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

Abstract

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. The purpose of this study was to characterize the histology and immunohistochemical features of myocardial sleeves in the wall of cardiac veins. Sections of 32 human hearts were investigated. Specimens of PVs, superior caval vein (SVC), CS, sinoatrial and atrioventricular nodes, and left ventricle were stained with Best's Carmine for selective staining of intracellular glycogen. Anti-connexin45 (Cx45)- and Cx43-specific antibodies were used to determine the conduction properties of extracardiac myocardium. Myocardial sleeve was found in the wall of PVs of 15 of 16 hearts, 21 of 22 SVCs, and 8 of 8 CSs. Bundles of glycogen-positive cardiomyocytes exhibiting pale cytoplasm and peripheral myofibrils were observed in the venous sleeves. Strong Cx45 and weak Cx43 labeling was detected in the extracardiac myocardium. Similar staining pattern was observed for the pacemaker and conduction system, whereas ventricular myocardium exhibited prominent Cx43 and no Cx45 immunoreactivity. Myocardial fibers of PVs, SVC, and CS exhibit morphology similar to that of Purkinje fibers and are enriched in glycogen. We provide data for the first time on prominent positive staining for Cx45 in the extracardiac myocardium, indicating its potential pacemaker and/or conducting nature.