The Coronary Sinus: A clinical perspective for the electrophysiologist.

The coronary sinus (CS) is a specialized cardiac structure whose embryologic and anatomic features may contribute to arrhythmogenesis. Composed of both venous and myocardial elements, it can be conceptualized as a distinct cardiac chamber with connections to both the left and right atria-characteristics that make it an important site for the initiation and maintenance of atrial arrhythmias, as well as a key structure in explaining the underlying physiology of atrioventricular nodal reentrant tachycardia (AVNRT) and the origin of epicardial bypass tracts. The vein, ligament, and myocardial bundle of Marshall arise from the proximal CS and maintain electrical connections with the left atrium and the left-sided pulmonary veins. Because of their electrophysiological and autonomic properties, these structures may contribute to both atrial and ventricular arrhythmias. Furthermore, the proximity of CS tributaries to the ventricular myocardium provides access for the mapping and ablation of selected ventricular arrhythmias, complementing the established role of these vessels in left ventricular pacing.