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\begin{document}

\title{Radiofrequency Ablation in Dense Ventricular Scar - Longer Continuous
Lesions may be Beneficial}



\author[1]{Jackson Liang}%
\author[2]{Pasquale Santangeli}%
\author[3]{Francis Marchlinski}%
\affil[1]{University of Michigan}%
\affil[2]{University of Pennsylvania}%
\affil[3]{Hospital of the University of Pennsylvania}%


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  \date{June 13, 2024}


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We read with great interest the recent study by Rogers, et al.
describing lesion formation with continuous versus intermittent
radiofrequency ablation.\textsuperscript{1} The authors applied 50
(ex-vivo) or 10 (in-vivo) watts with either intermittent (15-seconds x4,
30-seconds x2, or 60-seconds x1) or continuous (1, 2, 3, or 5 minutes)
radiofrequency applications and examined lesion size with each strategy.
Continuous lesions resulted in significantly larger lesion size with
possibly increased risk of steam pops at high power. In the ex-vivo
model, they saw rapid lesion formation in the first minute of ablation
with substantial drop-off in expansion of lesion size over time
especially after 3 minutes (down to 0.35mm/min at 5 minutes), and
suggest that there is only minimal incremental benefit of prolonging
ablation lesion duration beyond 3 minutes in normal tissue.

They have, however, appropriately recognized the limitation of their
model which lacks significant fibrosis, limiting the generalizability of
their findings to ablation in patients with scar. It is important to
recognize that lesion formation in scar-related ventricular tachycardia
(VT) is likely to differ dramatically compared to normal myocardial
tissue. Barkargan, et al. have shown in an in-vivo porcine model of
anterior myocardial infarction that lesion formation in normal versus
scar tissue can be substantially
different.\textsuperscript{2}Specifically, ablation lesions in scar
tissue were histologically quite heterogeneous, and connective tissue
tended to be more resistant to thermal injury than normal myocardium.

We have seen many cases where after identifying critical VT circuit
components with activation and entrainment mapping, VT slowing and
termination could only be achieved very late (4-5 minutes) into
radiofrequency application, suggesting continued lesion expansion due to
delayed effect of conductive heating in scar tissue can persist well
beyond 3 minutes. Historical data from Nath, et al. have demonstrated
that tissue temperature of \textgreater{}50\selectlanguage{ngerman}°C must be reached in order
to achieve nonreversible cellular damage.\textsuperscript{3} In the
setting of dense scar, as in patients with healed myocardial infarction
or dense basal septal scar in nonischemic cardiomyopathy, dynamics of
tissue heating and lesion formation are likely quite different than in
normal tissue. Especially in intramural substrates which are
``protected'' by dense subendocardial (or subepicardial if ablating from
the epicardium) scar, ablation with very long (\textgreater{}3 minute)
lesions may have a more pronounced effect than in normal tissue. While
in our experience, steam pops seem to occur less frequently when
ablating in dense scar- even with long, high power lesions, close
monitoring of ablation parameters including catheter tip temperature and
impedance remain necessary during ablation to assure continued safety to
avoid char formation and steam pops.

We enthusiastically applaud the authors for their valuable contribution
to the literature. While chronic cardiomyopathy models are technically
difficult to create and costly to maintain, additional studies examining
lesion formation in dense scar would be extremely helpful to delineate
optimal ablation strategies in patient with cardiomyopathy and difficult
VT substrates. Our clinical experience with late VT termination and
prevention of inducibility after 4-5 minute radiofrequency ablation
lesions in areas of marked fibrosis would support such additional study.

References:

\textbf{1.} Rogers AJ, Borne RT, Ho G, Sauer WH, Wang PJ, Narayan SM,
Zheng L, Nguyen DT. Continuous Ablation Improves Lesion Maturation
Compared with Intermittent Ablation Strategies. J Cardiovasc
Electrophysiol 2020.

\textbf{2.} Barkagan M, Leshem E, Shapira-Daniels A, Sroubek J, Buxton
AE, Saffitz JE, Anter E. Histopathological Characterization of
Radiofrequency Ablation in Ventricular Scar Tissue. JACC Clin
Electrophysiol 2019;5:920-931.

\textbf{3.} Nath S, DiMarco JP, Gallop RG, McRury ID, Haines DE. Effects
of dispersive electrode position and surface area on electrical
parameters and temperature during radiofrequency catheter ablation. Am J
Cardiol 1996;77:765-767.

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