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\title{Non-invasive assessment of Durability of Ablation Lesions with Magnetic
Resonance Imaging: are we there yet?}



\author[1]{Dhiraj Gupta}%
\affil[1]{University of Liverpool}%


\vspace{-1em}



  
  \date{June 17, 2024}


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Pulmonary Vein Isolation (PVI) remains the cornerstone for catheter
ablation for atrial fibrillation (AF). Achieving durable PVI safely with
Radiofrequency Catheter Ablation (RFCA) has proven challenging until
recently, even with the use of Contact Force (CF) sensing catheters and
electroanatomical mapping\textsuperscript{1}. Ablation success rates
improve markedly, including in persistent AF, when permanent PVI can be
achieved\textsuperscript{1,2}, which only underscores the critical role
of the Pulmonary Veins (PV) in AF arrhythmogenesis.

Historically, the only way to assess PVI durability has been through
invasive electrophysiology study, with all its associated risk,
inconvenience, and costs. This price appears particularly galling to pay
if the PVs are found to be isolated at repeat study, as is now becoming
increasingly common\textsuperscript{3}. Multiple randomised studies have
failed to show additional benefit from ablating extra-PV
structures\textsuperscript{4,5}, and the best outcomes following repeat
AF ablation procedures are restricted to those where PV reconnection is
identified and treated\textsuperscript{6}. As such, there remains a
pressing need for a non-invasive tool that can accurately assess PVI
durability, and ideally, the size and location of residual gaps. As
Magnetic Resonance Imaging (MRI) has increasingly been shown capable of
delineating atrial scar, there is much anticipation that it may serve
this important purpose\textsuperscript{7}.

RFCA and Cryoballoon ablation (CBA) are by far the most common
modalities used for PVI, and there is remarkable equivalence in their
clinical results\textsuperscript{8}. However, the handling of the two
technologies in the catheter laboratory is very different, and ultrahigh
density mapping has shown important differences in the number and
location of chronic gaps between the two\textsuperscript{9}. The use of
MRI in characterizing these differences has not been well described so
far.

In this issue of the journal, Kurose and colleagues present a small but
elegant study\textsuperscript{10}, in which 30 consecutive patients who
underwent PVI (18 with CBA, 12 with RFCA) were assessed by LGE-MRI two
months later, where lesion width and visual gap(s) around each vein were
assessed. The RF applications were delivered using a CF sensing
catheter, with a target lesion size index (LSI) of 5, and an
inter-lesion distance of \textless{}6mm. They found that the mean lesion
width on MRI was significantly wider in the CBA group (8.1\selectlanguage{ngerman}±2.2 mm) as
compared to the RFCA group (6.3±2.2 mm), p=0.032. However, there were
more visual gaps seen in the CBA group, especially in the bottom
segments of the two inferior veins. In the RFCA group, gaps were seen
most often seen in the left posterior segments where the target LSI
value could not be achieved because of esopheageal temperature rise.
Furthermore, the number of gaps visualised on MRI was linked to freedom
from AF at 12 months; receiver operating characteristic curve analysis
suggested a cut off value of less than 5 visual gaps per patient as
being predictive of a good outcome.

The authors deserve to be congratulated for their study, which builds on
their previous work where LGE-MRI was used to compare chronic lesions
between CBA and RFCA with non-CF sensing catheters\textsuperscript{11}.
It is notable that whilst the lesion width in their previous study was
also significantly greater in the CBA group than the RFCA group, the
mean number of gaps in the RFCA group was higher. This suggests that the
modern technique of delivering LSI-guided contiguous RFCA lesions has
resulted in a material improvement in PVI durability, something that is
borne out in clinical studies too\textsuperscript{3}.

Some limitations of the work should be mentioned. Patients were not
randomised to RFCA or CBA; rather, patients undergoing CBA were
pre-selected with those with left common PV or large PVs excluded. The
ablation technique used for CBA was unusual in that the use of RFCA was
allowed if PVI could not be achieved after a single 3-minute freeze.
This low bar for defining CBA failure led to as many as 3 patients out
of 25 being excluded from the study. Many readers will feel that the
mean procedural times of 129 minutes and fluoroscopy times of 39 minutes
for CBA are much longer than what is the norm today. They may also find
the RF powers used in this study unusual; only 30W was used on the
anterior wall, and 20-25W on the posterior wall, which was reduced even
further if esophageal temperature rise was observed. The field is moving
towards using higher power short duration (HPSD) RF applications, and as
HPSD lesions have been shown to be wider\textsuperscript{12}, it is
possible that the gaps on the posterior wall identified in this study
may not have been present had HPSD applications been used. Finally, the
definition of visual gap on MRI used in this study, a non-LGE site
larger than 4 mm, almost certainly overestimated the number of true
gaps. For instance, the authors observed at least one visual gap in each
of the 16 segments around the PVs in more than 10\% CB patients; this is
at odds with data obtained with ultrahigh density
mapping\textsuperscript{9}, and also with the good clinical outcomes
reported here. Future research should look at correlating these
MRI-visualised gaps with actual gaps seen on repeat electrophysiological
study, so that the clinical significance of these can be better defined.

