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Background: This study determined the histological features of the atrial myocardium connecting the coronary sinus and the left atrium in humans., Methods and Results: Ten necropsied hearts were studied by performing serial longitudinal sections parallel to the long axis of the coronary sinus that extended its full length using a large microtome. In all specimens, the venous wall of the coronary sinus was surrounded by a cuff of striated muscle extending 40+/-8 mm from the ostium. Striated myocardial connections of varying number and morphology left this coronary muscle cuff and connected to the left atrium; they ranged from 1 to 2 fascicles to a widely intermingled continuum (thickness, 2.79+/-2 mm; width, 2.91+/-3.5 mm). These connections originated 8.8+/-5.7 mm from the coronary sinus ostium and inserted 18+/-11 mm distally into the left atrium. The insulating compartment in which the connections traversed between the left atrium and the coronary sinus was mostly formed of adipose tissue. The valve of Vieussens was found in 6 hearts at a mean distance of 3.4+/-3.2 mm from the distal extremity of the coronary sinus muscle cuff., Conclusions: In the human heart, a consistent but morphologically variable left atrial coronary sinus myocardial connection was found. This emphasizes the need for surgical dissection or catheter ablation in or around the coronary sinus to eliminate these connections.

Paroxysmal tachycardias proved fatal in a middle-aged man with type A Wolff-Parkinson-White syndrome. Efforts to control his arrhythmias included a surgical incision into the left atrium, based on discovery of early left ventricular activation during epicardial mapping. The incision did not alter any electrocardiographic or clinical feature; at later necropsy examination it was found that the incision had not cut a nearby left atrioventricular (A-V) connection. Serial section study of the entire A-V rings and septal junction of this heart also demonstrated a second unusual A-V connection, between the atrial septum and the region of the His bundle. This latter connection was anatomically eccentric to the normal organization of this region and may have caused an alteration in the local electrophysiological behavior. The left lateral A-V connection may have been of no electrophysiological significance since it was composed of ordinary working myocardial cells. These and other possible correlations are discussed in the context of the clinical features, numerous electrophysiological observations, and the meticulously determined anatomical findings.