Cardiac Conduction System in Congenitally Corrected Transposition of the Great Arteries and Its Clinical Relevance

C ongenitally corrected transposition of the great arteries (ccTGA) is a rare cardiac malformation characterized by the combination of discordant atrioventricular and ventriculoarterial connections. The incidence has been reported to be around 1/33 000 live births, accounting for 0.05% of congenital heart malformations. Although a familial recurrence of heart defects in subjects with ccTGA has been reported, the etiology of this malformation is not currently known. The morphological right atrium is connected to the morphological left ventricle across the mitral valve, with the left ventricle then connected to the pulmonary trunk; the morphological left atrium is connected to the morphological right ventricle across the tricuspid valve, with the morphological right ventricle connected to the aorta. Because of this “double discordance,” the systemic venous return is pumped to the lungs, while the pulmonary venous return is directed to the body. In the context of usual atrial arrangement (situs solitus), the morphological left ventricle is thus positioned to the right and the aorta, arising from the morphological right ventricle, is more commonly left-sided. In mirror-image atrial arrangement (situs inversus), the morphological left ventricle is left-sided, and the aorta is usually positioned to the right. Most patients have at least 1 associated cardiac anomaly, mainly ventricular septal defect (VSD), subvalvular and/or valvular pulmonary stenosis, or abnormalities of the systemic (tricuspid) atrioventricular (AV) valve with coexisting accessory pathways. Because of the unusual position of the atrioventricular node and course of the atrioventricular conduction bundle, cardiac conduction disorders are frequent and markedly alter the natural history and management of the malformation. This article provides a comprehensive, up-to-date description of the characteristics of the cardiac conduction system in patients with ccTGA, their clinical sequelae, and their contemporary management.