Shock Efficacy of the Subcutaneous ICD for Prevention of Sudden Cardiac Death: Initial Multicenter Experience

Study Questions:

How efficacious is the subcutaneous implantable cardioverter-defibrillator (S-ICD)?


Forty patients (mean age 42 years) received a S-ICD for primary (n = 17) or secondary (n = 23) prevention of sudden death. The sensing/shocking lead was positioned subcutaneously parallel to the left of the sternum, and the generator was positioned between the mid- and anterior-axillary lines. Testing was performed with 65-J shocks, and 80-J shocks were delivered for spontaneous episodes of ventricular tachycardia/ventricular fibrillation (VT/VF). The shock zone was programmed at 170 or 200 bpm. The S-ICDs were interrogated at regular intervals during a median follow-up of 7.6 months.


Testing at the time of implantation was successful in 39/40 patients. Four of forty patients received appropriate S-ICD shocks for 25 episodes of VT/VF. The first-shock efficacy was 58%, and the overall shock efficacy was 96%. The S-ICD was exchanged for a conventional ICD because of inefficacy in two patients with idiopathic VF. Two patients received inappropriate shocks caused by T-wave oversensing or sinus tachycardia.


The first-shock efficacy of the S-ICD is approximately 60%, and overall efficacy is 96%.


The advantages of the S-ICD over the conventional ICD are the elimination of the need for venous access and fluoroscopy, and of complications such as pneumothorax and perforation. The disadvantages include the lack of antitachycardia pacing and long-term antibradycardia pacing. The results of this study do not support the widespread use of S-ICDs. It is disconcerting that the S-ICD was ineffective in 2/4 patients who required shocks for spontaneous episodes of VT/VF, despite the fact that testing at the time of implantation was successful in both.

Clinical Topics: Arrhythmias and Clinical EP, Implantable Devices, SCD/Ventricular Arrhythmias

Keywords: Tachycardia, Ventricular, Ventricular Fibrillation, Death, Sudden, Cardiac, Defibrillators, Implantable

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