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Background: Subcutaneous implantable cardioverter defibrillators (S-ICDs) are an attractive alternative to transvenous ICDs among those not requiring pacing. However, the risks of damage to the S-ICD electrode during sternotomy and adverse interactions with sternal wires remain unclear. We sought to determine the rates of damage to the S-ICD lead during sternotomy, inappropriate shocks from electrical noise due to interaction with sternal wires, and failure to terminate spontaneous or induced ventricular arrhythmias. Methods: Retrospective, multicenter study of patients undergoing sternotomy before or after S-ICD implantation. Clinical, procedural, and device-related data were collected by each center and analyzed by the coordinating center. These data were compared with a historical control cohort of nonsternotomy patients. Results: Of 196 identified patients (52±16 years, 47 females), 166 underwent S-ICD implantation after sternotomy and 30 sternotomy after S-ICD. There was no damage to any lead among those who underwent sternotomy after S-ICD. Defibrillation threshold testing was performed in 63% at implant, with 91% first shock success. During a median follow-up of 29 months (range, 1–188), S-ICD first shocks successfully terminated spontaneous ventricular arrhythmias in 31 of 32 patients (97%). Inappropriate shocks occurred in 22 patients, most commonly related to T wave oversensing (n=14). Compared with the nonsternotomy controls, there were no differences in rates of first shock success for induced or spontaneous arrhythmias or rate of inappropriate shocks. Conclusions: Sternotomy before or after S-ICD does not confer additional risk relative to a historical control group without sternotomy.

Introduction: Electrograms (EGMs) generated by implantable cardiac devices at the time of non-cardiac death may have artifact from non-arrhythmic sources, such as coagulated blood and air bubbles. While few studies have described the nature of terminal EGMs in non-cardiac death, it is clinically and medicolegally important to characterize these EGMs to elucidate events that may otherwise be misinterpreted as device failure. Here we investigated terminal EGM features that may aid clinicians in discerning cardiac from non-cardiac death. Methods: Terminal EGMs were analyzed by independent physician reviewers. Deaths were adjudicated as non-cardiac based on direct clinical data at the time of death using a modified Cardiac Arrhythmia Suppression Trial approach. In total, 16 non-cardiac terminal EGMs were identified and compared to a control cohort of true arrhythmic events. Using a subset of identified EGMs, an 8-question survey was administered to electrophysiologists blinded to cause of death. Several variables were identified as important for the correct classification of EGMs. The statistical performance of each variable for detecting non-cardiac death and true arrhythmias in our sample was evaluated. These results were shared, and the survey was readministered. Results: In our sample, absence of organized atrial activity had a sensitivity (SN) of 78.5%, specificity (SP) of 100%, and positive predictive value (PPV) of 100% for non-cardiac terminal EGMs. Cycle length <130 ms and absence of discernible deflections both had SPs and PPVs of 100% for non-cardiac death but were less sensitive (60% and 20%, respectively). An abrupt change following therapy and response to therapy both had SNs, SPs, and PPVs of 100% for true arrhythmias. Survey response rate was 68.8% and 62.5% for the pre- and post-survey, respectively. Pre-survey scores ranged from 50 – 87.5% correct with a mean of 72.7%. Post-survey scores ranged from 75 – 100% with a mean of 86.3% (p< 0.01). Conclusions: There is variability and inaccuracy among expert physicians' interpretation of EGMs during non-cardiac death. The variables identified in this study will aid in the development of a clinical risk score used to discern non-cardiac death and true device malfunction based on terminal EGMs.

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