\documentclass[10pt]{article}

\usepackage{fullpage}
\usepackage{setspace}
\usepackage{parskip}
\usepackage{titlesec}
\usepackage[section]{placeins}
\usepackage{xcolor}
\usepackage{breakcites}
\usepackage{lineno}
\usepackage{hyphenat}





\PassOptionsToPackage{hyphens}{url}
\usepackage[colorlinks = true,
            linkcolor = blue,
            urlcolor  = blue,
            citecolor = blue,
            anchorcolor = blue]{hyperref}
\usepackage{etoolbox}
\makeatletter
\patchcmd\@combinedblfloats{\box\@outputbox}{\unvbox\@outputbox}{}{%
  \errmessage{\noexpand\@combinedblfloats could not be patched}%
}%
\makeatother


\usepackage{natbib}




\renewenvironment{abstract}
  {{\bfseries\noindent{\abstractname}\par\nobreak}\footnotesize}
  {\bigskip}

\titlespacing{\section}{0pt}{*3}{*1}
\titlespacing{\subsection}{0pt}{*2}{*0.5}
\titlespacing{\subsubsection}{0pt}{*1.5}{0pt}


\usepackage{authblk}


\usepackage{graphicx}
\usepackage[space]{grffile}
\usepackage{latexsym}
\usepackage{textcomp}
\usepackage{longtable}
\usepackage{tabulary}
\usepackage{booktabs,array,multirow}
\usepackage{amsfonts,amsmath,amssymb}
\providecommand\citet{\cite}
\providecommand\citep{\cite}
\providecommand\citealt{\cite}
% You can conditionalize code for latexml or normal latex using this.
\newif\iflatexml\latexmlfalse
\providecommand{\tightlist}{\setlength{\itemsep}{0pt}\setlength{\parskip}{0pt}}%

\AtBeginDocument{\DeclareGraphicsExtensions{.pdf,.PDF,.eps,.EPS,.png,.PNG,.tif,.TIF,.jpg,.JPG,.jpeg,.JPEG}}

\usepackage[utf8]{inputenc}
\usepackage[english]{babel}



\usepackage{float}








\begin{document}

\title{Paradoxical delayed capture of the posterior wall in cavotricuspid
isthmus-dependent atrial tachycardia: What is the mechanism?}



\author[1]{Yosuke Nakatani}%
\author[1]{Tamotsu Sakamoto}%
\author[2]{Yoshiaki Yamaguchi}%
\author[3]{Akira Fujiki}%
\affil[1]{University of Toyama}%
\affil[2]{Graduate School of Medicine, University of Toyama}%
\affil[3]{Shizuoka Heart Rhythm Clinic}%


\vspace{-1em}



  
  \date{May 07, 2024}


\begingroup
\let\center\flushleft
\let\endcenter\endflushleft
\maketitle
\endgroup








\sloppy


\textbf{EP Rounds}

\textbf{Paradoxical delayed capture of the posterior wall in
cavotricuspid isthmus-dependent atrial tachycardia: What is the
mechanism?}

Yosuke Nakatani, MD;\textsuperscript{1} Tamotsu Sakamoto,
MD;\textsuperscript{2} Yoshiaki Yamaguchi, MD;\textsuperscript{2} Akira
Fujiki, MD\textsuperscript{3}

\textsuperscript{1}Division of Cardiology, Gunma Prefectural
Cardiovascular Center, Gunma, Japan

\textsuperscript{2}Department of Internal Medicine, Saiseikai Takaoka
Hospital, Toyama, Japan

\textsuperscript{3}Shizuoka Heart Rhythm Clinic, Shizuoka, Japan

Funding: None for any authors

Disclosures: None for any authors

Corresponding author: Dr. Yosuke Nakatani, Division of Cardiology, Gunma
Prefectural Cardiovascular Center, 3-12 Kameizumi-machi Kou, Maebashi,
Gunma 371-0004, Japan. Telephone: +81-27-269-7455; Fax: +81-27-269-1492;
E-mail:\emph{yosuke3gbst@gmail.com}

\textbf{KEYWORDS}

Atrial tachycardia; Cavotricuspid isthmus; Tricuspid annulus;
Entrainment pacing; Dual loop

\textbf{CASE PRESENTATION}

A 37-year-old man was referred to our institution for ablation of a
cavotricuspid isthmus (CTI)-dependent atrial tachycardia (AT). The AT
was terminated by linear ablation to the CTI. However, the same AT
recurred, and a second procedure was performed. A surface
electrocardiogram showed flutter waves with a negative deflection in the
inferior leads (Fig. 1A). To assess the detailed activation sequence of
the AT, two 20-pole deflectable electrode catheters were placed in a
parallel position on the tricuspid annulus (TA) and right atrial lateral
wall (LW) (Fig. 1B--D). During AT (cycle length: 280 ms),
counterclockwise activation was observed in both the catheters, and a
gap with conduction delay was observed on the anterior part of the CTI
block line (Fig. 2A). During entrainment pacing from the lateral TA, the
LW was captured one cycle later than the TA (Fig. 2B). In contrast,
during entrainment pacing from the proximal coronary sinus (CS), the TA
and LW were captured simultaneously (Fig. 2C). AT was terminated during
radiofrequency application to the gap on the CTI block line. After the
termination of AT, the completion of the CTI block line was confirmed.
AT did not recur after the procedure. What is the mechanism of the
delayed capture of the LW during entrainment pacing from the lateral TA?

