Intra-His Bundle Block Corresponds with Interruption of the Branching Portion of the His Bundle

We compared His-bundle electrograms with pathological findings of the atrioventricular conduction system in four patients with complete atrioventricular intra-His block with narrow QRS complexes on ECG. Split His electrograms were recorded at the time of electrophysiological study. The patients died from noncardiac causes at 10 days, 1 year, 4 years, and 9 years, respectively, after the pacemaker implantation. Serial sections through the atrioventricular conduction system revealed strictly localized more than 50% reduction of conducting cells replaced by fibrosis at the branching portion of His bundle. The proximal portions of the bundle branches also exhibited decrease of the conducting cells showing a rough positive relation with the patient's age. Therefore, we considered that the H₁ spikes seen on His-bundle electrograms originated from the penetrating portion of His, which was virtually intact in our cases, and that the H₂ spikes originated from the right side of the distal branching portion of His.     

A Degenerative Lesion of the Approach to the Atrioventricular Node Producing Second-Degree and Third-Degree Atrioventricular Block

We report a case of a degenerative approach lesion in an 83-year-old male with diabetes mellitus, hypertension, and ischemic heart disease. His ECGs changed from first-degree atrioventricular (AV) block 14 years ago, to third-degree AV (A-H) block. A pacemaker was implanted for bradycardia. He died 4 years later from heart and renal failure. Serial sections through the conduction system revealed total depletion and fatty replacement of the atrial muscle at the approaches to the AV node.