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Case Report

Unexpected Shocks From a Subcutaneous Implantable Cardioverter-Defibrillator Despite Attempted Reprogramming and Magnet Use: A Case Report

McFaul, Colleen M. MD, FRCPC*; Lombaard, Stefan MBChB, FANZCA; Arora, Vivek MD,; Van Cleve, William C. MD, MPH,; Rooke, G. Alec MD, PhD; Prutkin, Jordan M. MD, MHS

Author Information
A & A Practice: April 2020 - Volume 14 - Issue 6 - p e01178
doi: 10.1213/XAA.0000000000001178
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We present the case of a female patient with a subcutaneous implantable cardioverter-defibrillator (S-ICD) in situ presenting for a combined heart-kidney transplant. In 2012, the US Food and Drug Administration (FDA) approved the S-ICD for patient use.1 The S-ICD was developed to provide an alternative option to the transvenous ICD (TV-ICD), eliminating transvenous leads and their associated complications.2 Given its less frequent use,3,4 medical facilities and personnel may be unfamiliar with this device, including the procedures for deactivating antitachycardia therapies in the perioperative period, which can contribute to potential complications.

Written consent was obtained from the patient to publish this case report.


A 59-year-old female with a body mass index (BMI) of 24 (weight = 156 pounds, height = 67 inches) with a history of chemotherapy-associated cardiomyopathy and severely reduced left ventricular systolic function on chronic inotropic therapy presented to our facility for a combined orthotopic heart-kidney transplant. One year before, the patient underwent a mitral valve replacement and tricuspid valve repair for worsening valvular disease associated with progressive heart failure symptoms. One month before the presentation for transplant, she underwent placement of an S-ICD (A219 EMBLEM MRI, Boston Scientific, Marlborough, MA) for primary prevention of sudden cardiac death.

On the day of surgery, a specialized electrophysiology device–trained anesthesiologist5 attempted interrogation of the S-ICD with a standard Boston Scientific S-ICD programmer, which “crashed” and rebooted 3 times. A Boston Scientific representative explained that this represented a firmware/software mismatch between the device and programmer. Due to the urgency of surgery, device representatives recommended placing a standard “doughnut” magnet over the device to disable therapy. Due to operating room noise, the anesthesia team did not appreciate a beeping tone while positioning the magnet over various parts of the S-ICD. They did not use a stethoscope. The patient had no history of undergoing magnetic resonance imaging (MRI) with the S-ICD in situ. Following removal of the aortic cross-clamp, the anesthesia team noted ventricular fibrillation (VF) on the electrocardiogram (ECG). The surgical team performed 3 cardiac defibrillations with internal paddles. Unassociated with internal paddle defibrillation, the patient’s chest wall contracted 3 distinct times. These chest wall contractions were thought to be due to unexpected antitachycardia therapy delivered by the S-ICD. The remainder of the anesthesia-surgical course was unremarkable.

By the end of the orthotopic heart transplant, device representatives produced a programmer with compatible software. Interrogation of the S-ICD revealed that it had detected 5 events of VF and delivered therapy during 3 of these events. The cardiac anesthesiologist and fellow reviewed the patient’s electrogram on the programmer screen and confirmed that the 3 delivered therapies were in response to VF and not electromagnetic interference (EMI) and likely resulted in the witnessed chest wall contractions. The anesthesia providers then deactivated device therapies. Postprocedure, a printout of the electrogram was not possible, and it was not saved on the programmer. The device was later explanted for patient preference, and reinterrogation postexplant was not performed as it was sent for disposal.


S-ICDs have been developed as an alternative to TV-ICDs. In the United States, approximately 100,000 TV-ICDs are implanted each year, compared to 3200 S-ICDs,3,4 a number that continues to increase.4 Up to 20% of TV-ICD leads may require subsequent intervention due to problems such as lead failure, lead-associated infection, central venous stenosis, and tricuspid regurgitation.6 In contrast to the more common subclavicular position of the TV-ICD generator, the S-ICD pulse generator is placed in a subcutaneous pocket in the left lateral, midaxillary thoracic position (Figure 1). The S-ICD contains a single extrathoracic lead that is tunneled subcutaneously along the left parasternal border and can deliver up to 5 consecutive 80-Joule antitachycardia therapies. The S-ICD is not able to provide antitachycardia, antibradycardia, or cardiac resynchronization pacing but can provide postshock ventricular pacing for 30 seconds if asystole is detected.7 Although pocket infection is the most common complication associated with S-ICDs, there is minimal likelihood of systemic infection due to the absence of intravascular leads. Other less common complications of S-ICD placement include implant-site hematoma and device erosion.8

