Introduction: Fractionated electrograms and double potentials have been well described within the coronary sinus (CS) in humans. The pattern of circumferential activation in the CS has not been investigated. Furthermore, no data exist on conduction characteristics within the great cardiac vein (GCV) or the middle cardiac vein (MCV).

Methods and results: Twenty patients underwent catheter mapping of the CS, the MCV, and the GCV. Anatomical areas were verified by cannulation of the left superior pulmonary vein. The pattern of circumferential muscle activation within the proximal CS was also studied with a circular mapping catheter (Lasso 12 mm). At conventional mapping during sinus rhythm and high right atrial pacing, discrete double potentials or fractionated electrograms were recorded during left, right atrial and CS pacing at the CS ostium, mid-CS, and distal CS-ligament of Marshall area, in 2 (10%), 1 (5%), and 9 (45%) patients, respectively, whereas no patient displayed such signals in the MCV or GCV ( p < 0.001). Proximal CS mapping with the Lasso was accomplished in 10 patients, 7 of whom had no evidence of multicomponent potentials in the CS at conventional mapping. Specific CS potentials dissociated from the atrial electrograms were recorded in all patiens with the use of circumferential mapping. The perimetric distribution of electrograms within the CS suggested an oblique course of conduction across the CS musculature.

Conclusion: Potentials representing activation of the CS musculature, with an oblique course of conduction across the CS, can be recorded in human CS but not in the GCV or MCV. This is compatible with anatomical observations of sinus venosus musculature covering the CS but not other cardiac veins, and supports the rationale for the role of CS musculature in the generation of atrial arrhythmias.