Risk factors and outcomes associated with failed implantable cardioverter-defibrillator shocks.

Background: Implantable cardioverter-defibrillators (ICDs) deliver shocks to terminate ventricular tachycardia/ventricular fibrillation (VT/VF) to reduce the risk of sudden cardiac death. Failure of ICD shocks to terminate VT/VF, even if not resulting in death immediately, may signal patients at high risk of adverse outcomes.

Objective: We sought to identify predictors and outcomes associated with failed appropriate ICD shocks in patients with reduced left ventricular ejection fraction with a primary prevention ICD.

Methods: Our study cohort consisted of 5512 patients with an ICD or cardiac resynchronization therapy-defibrillator who were enrolled in the landmark Multicenter Automatic Defibrillator Implantation Trials and the Ranolazine in High-Risk Patients With Implanted Cardioverter-Defibrillator trial. Cox proportional hazards multivariate regression modeling was used to identify risk factors associated with the first occurrence of a failed ICD shock.

Results: Through 3 years of follow-up, the Kaplan-Meier rate of appropriate ICD shocks for VT/VF was 14.6% and rate of at least 1 failed ICD shock for VT/VF was 3.1%. Baseline risk factors associated with failed ICD shocks included younger age (hazard ratio [HR], 1.21 per 10 years younger age; 95% confidence interval [CI], 1.03-1.42; P = .019), male sex (HR, 2.21; 95% CI, 1.26-3.86; P = .006), and the occurrence of heart failure hospitalization after device implantation (HR, 2.06; 95% CI, 1.35-3.16; P = .001). Notably, the delivery of a successful ICD shock after device implantation was the most powerful risk factor for subsequent failed ICD shocks (HR, 6.72; 95% CI, 4.39-10.30; P < .001).

Conclusion: Our study identifies simple clinical risk factors that may be used to risk stratify patients at risk of having a failed ICD shock.