Shock timing lowers transvenous defibrillation energy requirement

Defibrillation Depends on Conductivity Fluctuations and the Degree of Disorganization in Reentry Patterns

“…A positive correlation between minimum defibrillation energy and the dominant frequency of chronic AF was shown 53 . A proper choice of shock timing can reduce energy requirements 54 . Experimentally, termination of VF could be achieved with shock energies in the millijoule range by first applying synchronized pacing 55 .…”

Synchronized defibrillation for ventricular fibrillation

“…Defibrillating shocks delivered at this time would therefore extend the refractory period of those cells in the high-density region late in their refractory period while the cells in the low-density region early in the action potential would have a long-enough refractory period to halt further propagation of wavefronts in these areas. 6,7 A small but significant reduction in defibrillation threshold energy was noted in a further study when rounded biphasic shocks were delivered timed to the peak and trough of the VF wave as compared to non-synchronized shocks. 11 Despite these earlier findings, we were not able to demonstrate similar results despite significant advancements in equipment function.…”

“…5 Further work has demonstrated a significant improvement in shock success and a reduction in delivered energy with shocks timed to the upslope of the VF wave as opposed to the downslope. 6,7 This benefit was seen only when shocks were timed to the endocardial (morphology) electrogram and not the surface ECG leads. 7 It has been postulated that this occurred because the regions in the ventricle which contribute most to the electrogram signal would be those that are in the highest current-density regions during the shock and the location of the upslope of the VF waveform in this lead would be moving in the optimum direction for defibrillation.…”

“…2,3 Studies have since demonstrated improvements in shock success when defibrillating shocks were timed to various parameters on the electrocardiogram (ECG). 4–8 No study as yet has demonstrated a significant improvement in shock success when synchronized shocks for VF are delivered transthoracically.…”

Kinetics of defibrillation shock-induced response: design implications for the optimal defibrillation waveform

“…However, others have reported changes in polarity having no effect on defibrillation thresholds [28] especially in the case of biphasic shocks [29,30] . Other studies have suggested that there may be an optimal time to deliver the defibrillation shock during ventricular fibrillation [31][32][33] .…”