ELECTRICAL ALTERNANS AND VULNERABILITY TO VENTRICULAR ARRHYTHMIAS

Background. Although electrical alternans (alternating amplitude from beat to beat on the electrocardiogram) has been associated with ventri cular arrhythmias in many clinical settings, its physiologic importanc e and prognostic implications remain unknown. Methods. To test the hyp othesis that electrical alternans is a marker of vulnerability to vent ricular arrhythmias, we developed a technique to detect subtle alterna tion 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 test ing, we prospectively examined whether levels of alternans predicted v ulnerability to arrhythmias as defined by the outcome of electrophysio logic testing and arrhythmia-free survival. Results. Sustained ventric ular arrhythmias were induced during electrophysiologic testing in 32 of the patients (39 percent). In this group, low-level electrical alte rnans (a beat-to-beat change in amplitude of < 15 muV) was detected ov er 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., th e phase of repolarization). Alternans during repolarization was a sign ificant and independent predictor of inducible arrhythmias on electrop hysiologic testing (sensitivity, 81 percent; specificity, 84 percent; relative risk, 5.2). Of 66 patients followed for up to 20 months, 13 h ad 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 surviv al without arrhythmia at 20 months was significantly lower among the p atients with T-wave alternans (19 percent) than among the patients wit hout T-wave alternans (94 percent). Conclusions. Electrical alternans affecting the ST segment and T wave is common among patients at increa sed risk for ventricular arrhythmias. Subtle electrical alternans on t he electrocardiogram may serve as a noninvasive marker of vulnerabilit y to ventricular arrhythmias.