[Complete congenital heart block. Its natural history and evolution].

This study describes the natural history and evolution of 67 patients with congenital auriculoventricular heart block admitted in the Instituto Nacional de Cardiología "Ignacio Chávez", Mexico, D.F. from 1944 to 1998. There were 35 (52%) females and 32 (47%) males, with mean follow up period of 93.7 +/- 104 months. Most of the patients were without structural cardiovascular disease (90%). The most frequent symptoms were dyspnea and syncope. Electrocardiograms showed a ventricular heart rate of 42.2 +/- 9 beats/minute. 85.7% of patients had a supra-Hisian complete heart block. In 31% of patients a pacemaker was implanted because syncope. Overall mortality was 4.4% and malignant ventricular arrhythmias were the principal contributors. Risk factors for mortality identified in this study were junctional escape rhythm lower than 50 beats/minute, inappropriate chronotropic response during exercise, R-R interval prolongation at night, enlargement of cardiac chambers, depressed left ventricular ejection fraction and prolonged QT interval. In all of these conditions we recommend permanent pacemaker implantation.