Intraventricular conduction time in patients with bundle branch block

Abstract

Summary His bundle electrograms (HBE) were recorded in 61 patients with various intraventricular conduction abnormalities. Seventeen patients also underwent right atrial pacing at various rates. Forty-six patients had a pattern of right bundle branch block (RBBB) and left axis deviation (LAD) (Group I). Five patients had RBBB with normal frontal plane axis (Group II). Left bundle branch block (LBBB) was the only conduction abnormality in six patients (Group III), and RBBB with right axis deviation (RAD) was present in four patients (Group IV). Intraventricular conduction time (H-Q interval) was recorded in each patient during supraventricular conduction. Eleven patients showed spontaneous Mobitz type II second degree atrioventricular (A-V) block or complete heart block (CHB) either before, during or subsequent to the study. In ten of these the H-Q interval was prolonged during orthograde conduction. Atrial pacing produced second degree A-V block distal to the His bundle potential in three patients with prolonged H-Q interval. Two of these had earlier shown transient CHB while the third developed CHB subsequently. It is concluded that the majority of patients with bundle branch block who show Mobitz type II or CHB have prolonged H-Q interval during supraventricular conduction. Atrial pacing may occasionally produce block distal to the His bundle in patients with prolonged H-Q interval.