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\begin{document}

\title{An unusual cause for inappropriate defibrillator shock.}



\author[1]{Debabrata Bera}%
\author[1]{Ayan Kar}%
\author[2]{Biswajit Majumder}%
\author[1]{Arup Kumar Ghosh}%
\author[1]{Debdutta Bhattacharyya}%
\affil[1]{Rabindranath Tagore International Institute of Cardiac Sciences}%
\affil[2]{RG Kar Medical College}%


\vspace{-1em}



  
  \date{May 25, 2024}


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\selectlanguage{english}
\begin{abstract}
A 50-year-old lady with dilated cardiomyopathy and scar VT underwent
single chamber implantable cardioverter-defibrillator (ICD, Medtronic
Ltd, \selectlanguage{english}Evera XT VR, DVBB2D1) implantation 2 months back. A Sprint Quattro
secure 6947 DF1 dual coil lead was placed at RV apex. Now, she presents
with an episode of ICD shock while having breakfast. The device
interrogation shows a 36 J shock in VF zone (Fig 1A). However, the
stored electrograms (EGM) reveal distinct QRS complexes in the far-field
EGM; hence, suggesting the shock is related to oversensing. Fig 1B shows
2 panels of another recent episode. Fortunately, there was aborted
therapy as there was intermittent resolution of the oversensing. The
lead impedance was normal but threshold was high. Is it possible to
predict the reason for the oversensing from the EGM and how to
troubleshoot?%
\end{abstract}%



\sloppy


\textbf{Title Page}

\textbf{Title:} An unusual cause for inappropriate defibrillator shock.

\textbf{Short title:} Late ICD lead perforation leading to defibrillator
shock.

\textbf{Authors:}

Debabrata Bera, DM, Dept of Cardiology, RTIICS, Kolkata. India.

Ayan Kar, DM, Dept of Cardiology, RTIICS, Kolkata. India.

Biswajit Majumder, DM, Dept of Cardiology, RG Kar Medical college,
Kolkata. India.

Arup Kumar Ghosh, Mch, Dept of Cardiothoracic Surgery, RTIICS, Kolkata.
India.

Debdatta Bhattacharyya, MRCP, Dept of Cardiology, RTIICS, Kolkata.
India.

\textbf{Corresponding author:}

Debabrata Bera. Rabindranath Tagore International Institute of Cardiac
Sciences (RTIICS), 124 Mukundapur, Kolkata. West Bengal, India. PIN-
700099.

Ph: +91-8013894181, Fax: +91-33 2426 4204.Email- debu2000pgi@gmail.com

\textbf{Key words: Defibrillator; ICD; inappropriate shock;
Diaphragmatic myopotential; Lead perforation.}

Word count: 817.

Funding: None

Conflict of interest: None

Consent has been taken from patient.

Data availability statement:

All raw data and recording during the case are available for review.



\textbf{Case}

A 50-year-old lady with dilated cardiomyopathy and scar VT underwent
single chamber implantable cardioverter-defibrillator (ICD, Medtronic
Ltd, \selectlanguage{english}Evera XT VR, DVBB2D1) implantation 2 months back. A Sprint Quattro
secure 6947 DF1 dual coil lead was placed at RV apex. Now, she presents
with an episode of ICD shock while having breakfast. The device
interrogation shows a 36 J shock in VF zone (Fig 1A). However, the
stored electrograms (EGM) reveal distinct QRS complexes in the far-field
EGM; hence, suggesting the shock is related to oversensing. Fig 1B shows
2 panels of another recent episode. Fortunately, there was aborted
therapy as there was intermittent resolution of the oversensing. The
lead impedance was normal but threshold was high. Is it possible to
predict the reason for the oversensing from the EGM and how to
troubleshoot?

\textbf{Commentary}

The possible options are:

\begin{enumerate}
\tightlist
\item
  Electromagnetic interference (EMI)
\item
  Lead noise (lead fracture / insulation failure)
\item
  Loose set screw
\item
  Diaphragmatic myopotential.
\item
  Pectoral myopotential.
\end{enumerate}

Few key observations in the tracings are:

\begin{enumerate}
\tightlist
\item
  There is more noise in the near field (NF, tip to ring) than far field
  (FF, Can to coil). In fact, there is hardly any QRS / clear
  electrogram in NF in spite of 10 times more magnification of NF
  electrogram {[}0.1 vs 1 mV scale{]}.
\item
  The oversensing in the marker channel is intermittent although there
  is background noise throughout. As the intensity of background noise
  varies, the oversensing varies simultaneously, making it intermittent
  in the marker channels.
\item
  The characteristic of the noise (which is clearer in panel 1B) is like
  myopotential (high frequency, low amplitude) as compared to make and
  break signals of lead fracture (high frequency and high amplitude).
\end{enumerate}

Based on the first point, EMI becomes unlikely in which both channels
have nearly equal noise in a majority of cases {[}1{]}. Noises related
to lead integrity issues have highly varying amplitude unlike a uniform
noise like the index case. The lead impedance was within normal range.
Loose set screw can have similar EGM quality and commonly present in
perioperative period. Moreover, abnormal impedance is often detected in
set screw related oversensing {[}2{]}. In the index case, prominent
noise in the NF channel makes an issue related to lead tip much more
likely {[}1{]}.

