Pathological basis of primary heart block.

The cause of chronic complete heart block is often obscure but was formerly assumed, in many cases, to be ischaemic in origin (Penton, Miller, and Levine, 1956). In recent years it has become apparent that coronary artery disease is a relatively uncommon cause of chronic heart block, and the terms, "isolated disease of the conduction system" (Portal et al., 1962) or "primary heart block" (Zoob and Smith, 1963) have been introduced for those patients with complete heart block, and no obvious cause. In a necropsy series at this hospital of 65 consecutive patients dying with chronic heart block, 26 were found to have bilateral bundlebranch fibrosis (Harris et al., 1969). The pathology of bundle-branch fibrosis has not been described in detail and the morphological findings in 27 cases are therefore presented in this paper.