Outcomes of Subcutaneous ICD in Congenital Heart Disease
What is the experience with the subcutaneous implantable cardioverter-defibrillator (S-ICD) in patients with congenital heart disease (CHD)?
An analysis of 865 patients who underwent implantation of an S-ICD for either primary or secondary prevention of sudden death was undertaken. Of these, 19 patients (2.2%) were defined as having CHD, and the remaining 846 patients received the ICD for other cardiac conditions. The CHD group was younger, and was comprised of more women, had more atrial fibrillation, but less heart failure. The indication was primary prevention in about 70% in both groups.
Over a median follow-up of 567 days, none of the 19 patients with CHD experienced appropriate therapies or death. The non-CHD patients experienced 111 appropriate shocks (in 59 patients) and 26 deaths over a median follow-up of 846 days. Inappropriate shocks occurred in 2/19 patients for T-wave oversensing, which occurred at a similar rate in the non-CHD group. The rate of successful defibrillation at 80 J was 100% and 99% in the CHD and non-CHD groups. Explantation of the S-ICD system was required in 1 (5%) and 75 (9%) patients, respectively.
The authors concluded that the S-ICD is a safe option in patients with CHD who are deemed to be at risk of sudden death.
The S-ICD system has previously been shown to be an effective device in preventing sudden death due to ventricular arrhythmias in patients with cardiac disease. This device has no transvenous or intracardiac components, which eliminates the risk of vascular complications, lung and cardiac perforation, and greatly reduces the risk of severe device/lead-related systemic infection. Patients without sustained ventricular tachycardia, and those who do not require pacing or resynchronization therapy, are good candidates for an S-ICD. Patients are screened to determine whether the electrode (implanted at the left sternal border) is able to adequately sense ventricular arrhythmias, and to minimize the risk of T-wave oversensing (R/T wave amplitude). The latter can result in double counting, leading to inappropriate detection and shocks. Updated sensing algorithms are expected to decrease the incidence of T-wave oversensing and inappropriate therapies. The risk of infection (not systemic infection) is probably higher with an S-ICD as compared to a conventional transvenous device, likely owing to more dissection and a greater number of incisions that are required. Overall, S-ICD devices are preferable in younger patients, given the prospect of multiple anticipated procedures for battery depletion and/or lead failure over time. Greater experience is required in patients with CHD, especially given variant anatomy, and presence of bundle branch block, which may interfere with optimal sensing.
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