Normal H-V time in a patient with right bundle branch block, left anterior hemiblock and intermittent complete distal his block.

everal investigators1-3 have recorded His bundle activity in patients with left axis deviation and right bundle branch block (RBBB), using the catheter method Scherlag et a1 described in 1969.4 According to the concepts of trifascicular conduct i ~ n , ~ conduction delay or block in the right bundle branch (RBB) and anterosuperior division of the left bundle branch (LBB) is responsible for this electrocardiographic manifestation and establishes the posteroinferior division of the left bundle branch as the major pathway leading to ventricular activation from the A-V node and His bundle. The anterosuperior division of the LBB and the RBB may contribute (to some degree) to ventricular activation, however. If the hemiblock concept is correct (the anatomic basis for which has been challenged recently ) ,6 His to ventricle conduction time (H-V) in these patients represents primarily conduction through the posterior fascicle of the left bundle branch plus conduction through the His bundle distal to the recording site, and the mainstem left bundle. Narula and Samet2 reported 75 percent of 68 patients with RBBB and left anterior hemiblock ( LAH ) have prolonged H-V time, strongly suggesting that these patients have im-