Effectiveness of subcutaneous implantable cardioverter-defibrillators and determinants of inappropriate shock delivery

Aims Assess subcutaneous implantable cardioverter-defibrillator (S-ICD) effectiveness in the prevention of sudden cardiac death and the impact of demographics and the initial detection algorithm in the delivery of inappropriate shocks (safety). Methods Real world prospective registry in which we assessed 54 patients (40 ± 17 years old, 85% males) who underwent S-ICD implantation for primary or secondary prevention of SCD. Safety and efficacy outcomes were defined as the delivery of inappropriate shocks and the prevention of sudden cardiac death, respectively. Tiered-therapy S-ICD had at least two programmed zones, determined by the longest RR interval. Results During a mean follow-up of 2.6 ± 1.9 years, 6 patients (11%) died, none due to sudden cardiac death. Six patients (11%) received appropriate therapies, irrespectively of the established detection algorithm (p = 0.59). All ventricular tachycardia and fibrillation episodes were adequately treated. Nine patients (17%) had inappropriate shocks: 6 without tiered-therapy vs 3 with previously programmed tiered-therapy (p = 0.001). The yearly rate of inappropriate shocks was 17%/year with single zone detection vs 4%/year with tiered-therapy programming (p = 0.007). Single-zone detection programming was an independent predictor of inappropriate shock delivery (HR 1.49, IC 95%: 1.05–18.80, p = 0.04). Conclusion In this selected population of patients, the S-ICDs proved effective in preventing sudden cardiac death. Tiered-therapy was independently associated with a lower rate of inappropriate shock delivery.