Figure 1.
Figure 1.:
Lateral (left) and anteroposterior (right) chest radiographs demonstrating the position of subcutaneous implantable cardioverter-defibrillator in lateral, midaxillary thoracic position. Image provided courtesy of Boston Scientific. ©2020 Boston Scientific Corporation or its affiliates. All rights reserved.

The S-ICD analyzes the heart rhythm by detecting a surface ECG signal formed between the sensing electrodes and the pulse generator. In the perioperative period, to reduce the risk of inappropriate antitachycardia therapies, different programming algorithms can be selected for patients undergoing procedures at risk of EMI.7 S-ICDs do not have a noise reversion mode like that found in TV-ICDs and are therefore more likely to deliver inappropriate antitachycardia therapies in response to EMI.9

In the perioperative period, ICDs may require deactivation depending on the likelihood of EMI. In the absence of a suitable programmer or in an emergency situation, a magnet can be used to deactivate therapy. With S-ICDs, appropriate placement of the magnet is variable depending on the device model: the first-generation device (model 1010 SQ-RX S-ICD) requires the magnet to be placed directly over the device (Figure 2A), while second- and third-generation (A209 and A219 EMBLEM S-ICD) models require the magnet to be applied either over the top or bottom half of the device (Figure 2B). This variability in magnet placement increases the risk of failed device deactivation. For patients with an elevated BMI or with greater distance between the magnet and the generator, Boston Scientific suggests using multiple magnets in a stacked configuration.10 With successful magnet placement, the S-ICD emits an r-wave synchronous beeping tone for 1 minute. No tone is emitted with magnet removal and device reactivation. Should the magnet position shift during a long procedure, there is no indication that the device has been reactivated and the patient is at risk for inappropriate shocks. In addition, if the patient has undergone MRI with an S-ICD in situ, the beeper of the S-ICD may become permanently disabled.10

Figure 2.
Figure 2.:
Magnet placement to disable 1st and 2nd generation S-ICD. A, Correct magnet placement (blue) for first-generation (model 1010 SQ-RX S-ICD) S-ICD with magnet placed directly over generator (grey). B, Correct magnet placement (blue) for second- and third-generation S-ICD (A209 and A219 EMBLEM S-ICD) with magnet placed either over top or bottom half of the generator (grey).*S-ICD indicates subcutaneous implantable cardioverter-defibrillator.

When considering ICD discharges, it is important to draw a distinction between inappropriate (antitachycardia therapy delivered when the patient is not in an aberrant cardiac rhythm) and unexpected therapies (appropriate antitachycardia therapy delivered despite attempts to deactivate the device). In the absence of perioperative reprogramming or correct magnet placement, there is a risk of inappropriate discharge due to EMI that can lead to myocardial injury and increased mortality.11 It is unclear in our case whether the magnet was positioned appropriately, as providers did not appreciate an audible confirmation of device deactivation. It is also possible that the magnet shifted during the prolonged procedure, leading to an undetected reactivation of antitachycardia therapy. As our patient’s BMI was 24, failure to deactivate the S-ICD was unlikely due to deep placement of the generator.

A meta-analysis by Auricchio et al12 reports an annual inappropriate shock rate of 6.4%. They found no significant difference in inappropriate shocks between patients with a single-chamber TV-ICD and S-ICD.12 While inappropriate shocks are undesirable and serve as a primary reason for disabling antitachycardia therapies during the perioperative period, less is known regarding the frequency of unexpected shocks in patients with ICDs. A case report and a case series of unexpected shocks despite magnet placement in patients with TV-ICDs have been published,13,14 but a Pubmed search for unexpected shocks in S-ICDs found no results (search terms: unexpected AND shock OR shocks OR therapy AND subcutaneous ICD OR S-ICD OR implantable ICD). Our case is the first published report of an unexpected shock delivered by an S-ICD. In an attempt to characterize the frequency of unexpected shocks, our group undertook a review of the FDA Manufacturer and User Facility Device Experience (MAUDE) dataset (search term in Product Problem field inappropriate shock, Product Class Implantable Cardioverter Defibrillator[non-Crt]), which contains reports of medical device problems.15 The Table lists unexpected shock therapies despite ICD reprogramming or disabling by magnet placement reported to the FDA between 2008 and 2018. A total of 6 patients received unexpected shocks; 2 of these occurred despite perioperative reprogramming, and 4 occurred despite magnet placement. While the number of reports appears small, the MAUDE database represents only a fraction of device problems due to underreporting from device representatives and delay of case presentation.