Myopotential appears to be the most likely possibility as per the high
frequency, low amplitude uniform nature of the noise. Both pectoral and
diaphragmatic myopotentials (DMP) are non-cyclical but can have
variation of the noise related to arm movement / respiration
respectively. However, pectoral myopotential tends to have more noise in
FF / leadless EGM as the IPG (Can) is nearby {[}1,3{]}. As ICDs do not
use FF signals as default sensing channel, pectoral myopotentials do not
lead to oversensing ( unless the sensing polarity is manually changed)
{[}2{]}. In the index case, NF predominant noise indicates oversensing
related DMP. Real time EGM during deep inspiration also confirmed the
same.

When oversensing is suspected due to DMP, lead perforation shall be the
prime suspect. This can be confirmed by signs
of~pericarditis~or~pericardial effusion {[}1{]}. With intact lead, DMP
oversensing is highly unlikely with true bipolar sensing in dedicated
bipolar leads {[}4{]}. It can however take place when sensitivity is
maximum e.g. after long diastolic intervals or ventricular paced events,
and often ends with a sensed R wave, which reduces sensitivity abruptly
{[}5{]}. Thus, it commonly occurs in pacing dependent ICD patients,~in
whom inhibition~of pacing maintains high ventricular sensitivity,
resulting in persistent oversensing as well as inappropriate detection
of VF {[}1{]}.

Our case had dedicated bipolar lead without pacing requirement, hence,
perforation was suspected upfront. However, echocardiography did not
show any pericardial effusion. The lead could be traced only upto the
apex. But the device parameters were grossly abnormal. R wave amplitude
(sensing) was \textless{} 1mV and loss of capture (LOC) was evident even
at highest output. In fact, the lowermost panel in Fig 1 shows
undersensing along with LOC (true / functional) in the Vp beat.
Interestingly, pacing and shocking impedance trends were all within
normal range. Finally, chest X ray (CXR) and fluoroscopy confirmed a
lead perforation as the lead was noted outside the cardiac silhouette
almost reaching the inner chest wall (Fig. 2).

Skeletal myopotentials including DMP have predominant frequencies in the
range of 75 Hz, but they have a proportion of frequency content up to
100 to 200 Hz and some as low as 20 Hz. In ICDs, low-pass filters in the
range of 40 to 80 Hz can attenuate high-frequency components, but at
times sufficient high-frequency signals can still bypass these filters
to give myopotential electrograms a distinctive appearance like our case
{[}1{]}. Newer ICDs have in-built algorithms to reliably suspect and
withhold therapies related to noise. In fact, the index patient had a
several more episodes of oversensing where therapy was aptly withheld
due to noise detection algorithm.

After explaining the scenario to the patient's relatives, she was
scheduled for lead extraction in a hybrid operation theater (OT). In the
OT under general anesthesia, the lead was unscrewed and pulled out.
Luckily no evidence of pericardial effusion/ tamponade was noted on
intraoperative trans-esophageal echocardiography (TEE). After waiting
for 10 min, a new single coil ICD lead was positioned into lower-mid
septum on the same sitting. Perioperative period was uneventful. To
summarise, this unique case describes one of the rarer causes of
inappropriate ICD discharges. This case also highlights the need for
careful implantation ICD leads which being heavier and stiffer, have
more preponderance for perforation then softer pacing leads.

\textbf{Fig legends}

Fig 1A: Stored electrograms of the treated episode in the VF zone. It
shows oversensing of noise dissociated from the native QRS.

Fig 1B: The lower 2 panels are continuous tracings from another recent
episode where the therapy got aborted as the noise amplitude became
below the RV lead sensitivity. The lowest panel also shows undersensing
and inadvertent RV pacing after the 2\textsuperscript{nd} QRS complex.
The LOC could be true or functional.

Fig 2: Preoperative chest X ray showing lead beyond cardiac silhouette
suggestive of perforation

\textbf{References}

1. Swerdlow CD, Asirvatham SJ, Ellenbogen KA, Friedman PA.
Troubleshooting implanted cardioverter defibrillator sensing problems I.
Circ Arrhythm Electrophysiol. 2014 Dec;7(6):1237-61. doi:
10.1161/CIRCEP.114.002344. PMID: 25516582.

2. Bera D, Saggu DK, Chandra Murthy GS, Yalagudri S, Sridevi C,
Narasimhan C. Inappropriate defibrillator shock due to oversensing. What
is the mechanism? Indian Pacing Electrophysiol J. 2021
Jan-Feb;21(1):54-58. doi: 10.1016/j.ipej.2020.09.005. Epub 2020 Sep 28.
PMID: 32998013; PMCID: PMC7854366.

3. Wiegand UK, Wilke I, Bonnemeier H, Eberhardt F, Bode F. Inadequate
ICD discharges due to diaphragmatic electromyopotential oversensing as
the first sign of right ventricular lead perforation. Pacing Clin
Electrophysiol. 2006 Oct;29(10):1176-8. doi:
10.1111/j.1540-8159.2006.00511.x. PMID: 17038150.

4. Kowalski M, Ellenbogen KA, Wood MA, Friedman PL.~Implantable cardiac
defibrillator lead failure or myopotential oversensing? An approach to
the diagnosis of noise on lead electrograms.Europace.~2008;~\emph{10}
:914--917.

5. Santos KR, Adrag\selectlanguage{ngerman}ão P, Cavaco D, Morgado FB, Candeias R, Lima S, Silva
JA. Diaphragmatic myopotential oversensing in pacemaker-dependent
patients with CRT-D devices. Europace. 2008 Dec;10(12):1381-6.\selectlanguage{english}
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