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Complete heart block or left bundle branch block occasionally occurs in patients with valvular heart disease.
In a necropsy study of 13 such patients, it was found that the conduction disturbance was due in all cases to infiltration of either calcium or fibrous tissue, report two pathologists at the National Institutes of Health.
Of these 13 patients, four had complete heart block and nine had left bundle branch block.
In each patient with complete heart block, the A-V node was destroyed by calcium. In patients with left bundle branch block, the left bundle was interrupted by calcium, fibrous tissue, or rheumatoid nodules.
"The extent of the pathological process appeared to be the principal factor determining whether complete heart block or left bundle branch block occurred," said Louis D. Wright, MD.
The close proximity of the heart valves to the A-V bundle and the proximal left and right branches in the
Conduction Disturbances Traced To Infiltration. JAMA. 1966;198(2):40. doi:10.1001/jama.1966.03110150020008