Table. - US Food and Drug Administration-MAUDE Database Review of Patients With ICD Receiving Unexpected Shock Therapy in the Past 10 Years
Manufacturer and Model Event Date Procedure Device Deactivation Event Leading to Shock Outcome
Guidant CRM CLONMEL IRELAND – COGNIS October 25, 2012 Epicardial lead implant Programmed off Safety modea activated by EMI No AE
Device replaced
Guidant CRM CLONMEL IRELAND – COGNIS August 11, 2011 Device placement Programmed off Safety mode activated by EMI No AE
Device replaced
Guidant CRM CLONMEL IRELAND – INOGEN September 28, 2017 Unknown procedure in prone position Magnet placement Magnet dislodged during prone position No AE
Biotronik SE & CO. KG – ITREVIA 7HF-T DF-1 March 23, 2018 None Magnet placement Magnet placed appropriately Unknown patient effects
Device replaced
St Jude Medical, Inc, CRMD – Unify CRT-D October 22, 2012 None Magnet placement Unknown Unknown
Sorin group Italia S.R.L – PARADYM August 6, 2013 None No reprogramming due to device interrogation error 3 magnets placed with partial device inhibition Unknown patient effects
Magnet placed 90 shocks total
bbreviations: AE, adverse events; EMI, electromagnetic interference; ICD, implantable cardioverter-defibrillator; MAUDE, Manufacturer and User Facility Device Experience.
Safety mode: device defaults to basic defibrillation and pacing function and cannot be reprogrammed.

Due to limited practitioner experience with S-ICD models and an inability to reprogram the device preoperatively, a magnet was placed but did not prevent delivery of antitachycardia therapies. The lack of appreciation of the device’s audible tone, coupled with limited practitioner experience with this device, and the potential for antitachycardia therapies to be silently re-enabled should the magnet shift position all represent potential mechanisms for these unexpected shocks.

Our case demonstrates potential threats to patient and provider safety when an ICD cannot be definitively deactivated during the perioperative period. A temporal gap may occur between new device software implementation and programmer software update. Device programmers should be checked regularly for potential software updates. When clinically indicated, providers must ensure that S-ICD deactivation has taken place, preferentially by preoperative reprogramming. Magnet deactivation of S-ICD is less reliable than TV-ICDs and should only be used in emergencies with careful consideration of the intricacies of magnet use.


Name: Colleen M. McFaul, MD, FRCPC.

Contribution: This author helped with clinical information about the patient’s course and wrote and reviewed the manuscript.

Name: Stefan Lombaard, MBChB, FANZCA.

Contribution: This author helped with background information and perioperative management of subcutaneous implantable cardioverter-defibrillator devices.

Name: Vivek Arora, MD.

Contribution: This author helped with clinical information about the patient’s course and helped draft and review the manuscript.

Name: William C. Van Cleve, MD, MPH.

Contribution: This author helped with clinical information about the patient’s course and literature search, performed the search of the MAUDE database, and helped with drafting and review of the manuscript.

Name: G. Alec Rooke, MD, PhD.

Contribution: This author helped draft and review the manuscript.

Name: Jordan M. Prutkin, MD, MHS.

Contribution: This author helped draft and review the manuscript.

This manuscript was handled by: BobbieJean Sweitzer, MD, FACP.


AE = adverse events

BMI = body mass index

ECG = electrocardiogram

EMI = electromagnetic interference

FDA = US Food and Drug Administration

MAUDE = Manufacturer and User Facility Device Experience

MRI = magnetic resonance imaging

S-ICD = subcutaneous implantable cardioverter-defibrillator

TV-ICD = transvenous implantable cardioverter-defibrillator

VF = ventricular fibrillation


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