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\begin{document}

\title{Cavotricuspid isthmus confined atrial flutter and macro-reentrant
typical atrial flutter in a single right atrium.}



\author[1]{Tyler Rasmussen}%
\author[2]{Steven Bailin}%
\affil[1]{The University of Iowa Hospitals and Clinics}%
\affil[2]{University of Iowa Hospitals and Clinics}%


\vspace{-1em}



  
  \date{June 12, 2024}


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\selectlanguage{english}
\begin{abstract}
Here we describe a case of a young female with congenital hypertrophic
cardiomyopathy presenting with a narrow complex tachycardia. She
underwent an electrophysiology study that revealed dual atrial flutter
circuity in a single right atrium. This case highlights the importance
of high-density electrical mapping for identification of complex atrial
arrhythmias.%
\end{abstract}%



\sloppy


\textbf{Cavotricuspid isthmus confined atrial flutter and
macro-reentrant typical atrial flutter in a single right atrium.}

\textbf{Running Title:} Dual atrial flutter circuitry in a single
atrium.

Tyler P. Rasmussen, MD, PhD and Steven J. Bailin, MD

University of Iowa Division of Cardiovascular Medicine, Iowa City, IA,
USA

\textbf{Corresponding Author:}

Tyler P. Rasmussen, MD, PhD

200 Hawkins Dr.

Iowa City, IA 52242

tyler-rasmussen@uiowa.edu

\textbf{Conflict of Interest Statement:} Neither author has conflict of
interests to disclose.

\textbf{Funding:} No funding was received for support of this
manuscript.

\textbf{Word Count (after abstract)t: 1,489}

\textbf{Abstract:}

Here we describe a case of a young female with congenital hypertrophic
cardiomyopathy presenting with a narrow complex tachycardia. She
underwent an electrophysiology study that revealed dual atrial flutter
circuity in a single right atrium. This case highlights the importance
of high-density electrical mapping for identification of complex atrial
arrhythmias.

\textbf{History of Present Illness}

A 36-year-old female with biventricular systolic heart failure secondary
to congenital hypertrophic cardiomyopathy, long QT syndrome, and
paroxysms of atrial fibrillation and atrial flutter presented to our
hospital because of hypotension and diarrhea. She was admitted to the
medical intensive care unit. Her hypotension improved with intravenous
crystalloid fluids and she never developed shock physiology. On
admission, the patient noted rapid increases in her heart rate with
erect posture and minimal exertion, such as stair climbing. She had
bothersome shortness of breath during moments of tachycardia. She had no
other cardinal features of decompensated heart failure. Physical
examination revealed a well appearing female without acute distress,
jugular venous pulse 8 cm above the right atrium, clear lung sounds, and
an irregular cardiac rhythm. 12-lead ECG was favored to represent
atypical atrial flutter with premature ventricular complexes and an
incomplete right bundle branch block pattern. Transthoracic
echocardiogram from a prior outpatient visit showed LVEF 20-25\%,
prominent LV trabeculations, decreased RV systolic function, enlargement
of the RV, and severe enlargement of the right atrium with a milder
degree of left atrial enlargement.

\textbf{Past Medical History}

Records indicated that she had been evaluated by a local
electrophysiologist regarding her paroxysmal atrial flutter. She was
taken for an atrial flutter ablation attempt, but the procedural notes
indicated a `massive' right atrium and inability to ablate her flutter.
During that procedure she was administered sotalol 40 mg IV, which per
the report, resolved her atrial flutter. She was maintained on sotalol
40 mg twice daily until the time she presented to our institution.
Medical history other than her cardiac diagnoses included depression,
anxiety, and migraine headaches.

\textbf{Differential Diagnoses}

We were consulted for concern of atrial fibrillation versus atrial
flutter as the cause of her persistent narrow complex tachycardia that
was recorded on telemetry. Telemetry had shown sustained tachycardia
within the range of 100-120 bpm range with rapid increases in heart rate
with activity. We hypothesized that the patient had an atypical atrial
flutter because she exhibited consistent R-R intervals with HR at 120
bpm. We also considered that she could have a focal trial tachycardia
that accelerated with movement or atrial tachycardia with paroxysms of
atrial fibrillation.

