Clinical pathology of the cardiac conduction system.

Abnormal architecture of the conduction system affects both the normally structured and the congenitally malformed heart. While the majority of malformed hearts have more-or-less normal arrangements of the conduction system, there are others with significant deviations. In particular, the derangements are related to malalignment of the ventricular septum in the case of the atrioventricular conduction tissues, and to atrial arrangement with regard to the sinus node. Congenital heart block can occur in isolation or in association with congenital heart defects. The anatomical substrate in heart block is an interruption of the atrioventricular conduction system. Lesions of the conduction system are also found in cases of sudden cardiac death in adults. Whether such lesions are congenital or 'acquired' as part of the ageing process remains to be clarified.