An investigation of inter-shock timing and electrode placement for double-sequential defibrillation.

Background: Double-Sequential Defibrillation (DSD) is the near-simultaneous use of two defibrillators to treat refractory VF. We hypothesized that (1) risk of DSD-associated defibrillator damage depends on shock vector and (2) the efficacy of DSD depends on inter-shock time. Methods: Part 1: risk of defibrillator damage was assessed in three anaesthetized pigs by applying two sets of defibrillation electrodes in six different configurations (near-orthogonal or near-parallel vectors). Ten 360J shocks were delivered from one set of pads and peak voltage was measured across the second set. Part 2: the dependence of DSD efficacy on inter-shock time was assessed in ten anaesthetized pigs. Electrodes were applied in lateral-lateral (LL) and anterior-posterior positions. Control (LL Stacked Shocks; one vector, two shocks similar to 10 s apart) and DSD therapies (Overlapping, 10 ms, 50 ms, 100 ms, 200 ms, 500 ms, 1000 ms apart) were tested in a block randomized design treating electrically-induced VF (n = similar to 89 VF episodes/ therapy). Shock energies were selected to achieve 25% shock success for a single LL shock. Results: Part 1: peak voltage delivered was 1833 +/- 48 V (mean +/- 95%CI). Peak voltage exposure was, on average, 10-fold higher for parallel than orthogonal vectors (p<0.0001). Part 2: DSD efficacy compared to Stacked LL shocks was higher for Overlapping, 10 ms, and 100 ms (p<0.05); lower at 50 ms (p < 0.05); and not different at 200 ms or longer inter-shock times. Conclusion: Risk of DSD-associated defibrillator damage can be mitigated by using near-orthogonal shock vectors. DSD efficacy is highly dependent on the inter-shock time and can be better, worse, or no different than stacked shocks from a single vector. Institutional Protocol Number: University of Alabama at Birmingham Institutional Animal Care and Use Committee (IACUC) Protocol Number 06860.