Progressive atrioventricular block after total correction of Fallot's tetralogy, documented by repeat electrophysiological studies.

A case of progressive trifascicular block late after correction of Fallot's tetralogy is reported. Progressive damage to the His bundle and/or its branches over 18 months after surgery was suggested by sequential ECGs and confirmed by repeat electrophysiological studies done 3 and 18 months postoperatively: the H-V interval increased from 55 to 80 ms over this period. With atrial pacing at increasing rates, supra-His 2:1 atrioventricular (AV) block occurred at a rate of 158/min at the first study; at the second study, infra-His block occurred at an atrial pacing rate of only 128/min. A permanent pacemaker was implanted prophylactically. 5 years after surgery, complete heart block occurred without symptoms, the pacemaker having taken over ventricular stimulation.