Discussion
The present study evaluated the effectiveness of a fixed, reproducible
‘upgraded 2C3L’ ablation strategy that combines the EI-VOM and RF
ablation targeting bilateral PVAI and bidirectional linear block of MI,
CTI, and LA roofline. This strategy is associated with higher sinus
rhythm maintenance compared with the conventional ’2C3L’ approach during
the 12-month follow-up.
Current guidelines have indicated that PVI alone is insufficient for
maintaining sinus rhythm in patients with PeAF[1], and varieties of
substrate modification strategies, including anatomical ablation (linear
ablation) and electrogram guided ablation(ablation of rotors,
fractionated electrograms, et al), have been widely adopted by
electrophysiologists in recent decades. In surgical ablation, linear
lesions have been proven to be effective in rhythm control[9].
Theoretically, linear ablation helps to achieve LA compartmentation,
stop the rotors roaming around the left atrium, and therefore preventing
the maintenance of AF[10]. But the conclusion is quite different for
catheter ablation. The main reason for this inconsistency lies in the
fact that transmural lesions cannot always be achieved by radiofrequency
catheter ablation. As is reported in the STAR AF II trial[3], where
LA linear ablation involving the roofline and mitral isthmus failed to
bring about higher SR maintenance compared with PVI alone, the overall
linear block rate was only 74%.
With the advancement of ablation technology, complete block of the
roofline and CTI can now be achieved in most cases. But the ablation of
the MI line remains challenging. In the ALINE study, even by using an
AI-guided, point-by-point optimized RF ablation, MI bidirectional block
can only be achieved in 80% of patients, while in most cases roofline
can be easily blocked.[11] Meanwhile, conduction recovery across the
MI line can occur in 38 of 52 patients with recurrent AF/AT[12].
Besides the atrial wall thickness and heat-sinking effect of epicardial
vessels, one important cause is epicardial conduction through the
ligament of Marshall[13]. In our previous study of the ’2C3L’
approach, perimitral atrial flutter accounts for 10 of 24 recurrent
AF/ATs after ablation for PeAF [2]. Moreover, it is reported that
the Marshall bundle (MB) participates in 30.2% of reentrant ATs after
AF ablation. Only 81.6% of these MB-related ATs could be terminated
using RF ablation, and the recurrence rate was as high as 41.3% during
18-months follow up[14].
EI-VOM may provide a solution to achieve MI bidirectional block. Through
the VOM and its collateral flow, the ethanol can infiltrate into the
atrial myocardium and rapidly cause transmural lesions that mainly
involve the posterolateral LA free wall and anterior part of the left
pulmonary antrum[15]. More importantly, lesions resulting from
ethanol infusion has been proved to have higher durability, which
prevents future reconnection across the blocked MI line[16]. For
persistent atrial fibrillation, data revealing the value of EI-VOM on
substrate modification is still limited. In the recently published VENUS
trial, EI-VOM before RF ablation significantly improved long-term AF
free survival and reduced AF burden compared with RF ablation
alone[5]. However, as is reported in its post-hoc analysis, patients
could benefit from EI-VOM only if MI was blocked[6]. Meanwhile, a
prospective, single-arm study has demonstrated that EI-VOM in
conjunction with a fixed strategy of LA linear ablation has ideal short-
and long-term effectiveness [17]. In view of current studies, an
anatomical ablation strategy targeting atrial compartmentation seems to
better take advantage of EI-VOM, compared with empirical substrate
modification.
Herein, we conducted a comparative study to further elucidate the value
of a fixed ablation strategy that combines EI-VOM and the
well-established ‘2C3L’ approach. At the very beginning of the
procedure, both the proximal and distal parts of the VOM were ablated
with ethanol infusion. With EI-VOM, anatomical structures refractory to
RF energy, like the Marshall bundle, left lateral ridge, and LA
myocardium near epicardial vessels can be easily injured transmurally.
Theoretically, it is promising in reducing the recurrence of perimitral
ATs. Meanwhile, facilitated LPV antrum ablation and better atrial
compartmentation by linear lesions further prevent the recurrence of
atrial fibrillation. Patients with AF triggers originating from the LOM
can also benefit from EI-VOM[18]. Moreover, as is observed in the
present study, in this fixed, less progressive ’upgraded 2C3L’ approach,
ablation is mostly performed at sites with the latest atrial activation
and is less likely to result in left atrial appendage conduction delay,
preventing the physiology of atria. As for safety concerns, the
incidence of the adverse event during EI-VOM is reasonably low in the
present study, as is also reported previously[19].
It is also important to realize the limitation of EI-VOM itself. The VOM
is not always accessible, and the accessible rate varies from
71.4%-96[5, 16, 17, 20]. The difference in techniques, limited
sample size of the reports could be the potential explanations that
require further research. Of special note, the annulus side of MI is not
covered by the EI-VOM lesion. In the present study, ablation in the
coronary sinus is equally required in both groups, and MI conduction gap
near the annular side is the cause of recurrent perimitral flutters in
group 1.