation, varied linearly with LV mass index (p = 0.003). Spatially, positive TWA (magnitude > or =1.9 microV) in orthogonal electrocardiographic axes overlaid scar or wall motion abnormalities in corresponding echocardiographic segments (p <0.05 in x and y axes). After a follow-up of 35 +/- 13 months, positive TWA predicted the combined end point of death or sustained ventricular arrhythmias in all patients (p = 0.025), with a trend for those with echocardiographic LV hypertrophy (p = 0.058). In conclusion, in patients with systolic dysfunction due to coronary artery disease, TWA may indicate arrhythmic contributions from regional myocardial scar and eccentric LV hypertrophy.
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Narayan SM. T-wave alternans and the susceptibility to ventricular arrhythmias. J Am Coll Cardiol 2006; 47:269-81. [PMID: 16412847 DOI: 10.1016/j.jacc.2005.08.066] [Citation(s) in RCA: 237] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/09/2005] [Revised: 07/20/2005] [Accepted: 08/01/2005] [Indexed: 11/17/2022]
Abstract
T-wave alternans (TWA) reflects beat-to-beat fluctuations in the electrocardiographic T-wave, and is associated with dispersion of repolarization and the mechanisms for sudden cardiac arrest (SCA). This review examines the bench-to-bedside literature that, over decades, has linked alternans of repolarization in cellular, whole-heart, and human studies with spatial dispersion of repolarization, alternans of cellular action potential, and fluctuations in ionic currents that may lead to ventricular arrhythmias. Collectively, these studies provide a foundation for the clinical use of TWA to reflect susceptibility to ventricular arrhythmias in several disease states. This review then provides a contemporary evidence-based framework for the use of TWA to enhance risk stratification for SCA, identifying populations for whom TWA is best established, those for whom further studies are required, and areas for additional investigation.
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Affiliation(s)
- Sanjiv M Narayan
- San Diego VA Healthcare System, University of California, Whitaker Institute for Biomedical Engineering, Cardiology, San Diego, California 92161, USA.
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Iwasa A, Hwa M, Hassankhani A, Liu T, Narayan SM. Abnormal Heart Rate Turbulence Predicts the Initiation of Ventricular Arrhythmias. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2005; 28:1189-97. [PMID: 16359285 DOI: 10.1111/j.1540-8159.2005.50186.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
BACKGROUND Abnormal heart rate turbulence (HRT) reflects autonomic derangements predicting all-cause mortality, yet has not been shown to predict ventricular arrhythmias in at-risk patients. We hypothesized that HRT at programmed ventricular stimulation (PVS) would predict arrhythmia initiation in patients with left ventricular dysfunction. METHODS We studied 27 patients with coronary disease, left ventricular ejection fraction (LVEF) 26.7 +/- 9.1%, and plasma B-type natriuretic peptide (BNP) 461 +/- 561 pg/mL. Prior to arrhythmia induction at PVS, we measured sinus cycles after spontaneous or paced premature ventricular contractions (PVCs) for turbulence onset (TO; % cycle length change following PVC) and slope (TS; greatest slope of return to baseline cycle). T-wave alternans (TWA) was also measured during atrial pacing. RESULTS At PVS, abnormal TO (> or =0%) predicted inducible ventricular tachycardia (VT; n = 10 patients; P < 0.05). TO was greater in inducible than in noninducible patients (2.3 +/- 3.1% vs -0.02 +/- 2.8%, P < 0.05) and correlated with LVEF (P < 0.05) but not with BNP. TS did not differ between groups. Conversely, ambulatory HRT differed significantly from HRT at PVS (TO -0.55 +/- 1.08% vs 0.85 +/- 3.02%, P < 0.05; TS 2.63 +/- 2.09 ms/RR vs 8.70 +/- 6.56 ms/RR, P < 0.01), and did not predict inducible VT but trended (P = 0.05) to predict sustained VT on 739 +/- 179 days follow-up. TWA predicted inducible (P < 0.05) and spontaneous (P = 0.0001) VT but did not co-migrate with HRT. CONCLUSIONS Abnormal HRT measured at PVS predicted the induction of sustained ventricular arrhythmias in patients with ischemic cardiomyopathy. However, HRT at PVS did not correlate with ambulatory HRT, nor with TWA, both of which predicted spontaneous ventricular arrhythmias. Thus, HRT may reflect the influence of autonomic milieu on arrhythmic susceptibility and is likely complementary to traditional arrhythmic indices.
