Europace Advance Access originally published online on July 17, 2007
Europace 2007 9(9):730-731; doi:10.1093/europace/eum136
© The European Society of Cardiology 2007. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org
IMPLANTABLE CARDIOVERTER-DEFIBRILLATORS
Delayed termination of ventricular tachycardia after cardioversion
Martin K. Stiles,
Dennis H. Lau,
Glenn D. Young and
Prashanthan Sanders*
1 Cardiovascular Research Centre, Department of Cardiology, Royal Adelaide Hospital and Disciplines of Medicine and Physiology, University of Adelaide, SA, Australia
Manuscript submitted 16 April 2007. Accepted after revision 18 June 2007.
* Corresponding author. Tel: +61 8 8222 2723; fax: +61 8 8222 2722. E-mail address: prash.sanders{at}adelaide.edu.au
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Abstract
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Both anti-tachycardia pacing and cardioversion via an implantable
cardioverter defibrillator are effective therapies for ventricular
tachycardia (VT). We report a case of VT where cardioversion
resulted in delayed termination of tachycardia. Potential mechanisms
for this observation are discussed.
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Case report
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A 72-year-old woman with ischaemic cardiomyopathy and an implantable
cardioverter defibrillator (ICD) presented following two shocks
(Epic VR, St Jude Medical, St Paul, MN, USA). The ICD was implanted
18 months earlier for treatment of clinical ventricular tachycardia
(VT). At implant, the defibrillation threshold was <20J.
The device was programmed to deliver anti-tachycardia pacing
followed by cardioversions for rhythms between 154 and 200 bpm,
and 30J defibrillation for rates >200 bpm. Interrogation
of her ICD demonstrated 10 episodes of VT; eight episodes fell
within the VT zone and successfully pace terminated on the first
attempt, whereas two episodes were >200 bpm and 30J
shocks were delivered. One of the latter episodes is shown in
Figure 1 (the other is near identical and not shown). Demonstrated
is the abrupt onset tachycardia with a cycle length of 300 ms
(Panel 1). The device appropriately senses the tachycardia and
delivers a 30J defibrillation (Panel 2). Following the fixed
1000 ms blanking period, the tachycardia is initially irregular,
and then resumes at an identical cycle length (Panel 3). However,
after
30 beats, tachycardia spontaneously terminates without
the need for further therapy (Panel 4). The defibrillation threshold
was re-evaluated and found to be <20J. During electrophysiology
study, VT was induced by programmed ventricular extrastimuli
and this broad complex tachycardia demonstrated identical electrogram
morphology on device interrogation to that shown in
Figure 1.
The device was re-programmed so that anti-tachycardia pacing
was the initial therapy given for rates up to 220 bpm.
She has not received further therapy from her device.
Delayed cardioversion after DC shock for atrial and ventricular
fibrillation has been described. Non-sustained VT has been observed
to follow 6% of ICD shocks for ventricular arrhythmias; however,
the mechanism is unclear. Delayed termination of re-entrant
rhythm models has been shown with large amplitude shocks delivered
out of phase, in contrast to clean termination with intermediate
amplitude shocks irrespective of phase. This patient demonstrates
two episodes of self-terminating VT following an above-defibrillation-threshold
shock for a rhythm readily treatable with pacing. This may be
because of tachycardia termination and re-initiation by ventricular
ectopics in the post-discharge period, or continuation of the
tachycardia after a large amplitude shock delivered out of phase
leading to delayed termination.
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Conflict of interest
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P.S. receives research and fellowship funding from St Jude Medical
and Medtronic Inc, is a member of the Speaker's Bureau for St
Jude Medical, and is a member of an advisory board for Medtronic
Inc.
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Acknowledgements
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M.K.S. is supported by the National Heart Foundation of New
Zealand and the Dawes Scholarship from the Royal Adelaide Hospital.
D.H.L. is supported by the Earl Bakken Electrophysiology Scholarship
from the University of Adelaide. P.S. is supported by the National
Heart Foundation of Australia.
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Abstract
Case report