Initial depolarizing potentials in Wolff-Parkinson-White syndrome using signal-averaged electrocardiograms: correlation with reciprocating tachycardia.

Initial depolarizing potentials were examined in patients with Wolff-Parkinson-White (WPW) syndrome using signal-averaging techniques. In all, 25 WPW patients and 21 age-matched healthy children were studied. Ten of the patients were symptomatic and 15 were asymptomatic. Symptomatic patients with supraventricular tachycardias had longer durations of low-amplitude signals (LAS) < 40 mu V in the initial portion of the QRS complex (initial LAS, 49 +/- 7 ms vs. 37 +/- 9 ms, p < 0.01) and lower root-mean-square (RMS) voltage in the initial 40 ms of the QRS complex (initial RMS, 12 +/- 4 mu V vs. 23 +/- 8 mu V, p < 0.01) compared with asymptomatic patients. When a symptomatic patient was defined as having an initial LAS of > 46 ms or an initial RMS of < 15 mu V, the sensitivity and specificity for predicting documented supraventricular tachycardia were 100 and 67%, respectively. These SA-ECG findings may reflect instability of conduction in symptomatic patients through an accessory pathway and may identify those at high risk for supraventricular tachycardia.