Funding Acknowledgements Type of funding sources: None. Background Ethanol Infusion in the Vein of Marshall (EIVOM) has been recently introduced as an efficient technique that helps achieving mitral isthmus block during ablation procedures for persistent atrial fibrillation (PAF) or peri-mitral atrial flutter. Purpose We have evaluated the safety of EIVOM and the duration required to perform this procedure.  Methods  We performed EIVOM in 121 patients for PAF (mean age of 65 years (range 40-83, 73% men; Mean EF 50%. The main steps of the EIVOM were as follows: the procedure commenced with catheterization of the coronary sinus, followed by the subsequent introduction of an angiography catheter that allowed for iodine contrast injection and vein of Marshall (VOM) localization, 1.5-2.5 mm angioplasty balloon over 0.014" guidewire placement and finally the ethanol injection up to 10 ml.  Results No major complications were observed during the ablation procedure or before hospital discharge. In 62 patients in whom procedure duration data was available the mean EIVOM procedure time was 41 min (range from 13 to 105 min). After the first 20 procedures, where the learning curve for the operators has to be taken into consideration, a reduction in the time required to achieve EIVOM was consistently noted, with an average of less than 30 min. and for the last 20 procedures less than 20 min. Factors which increase the time required for successful EIVOM include: difficulty in visualizing the ostium of the VOM, a VOM ostium located proximally, difficulty in advancing the angioplasty wire into the VOM and balloon displacement and repositioning. Conclusions Ethanol infusion in the Vein of Marshall is a safe and efficient technique that can be performed in an acceptable amount of time after an initial learning curve. Abstract Figure. Image 1 VOM

Funding Acknowledgements Type of funding sources: None. Background Ethanol Infusion in the Vein of Marshall (EIVOM) was recently proposed as an efficient adjunctive technique for obtaining mitral isthmus block during catheter ablation for persistent atrial fibrillation.  Purpose Given these considerations the objective of this research was to delineate the angiographic anatomy of the Vein of Marshall (VOM).  Methods Fluoroscopy images were obtained retrospectively in 124 patients with persistent atrial fibrillation who underwent coronary sinus angiography for EIVOM (96 patients) or cardiac resynchronization implant (18 patients). The measurements were performed using Osirix DICOM reader using the known diameter of the angiographic catheter for calibration. The distance between the ostium of the coronary sinus (CS) and the ostium of the VOM was measured in the anteroposterior view. Additionally, the angle at which the ostium of VOM opens in the CS was obtained.  Results The diameter of the VOM ostium was 1.8 ± 0.6mm. The length of the VOM was 18.6 ± 9.1mm. The distancebetween the CS ostium and VOM ostium was as follows: less than 10mm for 1 patient (1%), between 11-20mm for 10 patients (10.41%), between 21-30mm for 38 patients (39.58%), 31-40mm for 31 patients (32.29%), between 41-50mm for 15 patients (15.62%) and >50mm for 1 patients (1%) (53mm).  The average takeoff angleof the VOM from the CS between the main branch of the VOM and the CS was measured at 140 degrees (range 90-175 degrees). No correlation could be made between the takeoff angle and the distance between CS ostium and VOM ostium.  In the group of patients undergoing cardiac resynchronization the takeoff angle from the CS was 153°±17° and it correlated significantly with the left ventricular systolic diameter and the left ventricular ejection fraction determined by echocardiography(r = 0.52; p = 0.008 and respectively r = 0.50; p = 0.009). Conclusions Understanding the anatomy of the Vein of Marshall (VOM) is crucial in helping operators efficiently exploit the therapeutic potential of ethanol injection after accurate localization of such an important branch of the left atrial venous system. Abstract Figure. 1 Fig 1 Angle CS-VOM

Funding Acknowledgements Type of funding sources: None. Background Achieving bidirectional mitral isthmus block during radiofrequency (RF) ablation for persistent atrial fibrillation (AF) is still challenging. The conventional ablation method involves RF applications on the endocardial aspect of the Mitral Isthmus (MI), and for a majority of patients, in the distal coronary sinus (CS).  Purpose We have evaluated the acute success of obtaining mitral isthmus block by adding another epicardial component using ethanol infusion in the vein of Marshall (EIVOM) in addition to endocardial MI and epicardial CS ablation.  Methods  We studied 121 patients (pts.) with a mean age of 65 years (range 40-83) 73% men; 119 with longstanding persistent AF (98%) and 2 with perimitral flutter (2%). The mean duration of AF was 53 months (12-244 months). In the majority of patients, additional endocardial (on the ventricular aspect of the MI) and/or epicardial (distal CS) (RF) ablation was performed in order to achieve MIB. The ablation procedure was performed under general anesthesia (GA) for 81 pts (67%). EIVOM was perform with a mean 6 ml ethanol (range 2-10ml)  Results  Bidirectional MIB was obtained in 114 pts. (94,2%). The 7 patients without MIB were scheduled for another ablation procedure (4 pts under GA during the first procedure). The average RF delivery time to block was 160 seconds (range 42-480 seconds) for the endocardial MI RF ablation (point-by-point application with a power of 50W and an Ablation Index of 450-500, contact force 10-20g) and 156 seconds (range 55-438) for the epicardial MI RF ablation (applications with a power of 20W). Bidirectional endocardial and epicardial MIB was confirmed by conventional pacing maneuvers performed in sinus rhythm. No major complications were observed. The parameters associated with failure for MIB were AF duration, Left Atrial dilatation >200 ml, MI thickness (epicardial endocardial distance on the CARTO maps >15mm). Conclusion Ethanol infusion in the vein of Marshall is a safe approach and is associated with a higher success rate of obtaining acute bidirectional endocardial and epicardial mitral isthmus block when compared with the conventional method. Abstract Figure. Bloc Mitral Endo; Bloc Mitral Epi;