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Threshold reduction with biphasic defibrillator waveforms. Role of charge balance
1Department of Physiology and Biophysics, Georgetown University, Washington, DC, USA.
Journal of Electrocardiology
|January 1, 1995
Summary
Biphasic waveforms improve defibrillation by prolonging the heart's refractory period, unlike monophasic waveforms which can shorten action potential duration (APD90). This study confirms biphasic waveforms maintain longer APD90 for better defibrillation efficacy.
Area of Science:
- Cardiac Electrophysiology
- Biomedical Engineering
- Computational Biology
Background:
- The precise mechanism behind the superior defibrillation efficacy of biphasic waveforms at low intensities is not fully understood.
- Previous research indicates biphasic waveforms may prolong the ventricular refractory period, aiding fibrillation cessation.
- Monophasic waveforms, particularly hyperpolarizing ones during the refractory period, can shorten action potential duration (APD90), potentially hindering defibrillation.
Purpose of the Study:
- To test the hypothesis that balanced-charge biphasic waveforms maintain a longer mean action potential duration (APD) compared to monophasic waveforms.
- To investigate if biphasic waveforms prevent APD90 shortening in hyperpolarized regions and prolong it in depolarized regions.
- To elucidate the role of waveform characteristics in cardiac defibrillation success.
Main Methods:
- Utilized a computer model of the ventricular action potential to simulate transmembrane potential changes.
- Examined the effects of hyperpolarizing and depolarizing monophasic and balanced-charge symmetrical biphasic waveforms.
- Simulated shock intensities within the low-intensity 'window' (1.5-3 times diastolic threshold) where biphasic waveforms show higher efficacy.
Main Results:
- Biphasic waveforms (S2) produced significantly longer responses under both hyperpolarizing and depolarizing conditions compared to monophasic waveforms.
- A hyperpolarizing/depolarizing biphasic S2 resulted in a prolonged response with a distinct plateau.
- Following a depolarizing/hyperpolarizing biphasic S2, APD90 did not shorten, unlike with hyperpolarizing monophasic S2; repolarization was maintained with slight S1 APD90 prolongation.
Conclusions:
- Biphasic waveforms enhance the prolonged refractory periods crucial for effective defibrillation throughout the heart.
- This effect is observed even in cardiac regions experiencing both anodal and cathodal stimulation.
- The findings support the use of biphasic waveforms for improved defibrillation outcomes by optimizing cardiac electrophysiological responses.