SINUS NODE DYSFUNCTION, ATRIOVENTRICULAR-BLOCK, AND BUNDLE-BRANCH ANDFASCICULAR BLOCKS - MORPHOLOGIC ASPECTS

This review begins with an overview of the normal conduction system an d then considers the abnormal situations relevant to the morphologic b ases of sinus nodal dysfunction and atrioventricular, bundle branch, a nd fascicular blocks in children. The etiology for sick sinus syndrome is multifactorial but may show changes in histological appearance of the sinus node or occlusion of the nodal artery. Sinus node dysfunctio n in congenitally malformed hearts is usually related to trauma during surgical repair of the intracardiac lesions. With regard to the atrio ventricular conduction system, the morphologic substrates of congenita lly complete atrioventricular block are well recognized. Three pattern s of discontinuity of the conduction axis are described. Atrioventricu lar, bundle branch, and fascicular blocks are usually caused by damage , direct or indirect, to the conduction system during surgical repair or intracardiac defects.