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\begin{document}

\title{Ensuring Bi-Directional Cavo-Tricuspid Isthmus Conduction Block During
Ablation for Typical Atrial Flutter -- A New Twist on an Old Problem}



\author[1]{Gregory Feld}%
\affil[1]{University of California-San Diego}%


\vspace{-1em}



  
  \date{May 25, 2024}


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\selectlanguage{english}
\begin{abstract}
This editorial will review the new pacing method described by the
authors in this issue of the journal that they propose to ensure
bi-directional cavo-tricuspid isthmus (CTI) conduction block after
radiofrequency catheter ablation in patients with CTI dependent atrial
flutter.%
\end{abstract}%



\sloppy


Ensuring Bi-Directional Cavo-Tricuspid Isthmus Block During Ablation for
Typical Atrial Flutter -- A New Twist on an Old Problem

Gregory K. Feld, MD

Professor of Medicine

Depart of Medicine, Division of Cardiology

Director, Clinical Cardiac Electrophysiology Program

and CCEP Fellowship Training Program

University of California San Diego Health System

Address for Correspondence:

Gregory K. Feld, MD

9452 Medical Center Drive

Altman CTRI Building

3\textsuperscript{rd} Floor, Room 3E-313

La Jolla, CA 92037

Although it has been nearly 20 years since the first descriptions of the
methods for radiofrequency ablation (RFA) of the cavo-tricuspid isthmus
(CTI) for treatment of typical and reverse typical atrial flutter
(AFL)\textsuperscript{1,2}, and nearly 15 years since the first
description of methods to ensure bi-directional CTI conduction block to
improve efficacy of RFA for cure of AFL\textsuperscript{3,4}, this paper
by Jim\selectlanguage{ngerman}énez-López, et.al., in the current issue of Journal of
Cardiovascular Electrophysiology\textsuperscript{5}, provides subtle
additional methods to ensure that bidirectional CTI conduction block is
achieved during RFA in order to further reduce recurrence rates of this
common arrhythmia.

The limitations of current methods for determining CTI conduction block
(e.g. demonstration of a fully descending limb of electrical activation
in the contralateral atrial wall during pacing in sinus rhythm after
ablation\textsuperscript{5}, a trans-isthmus conduction time measured as
a double potential interval along the ablation line
\textgreater{}100-110 milliseconds (msec)\textsuperscript{5}, responses
to differential and incremental pacing maneuvers associated with
apparent CTI conduction block including changes in activation times and
electrogram morphology\textsuperscript{6.7}) are identified and compared
to the novel incremental pacing (IP) maneuver measurements proposed by
the authors in this paper.

Specifically, in this issue of the journal\textsuperscript{5}, the
authors propose a new method for measuring conduction times across and
adjacent to the CTI ablation line during IP, which are independent of
other anatomical determinants of conduction delays in the right atrium
that may be due to other factors (e.g. atrial scarring). In addition,
this new method of measurement allows for assessment of bi-directional
conduction across the CTI, whereas some other formerly accepted methods
only described uni-directional conduction assessment during
IP\textsuperscript{,5}.

Briefly, this novel or ``variant IP maneuver'' proposed by the authors
involves IP from the low lateral right atrium and the coronary sinus at
progressively shorter cycle lengths from 600 to 300 msec, while
measuring the activation time between two electrodes, one placed in
close proximity (\textless{}5mm) to the ablation line and one adjacent
to that but on the contralateral side from the pacing site. Using this
approach, the authors hypothesized that after initial CTI ablation a
\textgreater{} 10-ms increase in the time interval between the low
lateral right atrium and an adjacent site immediately contiguous
(\textless{} 5 mm) to the lateral aspect of the CTI line during IP from
the coronary sinus ostium would indicate persistent clockwise CTI
conduction, and vice versa with respect to the proximal coronary sinus
electrogram timing relative to the activation timing of an electrogram
just medial to the CTI line during pacing from the low lateral right
atrium. Furthermore, the authors hypothesized that their IP variant
maneuver would be more accurate in confirming bidirectional CTI
conduction block and uncovering functional CTI conduction block or
conduction delay (even in the presence of right inter-atrial conduction
delay) compared to conventional IP maneuvers or the so-call
His-to-coronary sinus IP maneuver, thus potentially ensuring adequate
ablation in some cases, reducing the amount of ablation needed in
others, and resulting in better long-term outcomes in patients
undergoing ablation for CTI dependent atrial flutter.

