Presence of cardiomyocytes exhibiting Purkinje-type morphology and prominent connexin45 immunoreactivity in the myocardial sleeves of cardiac veins.

Background: Pulmonary vein (PV) myocardium is a known source of atrial fibrillation. A debated question is whether myocardial extensions into caval veins and coronary sinus (CS) have similar properties. No studies have documented specific pacemaker and/or conducting properties of human extracardiac myocardium.