The impact of defibrillation current and pad position on return of spontaneous circulation during refractory ventricular fibrillation

BACKGROUND: Although pad position influences current delivery, the relationship between transthoracic current, pad position, and shock efficacy during external defibrillation for refractory ventricular (VF) has not been examined. OBJECTIVE: To assess the relationship between pad position, current delivery and return of spontaneous circulation (ROSC) among patients enrolled in the Double Sequential External Defibrillation for Refractory VF (DOSE VF) trial. METHODS: We conducted a secondary, per-protocol analysis of patients enrolled in DOSE VF. Transthoracic current was calculated for the first six shocks using defibrillator-derived measures of shock energy and impedance, applying manufacturer-provided formulas. Current delivery was compared across standard anterolateral (AL), vector-change (VC) anteroposterior (AP), and double sequential external defibrillation (DSED; AL + AP) shocks. Multivariable logistic regression and generalized estimating equation (GEE) models were used to examine associations between current delivery, pad position and ROSC. RESULTS: 342 patients were included (mean age 63.6 years; 85% male), contributing 849 interventional shocks (51.6% standard, 25.4% VC and 22.9% DSED). Mean current was significantly greater for AP shocks in both VC (19.6 A) and DSED (19.2 A), compared with standard AL (16.6 A) and DSED AL shocks (17.3 A) (P < 0.001). In GEE modeling, AP positioning was independently associated with ROSC compared to AL positioning (aOR 2.01; 95% CI: 1.12-3.59). Delivered current was not associated with ROSC. CONCLUSIONS: AP delivered higher current than AL positioning; however, pad position rather than delivered current was independently associated with ROSC. These findings suggest the additional AP pad position may be a key mechanistic contributor to the benefit of VC and DSED.