Discussion
In this study, we report the feasibility, efficacy, and complication
risks related to a moderate volume of VOM ethanol infusions for AF
ablation. We demonstrate that VOM ethanol infusion has a learning curve
with improved success rates and lowered fluoroscopy times with
accumulated experience, even across years of reasonable procedural
volume. Rates of VOM perforation, dissection, and overall ethanol
infusion success rate were remarkably similar to published reports in a
highly experienced
center.8
A majority of patients had a CIED or wearable monitors to assess
arrhythmia recurrence. In the context of a pandemic follow-up system
that was often limited to telemedicine without formal rhythm
assessments, and the fact that several procedures were performed in the
few months leading up to this study, the average follow-up duration was
9.5 months. We acknowledge that with longer follow-up durations and/or
continuous rhythm monitoring, more recurrences may have been detected.
Nonetheless, we observed extremely low clinical failure and redo
procedure rates, and a one year probability of 80% for arrhythmia
freedom. This is prominently viewed in light of a significant proportion
of long-standing persistent AF patients and the majority of redo
procedures enrolled featuring documented permanent PVI. The left atrial
size in this study is similar to that of the CONVERGE trial of hybrid
ablation,11 although
the proportion of long-standing persistent AF patients is much lower.
Studies of similar success rates in persistent AF patients with less
comprehensive ablation approaches have only featured subjects with much
smaller atrial sizes.12Unfortunately, the degree that any improved efficacy is due to the VOM
ethanol infusion per say is not possible to assess by this analysis. The
standard lesion set in this study encompassed isolation of the posterior
wall, CS, mitral isthmus, and cavotricuspid isthmus in almost all cases.
Additional ablation beyond this was not insignificant either,
particularly in redo procedures. Nonetheless, other studies have
questioned the value of these approaches, particularly for ablation
lines which were not found to be helpful in a large randomized
trial.3 Even if the VOM
ethanol infusion dominates as the marginal difference accounting for the
success in this cohort, the mechanism of benefit remains unclear. In
VENUS, the benefit was constrained to the patients with successful
mitral isthmus block.13It is possible that the VOM ethanol infusion merely ensures more
permanent mitral
block14-16 or isolation
around the left pulmonary vein antra. However additional effects of
autonomic
denervation17,
debulking of atrial mass, or direct suppression of ligament of Marshall
AF triggers18 are
plausible as well.
Despite excellent arrhythmia freedom in our cohort, review of these
patient outcomes unveiled important safety concerns that also may differ
in frequency from those after PVI alone. To the best of our knowledge,
we note the first demonstration of sinus nodal injury directly from VOM
ethanol infusion. The underlying mechanism is not clear. Although not
apparent on venography, we suspect that collateral vessels were present
and delivered ethanol to the sinoatrial region. We did not observe any
AV block, left atrial appendage isolation, or anaphylaxis that have been
described with VOM
ethanol.8 With respect
to the important complication of tamponade we demonstrated a high rate
of delayed pericardial effusions. Two of the four patients in this
cohort with delayed effusions had unrevealing echocardiograms days after
their ablations, only to later present with pericardial tamponade. A
third had a hematocrit less than 1% on the pericardial fluid despite a
bloody appearance. These findings suggest that the dominant mechanism of
delayed tamponade in these cases was inflammatory pericarditis rather
than hemorrhagic. Early on in our experience we adjusted our procedural
technique to minimize CS related complication. A retention wire is used
through the CS guide sheath to avoid CS wall trauma and the IMA catheter
is inserted over a wire. Furthermore, we probe for the VOM with a low
tip weight angioplasty wire (Suoh wire, Asahi) rather than localize the
VOM with contrast puffs. This should lower the risk of VOM
perforation/dissection or CS dissection and while we have neared a 100%
success rate with VOM ethanol infusion, we have noted a higher rate of
delayed tamponade than reported previously in the VENUS study or
Bordeaux
experience.8,12The rate is more in line with pericardial effusions in the CONVERGE
study of hybrid surgical
ablation.3 While the low
total number of cases leaves open the possibility that our increased
rate of delayed tamponade is due to chance alone, interestingly, all
four cases of delayed tamponade in our series occurred in the second
half of our cohort of patients. We have postulated that as we have
become more facile with the procedure, perhaps a brisker workflow with
faster ethanol infusions may have contributed. Thus while we typically
still instill four ethanol injections, we have minimized the total
volume of ethanol infused from an average of 10ml to 4-5ml, and each
injection is instilled slowly over 60 seconds. In addition, in order to
avoid contrast induced hydraulic dissections of the VOM, we do not any
longer systematically perform VOM venography unless there is uncertainty
of the vein identity (non-VOM), the quality of venous occlusion as
evidenced by balloon movement, or lack of demonstrable ethanol effects
on mapping or ICE. Further study is required to tell if this approach
will lower the rate of delayed effusions related to VOM ethanol.
Importantly, noting this complication has recalibrated our judgement and
patient selection in deciding when to employ the technique.
This study is limited by its retrospective nature, selected population,
and the fact that all cases were performed at a single center with a
single operator. As advances in ablation techniques and energy sources
bring us closer to ensuring permanent
PVI,9,10the role for VOM ethanol and other adjunctive techniques for AF ablation
may take on greater importance. Currently, there is a paucity of
published experience with VOM ethanol infusion and it is rarely
performed outside of select centers of excellence. We believe that cases
series such as this add important insights to the literature of this
technique, informing operators already performing or considering VOM
ethanol infusion in the future.