Sawtooth first phase biphasic defibrillation waveform: a comparison with standard waveform in clinical devices

A major limitation in a conventional truncated exponential waveform is the rapid drop in current that results in short duration of high current or longer duration with a lower average current. We hypothesized that increasing the first phase average current by boosting the decaying waveform prior to phase reversal may improve defibrillation efficacy.

To better simulate a "rectangular" waveform during the first phase, a "sawtooth" defibrillation waveform was constructed using "parallel-series" switching of capacitances (each 30 microF) during the first phase. This permitted a boost in the voltage late in the first phase. This sawtooth biphasic waveform (sawtooth) was compared to two clinical waveforms: a 135-microF capacitance (control-1) and a 90-microF capacitance (control-2) waveform. Defibrillation threshold (DFT) parameters were evaluated in 13 anesthetized pig 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 stored energy for sawtooth, control-1, and control-2 was 10.5 +/- 2.8 J, 12.3 +/- 3.7 J*, and 12.2 +/- 2.8 J*, respectively (*P < or = 0.01 vs sawtooth). The average current of the first phase for sawtooth, control-1, and control-2 was 7.6 +/- 1.3 A, 4.7 +/- 0.9 A*, and 6.2 +/- 0.9 A*, respectively (*P = 0.0001 vs sawtooth).

A sawtooth biphasic waveform utilizing a "parallel-series" switching system of smaller capacitors can improve defibrillation efficacy. A higher average current in the first phase generated by such a waveform may contribute to more efficient defibrillation by facilitating myocyte capture.