Characteristics of Multiple‐Shock Defibrillation

Multiple‐Shock Defibrillation. Introduction : A new method for defibrillation allows two shocks to be combined to defibrillate with reduced current by adjusting their separation according to the cycle length of the fibrillation event. We investigated various aspects of this new method to better understand its characteristics and applicability to defibrillation. Methods and Results : In 48 pentobarbital‐anesthetized dogs, we measured the current for 50% defibrillation success using the new method with sequences of rectangular shocks. Group 1 studied the role of shock total duration and found that two‐shock sequences followed a strength‐duration curve similar to, but below, that for single shocks. Group 2 studied the role of amplitude and duration balance between shocks and found that two‐shock sequences with equal shocks performed best. Group 3 studied whether the new method could be used with either biphasic waveforms or sequential shock pathways. Current reduction for the combined methods equaled the product of current reduction by each method, demonstrating that these methods can be effectively combined. Group 4 extended the method to include three‐shock and four‐shock sequences and found that a fourth shock did not further improve defibrillation. The optimum three‐shock sequence required 33% lower current (P < 0.002) and 34% greater energy (P < 0.095 = NS) than a single shock. Conclusions : The new method allows defibrillation to be distributed over several fibrillatory cycles and has an improved strength‐duration relationship. Two‐ or three‐shock sequences using equal shocks permit a substantial reduction of defibrillation current that can be combined with the reduction for biphasic and sequential methods. Thus, the method may have application in low‐current defibrillation devices.