Pathogenesis of persistent left superior vena cava with a coronary sinus connection.

The basis for persistence of the left superior vena cava (LSVC), usually associated with cardiac malformations, is poorly understood. We examined 351 staged, serially sectioned human embryos in the Carnegie Embryological Collection and 1208 specimens with congenital cardiovascular malformations in the Pathology Collection of the Johns Hopkins Hospital. A standardized questionnaire was answered for each embryo and autopsy case and a computer program was employed to tabulate concurrent anatomic features. In the normal embryos a symmetric venous system appeared with the heart tube at Carnegie stage 9; the sinoatrial junction translocated to the right and the relationship of the coronary sinus to the LSVC was established by stage 12. The LSVC was patent through stage 20 and subsequently underwent luminal obliteration by compression between the left atrium and the hilum of the left lung. Among the 1208 hearts with a congenital abnormality, 104 (9%) had a persistent LSVC with a coronary sinus connection. Statistically, significantly more frequent associations were found between persistent LSVC and atrioventricular canal defects, cor triatriatum, and mitral atresia and a significantly less frequent association was observed between persistent LSVC and atrial septal defect or patent foramen ovale as a primary defect. The normally late embryonic obliteration of the LSVC suggests that its persistence would be secondary to reduce cardiac compression or to blood flow redistribution at an early stage, and the malformations associated with persistent LSVC support that view. Identification of a persistent left superior vena cava with coronary sinus connection should suggest an associated malformation, especially atrioventricular canal, cor triatriatum, or mitral atresia.