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\begin{document}

\title{Lesion Size Index-guided high-power ablation for atrial fibrillation:
opening the therapeutic window}



\author[1]{Alan Hanley}%
\affil[1]{Massachusetts General Hospital}%


\vspace{-1em}



  
  \date{June 16, 2024}


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\selectlanguage{english}
\begin{abstract}
Radiofrequency (RF) ablation for the treatment of atrial fibrillation
has gained widespread acceptance since the concept was introduced by
Haissaguerre et al a quarter of a century ago. High power short duration
ablation has been widely adopted in the management of atrial
fibrillation. Evidence for combining lesion size index and high power
short duration ablation is lacking. In this issue of the journal, Cai et
al evaluated the combination of HPSD with LSI with a focus on long-term
efficacy.%
\end{abstract}%



\sloppy


Lesion Size Index-guided high-power ablation for atrial fibrillation:
opening the therapeutic window

\textbf{Author:} Alan Hanley

Radiofrequency (RF) ablation for the treatment of atrial fibrillation
has gained widespread acceptance since the concept was introduced by
Haissaguerre et al a quarter of a century ago\textsuperscript{1}. It
continues to gain traction with strengthening evidence for intervention
in different patient cohorts and as a primary approach for those in the
earlier stages of atrial fibrillation\textsuperscript{2}.

Delivery of RF current via an ablation catheter results in resistive
heating at the catheter tip-tissue interface, with tissue destruction at
the site. With increasing duration of ablation lesions, deeper tissues
are heated (and can be injured) by transfer of thermal
energy\textsuperscript{3}. Ablating at a higher power -- typically 45
watts and above -- for a shorter duration (HPSD) allows ablation of the
thin atrial wall while limiting thermal injury to deeper structures such
as the esophagus\textsuperscript{4}. The approach has been widely
adopted in the management of atrial fibrillation due to this theoretical
widening of the therapeutic window.

In parallel over the past decade, mapping systems have been embellished
by algorithms designed to remove variability from the procedure. Indices
including the Force Time Integral, and subsequently Ablation Index (AI)
and Lesion Size Index (LSI) have developed as a way of standardizing
energy delivery to the myocardium\textsuperscript{5,6}. They have the
advantage of identifying lesion endpoints, beyond which additional
ablation is unlikely to be therapeutic or may lead to an unacceptable
increase in adverse events such as steam pops. These technological
features were developed and validated in the era of lower power ablation
in the atrium, when lesion duration was longer\textsuperscript{5,7}.
HPSD has previously been shown to reduce esophageal injury when combined
with AI\textsuperscript{8}. The authors of the current paper have
previously published their findings on the safety and procedural
efficacy of HPSD and LSI\textsuperscript{9}. In this issue of the
journal, Cai et al evaluated the combination of HPSD with LSI with a
focus on long-term efficacy.

The study is a single-center retrospective study of 186 consecutive
ablations, in which procedures were performed by a single operator. The
ablations were performed at 50W with a target LSI of 4.5 to 5.5
anteriorly and 4.0 to 4.5 posteriorly. First pass isolation was achieved
in 83.9\% of cases. The complication rate was 3.7\% including 3 steam
pops. The 2-year freedom from AF was remarkably good at 87.1\% after one
procedure. Receiver operating characteristic analysis identified optimum
target LSIs of 4.7 for anterior lesions and 4.3 for posterior lesions.

The specific findings of the paper need to be interpreted cautiously,
however. The outcomes reported -- 90\% success rates -- are comparable
to other observational data, but exceed those of well-conducted
randomized trials of pulmonary vein isolation such as RAAFT-2, EARLY-AF,
STOP-AF and CAPLA\textsuperscript{2,10,11}. While these successes should
be lauded, they may indicate unmeasured confounders and inherent biases
that could limit the generalizability of the findings. Additionally, the
procedures were performed under conscious sedation. Extrapolating these
findings to the more common scenario in which AF ablation is performed
under general anesthesia is questionable, as the two approaches would be
expected to result in differences in catheter
stability\textsuperscript{12}.

Caution using an LSI guided approach to HPSD is required, particularly
when ablating posteriorly. One of the features of LSI is that the value
is only seen after 6 seconds of ablation, and with a higher amount of
contact force, the first LSI value seen would likely be above target in
many cases. Indeed, one of the steam pops that was reported in the paper
occurred in conjunction with an LSI of 5.9. It should also be noted that
the study provides evidence for LSI values when ablating around the
pulmonary veins. Ablation of other targets, such as the mitral isthmus,
SVC, or rare cases where isolation of the posterior wall is indicated,
may require use of lesion endpoints other than LSI as the targets may be
lower or higher than those presented here.

