Early detection of arrhythmias after congenital heart disease surgery is important because it can help decrease morbidity and mortality. Standard electrocardiograms (ECGs) contain frequencies between 0.05 and 100 Hz, but higher frequencies are also present. Using high-resolution technology, the highest amplitudes of these high-frequency components within the QRS complex can be recorded and analyzed. We studied the relationship between ventricular late potentials, ventricular arrhythmias and right ventricular systolic pressure in 22 patients who underwent tetralogy of Fallot repair (mean follow-up, 40.1 +/- 33.5 months). Holter ECG monitoring and signal-averaged electrocardiograms (SAECGs) were performed. SAECG parameters studied included the duration of the filtered QRS, the duration of terminal QRS below 40 mu V, and the root mean square amplitude of the terminal 40 msec. Cardiac catheterization was performed on 19 patients. Eighteen healthy volunteers were studied as a control. Ventricular arrhythmias were found in 13 patients; right ventricular systolic hypertension was found in 1 patient. No significant residual ventricular septal defects were detected. Eight patients had ventricular late potentials. Right ventricular systolic pressure did not differ significantly between patients with or without late potentials. There were significant differences between patients with ventricular arrhythmias and healthy volunteers; filtered QRS duration was significantly longer in patients with ventricular arrhythmias. SAECG may be beneficial in determining ventricular arrhythmia risk in tetralogy of Fallot patients postoperatively.