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

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.

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.

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.

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).

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