The effect of uniform and non-uniform electric fields on defibrillation thresholds for monophasic and biphasic waveforms

This study examines whether uniform and nonuniform electric field topologies as generated by different defibrillation electrode configurations influence defibrillation threshold energies (DFT) for monophasic (MP) and biphasic (BP) shock waveforms. Recent theoretical studies have suggested that the ability of BP to change transmembrane potential may be enhanced under non-uniform field conditions. This may also influence the efficacy of defibrillation of BP waveforms, Also, contradictory experimental results in the comparison of BP versus MP efficacy have been reported. These may be due to different experimental setups resulting in different shock electric field non-uniformity. To test the hypothesis that electric field non-uniformity influences relative defibrillation efficacy for MP and BP waveforms we determined DFT delivered to the heart under two electrode configurations. A catheter electrode was used to create a non-uniform field and a pair of parallel plates created a uniform field. The results show that BP is more efficacious than MP under both uniform and non-uniform field conditions (p<0.05) and that the efficacy off BP is enhanced under non-uniform fields (p<0.005) whilst there is no observed difference between uniform and non-uniform fields for MP waveforms.