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Contribution of the his bundle recording to the diagnosis of bilateral bundle branch conduction defects
Insights
His bundle electrogram studies reveal intraventricular conduction defects contribute significantly to atrioventricular (AV) delays and blocks. These defects are common in various bundle branch blocks and AV block degrees, impacting cardiac electrical activity.
Area of Science:
- Cardiology
- Electrophysiology
- Cardiac Conduction System
Background:
- Atrioventricular (AV) delays and blocks are often associated with intraventricular conduction defects.
- His bundle electrogram (HBE) is a key diagnostic tool for evaluating these conditions.
Purpose of the Study:
- To investigate the role of intraventricular conduction defects in AV delays and blocks using His bundle electrogram recordings.
- To correlate specific conduction abnormalities with different types and degrees of AV block and QRS enlargement.
Main Methods:
- His bundle electrogram recordings were performed in 239 patients with AV blocks and QRS duration > 0.12 seconds.
- Analysis included assessment of PR interval, HV interval, and localization of conduction defects.
Main Results:
- Intraventricular conduction delay (HV > 55 ms) was frequent in various bundle branch blocks, even without PR prolongation.
- In first-degree AV block, 66% showed HV prolongation.
- Second-degree AV block with wide QRS predominantly involved subnodal lesions (80%).
- Mobitz II block was consistently infranodal.
- Third-degree AV block with wide QRS was often due to bilateral bundle branch block (78%).
- Acute myocardial infarction with AV block showed characteristic conduction patterns based on infarct location.
Conclusions:
- Intraventricular conduction defects, particularly HV prolongation, are crucial in the pathophysiology of AV delays and blocks.
- His bundle electrogram effectively localizes conduction disturbances, aiding in diagnosis and understanding of AV block mechanisms.
- Bundle branch blocks significantly influence the site and severity of AV conduction abnormalities.
Abstract:
The participation of intraventricular conduction defects in the AV delays and blocks has been investigated by His bundle electrogram recording in 239 patients with different degrees of AV blocks and QRS enlargement (greater than 0.12 sec). In absence of PR prolongation, the His bundle electrogram can demonstrate intraventricular conduction delay (HV superior to 55 msec) with an increasing frequency in right bundle branch block and right bundle branch with left axis deviation, left bundle branch block and right bundle block with right axis deviation. In cases of first-degree AV block (PR greater than 0.20 sec) delay within the His bundle is present in 20% of the cases and HV prolongation, isolated or associated with an upper conduction defect is demonstrated in 66% of the cases. Second-degree AV block with QRS enlargement in the conducted beats is due to a subnodal lesions of the conducting tissue in 80% of the cases. Wenckebach phenomenon and bundle branch block is as frequent above as below the site of His bundle electrogram recording. Möbitz II block has always an infranodal localization. Third-degree AV block with wide QRS complexes is the consequence of a lesion within the His bundle in 11% and of a complete bilateral bundle branch block in 78% of the cases. Exploration of the AV conduction in acute myocardial infarction with AV block confirms the usual bilateral bundle branch lesion in anterior myocardial necrosis and the AH localization of the AV block in posterior myocardial infarction even in presence of enlarged QRS complexes. Unidirectional block occurs in 19 of the 82 cases of complete anterograde bilateral bundle branch block, with retrograde conduction to the atria in 11 and concealed retrograde conduction in 8 cases.