Role of microvolt T-wave alternans in assessment of arrhythmia vulnerability among patients with heart failure and systolic dysfunction: primary results from the T-wave alternans sudden cardiac death in heart failure trial substudy

Abstract

Background: Sudden cardiac death remains a leading cause of mortality despite advances in medical treatment for the prevention of ischemic heart disease and heart failure. Recent studies showed a benefit of implantable cardioverter defibrillator implantation, but appropriate shocks for ventricular tachyarrhythmias were noted only in a minority of patients during 4 to 5 years of follow-up. Accordingly, better risk stratification is needed to optimize patient selection. In this regard, microvolt T-wave alternans (TWA) has emerged as a potentially useful measure of arrhythmia vulnerability, but it has not been evaluated previously in a prospective, randomized trial of implantable cardioverter defibrillator therapy.

Methods and results: This investigation was a prospective substudy of the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) that included 490 patients at 37 clinical sites. TWA tests were classified by blinded readers as positive (37%), negative (22%), or indeterminate (41%) by standard criteria. The composite primary end point was the first occurrence of any of the following events: sudden cardiac death, sustained ventricular tachycardia/fibrillation, or appropriate implantable cardioverter defibrillator discharge. During a median follow-up of 30 months, no significant differences in event rates were found between TWA-positive or -negative patients (hazard ratio 1.24, 95% confidence interval 0.60 to 2.59, P=0.56) or TWA-negative and nonnegative (positive and indeterminate) subjects (hazard ratio 1.28, 95% confidence interval 0.65 to 2.53, P=0.46). Similar results were obtained with the inclusion or exclusion of patients randomized to amiodarone in the analyses.

Conclusions: TWA testing did not predict arrhythmic events or mortality in SCD-HeFT, although a small reduction in events (20% to 25%) among TWA-negative patients cannot be excluded given the sample size of this study. Accordingly, these results suggest that TWA is not useful as an aid in clinical decision making on implantable cardioverter defibrillator therapy among patients with heart failure and left ventricular systolic dysfunction.

Figure 1

A. Comparison of primary event rates for the TWA+ (broken line) and TWA- (solid line) patients among subjects randomized to ICD or Control (primary endpoint of the study). There was no significant difference between event rates for the 2 groups (HR =1.24, p=0.56). B. Comparison of event rates for the TWA non − (broken line) and TWA − (solid line) patients in the ICD and Control groups. Again event rates did not differ significantly for the groups (HR = 1.28, p=0.46).

Figure 1

A. Comparison of primary event rates for the TWA+ (broken line) and TWA- (solid line) patients among subjects randomized to ICD or Control (primary endpoint of the study). There was no significant difference between event rates for the 2 groups (HR =1.24, p=0.56). B. Comparison of event rates for the TWA non − (broken line) and TWA − (solid line) patients in the ICD and Control groups. Again event rates did not differ significantly for the groups (HR = 1.28, p=0.46).

Figure 2

Comparison of primary event rates for the TWA non - (broken line) and TWA- (solid line) patients among all 490 subjects in this study. There was no significant difference between event rates for the 2 groups (HR =1.11, p=0.72).