Eight pediatric cardiac centers pooled clinical and ECG data from 372 patients who survived the Mustard operation (intraatrial baffle directing pulmonary venous blood to the tricuspid orifice and systemic venous blood to the mitral orifice) for at least 3 months. The follow-up period ranged from 0.4 to 15.9 years, and the mean age at operation was 2 years.
The mean resting heart rate for patients who had the Mustard operation was consistently lower than age-matched controls. During the year of operation, 76% of patients had normal sinus rhythm; this percentage declined yearly to 57% by the end of the eighth postoperative year. Active arrhythmias increased after the tenth year. Second or third-degree heart block occurred in 33% of patients during the year of operation and changed very little thereafter. Of the total 372 patients, 39 received pacemakers, 52% during the year of surgery and 48% evenly distributed throughout the follow-up period.