What can we take away from this study? Firstly, the use of MRI to assess
post-ablation scar is now a reality in many labs, allowing assessment of
PVI durability to help decide whether or not to offer a repeat procedure
to a patient with AF recurrence. Secondly, the evolution of the RFCA
technique to include target lesion indices and inter-lesion distance has
made RFCA at least as effective as CBA in achieving durable PVI.
Finally, this is an area ripe for further research, and we look forward
to similarly valuable contributions from Kurose and colleagues in the
future.

\textbf{References}

\begin{enumerate}
\tightlist
\item
  Das M, Wynn G, Saeed Y, et al. Pulmonary vein re-isolation as a
  routine strategy regardless of symptoms: The PRESSURE randomized
  controlled trial. JACC Clin Electrophysiol 2017;3(6):602-61
\item
  Hussein A, Das M, Riva S, et al. Use of ablation index-guided ablation
  results in high rates of durable pulmonary vein isolation and freedom
  from arrhythmia in persistent atrial fibrillation patients. Circ
  Arrhythm Electrophysiol 2018;11: e006576.
\item
  De Pooter J, Strisciuglio T, El Haddad M, et al. Pulmonary Vein
  Reconnection No Longer Occurs in the Majority of Patients After a
  Single Pulmonary Vein Isolation Procedure. JACC Clin Electrophysiol
  2019;5(3):295-305
\item
  Verma A, Jiang C, Betts TR, et al. Approaches to Catheter Ablation for
  Persistent Atrial Fibrillation. N~Engl J Med 2015 May
  7;372(19):1812-22
\item
  Wynn GJ, Panniker S, Morgan M, et al. Biatrial linear ablation in
  sustained nonpermanent AF: results of the substrate modification with
  ablation and antiarrhythmic drugs in nonpermanent Atrial Fibrillation
  (SMAN-PAF) trial. ~Heart Rhythm 2016;13(2):399-406
\item
  Kim T-H, Park J, Uhm J-S, et al. Pulmonary vein reconnection predicts
  good clinical outcome after second catheter ablation for atrial
  fibrillation. Europace 2017;19(6):961-967
\item
  Ranjan R, Kato R, Zviman MM, et al. Gaps in the ablation line as a
  potential cause of recovery from electrical isolation and their
  visualization using MRI. Circ Arrhythm Electrophysiol.
  2011;4(3):279-286.
\item
  Andrade J, Champagne J, Dubuc M, et al. Cryoballoon or radiofrequency
  ablation for atrial fibrillation assessed by continuous monitoring: a
  randomized clinical trial. Circulation 2019;140:1779-1788
\item
  Gunawardene MA, Eickholt C, Akbulak RÖ, Jularic M, Klatt N, Hartmann
  J, Schlüter M, Meyer C, Willems S, Schaeffer B. Ultra-high-density
  mapping of conduction gaps and atrial tachycardias: distinctive
  patterns following pulmonary vein isolation with cryoballoon or
  contact-force-guided radiofrequency current. J Cardiovasc
  Electrophysiol 2020;31(5):1051-1061
\item
  Kurose J, Kiuchi K, Fukuzawa K, et al. Lesion characteristics between
  cryoballoon ablation and radiofrequency ablation with a contact-force
  sensing catheter: late-gadolinium enhancement magnetic resonance
  imaging assessment. J Cardiovasc Electrophysiol 2020 (in press)
\item
  Kurose J, Kiuchi K, Fukuzawa K, et al. The lesion characteristics
  assessed by LGE-MRI after the cryoballoon ablation and conventional
  radiofrequency ablation. J Arrhythm. 2018;34(2):158-166.
\item
  Leshem E, Zilberman I, Tschabrunn CM, et al. High-power and
  short-duration ablation for pulmonary vein isolation: biophysical
  characterization. JACC Clin Electrophysiol 2018 Apr;4(4):467-479
\end{enumerate}

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