\textbf{DISCUSSION}

CTI-dependent AT has been considered a single-loop tachycardia on the
TA.\textsuperscript{1,2} However, previous
studies\textsuperscript{3,4}suggested that a portion of CTI-dependent
ATs is a dual-loop tachycardia with an anterior circuit on the TA and a
posterior circuit around the functional block line on the posterior
wall. In the present case, the LW was captured later than the proximal
CS during entrainment pacing from the lateral TA (Fig. 2B). This
phenomenon is paradoxical for the single-loop mechanism because a site
close to the pacing site was captured later than a site remote from the
pacing site (paradoxical delayed capture). The dual-loop mechanism might
explain this paradoxical delayed capture. During entrainment pacing from
the lateral TA, pacing directly captured the anterior circuit on the TA,
and then the activation propagated to the proximal CS through the CTI.
Thereafter, the activation propagated to the posterior circuit and
reached the LW (Fig. 3A).

Moreover, the anterior and posterior circuits should have a common
isthmus. The TA and LW were captured simultaneously during entrainment
pacing from the proximal CS (Fig. 2C). This finding suggests that the
inferior septum around the proximal CS is the common isthmus, where
pacing can capture both the anterior and posterior circuits (Fig. 3B).
Moreover, the CTI should also be the common isthmus of the two circuits
as the radiofrequency application in the gap on the CTI block line
terminated the AT. Therefore, the mechanism of AT was a figure-8
dual-loop macroreentry with the common isthmus on the CTI and inferior
septum.

It is noteworthy that the dual-loop mechanism in the present case cannot
be revealed by activation mapping, as both circuits propagate in the
same direction. Therefore, this case provides proof that conventional
pacing maneuvers are still useful in this high-density mapping era.

\textbf{REFERENCES}

1) Kalman JM, Olgin JE, Saxon LA, Fisher WG, Lee RJ, Lesh MD. Activation
and entrainment mapping defines the tricuspid annulus as the anterior
barrier in typical atrial flutter. Circulation 1996;94:398-406.

2) Cosio FG, Lopez-Gil M, Goicolea A, Arribas F, Barroso JL.
Radiofrequency ablation of the inferior vena cava-tricuspid valve
isthmus in common atrial flutter. Am J Cardiol 1993;71:705-709.

3) Fujiki A, Nishida K, Sakabe M, Sugao M, Tsuneda T, Mizumaki K, Inoue
H. Entrainment mapping of dual-loop reentry in common atrial flutter:
new insights into the atrial flutter circuit. J Cardiovasc
Electrophysiol 2004;15:679-685.

4) Tai CT, Chen SA. Conduction barriers of atrial flutter: relation to
the anatomy. Pacing Clin Electrophysiol 2008;31:1335-1342.

\textbf{FIGURE}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

\textbf{Figure 1.} A: Surface electrocardiogram during atrial
tachycardia. B, C: Catheter locations in right anterior oblique (RAO, B)
and left anterior oblique (LAO, C) views. A 20-pole electrode catheter
was placed on the tricuspid annulus (TA) with distal electrodes inside
the coronary sinus, and another catheter was parallelly placed on the
right atrial lateral wall (LW) close to the crista terminalis (CT). D:
The schema of electrode locations. CS, coronary sinus; IVC, inferior
vena cava; SVC, superior vena cava.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

\textbf{Figure 2} \textbf{.} Tracings show surface electrocardiograms in
leads I, aVF, and V1, and electrograms of the tricuspid annulus (TA) and
right atrial lateral wall (LW). A: During atrial tachycardia.
Counterclockwise activation was observed in both the TA and LW.
Activation was blocked in LW1, located on the posterior part of the
cavotricuspid isthmus (CTI), and conduction delay was observed between
TA4 and TA1, located on the anterior part of the CTI. B: During
entrainment pacing from the lateral TA. The asterisks indicate the last
captured beats, which returned with the pacing cycle length. The TA was
captured directly by pacing (arrow a), whereas the LW was captured one
cycle later than the TA (arrow b). Note that the LW was captured later
than the proximal CS (TA1). C: During entrainment pacing from the
proximal coronary sinus (TA1). The TA and LW were captured
simultaneously by pacing (arrows c and d).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

\textbf{Figure 3.} A: Activation during entrainment pacing from the
lateral tricuspid annulus (TA). Pacing (star) directly captured the
anterior circuit (arrow a) on the TA and the posterior circuit (arrow b)
around the block line on the posterior wall later. B: Activation during
entrainment pacing from the proximal coronary sinus (CS). Pacing
captured the anterior circuit (arrow c) and posterior circuit (arrow d)
simultaneously. The letters on the arrows correspond to those in Fig. 2.
IVC, inferior vena cava; SVC, superior vena cava.

\selectlanguage{english}
\FloatBarrier
\end{document}