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Affiliation(s)
- Atsushi Iwasa
- University of California, Veterans Administration Medical Centers, San Diego, CA 92161, USA
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RAATIKAINEN MPEKKA, HUIKURI HEIKKIV. Response to the Letter of Drs. Sanjiv M. Narayan, Joseph M. Smith, and Michael E. Cain:. Pacing Clin Electrophysiol 2005. [DOI: 10.1111/j.1540-8159.2005.00232_2.x] [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] [Indexed: 11/30/2022]
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Narayan SM, Hassankhani A, Feld GK, Bhargava V. Separating non-isthmus- from isthmus-dependent atrial flutter using wavefront variability. J Am Coll Cardiol 2005; 45:1269-79. [PMID: 15837261 DOI: 10.1016/j.jacc.2004.12.070] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/04/2004] [Revised: 12/06/2004] [Accepted: 12/07/2004] [Indexed: 11/17/2022]
Abstract
OBJECTIVES The aim of this study was to separate isthmus-dependent atrial flutter (IDAFL) from non-isthmus-dependent atrial flutter (NIDAFL) from the electrocardiogram (ECG) based on functional differences. BACKGROUND The ECG analyses of F-wave shape suboptimally separate NIDAFL from IDAFL. The authors hypothesized that anatomic and functional differences may result in greater wavefront variability in NIDAFL than IDAFL, allowing their separation. The authors tested this hypothesis in patients undergoing ablation for atrial flutter using a novel ECG algorithm to detect subtle F-wave variability, validated by intracardiac measurements. METHODS In 62 patients (23 NIDAFL, 39 IDAFL) ECG atrial wavefronts were represented as correlations of an F-wave template to the ECG over time. Correlations in orthogonal ECG lead-pairs were plotted at each time point to yield loops reflecting temporal and spatial regularity in each plane. The ECG analyses were compared with intracardiac standard deviations of: 1) atrial electrograms (temporal variability), and 2) bi-atrial activation time differences (spatial variability). RESULTS Atrial ECG temporospatial loops were reproducible in IDAFL, but varied in NIDAFL (p < 0.01) suggesting greater variability that correctly classified IDAFL (39 of 39 cases) from NIDAFL (22 of 23 cases; p < 0.001). Intra-atrial mapping confirmed greater temporal variability for NIDAFL versus IDAFL, in lateral (p < 0.01) and septal (p = 0.03) right atrium, and proximal (p = 0.02) and distal (p < 0.01) coronary sinus. Spatial variability was greater in NIDAFL than IDAFL (p = 0.02). CONCLUSIONS Greater cycle-to-cycle atrial wavefront variability separates NIDAFL from IDAFL and is detectable from the ECG using temporospatial analyses. These results have implications for guiding ablation and support the concept that IDAFL and NIDAFL lie along a spectrum of intracardiac organization.
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Affiliation(s)
- Sanjiv M Narayan
- University of California and Veterans Administration Medical Centers, San Diego, California 92161, USA.
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Narayan SM, Smith JM, Schechtman KB, Lindsay BD, Cain ME. T-wave alternans phase following ventricular extrasystoles predicts arrhythmia-free survival. Heart Rhythm 2005; 2:234-41. [PMID: 15851310 DOI: 10.1016/j.hrthm.2004.12.010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/18/2004] [Accepted: 11/30/2004] [Indexed: 10/25/2022]
Abstract
OBJECTIVE The purpose of this study was to assess the value of T-wave alternans (TWA) following ventricular extrasystoles in predicting arrhythmia-free survival. BACKGROUND Stratifying risk for sudden death in patients with coronary disease and moderate left ventricular (LV) dysfunction remains a challenge. We hypothesized that, in such patients, a discontinuity in beat-to-beat T-wave alternation (TWA phase reversal) following single ventricular extrasystoles reflects transiently exaggerated repolarization dispersion, and predicts spontaneous ventricular arrhythmias. METHODS We studied 59 patients with ischemic LV dysfunction (mean LV ejection fraction 38.7 +/- 5.3%) and nonsustained ventricular tachycardia undergoing programmed stimulation. TWA was computed spectrally from the ECG during ventricular pacing, and TWA phase reversal was reflected by a discontinuity in T-wave oscillation after single ventricular extrasystoles. RESULTS Patients induced into ventricular arrhythmias (n = 36) had greater TWA magnitude (V(alt): 6.60 +/- 6.46 microV vs 2.61 +/- 1.97 microV; P = .001) and more frequent TWA phase reversal (62.1% vs 44.4%; P = .02) than those who were not (n = 23). During a mean follow-up of 36 +/- 12 months, positive TWA (V(alt) > or =1.9 microV) and TWA phase reversal both (P < .05) predicted events (all-cause mortality, ventricular tachycardia, ventricular fibrillation). Univariate predictors of arrhythmia-free survival were TWA phase reversal (P < .005), positive TWA (P < .05), age (P = .008), and LV mass index (P = .043). On multivariate analysis, only TWA phase reversal and age predicted events; if TWA phase was excluded, only positive TWA and age predicted events. CONCLUSION Phase reversal in TWA following ventricular extrasystoles predicts spontaneous ventricular arrhythmias and all-cause mortality in patients with moderate ischemic LV dysfunction and was a better predictor than positive TWA or programmed ventricular stimulation.
