CHARACTERISTICS OF MULTIPLE-SHOCK DEFIBRILLATION

Introduction: A new method for defibrillation allows two shocks to be combined to defibrillate with reduced current by adjusting their separ ation according to the cycle length of the fibrillation event, We inve stigated various aspects of this new method to better understand its c haracteristics and applicability to defibrillation. Methods and Result s: In 48 pentobarbital-anesthetized dogs, we measured the current for 50% defibrillation success using the new method with sequences of rect angular shocks, Group 1 studied the role of shock total duration and f ound that two-shock sequences followed a strength-duration curve simil ar 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 t he new method could be used with either biphasic waveforms or sequenti al shock pathways, Current reduction for the combined methods equaled the product of current reduction by each method, demonstrating that th ese methods can be effectively combined, Group 4 extended the method t o 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 energ y (P < 0.095 = NS) than a single shock. Conclusions: The new method al lows defibrillation to be distributed over several fibrillatory cycles and has an improved strength-duration relationship, Two- or three-sho ck sequences using equal shocks permit a substantial reduction of defi brillation current that can be combined with the reduction for biphasi c and sequential methods, Thus, the method may have application in low -current defibrillation devices.