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\begin{document}

\title{Wide complex tachycardia with changing QRS-axis on loop recorder}



\author[1]{Luis Quininir}%
\author[2]{Hariharan Raju}%
\author[1]{Kim Chan}%
\author[3]{Chrishan Nalliah}%
\author[1]{Edward Toal}%
\author[1]{Raymond Sy}%
\affil[1]{Royal Prince Alfred Hospital}%
\affil[2]{Macquarie University}%
\affil[3]{Macquarie University Hospital}%


\vspace{-1em}



  
  \date{June 17, 2024}


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\section*{Wide complex tachycardia with changing QRS-axis on loop
recorder}

{\label{wide-complex-tachycardia-with-changing-qrs-axis-on-loop-recorder}}

\textbf{Short title:} QRS-axis changes on loop recorder

\textbf{Authors:}

Luis \emph{Quininir} MD \textsuperscript{a}

Hariharan \emph{Raju} MBChB PhD \textsuperscript{a, c, d}

Kim \emph{Chan} MBBS, PhD \textsuperscript{a,b}

Chrishan \emph{Nalliah} MBBS, PhD \textsuperscript{d}

Edward \emph{Toal} RN \textsuperscript{a}

Raymond W \emph{Sy} MBBS, PhD \textsuperscript{a,b,c}

Word Count: 756 (inc references)

\textbf{Affiliations:}

a Department of Cardiology, Royal Prince Alfred Hospital, Sydney,
Australia

b Faculty of Medicine and Health, The University of Sydney, Australia,

c Department of Cardiology, Concord Repatriation General Hospital,
Sydney, Australia

d Macquarie University, Sydney, Australia

\textbf{Funding:} No external financial support.

\textbf{Declarations of interest:} None.

\textbf{Address for correspondence:}

A/Prof Raymond Sy, Department of Cardiology, Royal Prince Alfred
Hospital, Missenden Rd Camperdown, NSW, Australia

Tel: +612 -9515 8063 Fax: +612 -- 9550 6262 Email:
Raymond.sy01@gmail.com

\textbf{Keywords:} Alternating bundle-branch-block, Implantable loop
recorder, Rhythm monitoring, Troubleshooting



\textbf{Case:}

A 74-year-old female was admitted due an episode of loss of
consciousness with a 3-year history of recurrent syncope and previous
loop recorder implant (Medtronic Reveal Linq\selectlanguage{ngerman}®). There was no history of
coronary artery disease, structural heart disease, or other
cardiovascular implantable electronic devices (CIED). Resting
echocardiogram and stress testing were normal. Electrocardiogram (ECG)
at baseline showed left bundle branch block (LBBB) (Figure 1), with no
history of pre-excitation. She was not on antiarrhythmic medications.
Interrogation of the device showed multiple episodes of wide complex
tachycardia temporally unrelated to the loss of consciousness, with a
changing QRS morphology (Figure 2). What are the differential diagnoses
for the arrhythmia?

\textbf{Commentary}

Careful examination of the loop recorder tracing showed a wide complex
tachycardia with mild variability in cycle length (TCL) 280-340 ms,
followed by abrupt termination into presumed sinus rhythm. The QRS
morphology changed during the tachycardia. The initial QRS morphology
(qR), was followed by a transition zone and then a different QRS
morphology (QS) (Figure 2). The latter was similar, although not
identical to the QRS morphology during sinus rhythm.

Initial differential diagnoses included supraventricular tachycardia
(SVT) with alternating bundle branch block (BBB), polymorphic
ventricular tachycardia (PMVT), Ventricular tachycardia (VT) with
\textgreater{}1 exit site, SVT with bystander pre-excitation, and dual
tachycardia with progressive fusion from ventricular tachycardia to SVT
with BBB (or vice-versa).

SVT with alternating BBB was excluded because it would not explain the
transition zone where fusion was observed. The appearance was also not
consistent with PMVT because the initial and terminal component of the
tachycardia showed a consistent `monomorphic' appearance. A single VT
with 2 distant exit sites was felt to be extremely unlikely in the
absence of structural heart disease. SVT with bystander pre-excitation
could not be excluded, but the patient never exhibited pre-excitation on
multiple baseline ECGs. Dual tachycardia with progressive fusion
transitioning between VT and SVT was possible, but unlikely given the
changing QRS morphology was observed repeatedly during multiple
arrhythmia episodes, and an abrupt change in cycle length was not
observed coincident with the change in QRS morphology. Given that the
clinical history was not consistent with a high probability of VT or
pre-excitation, we then also considered the possibility of an
artefactual cause for the QRS change.

On physical examination and interrogation of ILR, the loop recorder was
implanted in the 4th intercostal space in a parasternal position and
rotation of the patient from decubitus supine to left lateral position
reproduced a change in QRS morphology similar to that observed during
tachycardia. (Figure 3)

Hence, the tachycardia was thought to be most likely supraventricular
origin, with pseudo-QRS alternans due to change of ILR position.

The Medtronic Reveal Linq stores the recorded bipolar signal, obtained
with sensing electrodes built into the ILR shell. Changes in the device
position against the heart would lead to changes in `far field' QRS
morphology. To our knowledge, there is at least one other case report of
position-related pseudo-alternating BBB on implantable loop recorder
{[}1{]}.

Positional change in the recording vector should be considered as an
important differential diagnosis when apparent QRS morphology changes
are observed during interrogation of an ILR and possibly other CIEDs
employing a subcutaneous vector for ECG acquisition. A gradual
transition in QRS morphology provides a clue and it can be confirmed
with ILR recording during dynamic manoeuvres.



\textbf{REFERENCES}

Perrin T, Kühne M, Novak J. Positional pseudo-alternating
bundle-branch-block on implantable loop recorder
electrogram.~\emph{Indian Pacing Electrophysiol J} . 2018;18(6):240-241.
doi:10.1016/j.ipej.2018.09.001



\textbf{FIGURES}

\textbf{Figure legend} : LBBB= left bundle block, VS= ventricular sense,
TS = tachycardia sense

\textbf{Figure 1}

Baseline ECG: Sinus rhythm with LBBB.\selectlanguage{english}
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\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

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\textbf{Figure 2}

Implantable loop recorder tracing during tachycardia detection. Speed
25mm/s.\selectlanguage{english}
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\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

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\textbf{Figure 3}

Implantable loop recorder interrogation during position changes. Speed
25mm/s.\selectlanguage{english}
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