Differential Pacing Maneuver From the Vein of Marshall

BACKGROUND: Bidirectional mitral isthmus (MI) block is conventionally verified by differential pacing from the coronary sinus (CS) and its sequence change. This study aimed to evaluate the ability of differential pacing from the vein of Marshall (VOM) to detect epicardial MI connections. METHODS: Radiofrequency and VOM ethanol MI ablation were performed with a VOM electrode catheter inserted to the septal side of the ablation line. MI block was verified using conventional CS pacing. To perform differential VOM pacing analysis, initial pacing was delivered from a distal VOM bipole closer to the block line, and then from a proximal VOM bipole. The intervals from pacing stimulus during different VOM pacing sites to the electrogram recorded through the CS catheter on the opposite side of the line were compared. When the interval during distal VOM pacing was longer than that during proximal VOM pacing, it indicated a VOM connection block; however, if the former interval was shorter, the connection through the VOM was considered persistent. RESULTS: Overall, 50 patients were evaluated. According to CS pacing, MI ablation was incomplete in 9 patients, in whom the analysis indicated persistent VOM connection. Among 41 patients with complete MI block, confirmed by CS finding, in 30 (73%) patients, the interval during distal VOM pacing was longer than that during proximal VOM pacing by 11±5 ms. However, in 11 patients (27%) the former interval was revealed to be shorter than the latter by 16±8 ms, indicating residual VOM connection. Conduction time across the line was significantly shorter in 11 patients than in the other 30 (166±21 versus 197±36 ms; P <0.01). Ten successful reevaluated analyses after VOM ethanol and further radiofrequency ablation of the connection indicated VOM block achievement. CONCLUSIONS: Differential VOM pacing maneuver reflects the VOM conduction status. This maneuver can uncover residual epicardial connections that are missing with CS pacing.