Later potentials on signal-averaged electrocardiograms in children after right ventriculotomy.

After corrective surgery for congenital heart defects, scars may create fractionation and delay of the electrical signals in the heart muscle, providing a substrate for arrhythmias. Signal-averaged electrocardiograms (SAECGs) were obtained from 33 children after right ventriculotomy, on average 6 years after surgery, and from 38 healthy controls of the same age. The duration of the filtered QRS complex (fQRS), the duration of the low amplitude signal (< 40 microV) in the terminal QRS complex (LAS40), and the root mean square amplitude of the terminal 40 ms of the QRS complex (RMS40) were determined. The values of fQRS > or = 117 ms, RMS40 < or = 25 microV, and LAS40 > or = 35 ms, which were beyond the mean +/- 2 SD of the healthy controls, were considered abnormal. Most patients had right bundle branch block and therefore a prolonged fQRS. Late potentials were defined as present if both the RMS40 and LAS40 were abnormal. Altogether nine patients (27%) had late potentials. In the patients with late potentials the incidence of serious ventricular arrhythmias was 44% (4 of 9) and in the patients without late potentials 0% (0 of 24). In seven patients with enlargement of the right ventricle, the incidence of arrhythmias was 57% (4 of 7) when late potentials were present and 0% (0 of 7) when they were absent. In the present study late potentials were associated with a history of arrhythmias, especially when the right ventricle was enlarged. Therefore the SAECG may be useful for determining the risk of serious arrhythmia events in children operated for congenital heart defects.