Myocardium of the Superior Vena Cava, Coronary Sinus, Vein of Marshall, and the Pulmonary Vein Ostia: Gross Anatomic Studies in 620 Hearts

Anatomy of Myocardial Extensions in Thoracic Veins. Introduction: Radiofrequency ablation for atrial fibrillation (AF) frequently involves energy delivery at the ostia of the thoracic veins. Detailed evaluation of the myocardium extending into the caval veins, vein of Marshall, as well as at the pulmonary vein ostia has not been completely evaluated. Methods and Results: Post-mortem assessment of 620 formalin-fixed hearts (mean age 60 +/- 23 years, 44% female) was performed. The hearts were examined for integrity of venous structures and their atrial connections. Systematic gross anatomic evaluation including measurements on myocardial extensions in these veins was performed. Macroscopic myocardial extensions into pulmonary veins were noted in 99% of specimens evaluated and were circumferentially symmetric (99.6%). Myocardial extensions into the superior vena cava (SVC) occurred in 78% with the majority being circumferentially asymmetric (61%). Occasionally, myocardium extended into the azygos vein (6%). There were no myocardial extensions in the inferior vena cava (IVC). In some cases, the right atrial pectinate muscle extended into the coronary sinus (7%). The vein of Marshall was consistently located anterior to the left-sided pulmonary veins and posterior to the left atrial appendage, overlying the left atrial endocardial ridge. Conclusions: Myocardial extensions into the pulmonary veins are usually circumferential at the ostia validating the necessity for wide area rather than segmental ablation to isolate these veins during AF ablation. Myocardial extensions into the SVC are common and less likely to be circumferential, whereas extensions into the IVC are not present. The left atrial ridge is a reliable endocardial target for radiofrequency ablation of the vein of Marshall. (J Cardiovasc Electrophysiol, Vol. 23, pp. 1304-1309, December 2012)