SAWTOOTH FIRST-PHASE BIPHASIC DEFIBRILLATION WAVE-FORM - A COMPARISONWITH STANDARD WAVE-FORM IN CLINICAL DEVICES

Introduction: A major limitation in a conventional truncated exponenti al waveform is the rapid drop in current that results in short duratio n of high current or longer duration with a lower average current. We hypothesized that increasing the first phase average current by boosti ng the decaying waveform prior to phase reversal may improve defibrill ation efficacy. Methods and Results: To better,simulate a ''rectangula r'' waveform during the first phase, a ''sawtooth'' defibrillation wav eform was constructed using ''parallel-series'' switching of capacitan ces (each 30 mu F) during the first phase, This permitted a boost in t he voltage late in the first phase. This sawtooth biphasic waveform (s awtooth) was compared to two clinical waveforms: a 135-mu F capacitanc e (control-1) and a 90-mu F capacitance (control-2) waveform. Defibril lation threshold (DFT) parameters were evaluated in 13 anesthetized pi g models using a system consisting of a transvenous right ventricular apex lead (anode) and a left pectoral ''hot can'' electrode (cathode) system. DFT was determined by a ''down-up down-up'' protocol. The stor ed energy for sawtooth, control-1, and control-2 was 10.5 +/- 2.8 J, 1 2.3 +/- 3.7 J, and 12.2 +/- 2.8 J*, respectively (*P less than or equ al to 0.01 vs sawtooth). The average current of the first phase for sa wtooth, control-1, and control-2 was 7.6 +/- 1.3 A, 4.7 +/- 0.9 A, an d 6.2 +/- 0.9 A, respectively (*P = 0.0001 vs sawtooth). Conclusion: A sawtooth biphasic waveform utilizing a ''parallel-series'' switching system of smaller capacitors can improve defibrillation efficacy. A h igher average current in the first phase generated by such a waveform may contribute to more efficient defibrillation by facilitating myocyt e capture.