Background: The optimal waveform for internal atrial defibrillation (IAD) in humans is unknown. This study tested the effect of waveform duration and phase duration on the efficacy of biphasic waveforms for IAD.
Methods and results: Electrodes were positioned in the right atrial appendage and coronary sinus in 13 patients. In part 1, the atrial defibrillation thresholds (ADFTs) for 5 monophasic waveforms (2, 4, 6, 10, and 20 ms) and 5 symmetrical biphasic waveforms (1/1, 2/2, 3/3, 5/5, and 10/10 ms) were compared in 6 patients. In part 2, the ADFTs for two asymmetrical biphasic waveforms (7.5/2.5 and 2.5/7.5 ms) were compared with those for a symmetrical biphasic waveform (5/5 ms) and a monophasic waveform (10 ms) in 7 patients. In part 1, biphasics with total durations of 4 to 20 ms had significantly lower ADFTs than monophasic waveforms of the same total duration. For a total duration of 2 ms, there was no significant difference in ADFTs between the biphasic and the monophasic waveforms. There was no difference between symmetrical biphasic waveforms of 4 to 20 ms. In part 2, the 7.5/2.5 ms asymmetrical biphasic had significantly lower ADFTs than the three other waveforms tested. Both the 7.5/2.5 ms asymmetrical and the 5/5 ms symmetrical biphasic waveform had significantly lower ADFTs than the 2.5/7.5 ms asymmetrical biphasic and the 10 ms monophasic waveforms.
Conclusions: For IAD in humans, biphasic waveforms were more efficacious than monophasic waveforms. This improved efficacy is related to the total duration of the biphasic waveform and each individual phase duration of the biphasic waveform.