Clinical value of T-wave alternans assessment

Microvolt-level T-wave alternans (TWA) is a new arrhythmia risk marker to assess subtle changesin repolarization that has been introduced for arrhythmia risk stratification. Recent experimental studies havedemonstrated that it reflects a heartrate dependent increased spatial dispersion of repolarization associated withunidirectional conduction block, and reentry that may result in the occurrence of ventricular fibrillation.Clinical studies have convincingly demonstrated that TWA is closely related to arrhythmia induction in theelectrophysiology (EP) laboratory as well as to the occurrence of spontaneous ventriculartachyarrhythmias in patients undergoing EP study. Subsequent studies showed that TWA—assessednoninvasively—is predictive of future arrhythmic events in patients with implanted ICDs as well as forventricular tachyarrhythmias in patients with congestive heart failure without a prior history of arrhythmias.There is still controversy, however, about the predictive value of TWA in patients following acute myocardialinfarction (MI). Several studies which differ in patient selection, pharmacologic treatment of thepatients, and endpoint definitions, have reported conflicting results. Therefore, studies with a large number ofunselected patients after acute MI on optimal treatment according to contemporary therapeutic guidelines as wellas of patients with reduced left ventricular ejection fraction following MI are needed to define its role withregard to identifying patients who may benefit from primary preventive ICD therapy. Future research should alsofocus on evaluation of alternative methods to increase heart rate (i.e., pharmacological stimulation) inan attempt to reduce the proportion of incomplete tests in patients with insufficient increase in heart rateduring exercise testing.     

Predictive value of microvolt T-wave alternans for cardiac death or ventricular tachyarrhythmic events in ischemic and nonischemic cardiomyopathy patients: a meta-analysis

Background: Microvolt T‐wave alternans (MTWA) has been proposed as a predictor of the risk of ventricular tachyarrhythmias (VT) and sudden cardiac death (SCD). Aim of this study was to perform a systematic review of the literature and a meta‐analysis of MTWA in primary prevention patients with ischemic and nonischemic cardiomyopathy. Methods: The positive predictive value (PPV), negative predictive value (NPV), and relative risk (RR) of MTWA in predicting death, cardiac death, and SCD during follow‐up were reported. Results: Fifteen studies involving 5681 patients (mean age 62 years, mean ejection fraction 32%) were included. The summary PPV during the average 26‐month follow‐up was 14% (95% CI: 13–15); NPV was 95% (95% CI: 94–96), and the univariate RR was 2.35 (95% CI: 1.68–3.28). The predictive value of MTWA was similar in patients with ischemic and nonischemic cardiomyopathy. The average RR for SCD or VT events of an abnormal MTWA was 2.40, similar to that for cardiac death. When we grouped the studies together depending upon whether beta‐blockers were withheld prior to MTWA screening, the beta‐blockers group showed an RR of 5.88. By contrast, the group in which beta‐blocker therapy was withheld had an RR of 1.63. Conclusion: A positive MTWA determined an approximately 2.5‐fold higher risk of cardiac death and life‐threatening arrhythmia and showed a very high NPV both in ischemic and nonischemic patients. An abnormal MTWA test was associated with a 5‐fold increased risk for cardiac mortality in the low‐indeterminate group and about a 6‐fold increased risk in beta‐blockers group. Ann Noninvasive Electrocardiol 2011;16(4):388–402     

Microvolt T-wave alternans in early repolarization syndrome associated with ventricular arrhythmias: A case report

Despite early repolarization (ER) syndrome being usually considered benign, its association with severe/malignant ventricular arrhythmias (VA) was also reported. Microvolt T-wave alternans (MTWA) is an electrocardiographic marker for the development of VA, but its role in ER syndrome remains unknown. A 90-second 6-lead electrocardiogram from an ER syndrome patient, acquired with the Kardia recorder, was analyzed by the enhanced adaptive matched filter for MTWA quantification. On average, MTWA was 50 μV, higher than what was previously observed on healthy subjects using the same method. In our ER syndrome patient, MTWA plays a potential role in VA development in ER syndrome.     

