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Intra-His bundle block corresponds with interruption of the branching portion of the His bundle
Y Nakazato1, Y Nakata, T Tokano
1Department of Cardiology, Juntendo University School of Medicine, Tokyo, Japan.
Insights
This study links His-bundle electrograms to pathology in patients with atrioventricular block. Findings reveal fibrosis in the His bundle branching, explaining electrogram signals.
Area of Science:
- Cardiology
- Electrophysiology
- Pathology
Background:
- Complete atrioventricular block with narrow QRS complexes can present diagnostic challenges.
- His-bundle electrograms (HBE) are crucial for evaluating the atrioventricular conduction system.
Observation:
- Four patients with intra-His block underwent electrophysiological studies and subsequent pathological analysis.
- Patients received pacemakers and died from non-cardiac causes at varying intervals post-implantation.
Findings:
- Pathology revealed significant fibrosis and loss of conducting cells (>50%) at the His bundle branching portion.
- Proximal bundle branches showed age-related decreases in conducting cells.
- HBE analysis suggested H1 spikes originate from the intact penetrating His bundle, and H2 spikes from the distal branching His bundle.
Implications:
- This correlation aids in understanding the origin of HBE signals in specific conduction abnormalities.
- Pathological findings provide a basis for interpreting electrophysiological data in intra-His block.
- The study highlights the localized nature of His bundle pathology in narrow complex atrioventricular block.
Abstract:
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.