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

Abstract

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. 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. 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. 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. 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.