Short-term reproducibility of T wave alternans measurement

INTRODUCTION: Microvolt T wave alternans (TWA) has been proposed as a strong independent predictor of malignant ventricular tachyarrhythmias and sudden cardiac death. TWA reproducibility during bicycle stress test has not been previously investigated. We sought to assess the short-term reproducibility of TWA, as well as heart rate (HR) threshold for TWA, and its spatial distribution and magnitude. METHODS AND RESULTS: The study enrolled 42 patients who were able to complete two bicycle stress tests with HR at peak exercise >110 beats/min within 4 hours of each other and who had technically adequate recordings for TWA analysis during both tests. Concordant results for TWA determination were obtained in 39 (93%) of 42 cases. TWA was present during both tests in 23 patients and was absent during both tests in 16 patients. In the 23 patients with two positive tests, HR at the onset of TWA was not significantly different during the two tests. Further, the number of leads showing TWA and the magnitude of TWA were not significantly different between the two tests. CONCLUSION: TWA is characterized by satisfactory short-term reproducibility and, when present, by high temporal and spatial stability.     

Brugada波电交替及临床意义探讨

目的分析Brugada波的电交替现象。方法回顾性分析存在1型Brugada波且伴ST段和/或T波电交替现象的5例患者的心电图及临床特点。结果 5例患者均为男性,年龄18~50岁,入院时均存在1型Brugada波,并且分别在病因诊断确立或病情得到纠正过程中见到ST段和/或T波的电交替现象。ST段电交替可表现为抬高程度(高和低)的交替和抬高类型的(穹隆型和马鞍型)的交替,T波电交替表现为振幅(高和低)的交替和方向(双向和倒置)的交替。结论 Brugada波电交替现象可以发生于多种情况,同样具有多变性的特点。     

微伏级T波电交替与焦虑情绪的相关性

目的:分析微伏级T波电交替(Microvolt T wave alternans,MTWA)值和患者焦虑状况的关系。方法:随机选择武汉大学人民医院2012年8月~2013年10月行平板运动试验(treadmill exercise test,TET)的患者136(男59,女77)例,年龄(53±10)岁。采用GE公司提供的Marquette MTWA分析程序,进行标准时域运动试验,记录胸前V1~V6导联的MTWA值,其中最大值以Max Valt表示,并对其进行焦虑自评量表(SAS)的问卷调查,按SAS评分将患者分为焦虑组(38例)和非焦虑组(98例),进行组间比较和相关分析。结果:在峰值心率V3导联两组MTWA值有显著差异(P0.01)。焦虑评分与峰值心率V3导联时的MTWA值呈负相关(r=-0.245,P0.01)。结论:行TET时峰值心率情况下V3导联MTWA与焦虑情绪有相关性。     

Optimizing ambulatory ECG monitoring of T-wave alternans for arrhythmia risk assessment

Considerable scientific data support the potential value of T-wave alternans (TWA) as anindex of vulnerability to ventricular fibrillation. This chapter summarizes our state of knowledge regardingthe use of routine ambulatory ECGs to evaluate TWA and discusses recent methodologic approaches designed tooptimize AECG-based TWA analysis for arrhythmia risk stratification. Newer methods, including the nonspectraltechnique of Modified Moving Average analysis, appear promising in detecting TWA during the changingconditions associated with daily activities. The Modified Moving Average approach does not requirespecialized electrodes and is not encumbered by the need to achieve target heart rates, as is the case forconventional spectral-based methods. Guidelines are provided for evaluating latent cardiac electricalinstability using AECG-based TWA testing. These recent developments make possible the TWA analysis ofambulatory ECGs not only in prospective trials but also in vast stores of archival data.     

Ambulatory ECG-based T-wave alternans predicts sudden cardiac death in high-risk post-MI patients with left ventricular dysfunction in the EPHESUS study