\textbf{Early Management}

Sotalol was increased to 80 mg twice daily and the patient was started
on anticoagulation. The following day, the patient's biventricular ICD
was interrogated and showed atrial flutter with 2:1 atrioventricular
conduction block and intermittent ventricular pacing. The cycle length
of the atrial flutter was 400ms. The atrial flutter was pace terminated
with a cycle length of 320ms. The underlying rhythm was sinus
bradycardia.

\textbf{Investigation and Management}

After discussion with the cardiomyopathy service, it was decided that
the patient would benefit from a repeat attempt at atrial flutter
ablation.

The patient was brought to the electrophysiology laboratory in a fasting
state. Monitored anesthesia care was used for the procedure. 6 Fr and 8
Fr introducer sheaths were inserted sequentially in the right femoral
vein using ultrasound guidance. A decapolar electrophysiology catheter
was advanced to the coronary sinus for the purpose of left atrial
recording and pacing. Atrial flutter was inducible with burst pacing
from the coronary sinus.

A baseline electrophysiology study was performed and showed a
His-Ventricular time of 37ms during atrial flutter. The right atrial
effective refractory period with pacing from the right atrial septum
atrio-ventricular 1:1 was 410 msec. Atrioventricular nodal effective
refractory period was 600/340ms. The atrial flutter exhibited normal
decremental antegrade conduction.

Three distinct arrhythmias were recorded at tachycardia cycle lengths of
380ms (Figure 1a), 260ms (Figure 1b) and 505ms (Figure 1c).
Electro-Anatomical Mapping was performed in the right atrium for each
tachycardia using the Rhythmia HDx mapping system using an IntellaMAP
Orion mini basket catheter (Boston Scientific, Boston, MA) catheter. The
right atrium was severely dilated and the estimated volume was 400mL.
The lateral right atrium was severely dilated and scarred, but high
density (HD) activation mapping during the 380ms atrial flutter
demonstrated counter clockwise pattern around the tricuspid annulus
indicative of typical cavotricuspid dependent atrial flutter (Figure 2).
During mapping, the cycle length of the atrial flutter changed from
465ms to 300ms with identical coronary sinus activation. A separate
high-density electrical mapping exhibited a small macro-reentrant
circuit confined to the cavotricuspid isthmus (Figure 3). Radiofrequency
energy was applied to the lateral cavotricuspid isthmus, which
interrupted both arrhythmias. A third tachycardia was induced with
similar coronary sinus activation and was assessed to be a focal atrial
tachycardia originating from the coronary sinus ostium (Figure 4).
Radiofrequency ablation within the coronary sinus ostium terminated the
automatic tachycardia. Differential atrial pacing was preformed to
ensure bidirectional block across the cavotricuspid isthmus. Burst
pacing was performed without inducibility of any further tachycardia.

\textbf{Discussion}

Typical atrial flutter is a common macro-reentrant tachycardia that is
typified by a circuit dependent on conduction involving the
cavotricuspid isthmus. Atrial flutter affects an estimated 90,000
Americans per year\textsuperscript{1} and is associated with an
increased risk of atrial fibrillation, myocardial infarction, heart
failure, stroke, and death\textsuperscript{2}. Congenital hypertrophic
cardiomyopathy is a rare condition marked by infantile onset hypertrophy
of the left ventricle and has a poor prognosis compared to more common
forms of hypertrophic cardiomyopathy \textsuperscript{3}. Atrial
fibrillation is common in patients with hypertrophic cardiomyopathy with
an annual incidence of 2\%/year\textsuperscript{4}, but the burden of
atrial arrhythmias in patients with congenital hypertrophic
cardiomyopathy is unknown.

This case described a trigenarian with congenital hypertrophic
cardiomyopathy and multiple atrial tachycardia circuits involving the
cavotricuspid isthmus in a severely enlarged right atrium. To our
knowledge, this is the first case to describe dual use of the
cavotricuspid isthmus for typical macro-reentrant isthmus dependent
atrial flutter and small macro-reentrant atrial flutter confined to the
cavotricuspid isthmus. There has been a small case series describing a
group of patients with small macro-reentrant atrial flutter confined to
the cavotricuspid isthmus, but none of these patients exhibited
simultaneous typical atrial flutter and the circuit was believed to
involve the coronary sinus os\textsuperscript{5}. Little is known about
this rare form of atypical macro-reentrant atrial flutter. Further study
is warranted.

