Mitral isthmus gaps have been ascribed to an epicardial musculature anatomically related to the great cardiac vein (GCV) and the vein of Marshall (VOM). Their lumen offers an access for radiofrequency application or ethanol infusion, respectively.

To evaluate the frequency of mitral isthmus gaps accessible via the GCV lumen, to assess their location around the GCV circumference, and to propose an efficient ablation strategy when present.

One hundred consecutive patients underwent VOM ethanol infusion (step 1) and endocardial linear ablation from the mitral annulus to the left inferior pulmonary vein (step 2). In cases of mitral isthmus gap, endovascular ablation of the GCV anchored wall facing the left atrium was systematically performed (step 3), while the opposite GCV free wall was targeted in case of block failure only (step 4).

After VOM ethanol infusion and endocardial ablation, mitral isthmus block occurred in 51 patients (51%). Pacing maneuvers and activation sequences demonstrated an epicardial gap via the VOM in 2 patients (2%), and via the GCV in 47 patients (47%). In the latter case, block was achieved at the GCV anchored wall in 42 patients (89%), and the GCV free wall in 5 patients (11%). Global success rate of mitral isthmus block was 98%. No tamponade occurred.

With the advent of VOM ethanol infusion, residual mitral isthmus gaps are mostly eliminated within the first centimeter of the GCV. Thorough mapping of the entire circumference of the GCV wall can help identify these epicardial gaps.