T-wave Alternans Testing in Pacemaker Patients

Abstract and Introduction

Abstract

Background: T-wave alternans (TWA) is a useful method for identifying patients who are at risk for sudden cardiac death. We aimed to determine the effects of different pacing modes on test results and long-term prognostic relevance of TWA in patients following a dual-chamber (DDD) pacemaker implantation.
Methods: Sixty-three patients (mean age 68 ± 13 years) with structural heart disease and recently implanted DDD pacemakers were enrolled. Left ventricular (LV) function was normal or moderately impaired (mean LV ejection fraction 61 ± 13%). All patients underwent sequential TWA testing using atrial and ventricular pacing.
Results: During atrial pacing requiring physiologic conduction to the ventricles, 21% of TWA tests were positive, 43% negative, and 36% indeterminate. When using right ventricular (RV) pacing in the same patients, 19% of tests were positive, 40% negative, and 41% indeterminate. When positive and indeterminate tests were grouped as nonnegative, the concordance between atrial and ventricular pacing was 62% (κ= 0.22). After a mean follow-up of 5.9 ± 1.9 years, 18 (29%) patients had died. Improved survival was predicted by a negative TWA test using atrial pacing (P = 0.028), but not with ventricular pacing (P = 0.722).
Conclusions: In patients with dual-chamber pacemakers, there is a low concordance of TWA test results between atrial pacing with intrinsic conduction to the ventricles and apical RV pacing via pacemaker electrode. However, TWA during atrial pacing clearly exerts long-term prognostic relevance in a patient group with preserved LV function and structural heart disease.

Introduction

The noninvasive assessment of microvolt T-wave alternans (TWA) has been established as a useful tool to identify individuals at elevated risk for sudden cardiac death (SCD) from ventricular tachyarrhythmias.^[1,2] Microvolt TWA refers to the presence of subtle beat-to-beat fluctuations in the electrocardiogram's (ECG) T-wave amplitude and morphology.^[3] Although the precise link with arrhythmogenesis is as yet unclear, microvolt TWA probably reflects increased heterogeneity in ventricular repolarization that is a substrate for promoting electrical wavebreak and development of ventricular tachycardia (VT) and ventricular fibrillation (VF).^[3,4]

The results of numerous clinical studies showed that TWA predicts arrhythmic events and all-cause mortality in high-risk patients with ischemic cardiomyopathy and reduced left ventricular (LV) function.^[5–7] Because of its high negative predictive value, TWA could potentially be used to identify those patients who would not benefit from the implantation of an implantable cardioverter-defibrillator (ICD).^[8,9] The prognostic value of microvolt TWA has also been shown for other populations such as post myocardial infarction (MI) patients with preserved cardiac function.^[10]

Microvolt TWA testing requires controlled increase of heart rate that is usually achieved by means of physical exercise.^[11] In patients who cannot exercise, an atrial pacing protocol upon invasive electrophysiologic study has been shown to yield similar TWA results.^[12] For situations when atrial pacing is impossible because of complete atrioventricular (AV) block or atrial fibrillation, recent studies have investigated right ventricular (RV) pacing as an alternative.^[13–15] Their findings were, however, equivocal and only patients with an LV ejection fraction ≤ 40% were studied. Importantly, none of the studies provided follow-up data and information on the prognostic value of the employed pacing protocols.

The current prospective study therefore aimed to evaluate the effects of different pacing modes on acute test results and long-term prognostic relevance of microvolt TWA in patients with recent dual-chamber (DDD) pacemaker implantation. As a consequence, the study population consisted largely of patients with preserved LV function (LV ejection fraction >40%) and an intermediate risk of SCD.

Pacing Clin Electrophysiol. 2011;34(9):1054-1062. © 2011 Blackwell Publishing

Cite this: T-wave Alternans Testing in Pacemaker Patients - Medscape - Sep 01, 2011.