Histopathology of conducting system in left anterior hemiblock

Area of Science:

• Cardiovascular Pathology
• Electrophysiology
• Cardiac Histology

Background:

• Left anterior hemiblock (LAH) is an electrocardiographic finding indicating conduction delay in the heart's left bundle branch.
• Understanding the precise histological basis of LAH is crucial for accurate diagnosis and patient management.
• Previous studies have suggested specific anatomical correlates for LAH, but comprehensive histological data remain limited.

Purpose of the Study:

• To investigate the histological changes in the cardiac conduction system in patients with left anterior hemiblock, often combined with right bundle-branch block.
• To correlate the observed pathological findings with the electrocardiographic patterns.
• To evaluate the consistency of current terminology like 'anterior fascicular block' with histological evidence.

Main Methods:

• Histological examination of serial sections of the conducting system of the heart.
• Analysis of 8 cases presenting with left anterior hemiblock, 7 of which also had right bundle-branch block.
• Assessment of acute and chronic pathological changes, including myocardial infarction and fibrosis.

Main Results:

• Pathological changes were present in the left bundle-branch in all 8 cases, but predominantly in the anterior part in only 2 cases.
• Acute changes (myocardial infarction) were found in 6 cases, and fibrosis in 2 cases of chronic heart disease.
• In 7 cases with right bundle-branch block, fibrosis disrupted the right bundle-branch in 6 instances; minor AV node changes were seen in 1 case.

Conclusions:

• Widespread damage to the left bundle-branch in most cases is inconsistent with the limited clinicopathological correlation of 'anterior fascicular block' or 'hemiblock'.
• Reversible lesions may play a pathogenetic role in acute hemiblocks.
• Other cardiac lesions, both within and outside the left bundle-branch, likely contribute to the observed electrocardiographic pattern.