ECG conduction disturbance in the first-degree relatives of children with ventricular septal defect.

A detailed cardiological examination was made in the first-degree relatives of 94 index patients with ventricular septal defect and in 94 matched control cases. Incomplete or suspect right bundle branch blocks were found in 18.3% and in 4.1%, respectively, of first-degree relatives of index and control groups. The difference is highly significant. These intraventricular conduction disturbances may be subthreshold signs of septal defects.