Single and dual coil shock efficacy and predictors of shock failure in patients with modern implantable cardioverter defibrillators—a single-center paired randomized study

Purpose: Implantable cardioverter defibrillators (ICDs) can treat life-threatening tachyarrhythmia with high-voltage shocks. The aims were to compare the efficacy of single and dual coil shock vectors in modern ICDs and to identify predictors of shock failure. Methods: This is a single-center paired randomized study including 216 patients with mixed indications and ICDs from four manufacturers. All patients underwent two implant defibrillation tests using single and dual coil vectors with the test order randomized. Tested shock energy differed slightly between manufacturers because of differences in device programmability: first shock approximately 15 J below maximal output—if failed, second shock approximately 10 J below maximal output—if failed, third shock at maximal output. Results: First shock success rate was 399/432 (92.4%). Comparing single and dual coil vectors, no differences were seen in first shock efficacy (91.7% vs. 93.1%, P = 0.629) or lowest tested succesfully stored energy (27.2 J vs. 27.1 J, P = 0.620). All successive internal shocks failed in 4/432 (0.9%) of inductions requiring external rescue shocks to restore circulation. Multivariate predictors of first shock failure were QRS duration (relative risk 0.81 per 10 ms, P = 0.001), amiodarone treatment (relative risk 3.30, P = 0.003), and body height (relative risk 1.70 per 10 cm, P = 0.019). Conclusions: Implant defibrillation testing of modern intravenous ICD systems demonstrates high shock efficacy with no difference between single and dual coil vectors.