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Walker ML, Wan X, Kirsch GE, Rosenbaum DS. Hysteresis effect implicates calcium cycling as a mechanism of repolarization alternans. Circulation 2003; 108:2704-9. [PMID: 14581412 DOI: 10.1161/01.cir.0000093276.10885.5b] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND T-wave alternans is due to alternation of membrane repolarization at the cellular level and is a risk factor for sudden cardiac death. Recently, a hysteresis effect has been reported in patients whereby T-wave alternans, once induced by rapid heart rate, persists even when heart rate is subsequently slowed. We hypothesized that alternans hysteresis is an intrinsic property of cardiac myocytes, directly related to an underlying mechanism for repolarization alternans that involves intracellular calcium cycling. METHODS AND RESULTS Stepwise pacing was used to induce alternans in Langendorff-perfused guinea pig hearts from which optical action potentials were recorded simultaneously at 256 ventricular sites with voltage-sensitive dyes and in whole-cell patch-clamped cardiac myocytes treated with or without BAPTA-AM (1,2-bis[2-aminophenoxy]ethane-N,N,N',N'-tetraacetic acid tetrakis [acetoxymethyl ester]). Alternans hysteresis was observed in every isolated heart: threshold heart rate for alternans was 280+/-12 bpm, but during subsequent deceleration of pacing, alternans persisted to significantly slower heart rates (238+/-5 bpm, P<0.05). Optical mapping showed that this effect also applied to the threshold for spatially discordant alternans (313+/-2.2 bpm during acceleration versus 250+/-6.6 bpm during deceleration, P<0.05). Alternans hysteresis was also observed in isolated cardiac myocytes. Moreover, calcium chelation by BAPTA-AM raised the threshold for alternans and inhibited hysteresis in a dose-dependent manner with no effect on baseline action potential duration. CONCLUSIONS Alternans hysteresis is an intrinsic property of cardiac myocytes that can lead to persistence of arrhythmogenic discordant alternans even after heart rate is slowed. These results also support an important underlying role of calcium cycling in the mechanism of alternans.
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Affiliation(s)
- Mariah L Walker
- Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 MetroHealth Dr, Hamman 330, Cleveland, Ohio 44109-1998, USA
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Narayan SM, Bode F, Karasik PL, Franz MR. Alternans of atrial action potentials during atrial flutter as a precursor to atrial fibrillation. Circulation 2002; 106:1968-73. [PMID: 12370221 DOI: 10.1161/01.cir.0000037062.35762.b4] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND The mechanisms underlying the transition of typical atrial flutter (Afl) to fibrillation (AF) remain unclear. We set out to test the hypothesis that Afl disorganizes to AF via alternans of atrial action potentials. METHODS AND RESULTS In 38 patients with Afl, monophasic action potentials (MAPs) were recorded at the isthmus and either high or low right atrium (HRA, LRA) during overdrive pacing to 160 ms or to the initiation of AF, whichever came first. MAP duration measured at 90% repolarization was longer at the isthmus in all patients, and failed to shorten with rate, compared with the HRA (n=38) or LRA (n=5). In 20 patients who developed AF, progressive pacing first caused alternans of isthmus MAP duration and amplitude at mean cycle length of 219+/-45 ms, followed by AF at a mean onset cycle length of 184+/-38 ms. Subsets of this group showed spontaneous action potential duration alternans at the isthmus (11 of 20 patients) and 2:1 isthmus conduction block immediately preceding AF (4 of 20 patients). In the 18 patients who did not develop AF, MAP alternans was less common (9 of 18 patients; P<0.0003), and occurred only at faster pacing (cycle length=169+/-25 ms; P<0.05). CONCLUSIONS In patients with typical Afl, action potential duration rate maladaptation at the isthmus may lead to action potential duration alternans and conduction block preceding the transition to AF. These isthmus characteristics may enable the spontaneous initiation of AF through wavefront fractionation and may explain the benefits of isthmus ablation in preventing AF recurrence.
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Affiliation(s)
- Sanjiv M Narayan
- University of California and Veterans Affairs Medical Center, San Diego, Calif, USA
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