From the data reported by the authors it appears that about 14\% (15 of
108) of their patients had fractionated or indeterminate electrograms
recorded on or near the CTI ablation line making measurements during IP
maneuvers impossible, and thus these patients were excluded from the
analysis. This is not an insignificant number of patients in whom this
type of analysis cannot be performed, and in this author's observations,
rapid atrial pacing to demonstrate persistent inducibility of typical or
reverse typical AFL, and observing atrial activation patterns during
pacing maneuvers with 3-dimensional electro-anatomical mapping (3-D EAM)
when being used, may help to identify patients in this group that cannot
be evaluated with conventional or variant IP maneuvers or those with
false positive findings suggesting complete CTI conduction block. The
authors of this paper don't reiterate the importance of ruling out
persistently inducible atrial flutter in all their patients after CTI
ablation, but it is likely that they do so, as well as perform the
described pacing maneuvers to ensure bi-directional CTI conduction
block, but this might have an influence on long-term outcomes as well.
In addition, there is no mention of the use of 3-dimensional mapping in
their patients, but it has also been this author's observation that 3-D
EAM may identify small gaps in the CTI ablation line with functional
block or slow conduction, that allows persistently inducible AFL and
late AFL recurrence.

Among those patients in whom this variant IP maneuver could be
performed, the authors found that their novel method increased the
number and percentage of patients in whom persistent functional
conduction block or conduction delay could be identified in comparison
to the conventional IP maneuver (e.g. from 69 {[}74\%{]} using the
gold-standard conventional IP maneuver to 65 {[}68\%{]} using the novel
IP maneuver), resulting in additional ablation being performed along the
ablation line. But, there was apparently no difference when compared to
the conventional His-to-coronary sinus IP maneuver.

Another potentially important finding from the prospective arm of this
study in patients who also had right inter-atrial conduction delay, is
that the author's novel IP maneuver allowed reclassification of 7 of 11
(64\%) patients from a functional to complete block status, thus
preventing the need for additional ablation that might have otherwise
been deemed necessary if only the conventional IP maneuvers were used to
assess CTI conduction. This might be considered a safety benefit by
some.

The authors also included in their study, an evaluation of the effect of
this novel IP maneuver in comparison to conventional IP maneuvers on the
long-term recurrence rates of AFL. Although the numbers of patients with
AFL recurrence in this study is very small, and this observation would
have to be evaluated and reproduced in a much larger population of
patients, the findings were nonetheless statistically significant with
respect to the use of this novel IP maneuver compared to the
conventional IP maneuver studied (p=0.1). This observation can be seen
in the negative and positive predictive values presented by the authors
for the conventional IP maneuver, the standard His-to-coronary sinus IP
maneuver and their novel IP maneuver (i.e. 50\%, 75\% and 100\% negative
prediction value and 97\%, 98\% and 100\% positive predictive value,
respectively).

Furthermore, with regards to the follow-up of patients in this study to
assess for recurrence of AFL, the authors note in their limitations
section of the paper that the study might be negatively impacted by the
small numbers (as mentioned above), but also by the lack of use of an
internal loop recorder. While the use of such monitoring may help
identify a higher percentage of patients with arrhythmia recurrence,
especially asymptomatic recurrences, this technique may not be employed
in many studies or even required by some regulatory agencies (e.g. in
some cases only an extended monitor such as a 48-hour Holter is required
during follow-up). In this study a 24-hour Holter monitor was only
applied when ``relapses were suspected'', suggesting that it was applied
only in case of symptomatic recurrence. This lack of systematic use of a
Holter monitor (or extended event monitor) or implantable loop
recorder\textsuperscript{8} may have indeed led in part to the small
number of recurrences of AFL observed in this study, since reported
recurrence rates of AFL are usually closer to 10\% in most studies after
CTI ablation\textsuperscript{9}. Thus, both a much larger study and the
routine use of extended monitoring may have resulted in more reliable
data to support the authors' contention that use of this novel IP
maneuver improves long-term outcomes with regards to recurrence of AFL
in patients undergoing CTI ablation.

In summary, this study adds a small but useful tool to our armamentarium
for assessment of bi-directional conduction block in patients undergoing
RF ablation for CTI dependent AFL. The greater ability of this novel IP
maneuver, compared to conventional IP maneuvers, to distinguish complete
CTI conduction block from functional block or conduction delay, may help
reduce unnecessary ablation by confirming the presence of complete
conduction block when other methods suggest only incomplete block, and
may also improve long-term outcomes after RF ablation for CTI dependent
AFL by confirming the presence of complete conduction block which is
known to be necessary to prevent AFL recurrence (again with the caveat
that larger studies with more robust methods of detecting recurrences
may be necessary to confirm this latter suggestion).

References

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\tightlist
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\item
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  Poty H, Saoudi N, Aziz AA, Nair M, Letac B. Radiofrequency catheter
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\item
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\item
  Shah D, Haissaguerre M, Takahashi A, Jais P, Hocini M, Clemency J.
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\end{enumerate}

\selectlanguage{english}
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