4.2 | Efficacy of VOM-EI
In our study, we achieved mitral isthmus block in all patients
undergoing VOM-EI. Other groups described comparable results of mitral
isthmus block in 98.7-100% of cases.10,13,16
Importantly, ancillary radiofrequency ablation was necessary in 63% of
our patients, mainly on the annular side of the mitral isthmus both
endocardially and epicardial from within the CS. As previously described
and expected for anatomical reasons, the main impact of VOM-EI is on the
pulmonary venous side of the mitral isthmus, sparing the annular
aspect.9 The pulmonary venous side of the mitral
isthmus is generally thicker and protected from endocardial
radiofrequency ablation by adipose tissue.17,18Epicardial ablation via the CS is often required for mitral isthmus
ablation. Because of the course of the CS, epicardial ablation usually
targets the annular side of the mitral isthmus. VOM-EI can elegantly
overcome the limitations of radiofrequency ablation by targeting
primarily the pulmonary venous side. Correspondingly, several reports
from the Bordeaux group demonstrated that endocardial radiofrequency
ablation at the annular aspect of the mitral isthmus was mainly required
to achieve mitral isthmus block after VOM-EI.13,19 The
ablation time to achieve mitral isthmus block was significantly shorter
with supplement VOM-EI compared to radiofrequency ablation alone.
Termination of ongoing perimitral flutter during VOM-EI has been
reported in 26-56% of cases.9,10,15 Consistent with
these results, perimitral flutter terminated or slowed during VOM-EI in
58% of our cases.
Radiofrequency ablation of atrial fibrillation increases cardiac
biomarkers like hs-TnT. Haegeli et al. reported hs-TnT levels of 850
ng/L six hours after atrial fibrillation ablation whereas Reichlin et
al. observed hs-TnT levels of 1996 ng/L 24 hours after the procedure and
found a significant correlation of hs-TnT levels with total
radiofrequency time and energy delivery.20,21 In our
study, hs-TnT increased significantly from 330 to 598 ng/L within 24
hours after the procedure. Tissue necrosis induced by VOM-EI is
therefore not excessive, as compared to a regular atrial fibrillation
ablation procedure.
Low-voltage areas induced by VOM-EI can have various sizes, and probably
depend on the vascular tributaries of the vein of Marshall as well as
volume and infusion rate of ethanol injection.9,22Some cases of chemical ablation have been reported that resulted in
large low-voltage areas, including the left atrial appendage or the
posterior wall.23,24 In previous studies, mean
low-voltage areas induced by VOM-EI have been described in the range of
7.7±3.2 cm2 to 12.7±8.3
cm2.8,9,10,25 Generally, 2 to 4 ml
of ethanol were injected in these studies, but some groups reported
higher volumes of ethanol injection up to 12 ml.10After injection of a median of 4 ml of ethanol, we observed a
low-voltage area of 13.2 cm2. Low-voltage area in our
study correlated significantly with the volume of ethanol injected (P =
0.03).