714-4 What is the Optimal Pulse Duration for Defibrillation? Insights from a Porcine Animal Model

We investigated the effect of modifying total biphasic shock duration (SDur) in 7 anesthesized pigs while keeping pulse 1/pulse 2 duration ratio constant (60%/40%; pulse 1=first part, pulse 2=second part of biphasic shock). Different SDurs of 10.8ms (pulse 1: 6 ms(Interpulse delay: 0.8ms/pulse 2: 4ms), 7.1ms (3.8/0.8/2.5ms) and 3.6 ms (1,7/0.8/1.1 ms) generated by an external capacitor (Medtronic 2349®) were tested in a randomized protocol against a SDur of 14.3 ms (8.1/0.8/5.4 ms) used by a currently available defibrillator system (CPI ECD®). 5 shocks were delivered at each energy level between 5 and 40 Joules (J) in 5 J steps through a transvenous/subcutaneous lead system (CPI Endotak C®/SubQ®). Voltage and current were recorded on an oscilloscope and impedance calculated as voltage divided by current.ResultsCumulative success at all energy levels was higher with 7.1 ms SDur (70%) than with 10.8 ms (56%, p<0.01). 14.3 ms (37%, p<0.001) and 3.6 ms (48%, p<0.001). SOur of 10.8 ms were significantly more successful than 14.3 ms (p<0.001; x2-test). Shocks of 14.3 ms had a significantly lower impedance at the trailing edge of pulse 2 compared to shorter SDur (31.6±9.3rl vs. 37±7.9rl/l0.8 ms, 36.2±7Ω/7.1 ms and 35±9Ω/3.6 ms).Conclusions1) In analogy to chronaxy in electrostimulation there is an optirnal SDur for defibrillation. 2) In this animal model the optimal SDur for biphasic shocks is considerably shorter than the one used with currently available defibrillator systems. 3) This may be due to a significantly lower impedance at the trailing edge of pulse 2 for longer SDur possibly leading to refibrillation. 4) Shorter SDurs may allow the use of smaller capacitors in future clinical devices