Surgical Open-Chest Ventricular Defibrillation:. Triphasic Waveforms Are Superior to Biphasic Waveforms

The effects of second and third phase duration on defibrillation efficacy of triphasic rectangle waveforms

BACKGROUND

Biphasic waveforms are superior to monophasic waveforms for the termination of ventricular fibrillation (VF). However, whether triphasic waveforms are more effective than biphasic ones is still controversial. In the present study, we investigated the effects of second and third phase duration of triphasic rectangle waveform on defibrillation efficacy in a rabbit model of VF.

METHODS

VF was electrically induced and untreated for 30s in 20 New Zealand rabbits. A defibrillatory shock was applied with one of the 7 waveforms: 6 triphasic rectangle waveforms and a biphasic rectangle waveform. The triphasic waveforms had identical first duration but with different second and third phase durations. A 5 step up-and-down protocol was utilized for determining the defibrillation threshold (DFT). After a 5min interval, the procedure was repeated. A total of 35 cardiac arrest events and defibrillations were investigated for each animal.

RESULTS

Two triphasic waveforms with identical first and second phase duration but shorter third phase duration had significantly lower DFT energy than biphasic waveform (0.57±0.18J vs. 0.80±0.28J, p=0.001; 0.60±0.18J vs. 0.80±0.28J, p=0.003). However, no statistical difference in DFT energy was observed between the two triaphsic waveforms that had identical phase duration but different voltages (0.57±0.18J vs. 0.60±0.18J, p=0.638).

CONCLUSIONS

Phase durations played a main role on defibrillation success for triphasic rectangle waveforms. The optimal triphasic rectangle waveforms that composed of identical second and first phase durations but with shorter third pulse were superior to biphasic rectangle waveform for ventricular defibrillation.

Simultaneous comparison of many triphasic defibrillation waveforms

Biphasic defibrillation waveforms are now accepted as being more effective at terminating ventricular fibrillation (VF) than monophasic waveforms. If two phases are better than one, this naturally leads to the hypothesis that additional phases improve efficacy. This study tests the hypothesis by adding one additional phase. We examined the efficacy of 18 different triphasic waveforms simultaneously.

We tested the rate of recovery, i.e., successful defibrillation, of 21 guinea pigs (820-1,050 g) using triphasic, monophasic and biphasic defibrillation waveforms. The biphasic and monophasic were control waveforms. VF was electrically induced twenty times per animal and a single defibrillation attempt was made using a test waveform VF episode. Every waveform was adjusted to the energy required to defibrillate that animal 50% of the time, using a biphasic waveform as a control. The success rate of each triphasic waveform was pair-wise compared to the biphasic and monophasic control using the adjusted McNemar statistical test.

Of the 18 triphasic waveforms tested, two were significantly poorer than the monophasic control (p<0.05). One was superior to the biphasic waveform (p<0.1), but not statistically so. We concluded that, while adding a phase to a monophasic waveform does improve efficacy, adding an additional phase to a biphasic waveform does not necessarily improve efficacy.

Quadriphasic waveforms are superior to triphasic waveforms for transthoracic defibrillation in a cardiac arrest swine model with high impedance

BACKGROUND

We have demonstrated previously that triphasic waveform shocks were superior to biphasic waveform shocks for transthoracic defibrillation. Our purpose was to compare the efficacy and safety of quadriphasic versus triphasic shocks for transthoracic defibrillation in a porcine model.

METHODS

Sixteen adult swine (19-25 kg, mean: 21.5 kg) were deeply anesthetized and intubated. To simulate impedance of the human chest, fixed electrical resistors (25 or 50 ohms) was placed in series with the defibrillator and the chest of each pig. After 30 s of electrically induced VF, each pig received transthoracic shocks, using either a truncated exponential triphasic waveform (5 ms positive pulse duration, 5 ms negative pulse duration and 5 ms positive pulse duration, total waveform duration 15 ms) or a quadriphasic waveform (5/5/5/5 ms, total waveform duration 20 ms). Each pig received transthoracic triphasic and quadriphasic shocks at three selected energy levels (50, 100 and 150 J) in random sequence. Four shocks were delivered at each energy level to construct an energy versus % success curve. Success was defined as VF termination at 5 s after shock. The total shocks were divided into three groups based on the delivered energy actually delivered to the animal: <40, 40-65 and >65 J. Delivered energy = (animal impedance/total impedance) times selected energy of the shock.

RESULTS

For high-impedance animals (86-102 ohms), quadriphasic waveform shocks achieved significantly higher percent shock success than triphasic shocks for the termination of VF at the energy levels of >65 J actually delivered (quadriphasic 72.7+/-12.2%, triphasic 38.9+/-7.7%, p<0.02). No differences in the shock success between quadriphasic and triphasic waveforms were found for other two energy levels. There were no differences in ventricular tachycardia or asystole after shocks between quadriphasic and triphasic waveforms.

CONCLUSION

In this porcine model, 20 ms (5/5/5/5) quadriphasic shocks were superior to 15 ms (5/5/5) triphasic shocks for transthoracic defibrillation in animals with impedances that simulated high impedance in humans.