Signal-averaged isoharmonic body surface maps of patients with ischemic cardiomyopathy

Prevention of sudden arrhythmic cardiac death depends on accurate identification of individuals at high risk. Previous studies of signals recorded directly from arrhythmogenic tissue suggested that the predictive value of the signal-averaged ECG could be enhanced by expanded temporal, spectral, and spatial analysis. Accordingly, we performed a prospective study of 192-lead signal-averaged body surface maps from 43 patients with ischemic cardiomyopathy referred for electrophysiologic study. Three groups were included: 15 patients with clinical ventricular tachycardia (VT), 12 patients with inducible VT, and 16 patients with non-VT.

The patients were well matched with regard to age, gender, infarct location, ejection fraction (28% +/- 9%), QRS duration, and incidence of nonsustained VT (96%). Isoharmonic maps of the entire cardiac cycle were constructed for each patient. The peaks of the 1-7 Hz isoharmonic maps distinguished patients with clinical VT from non-VT and inducible VT patients (1,152 +/- 273, 852 +/- 283, and 808 +/- 272, respectively; P = 0.003). After prospective observation for 22 +/- 16 months, the combined endpoint of spontaneous sustained VT, ventricular fibrillation, appropriate defibrillator therapy, and death was predicted by inducibility of VT (relative risk 3.8, P = 0.008) and by the signal-averaged isoharmonic body surface map (relative risk 3.1, P = 0.02).

These results confirm the diagnostic utility of signal-averaged isoharmonic body surface maps in a rigorously defined patient population.