Electrical Alternans and Vulnerability to Ventricular Arrhythmias

TLDR

Electrical alternans has been linked to ventricular arrhythmias, yet its physiological significance and prognostic value remain unclear. The study aimed to determine whether electrical alternans marks vulnerability to ventricular arrhythmias by developing a sensitive detection technique for subtle ECG morphologic changes. In a prospective cohort of 83 patients undergoing electrophysiologic testing, the investigators measured alternans levels and found that 39 % of subjects had inducible sustained ventricular arrhythmias. Low‑level alternans, particularly in the ST segment and T wave, independently predicted inducible arrhythmias (81 % sensitivity, 84 % specificity, RR 5.2) and was associated with markedly reduced arrhythmia‑free survival over 20 months, suggesting it may serve as a noninvasive marker of ventricular arrhythmia risk.

Abstract

Although electrical alternans (alternating amplitude from beat to beat on the electrocardiogram) has been associated with ventricular arrhythmias in many clinical settings, its physiologic importance and prognostic implications remain unknown.To test the hypothesis that electrical alternans is a marker of vulnerability to ventricular arrhythmias, we developed a technique to detect subtle alternation in the morphologic features of the electrocardiogram (which would not be detectable by visual inspection of the electrocardiogram). In a group of 83 patients referred for diagnostic electrophysiologic testing, we prospectively examined whether levels of alternans predicted vulnerability to arrhythmias as defined by the outcome of electrophysiologic testing and arrhythmia-free survival.Sustained ventricular arrhythmias were induced during electrophysiologic testing in 32 of the patients (39 percent). In this group, low-level electrical alternans (a beat-to-beat change in amplitude of < 15 microV) was detected over a broad range of physiologic heart rates (from 95 to 150 beats per minute) and primarily involved the ST segment and the T wave (i.e., the phase of repolarization). Alternans during repolarization was a significant and independent predictor of inducible arrhythmias on electrophysiologic testing (sensitivity, 81 percent; specificity, 84 percent; relative risk, 5.2). Of 66 patients followed for up to 20 months, 13 had arrhythmic events. Alternans affecting the T wave and inducibility of ventricular arrhythmias were significant and essentially equivalent predictors of survival without arrhythmia (P < 0.001). Actuarial survival without arrhythmia at 20 months was significantly lower among the patients with T-wave alternans (19 percent) than among the patients without T-wave alternans (94 percent).Electrical alternans affecting the ST segment and T wave is common among patients at increased risk for ventricular arrhythmias. Subtle electrical alternans on the electrocardiogram may serve as a noninvasive marker of vulnerability to ventricular arrhythmias.