Defibrillation Testing in Patients With Subcutaneous ICD

Study Questions:

Which factors might influence the decision to perform defibrillation testing (DFT) in patients undergoing an implantation of a subcutaneous implantable cardioverter-defibrillator (S-ICD)?


Hospital records of 7,960 patients who were undergoing S-ICD implantation, and who were included in the National Cardiovascular Data Registry ICD Registry were reviewed. The mean age of the patients was 53 years, and 30% were women. There was roughly an even distribution of ischemic and nonischemic etiology of left ventricular (LV) dysfunction (mean ejection fraction [EF], 32%).


Among the 7,960 patients, DFT was performed in 5,624 (70.7%) patients. Deferral of DFT was associated with increasing body mass index, severe LV dysfunction (EF <20%), hemodialysis, use of warfarin, and anemia. The decision to proceed with DFT was more likely to be associated with physician preference, as opposed to patient-related factors. Insufficient safety margin (ISM), defined as successful defibrillation at energies >65 J (maximum output, 80 J), was noted in 336 (7%) patients. ISM was more likely among white patients, those requiring ventricular pacing, those with higher blood pressure, and those of larger size and lower EF. There was no difference in in-hospital outcomes among patients who did or did not undergo DFT.


DFT was not performed in about one-third of the patients receiving an S-ICD. Its deferral was more likely related to physician-related, as opposed to patient-related factors.


The major advantage of an S-ICD is the lack intravascular or intracardiac components that eliminates or greatly diminishes risks such as perforation, pneumothorax, thrombosis/occlusion, and severe infection such as bacteremia/endocarditis. The subcutaneous location also results in a higher defibrillation threshold, i.e., the minimum energy required to convert ventricular fibrillation, as compared to transvenous devices. Data suggest that DFT may be bypassed in most patients receiving a transvenous ICD for primary prevention. However, given higher energy requirements, DFT is recommended at the time of implantation of an S-ICD. This study shows that these recommendations are not adhered to in about one-third of the patients, and this is more likely related to physician preference as compared to patient characteristics. The reasons behind deferral of DFT are unknown, but may be due to physician practice/assumption that DFT does not improve outcomes, the fact that these data were obtained from transvenous patients notwithstanding. Another possibility is the paucity of options (e.g., moving the transvenous electrode, adding or removing coils, etc.) in the setting of ISM.

Clinical Topics: Anticoagulation Management, Arrhythmias and Clinical EP, Prevention, Implantable Devices, EP Basic Science, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias

Keywords: Anemia, Arrhythmias, Cardiac, Blood Pressure, Body Mass Index, Defibrillators, Implantable, Electric Countershock, ICD Registry, National Cardiovascular Data Registries, Primary Prevention, Secondary Prevention, Stroke Volume, Ventricular Fibrillation, Warfarin

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