Intraventricular trifascicular block verified by His bundle electrocardiography.

A patient with the combination of right bundle branch block and intermittent left anterior and left posterior hemiblock is presented. His bundle recordings proved that this type of intraventricular conduction defect appeared when the two left fascicles were damaged partially, and to a varying degree. The recordings also revealed a Grade 2 A-V block distal to the A-V node. The mechanism is discussed.