ELECTRICAL-CONDUCTION BETWEEN THE RIGHT ATRIUM AND THE LEFT ATRIUM VIA THE MUSCULATURE OF THE CORONARY SINUS

Background-The purpose of this study was to determine whether the coro nary sinus (CS) musculature has electrical connections to the right at rium (RA) and left atrium (LA) and forms an RA-LA connection. Methods and Results-Six excised dog hearts were perfused in a Langendorff prep aration. A 20-electrode catheter (2-4-2-mm spacing center to center) w as placed along the CS, Excision of the pulmonary veins provided acces s to the LA, and a second 20-electrode catheter was placed along the L A endocardium opposite the CS catheter. An incision opened the CS long itudinally, and microelectrodes were inserted into the CS musculature and adjacent LA myocardium. Continuous CS musculature was visible alon g a 35+/-9-mm length of the CS beginning at the ostium. During lateral LA pacing, CS electrodes recorded double potentials, a rounded, low-f requency potential followed by a sharp potential. The rounded initial potential propagated in the lateral-to-septal direction and represente d ''far-field'' LA activation (timing coincided with adjacent LA poten tials and with action potentials recorded from microelectrodes in adja cent LA cells). The sharp potential represented CS activation (timing coincided with action potentials recorded from CS musculature). A dist al LA-CS connection (earliest sharp potential in the CS during lateral LA pacing) was located 26+/-7 mm from the ostium. During RA pacing po sterior to the CS ostium, CS electrodes recorded septal-to-lateral act ivation of the high-frequency potential, with slightly later activatio n of the rounded potential (LA activation). Incisions surrounding the CS ostium isolating the ostium from the RA had no effect on the CS mus culature and LA potentials during RA pacing within the isolated segmen t containing the CS ostium. RA pacing outside the isolated segment del ayed activation of the CS musculature until after LA activation, confi rming that the RA-CS connection was located in the region of the CS os tium as well as confirming the presence of the LA-CS connection. Concl usions-In canine hearts, the CS musculature is electrically connected to the RA and the LA and forms an RA-LA connection.