Background: Exercise microvolt T‐wave alternans (TWA) identifies sudden cardiac death (SCD) risk. TWA can be measured from ambulatory ECGs (AECGs) using modified moving average (MMA) method. Whether MMA TWA from AECGs predicts SCD in post‐MI patients with left ventricular dysfunction (LVD) is unknown. Methods: EPHESUS enrolled hospitalized post‐MI patients with heart failure and/or diabetes with LVD. Before randomization to drug treatment, AECGs were obtained in 493 patients. Of them, 46 died of cardiovascular causes, including 18 of SCD. Patients alive at end of follow‐up (N = 92) were matched with 46 nonsurvivors based on age, gender, and diabetes. MMA TWA was analyzed using MARSPC system (GE Healthcare, Milwaukee, WI, USA). The three highest TWA values from artifact‐free periods were averaged for AECG channels corresponding to leads V₁ and V₃. SCD prediction was tested with a prespecified 47 μV cutpoint and at a cutpoint maximizing the separation between SCD patients versus survivors or non‐SCD. Results: TWA in either lead was higher for patients with SCD (P ≤ 0.05) versus survivors or non‐SCD. TWA ≥ 47 μV was associated with RR = 5.2 (95%CI = 1.8–13.6, P = 0.002) in V₁ and RR = 5.5 (95% CI = 2.2–13.8, P < 0.001) in V₃ for SCD. The optimal cutpoint for TWA in V₁ was ≥43 μV (RR = 5.9 [95%CI = 2.2–15.8, P < 0.001]). The optimal cutpoint in V₃ was ≥47 μV. TWA greater than the optimal cutpoint in either lead was associated with RR = 7.1 (95%CI = 2.7–18.3, P < 0.001) for SCD, with 11 out of 18 patients dying of SCD. Conclusions: AECG‐based TWA measured with MMA is a powerful predictor of SCD in high‐risk post‐MI patients with LV dysfunction.     

微伏级T波电交替的研究进展

T波电交替是心肌电活动不稳定的标志,可作为室性心律失常高危患者的危险分层,是人类及动物缺血心肌发生室性心动过速、心室颤动的标志,是发生恶性室性心律失常及心性猝死的无创预测指标。现结合文献对T波电交替的机制、检测方法、研究现状、适应证、临床意义及优缺点作一综述。     

Interpretation and classification of microvolt T wave alternans tests

Measurement of microvolt-level T wave alternans (TWA) during routine exercise stress testing now is possible as a result of sophisticated noise reduction techniques and analytic methods that have become commercially available. Even though this technology is new, the available data suggest that microvolt TWA is a potent predictor of arrhythmia risk in diverse disease states. As this technology becomes more widely available, physicians will be called upon to interpret microvolt TWA tracings. This review seeks to establish uniform standards for the clinical interpretation of microvolt TWA tracings.     

T波电交替计算机检测及其临床研究进展

T波电交替现象可见于长QT综合征、急性心肌缺血、变异型心绞痛、心脏性猝死以及电解质紊乱等。它在预测室性心律失常方面与电生理检查具有高度的一致性,是恶性室性心律失常和心脏性猝死的独立预测指标,是评定恶性心律失常以及心脏性猝死的可信、实用的技术之一。现在,T波电交替已经成为了一种廉价、方便的非侵入式心电检测方法。现综述T波电交替的研究背景、产生机制、检测方法及其临床研究,并简要分析了T波电交替的研究方向和发展前景。     

Two-year case collection of the Brugada syndrome electrocardiogram pattern at a large teaching hospital

BACKGROUND: Recommendations have recently emerged suggesting that the presence of the Brugada electrocardiographic (ECG) pattern in an otherwise asymptomatic individual warrants electrophysiologic testing for inducible ventricular arrhythmias. However, the prevalence of this pattern in the general population and its specificity for identifying those likely to develop the true Brugada syndrome are not known. HYPOTHESIS: The purpose of this study was to collect ECGs that displayed the Brugada pattern from unselected, noncardiac patients at a single institution to determine whether the implied prevalence in the literature may represent a significant underestimation of the true prevalence. METHODS: We performed a prospective case collection of Brugada-patterned ECGs over a 2-year time period from unselected, noncardiac patients at a large urban teaching hospital. RESULTS: Of approximately 12,000 noncardiac patients, 52 were found to have an ECG pattern fully consistent with the Brugada sign. CONCLUSIONS: The Brugada type ECG pattern is much more prevalent than previously reported when rigorously searched for in a prospective manner. More data are needed on its specificity for predicting future arrhythmic events in asymptomatic individuals before recommendations are made for extensive evaluation in this group.     

