Etiology of right bundle-branch block pattern after surgical closure of ventricular-septal defects.

An incidence of 60 per cent of postoperative RBBB in the ECG's and available VCG's of 26 patients with isolated muscular VSD repaired was noted after ventriculotomy. In the 38 patients with VSD's near the membranous septum who underwent repair via the tricuspid valve, the incidence of postoperative RBBB was 44 per cent. Results suggested that either ventriculotomy or injury to the right bundle near the VSD can cause RBBB after surgical closure of the defect. Changes in the initial 0.02 second electrovectocardiographic forces in patients with postoperative RBBB were thought to result from central injury to the specialized conduction tissue supplying the interventricular septum. Peripheral RBBB, therefore, could be separated from central RBBB, by the appearance of the initial electrovectorcardiographic forces. For detection of these changes in initial forces, both the ECG recorded at 50 mm. per second and the Frank VCG were useful.