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Electrophysiologic and histologic correlations in chronic complete atrioventricular block
Insights
Chronic complete atrioventricular block (CAVB) with AH block can stem from His bundle lesions. CAVB with HV block indicates bilateral bundle branch disease, correlating electrophysiology with histology.
Area of Science:
- Cardiology
- Electrophysiology
- Histopathology
Background:
- Chronic complete atrioventricular block (CAVB) requires precise localization of conduction system disease.
- His bundle electrogram (HBE) and histologic examination are key diagnostic tools.
Observation:
- Two patient groups with CAVB were studied: Group 1 (narrow QRS, AH block) and Group 2 (wide QRS, HV block).
- Histology correlated with HBE findings to identify the precise location of conduction system lesions.
Findings:
- In Group 1 (AH block), lesions were found in the His bundle (penetrating or branching portions), not solely the AV node.
- In Group 2 (HV block), lesions consistently involved bilateral bundle branches, consistent with trifascicular block.
Implications:
- HBE findings of AH block in CAVB can indicate His bundle lesions.
- HV block in CAVB strongly suggests bilateral bundle branch disease.
- Correlating electrophysiologic and histologic data refines understanding of CAVB pathophysiology.
Abstract:
Electrophysiologic studies using the His bundle electrogram (HBE) and histologic studies of serial sections of the conduction system were correlated in two groups of deceased patients. Group 1 consisted of five patients with chronic complete atrioventricular block (CAVB) who had narrow QRS complexes and AH block (block proximal to the His bundle deflection). Group 2 consisted of four patients with chronic CAVB who had wide QRS complexes and HV block (block distal to the His bundle deflection). In group 1, the sites of the main lesion were not located in the approaches to the atrioventricular (AV) node or the AV node, but were found in the penetrating portion of the His bundle in one patient and in the branching portion of the His bundle in three patients. In the remaining patient, the main site of block could not be demonstrated histologically in the AV conduction system, but marked fibrosis of the approaches to the sinoatrial node and surrounding atrial muscle was found. In all patients of group 2, the site of the main lesion was located in the bilateral bundle branches, and thus was compatible with so-called trifascicular block. This correlation study between the His bundle electrogram and histologic findings of the AV conduction system showed that in some cases, CAVB presenting as AH block on the HBE can be associated with a lesion in the branching portion of the His bundle (distal His), and that CAVB presenting as HV block on the HBE is associated with a bilateral lesion of the bundle branches.