Is the second phase of a biphasic defibrillation waveform the defibrillating phase?

Area of Science:

• Cardiovascular Research
• Biomedical Engineering
• Electrophysiology

Background:

• Biphasic waveforms are used in defibrillation, but the mechanism for their efficacy compared to monophasic waveforms is not fully understood.
• A hypothesis suggests the first phase of a biphasic waveform conditions the heart for defibrillation by the second phase.

Purpose of the Study:

• To investigate whether the second phase of a biphasic waveform is the primary determinant of defibrillation efficacy.
• To compare the defibrillation effectiveness of various monophasic and biphasic waveform shapes and durations.

Main Methods:

• 18 open-chest pigs underwent defibrillation threshold testing with monophasic and biphasic waveforms of varying shapes (ascending ramp, square, descending ramp) and durations (16ms and 6ms).
• Defibrillation thresholds were ranked based on mean current and energy required for successful defibrillation.

Main Results:

• For 16/16-ms biphasic waveforms, efficacy correlated with the second phase's waveshape, supporting the hypothesis.
• However, for clinically relevant 6/6-ms biphasic waveforms, efficacy was not solely dependent on the second phase's waveshape.
• 16/16-ms biphasic waveforms were less effective than 16-ms monophasic waveforms, while 6/6-ms biphasic waveforms were more effective than 6-ms monophasic waveforms.

Conclusions:

• The second phase of biphasic waveforms plays a significant role in defibrillation efficacy for longer durations.
• The hypothesis that the second phase is the sole defibrillating phase is not supported for shorter, clinically relevant biphasic waveforms.
• Waveform duration and shape interact complexly to determine defibrillation effectiveness.