Oversensing of atrial fibrillatory waves in a subcutaneous implantable cardioverter-defibrillator

Introduction Implantable cardioverter-defibrillators (ICDs) have been shown to improve survival in patients with ischemic or nonischemic cardiomyopathy when used for primary and secondary prevention settings. The limitations of transvenous ICDs include postimplant adverse events, defibrillator lead failure, and inappropriate shocks for atrial tachyarrhythmias due to fast ventricular response rate that are associated with an increase in all-cause mortality. Given these shortcomings, subcutaneous ICDs (S-ICDs) may offer several potential advantages. Prior S-ICD studies have shown a complication rate and shock efficacy comparable to transvenous systems and significantly better supraventricular tachycardia (SVT) discrimination compared to transvenous ICDs. Inappropriate shocks in S-ICDs are almost exclusively due to double counting secondary to Twave oversensing. We report a patient with an S-ICD and hypertrophic cardiomyopathy (HCM) who received an inappropriate shock for atrial fibrillation due to oversensing of atrial fibrillatory waves. This has not been reported previously.