His bundle electrograms were recorded in four patients with ectopic rhythms showing a right bundle-branch block - superior axis pattern. In one case what appeared to be a slow idioventricular rhythm was identified as a His bundle rhythm with transient right bundle-branch block and left anterior hemiblock. The second patient had an idioventricular tachycardia. H deflections were not seen in front of the corresponding QRS complexes. Impulse formation probably occurred in the posteroinferior wall of the left ventricle. To test this assumption regarding the pacemaker site, the latter area was stimulated through a catheter introduced into the middle cardiac vein. Extrasystoles, thus induced, showed a superior axis deviation with predominant R waves in the right chest leads and a VH interval of 50 msec. The ectopic beats observed in the third patient arose in the posteroinferior division of the left branch. The diagnosis was based on the left anterior hemiblock - incomplete right bundle-branch block morphology, and short (15 msec) VH interval. In the last patient (who had established right bundle-branch block and left anterior hemiblock) the extrasystoles arising from a focus below the His bundle could have originated either in the right branch or anterosuperior division of the left branch proximally to the area of block; or anywhere within the posteroinferior division. His bundle recordings should be analysed not only in the light of the coexisting AV and VA conduction patterns but also considering the morphological QRS changes as well.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine