Europace Advance Access originally published online on September 6, 2007
Europace 2007 9(11):1059-1060; doi:10.1093/europace/eum186
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ICDS
Fatal outcome from inappropriate defibrillation
Cardiovascular Research Centre, Department of Cardiology, Royal Adelaide Hospital and the Disciplines of Medicine and Physiology, University of Adelaide, Adelaide, South Australia 5000, Australia
Manuscript submitted 26 June 2007. Accepted after revision 3 August 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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 Top Abstract Acknowledgements |
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We present a 51-year-old morbidly obese man who underwent insertion of a single-chamber implantable cardioverter defibrillator for monomorphic ventricular tachycardia occurring after myocardial infarction. After a period of satisfactory device function, a sudden change in R-wave with atrial over-sensing heralded inappropriate defibrillation and induction of ventricular fibrillation, with subsequent death of the patient.
Key Words: Ventricular tachycardia, ventricular fibrillation, inappropriate shock, fefibrillation, implantable cardioverter defibrillator, lead dislodgement
A 51-year-old morbidly obese man underwent insertion of a single-chamber implantable cardioverter defibrillator (ICD) with a dual-coil active fixation lead placed at the right ventricular (RV) apex (Medtronic Maximo VR 7232Cx; lead model no. 6947; Medtronic Inc., MN, USA) for monomorphic ventricular tachycardia occurring after myocardial infarction. The implant was uncomplicated with satisfactory lead parameters and defibrillation threshold (pacing threshold 1.0 V at 0.5 ms; lead impedance 348 
; R-wave 5 mV; defibrillation threshold 
20 J). During VF, the device sensing was programmed to 0.3 mV with good sensing of VF.
At his 3-month review after ICD implant, he had received multiple appropriate therapies from his device. Figure 1A demonstrates appropriate sensing of an event of VF and successful cardioversion with a maximum output shock. Figure 1B shows sensing of VT with successful anti-tachycardia pacing. Five months post-ICD implant, he presented to the emergency after receiving multiple shocks. On arrival, he received an inappropriate shock that induced VF from which he could not be resuscitated despite device and external cardioversions.
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Postmortem interrogation of the device revealed repeated episodes of sudden onset tachycardia, which were reverted with shock therapy. Figure 1C demonstrates the stored electrograms of one of the episodes treated by defibrillation and shows marked atrial over-sensing that was not apparent at his 3-month review (post-cardioversion electrograms in Figure 1B). Figure 1D demonstrates the terminal event for this patient, which again resulted from atrial over-sensing and shock delivery with resultant VF. In this Medtronic device, the first VF shock is synchronized to the second non-refractory R-wave after charging is completed. On this occasion, due to atrial over-sensing, the shock is actually synchronized to the atrial event that occurs 220 ms after the last true ventricular-sensed event culminating in VF. The lead performance trends retrieved from the device demonstrated a sudden decrease in the sensed R-wave to 1 mV on the day of presentation. This was associated with a change in the electrograms recorded, strongly suggesting lead dislodgement to the annulus or coronary sinus. No historical event could be identified to have triggered lead dislodgement. The ‘sensing integrity counter’, which analyses the ventricular channel for non-physiological signals, did not report the possibility of a lead integrity issue or loose set screws. Although lead dislodgement precluded successful device defibrillation, his morbid obesity is likely to have contributed to failed external therapy. Unfortunately, a postmortem chest roentograph was not performed.
Major complications that may arise from ICD implantation and malfunction include operative failures. The incidence for inappropriately delivered ICD therapies has been reported to be up to 10–25%. The literature reports an incidence of 1.5–5% for RV lead dislodgement. In this case, the RV lead dislodged resulted in over-sensing of the atrial chamber, suggesting retraction of the lead to the tricuspid annulus or possibly inadvertent displacement to the coronary sinus. This culminated in an inappropriate shock during tachycardia, which would have otherwise been ignored on the basis of cycle length. As a result of the synchronization with an atrial event, the shock fell within the vulnerable period of the T-wave to become pro-arrhythmic and induced VF, which was unable to be reverted. Tele-monitoring with early physician alerts is being introduced as a means of preventing such cases; however, the short time between dislodgement and terminal event suggests that it is unlikely to have changed the outcome in the current case.
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Acknowledgements |
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TopAbstractAcknowledgements |
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H.D. is supported by a Postgraduate Scholarship from the Cardiac Society of Australia and New Zealand. B.J. is supported by the Biosense-Webster Electrophysiology Scholarship, University of Adelaide. P.S. is supported by the National Heart Foundation of Australia.
Conflict of interest: none declared.
P.S. receives research and fellowship funding from Medtronic Inc. and St. Jude Medical Inc., is a member of an advisory board for Medtronic Inc. and is a member of the ‘Speaker's Bureau’ for St. Jude Medical inc.
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