Clinical applications of T-wave alternans assessed during exercise stress testing and ambulatory ECG monitoring

Analytical methods to measure T-wave alternans (TWA), a beat-to-beat fluctuation in the morphology of the ST-segment and T wave in the electrocardiogram (ECG), have been developed to address the unmet challenge of identifying individuals at increased risk for sudden cardiac death. Conventional noninvasive markers including left ventricular ejection fraction have significant limitations as many individuals who die suddenly have relatively preserved ventricular mechanical function. TWA is an attractive marker as it is closely linked to ECG heterogeneity and abnormalities in calcium handling, key factors in arrhythmogenesis. The objectives of this review are to summarize the clinical evidence supporting use of TWA in risk stratification and to discuss its current and potential applications in guiding device and medical therapy.     

Microvolt T‐wave alternans in early repolarization syndrome associated with ventricular arrhythmias: A case report

Despite early repolarization (ER) syndrome being usually considered benign, its association with severe/malignant ventricular arrhythmias (VA) was also reported. Microvolt T‐wave alternans (MTWA) is an electrocardiographic marker for the development of VA, but its role in ER syndrome remains unknown. A 90‐second 6‐lead electrocardiogram from an ER syndrome patient, acquired with the Kardia recorder, was analyzed by the enhanced adaptive matched filter for MTWA quantification. On average, MTWA was 50 μV, higher than what was previously observed on healthy subjects using the same method. In our ER syndrome patient, MTWA plays a potential role in VA development in ER syndrome.     

T波电交替的研究进展

通过对近年来国内外对T波电交替的机制及其临床意义的研究总结,认为T波电交替是人类及动物缺血心肌发生室速、室颤的标志,是预测发生恶性室性心律失常及猝死的危险性独立的意义指标.     

Intravenous administration of class I antiarrhythmic drugs induced T wave alternans in a patient with Brugada syndrome

A 71-year-old man who experienced aborted sudden death was referred to our hospital. Coronary artery disease and cerebral accident were ruled out by conventional tests. The 12-lead ECG obtained at rest showed a right bundle branch block pattern and ST segment elevation in leads V1 to V3. Double ventricular extrastimuli at coupling intervals >180 msec induced ventricular fibrillation (VF) twice during electrophysiologic study. Intravenous administration of procainamide accentuated ST segment elevation in leads V1 to V3, and visible T wave alternans was induced in leads V2 and V3 at a dose of 450 mg. Initiation of T wave alternans was not associated with changes of the cardiac cycle or development of premature beats. When procainamide infusion was discontinued, T wave alternans disappeared before the elevated ST segment returned to the control level. Pilsicainide also accentuated ST segment elevation and induced similar T wave alternans in leads V2 and V3. Class I antiarrhythmic drug-related T wave alternans has been reported rarely in Brugada syndrome, but it may represent enhanced arrhythmogenicity of VF. We need to monitor closely and study the clinical implications of T wave alternans in Brugada syndrome.     

T波电交替的研究进展

T波电交替是指在规整的心律时,体表心电图上T波形态、极性和振幅出现逐搏交替变化的现象,其与恶性室性心律失常以及心脏性猝死的发生有着极为密切的联系。T波电交替的检测方法有频域分析和时域分析方法两种。临床试验证实,T波电交替对恶性室性心律失常事件的预测价值与有创的电生理检测价值相似。但微伏级T波电交替检测作为一种无创的检测手段,其对于发生各种致死性心脏病危险分级的作用仍需要临床实验进一步研究证实,现就T波电交替的发生机制、临床意义以及发展现状等进行综述。     

Brugada综合征患者的心电图及临床特点分析

目的分析Brugada综合征患者的心电图及临床特点。方法对我院近5年诊断的8例Brugada综合征住院患者的心电图及临床情况进行长期随访观察。结果8例Brugada综合征患者均为男性，年龄平均（40±13）岁。心电图Ⅰ型Brugada波者3例，Ⅱ型4例，Ⅲ型1例；Brugada波具有多变性，提高肋间描记右胸导联心电图可显现Brugada波或使其更明显。8例中4例有猝死家族史，5例有晕厥史，3例在住院期间发生室速／室颤，随访期间2例猝死。结论心电图Brugada波（尤其Ⅰ型）是诊断Brugada综合征的必要条件，明确诊断Brugada综合征尚需联合其他几项临床指标；Brugada综合征患者猝死的风险高，消除晕厥或室速／室颤的诱因是预防的关键。