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A 44-year-old woman with dilated cardiomyopathy while receiving maximally tolerated guideline-directed medical therapy presented after ventricular fibrillation arrest and subsequently underwent an uneventful implant of a subcutaneous cardioverter defibrillator (S-ICD; EMBLEM, version A219; Boston Scientific) for secondary prevention. The device was programmed with a conditional shock zone of 200 beats per minute and a shock zone of 230 beats per minute. Postprocedure chest radiography results showed appropriate device placement. Postimplant interrogation results showed appropriate device function. The patient was discharged the day after implant. Two weeks later, she presented to the emergency department (ED) after receiving several shocks from the device during the early morning, waking her up from sleeping. There were no reported symptoms associated with shortness of breath, chest pain, or syncope. Physical examination results revealed no signs of decompensated heart failure. Device interrogation results showed shock therapies delivered postimplant on days 3, 5, 6, and 10. The surface electrogram from the events, recorded at a paper speed of 25 millimeters per second and an amplitude of 2.5 mm/mvV) is shown in Figure 1. Repeated chest radiography at the ED showed appropriate device location, lead pin, and an absence of subcutaneous air trapping at the proximal and distal sense electrodes.
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Inappropriate S-ICD shock from the oversensing of the electrical noise
B. Subcutaneous ICD reprogramming and observation
The surface electrogram results from all the events shared similar characteristics and revealed an inappropriate ICD shock due to an oversensing of the electrical noise. The noise has the appearance of “flutter waves,” which terminated after the shock therapies. Initially, this noise could be interpreted as ventricular or atrial arrhythmia. There are few points used to accurately differentiate between appropriate and inappropriate therapy in this case. First, the marching intrinsic QRS complexes through tracing can be identified within this electrical rhythm with varying degrees of superimposition of the flutterlike wave on the R wave. Second, the morphology and amplitude of the flutter waves are irregular and variable in cycle length, suggesting that the flutter waves are unlikely to be caused by reentry mechanism. Third, the intrinsic ventricular rate in the range of 90 to 100 beats per minute remained the same before and after the shocks were administered.
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Corresponding Author: Tanyanan Tanawuttiwat, MD, MPH, University of Mississippi Medical Center, 2500 N State St, Jackson, MS 39216 (firstname.lastname@example.org).
Published Online: July 17, 2019. doi:10.1001/jamacardio.2019.1146
Conflict of Interest Disclosures: None reported.
Additional Contributions: We thank Burwell Barton and Steve Donnelley, Boston Scientific, for assistance in confirming the technical accuracy of this article and the patient for granting permission to publish this information.
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