This case demonstrated the tangible benefit of high-density electrical
mapping in patients with complex congenital heart disease and advanced
electrical remodeling of the atria. There is considerable debate about
the utility of high-density electrical mapping, but recent studies
suggest that its use may portend to better clinical outcomes in patient
undergoing ablation of atrial arrhythmias\textsuperscript{6-8}. It is
unlikely that we would have discovered the mechanism of the small
macro-reentrant atrial flutter confined to the cavotricuspid isthmus
without the use of high-density mapping. Further research, and
specifically randomized trials, is needed to determine to what extent,
if any, high-density electrical mapping aids in the diagnosis and
treatment of atrial arrhythmias.

\textbf{Follow-Up}

The patient was seen in follow-up 1 week after the ablation without
return of atrial flutter.

\textbf{Conclusion}

A 36-year-old female with congenital hypertrophic cardiomyopathy was
found to have atrial flutter. She underwent an electrophysiology study
with the use of high-density electrical mapping to identify 3 distinct
atrial arrhythmias within a severely enlarged right atrium: 1. typical
cavotricuspid isthmus dependent atrial flutter, 2. Small macro-reentrant
atrial flutter confined to the cavotricuspid isthmus and 3. focal atrial
tachycardia originating from the coronary sinus ostium. Radiofrequency
ablation was successful at terminating all 3 arrhythmias.

\textbf{Funding Sources}

This research did not receive any specific grant from funding agencies
in the public, commercial, or not-for-profit sectors.

\textbf{Consent Statement}

The patient gave written consent to publish de-identified information in
a medical journal.

\textbf{References}

1. Naccarelli GV, Varker H, Lin J, Schulman KL. Increasing prevalence of
atrial fibrillation and flutter in the United States. \emph{Am J
Cardiol.} 2009;104(11):1534-1539.

2. Rahman F, Wang N, Yin X, et al. Atrial flutter: Clinical risk factors
and adverse outcomes in the Framingham Heart Study. \emph{Heart
Rhythm.}2016;13(1):233-240.

3. Badertscher A, Bauersfeld U, Arbenz U, Baumgartner MR, Schinzel A,
Balmer C. Cardiomyopathy in newborns and infants: a broad spectrum of
aetiologies and poor prognosis. \emph{Acta
Paediatr.}2008;97(11):1523-1528.

4. Olivotto I, Cecchi F, Casey SA, Dolara A, Traverse JH, Maron BJ.
Impact of atrial fibrillation on the clinical course of hypertrophic
cardiomyopathy. \emph{Circulation.} 2001;104(21):2517-2524.

5. Yang Y, Varma N, Keung EC, Scheinman MM. Reentry within the
cavotricuspid isthmus: an isthmus dependent circuit. \emph{Pacing Clin
Electrophysiol.} 2005;28(8):808-818.

6. Pappone C, Ciconte G, Vicedomini G, et al. Clinical Outcome of
Electrophysiologically Guided Ablation for Nonparoxysmal Atrial
Fibrillation Using a Novel Real-Time 3-Dimensional Mapping Technique:
Results From a Prospective Randomized Trial. \emph{Circ Arrhythm
Electrophysiol.} 2018;11(3):e005904.

7. Siebermair J, Neumann B, Risch F, et al. High-density Mapping Guided
Pulmonary Vein Isolation for Treatment of Atrial Fibrillation - Two-year
clinical outcome of a single center experience. \emph{Sci
Rep.}2019;9(1):8830.

8. Anter E, McElderry TH, Contreras-Valdes FM, et al. Evaluation of a
novel high-resolution mapping technology for ablation of recurrent
scar-related atrial tachycardias. \emph{Heart
Rhythm.}2016;13(10):2048-2055.\selectlanguage{english}
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