MI reconnection after EIVM and considerations for associated RF
lesions
The success rate of RF alone to achieve acute MI block ranged from 32%
to 91% in several studies.19–22, 25 Also, MI
reconnection rate late after endo-epicardial RF has been reported as
high as 73%.23 These variable and overall low acute
and late outcomes are due to the heterogeneous and complex structure of
the MI, consisting of a thick myocardium, vascular and nervous
structures, epicardial muscular fibers sometimes requiring extensive
ablation within the CS and difficulty to achieve catheter-tissue contact
and stability.22 Added to RF, EIVM significantly
increases MI block success, PMLAF termination rate and long-term freedom
from PMLAF relapse.7,8,11,12, 16 In a recent study of
84 patients undergoing EIVM added to RF for MI ablation, MI block was
successful in 93% of patients.18 In our study, EIVM
added to RF achieved successful MI block in 83% of cases. One case of
intra-EIVM scar reentrant AT has been reported,24 but
EIVM has consistently been found to create homogenous lesions — in
terms of endocardial voltage — and additional RF mostly needed at the
mitral annulus edge of the MI.12 Our results are in
line with Nakashima’s et al study25, showing same rate
of MI reconnection and sites of reconnection. In our study of 24
consecutive patients referred for CA of recurrent AF or AT after EIVM,
the MI was reconnected in 25%. The site of MI reconnection was not
within the EIVM-related scar but rather at its mitral annulus border in
40% of patients and within the CS in 60%. Additionally, in patients
with acute MI ablation failure, residual MI conduction was found at the
ridge aspect of the MI at procedure redo.
MI reconnection at its mitral annulus extremity after EIVM could be
explained by 3 phenomena: 1) MI mitral annulus extremity being outside
of VOM drainage territory, 2) incomplete VOM alcoolization related to
balloon-occlusion of the most proximal branches and 3) progressive
retraction of the EIVM-created lesion at its border. Scar measurement by
using EAM systems may not be accurate enough to reliably assess the last
hypothesis, and histopathological works in animals late after EIVM may
shed light on this matter. Further works are also needed to optimize the
EIVM technique. Ethanol infusion of the entire VOM network may be
incomplete in some patients because of the great interindividual
anatomical variability and the exclusion of most proximal VOM branches
when using balloon occlusion. Development of a technique not involving
balloon occlusion could be useful for that purpose. Finally, our results
should encourage physicians to consolidate RF lesions at both
extremities of the EIVM-created lesion.