Assessment of atrioventricular conduction in left and right bundle branch block using his bundle electrograms and atrial pacing

Abstract

His bundle recordings during atrial pacing were made in 26 patients with electrocardiographic evidence of either complete left bundle branch block or right bundle branch block with partial left bundle branch block (anterior superior or posterior inferior hemiblock). Twenty-four patients had sinus rhythm and 2 had complete heart block (trifascicular block). All patients with sinus rhythm showed a normal gradual increase in the P to His interval with increasing heart rate, whereas the His to QRS interval remained constant. When Wenckebach periods occurred, block was proximal to the area of the His potential (normal). The 2 patients with complete heart block showed block distal to the area of the His potential. Conduction time from the His bundle to the QRS interval was shorter in most of those patients with right bundle branch block and partial left bundle branch block than in those with complete left bundle branch block, thereby suggesting that conduction through the right bundle branch takes a longer time than conduction through the radiations of the left bundle. Even when subjected to heart rate stress, atrioventricular conduction through the remaining fascicles is adequate in most patients with bifascicular block and normal sinus rhythm.