Defibrillation Testing During Implantation of Subcutaneous Implantable Cardioverter Defibrillators

Defibrillation testing (DT) remains recommended during subcutaneous implantable cardioverter defibrillator (S-ICD) implantation due to limited supporting evidence.

The objective of this study was to evaluate the long-term impact of DT during S-ICD implantation.

The HONEST (coHOrte fraNcaise des dEfibrillateurs Sous cuTanés) study is a nationwide, ongoing observational study, including all S-ICD recipients in France (2012-2019). Five-year endpoints were centrally adjudicated, and propensity score-weighted analyses compared outcomes by DT status.

Among 4,924 patients, DT was performed in 4,066 (82.6%), decreasing from 85.4% (2012-2014) to 66.9% in 2019 (P < 0.001). Nontested patients were older (51.2 vs 49.6 years; P = 0.007), had lower left ventricular ejection fraction (37.6% vs 43.3%; P < 0.001), and were more frequently implanted for primary prevention (68.0% vs 62.4%; P = 0.002) and structural heart disease (84.9% vs 76.8%; P < 0.001). DT-related complications occurred in 0.1%, including 2 deaths. Failure rate was 1.0%, with 87.8% undergoing corrective reinterventions. Independent predictors of DT failure were elevated shock impedance (≥89 Ω; OR: 4.60; 95% CI: 2.32-9.66; P < 0.001) and obesity (body mass index ≥30 kg/m²; OR: 2.17; 95% CI: 1.01-4.55; P = 0.007). After adjustment, DT omission was not associated with increased risks of overall mortality (HR: 1.17; 95% CI: 0.86-1.61; P = 0.313), cardiovascular mortality (HR: 1.04; 95% CI: 0.70-1.56; P = 0.846), sudden cardiac death (HR: 0.27; 95% CI: 0.04-1.72; P = 0.167), and appropriate (HR: 1.01; 95% CI: 0.78-1.30; P = 0.945) or inappropriate shocks (HR: 0.98; 95% CI: 0.78-1.23; P = 0.865). Combined rates of ineffective shocks or undetected ventricular arrhythmias were similar (0.05 vs 0.06 per 100 person-years).

Our findings suggest that DT can be safely omitted in the majority of S-ICD recipients, whereas selective DT may be considered in higher-risk subgroups. (S-ICD French Cohort Study (HONEST); NCT05302115).