Although the very first commercial defibrillator used a biphasic waveform for the treatment of ventricular defibrillation, commercial external defibrillators in the western world adopted monophasic waveforms at least 30 years ago, and these have been used almost exclusively until recently. Thus, much of our clinical experience comes from the use of monophasic waveforms.
Conventional defibrillators produce monophasic shocks where the current flows in one direction.
Biphasic waveform technology has developed from electrophysiological work on the design of implantable defibrillators. External defibrillators that utilise biphasic waveforms are now available and licensed for clinical use. These devices have a number of advantages. Low energy biphasic shocks are as effective as higher energy monophasic shocks. This may result in less damage to the myocardium and a reduced frequency of post-shock contractility and arrhythmic problems.