Pathology of chronic A-V Block.

Study of 177 cases of permanent A-V block shows idiopathic bilateral bundle branch fibrosis to be the commonest single cause (33%). This entity covers a spectrum of localised loss of conduction fibres in the proximal left bundle branch and bifurcating main bundle (Lev's disease) to moore periphery loss of conduction fibres in the bundle branches alone (Lenègre's disease). The aetiological factors in idiopathic bundle branch fibrosis are still obscure. Ischaemic damage is responsible for 17% of cases and are usually patients who have survived destruction of the bundle branches in septal infarction. Calcific A-V block is the term applied to destruction of the main bundle by large masses of calcification in the mitral or aortic valve rings and is responsible for 10% of cases of chronic A-V block. The mass of calcium is visible to the naked eye at autopsy or by X ray in life. Cardiomyopathies of all types (except hypertrophic obstructive cardiomyopathy) involve the conduction system and produce 14% of cases of A-V block. The remaining numerous causes of chronic A-V block are individually very rare ranging through tumour involvement, congenital defects, collagen diseases and surgical or traumatic damage.