Conduction disturbances located within the His bundle.

SUMMARY Four patients are described with different degrees of conduction disturbance within the His bundle. In one patient with a Mobitz type II atrioventricular (A-V) block with normal QRS complexes the blocked atrial beats were followed by a His potential. Since the QRS complexes of the conducted beats were completely normal, the site of the block was thought to be in the distal part of the His bundle. In the other three patients with a 2:1 A-V block, a nearly complete A-V block, and a complete A-V block, two distinct His potentials could be discerned, one (H) following each atrial beat, the other (H') preceding each ventricular activation. In the patient with 2:1 A-V block a Wenckebach phenomenon within the His bundle could be produced at certain atrial driving rates. Impulse conduction through the A-V node was normal in all four cases, as could be concluded from the effect of increased atrial driving rate and of accurately timed atrial premature beats. The site of the block could nlot be predicted from the conventional electrocardiogram. Stimulation studies SEVERAL recent studies1-5 have demonstrated that the recording of His bundle electrograms6 is a useful method for the localization of the conduction defect in patients with atrioventricular (A-V) conduction disturbances. It has been shown that most patients with complete heart block have in fact a bilateral bundle-branch block, a finding which is consonant with the outcome of histopathologic studies.7 10 In patients with a The refractory periods of the A-V conduicting partial (first-degree or second-degree) atrio-ventricular block the conduction defect may be localized between the atrium and the His potential recording site (that is, within the A-V node) or in the peripheral part of the 612 conduction system, which means most frequently conduction impairment in both bundle branches. A few studies,4 11 however, mention the existence of a conduction disturbance within the His bundle as a third possibility. This communication describes our findings in four patients with different degrees of atrioventricular block in whom the defect could be attributed to conduction impairment within the His bundle. Methods The stimulation procedure used was similar to that described in an earlier paper.} Two bipolar catheters were introduced into the femoral veins using the Seldinger technique; one was positioned against the atrial septum, and the other in the apex of the right ventricle. These catheters were connected with the stimulator used in our catheterization laboratory for electrophysiologic …