Most improvements in interventional subspecialities occur in relatively
frequent and small increments until a much larger disruption (such as
the advent of pulsed field ablation), after which the whole field
shifts, and the process begins anew. The interregnum between disruptive
changes is characterized by individual operators incorporating these
smaller, incremental improvements in a variety of untested combinations.
Large scale randomized trials of every combination are not feasible, so
we rely on data from lower down the chain of evidence including,
importantly, the experience of our peers. The current study, although
limited in scope, is a welcome and necessary effort at evaluating the
long-term benefit of combining HPSD and LSI and adds to the evidence
that the practice is safe and likely an effective means of achieving
durable PVI.

\textbf{References}

1. Ha\selectlanguage{ngerman}ïssaguerre M, Jaïs P, Shah DC, et al. Spontaneous Initiation of
Atrial Fibrillation by Ectopic Beats Originating in the Pulmonary
Veins.\emph{N Engl J Med} . 1998;339(10):659-666.
doi:10.1056/NEJM199809033391003

2. Morillo CA, Verma A, Connolly SJ, et al. Radiofrequency ablation vs
antiarrhythmic drugs as first-line treatment of paroxysmal atrial
fibrillation (RAAFT-2): a randomized trial. \emph{JAMA} .
2014;311(7):692-700. doi:10.1001/jama.2014.467

3. Haines DE. The biophysics of radiofrequency catheter ablation in the
heart: the importance of temperature monitoring. \emph{Pacing Clin
Electrophysiol} . 1993;16(3):586-591.

4. Ali-Ahmed F, Goyal V, Patel M, Orelaru F, Haines DE, Wong WS.
High-power, low-flow, short-ablation duration-the key to avoid
collateral injury? \emph{J Interv Card Electrophysiol Int J Arrhythm
Pacing} . 2019;55(1):9-16. doi:10.1007/s10840-018-0473-5

5. Das M, Loveday JJ, Wynn GJ, et al. Ablation index, a novel marker of
ablation lesion quality: prediction of pulmonary vein reconnection at
repeat electrophysiology study and regional differences in target
values. \emph{EP Eur} . 2017;19(5):775-783. doi:10.1093/europace/euw105

6. Squara F, Latcu DG, Massaad Y, Mahjoub M, Bun SS, Saoudi N. Contact
force and force-time integral in atrial radiofrequency ablation predict
transmurality of lesions. \emph{Europace} . 2014;16(5):660-667.
doi:10.1093/europace/euu068

7. Whitaker J, Fish J, Harrison J, et al. Lesion Index--Guided Ablation
Facilitates Continuous, Transmural, and Durable Lesions in a Porcine
Recovery Model. \emph{Circ Arrhythm Electrophysiol} .
2018;11(4):e005892. doi:10.1161/CIRCEP.117.005892

8. Müller J, Berkovitz A, Halbfass P, et al. Acute oesophageal safety of
high-power short duration with 50 W for atrial fibrillation
ablation.\emph{Eur Eur Pacing Arrhythm Card Electrophysiol J Work Groups
Card Pacing Arrhythm Card Cell Electrophysiol Eur Soc Cardiol} .
2022;24(6):928-937. doi:10.1093/europace/euab329

9. Cai C, Wang J, Niu HX, et al. Optimal Lesion Size Index for Pulmonary
Vein Isolation in High-Power Radiofrequency Catheter Ablation of Atrial
Fibrillation. \emph{Front Cardiovasc Med} . 2022;9:869254.
doi:10.3389/fcvm.2022.869254

10. Andrade JG, Wells GA, Deyell MW, et al. Cryoablation or Drug Therapy
for Initial Treatment of Atrial Fibrillation. \emph{N Engl J Med} .
2021;384(4):305-315. doi:10.1056/NEJMoa2029980

11. Berte B, Hilfiker G, Russi I, et al. Pulmonary vein isolation using
a higher power shorter duration CLOSE protocol with a surround flow
ablation catheter. \emph{J Cardiovasc Electrophysiol} .
2019;30(11):2199-2204. doi:10.1111/jce.14122

12. Garcia R, Waldmann V, Vanduynhoven P, et al. Worldwide sedation
strategies for atrial fibrillation ablation: current status and
evolution over the last decade. \emph{EP Eur} . 2021;23(12):2039-2045.
doi:10.1093/europace/euab154

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