Defibrillation testing at implant of subcutaneous implantable cardioverter defibrillator: weighting propensity score analysis and results from nationwide HONEST cohort

Background While strong evidence supports omitting defibrillation testing (DT) in transvenous implantable cardioverter defibrillator (ICD), the same cannot be assumed for subcutaneous ICD (S-ICD), where DT is still recommended due to limited evidence. Purpose This study aims to compare the long-term outcomes of S-ICD recipients with and without DT, focusing on cause-specific mortality, especially sudden cardiac death (SCD), and the incidence of shocks. Methods We analyzed data from the HONEST cohort, which includes 4,924 patients who received an S-ICD between 2012 and 2019 across150 French centers. Clinical follow-up and remote monitoring were used to track outcomes, including overall death, cardiovascular (CV) death, sudden cardiac death (SCD), a composite of SCD and deaths from unknown causes, as well as the incidence of appropriate and inappropriate shocks. Vital status was confirmed via the National Institute of Statistics and Economic Studies database, which tracks all deaths in France. Causes of death were adjudicated and classified following ESC guidelines. Propensity score weighting was used to adjust for confounding variables in comparisons between patients with DT (S-ICD Testing (+)) and those without DT (S-ICD Testing (-)). database Results In the HONEST cohort, 82.6% of the 4,924 patients underwent DT at S-ICD implantation, with a high success rate of 97.3%. Patients without DT were generally older (51.2 vs. 49.6 years, SMD=0.107), had a lower LVEF (37.6 vs. 43.3%, SMD=0.343), and were more frequently receiving S-ICD for primary prevention (68.0 vs. 62.4%, SMD=0.118). Crude analysis suggested lower overall mortality with DT (10.6 vs. 13.6%, HR=0.68, 95% CI 0.55–0.84, p<0.001), though this association did not remain significant after propensity score weighting (HR=0.89, 95% CI 0.73–1.10, p=0.285). No significant differences were observed in cardiovascular mortality (5.34 vs. 8.15%, HR=0.80, 95% CI 0.61–1.05, p=0.112), SCD (0.12 vs. 0.59%, HR=0.82, 95% CI 0.44–1.50, p= .978), or the composite of SCD and unknown causes (2.56 vs. 2.71%, HR=0.74, 95% CI 0.54–1.02, p=0.066). Rates of appropriate (12.10 vs. 12.34%, HR=0.92, 95% CI 0.74–1.14, p=0.442) and inappropriate shocks (12.20 vs. 10.10%, HR=1.07, 95% CI 0.85–1.35, p=0.572) were also similar. Conclusions Routine DFT does not significantly impact long-term outcomes, including overall mortality, cardiovascular death, SCD, composite outcomes of SCD and unknown death, or the incidence of appropriate and inappropriate shocks in the general population of S-ICD recipients.