Abnormal signal averaged ECG after surgical repair of tetralogy of fallot. A Combined Analysis in the Time and Frequency Domain.

PURPOSE: The clinical significance of abnormal signal averaged ECG (SA-ECG) determined by time and frequency domain analyses was assessed in tetralogy of Fallot patients after surgical repair, and the methods of analysis were compared. MATERIALS AND METHODS: SA-ECG was performed in 42 patients (mean age, 9.4 years) after radical surgical repair of tetralogy of Fallot, and in 11 preoperative patients (mean age, 2.6 years). Abnormal SA-ECGs were defined by time domain analysis (vector magnitude method) and frequency domain analysis (fast Fourier transformation). RESULTS: Abnormal SA-ECGs were recognized in 10 postoperative, patients (3 by time domain and 9 by frequency domain, analysis), but in none of the preoperative patients. Three patients with abnormal SA-ECGs had nonsustained ventricular tachycardia, 5 others had premature ventricular contractions, and the remaining 2 had no ventricular tachyarrhythmias documented by 24 h Holter monitoring. Patients with abnormal SA-ECGs more commonly had ST-T segment depression on standard ECG during exercise (8/10 versus 8/32, p < 0.001), a history of resection of a hypertrophic septoparietal muscle band (8/10 versus 2/32, p < 0.001) and histologically documented myocardial fibrosis at radical surgical repair (9/10 versus 5/19, p < 0.002). CONCLUSION: A Combination of time and frequency domain analyses was necessary to detect abnormal SA-ECGs in postoperative patients because of ventricular conduction disturbance. This technique might increase our ability to identify patients at risk of ventricular tachyarrhythmia, or those with underlying myocardial abnormalities.