Purpose: Although experimental data have suggested that temporary occlusion of the coronary sinus (CS) can facilitate the creation of transmural lesions across the atrial wall (AW) during mitral isthmus radiofrequency (RF) ablation, no computer modeling study has yet been made on the effect of the blood flow inside the epicardial vessels and its stoppage by an occlusion balloon. Methods: Computer simulations using constant power were conducted to study these phenomena by two methods: (1) by setting blood velocity in the CS to zero, which mimics a distal occlusion; and (2) by including a balloon filled with air in the model just below the ablation site, which mimics a proximal occlusion. Results: For short ablations (15 s) and perpendicular electrode/tissue orientation, lesion size was smaller with proximal occlusion compared to distal or no occlusion, regardless of the AW-CS distance (from 0.5 mm to 3.4 mm). For other angulations (0 and 45 ) lesion size was almost the same in all cases. For longer ablations (60 s), the internal CS blood flow (no occlusion) considerably reduced lesion size, while stoppage combined with the proximal presence of a balloon produced the largest lesions. This performance was similar for different catheter angulations (0, 45 and 90 ). Balloon length (from 10 to 40 mm) was found to be an irrelevant parameter when proximal occlusion was modeled. Conclusions: Using an air-filled balloon to occlude CS facilitates mitral isthmus ablation in long ablations, while proximal occlusion could impede transmural lesions in the case of short ablations (15 s).

This work was supported by the Spanish Ministerio de Economía, Industria y Competitividad under “Plan Estatal de Investigacion, Desarrollo e Innovación Orientada a los Retos de la Sociedad”, Grant Nº “RTI2018- 094357-B-C21”. A. González-Suárez has a “Juan de la Cierva-formación” Postdoctoral Grant [FJCI-2015-27202] and a “Jose Castillejo” Postdoctoral Mobility Grant [CAS18/00390] from the Spanish Ministerio de Economía, Industria y Competitividad.