What Is a Biphasic Defibrillator?

Defibrillators are lifesaving medical devices used by emergency services personnel and physicians. They are common in emergency rooms, ambulances and doctors offices. They are used to re-establish a heart rhythm that falls within the norm when life threatening arrhythmias or heart attacks occur by delivering an electric shock to the heart. Biphasic refers to the manner in which the defibrillator delivers the current.

History

• According to Case Western University's Dittrick Medical History Center, the first successful human defibrillation was performed in 1947 by Dr. Claude Beck. Defibrillation was initially performed directly on the heart only during surgery. The early defibrillation machines all employed alternating current until the transition to direct current. The direct current defibrillators (developed in the late 1950s) employed a Lown waveform, meaning the machines delivered a uniphasic (one way or monophasic) current from one paddle to the other. This was standard for nearly 30 years until the introduction of the biphasic waveform.

Uniphasic defibrillation

• Despite being the standard for several decades, uniphasic defibrillation was not an ideal solution. The uniphasic waveform called for a single burst of current between 200 and 360 joules to be passed through the torso for a fraction of a second. Although this method could restore a normal rhythm, it could also take several shocks to restore the rhythm. The repetition of shocks and higher energy shocks could cause skin burns and inflict damage to the heart muscle.

Biphasic Defibrillation

• In biphasic defibrillation, current travels in one direction from paddle to paddle and then in the other direction. The energy levels delivered vary over the course of the delivery, which is slightly longer than in uniphasic defibrillators, but still less than a second. The advantages of the biphasic procedure are that it requires less energy to restore a normal heart rhythm, even in high impedance (resistance to current) individuals. There is some evidence that this lowers the risks of burns and cellular damage to the heart.

ICD's

• An application of the biphasic defibrillation method is in implantable cardioverter-defibrillators (ICD). ICD's were developed as a treatment for those at high risk for deadly cardiac events. They are surgically implanted in the chest and monitor the heart for ventricular fibrillation and tachychardia. In the event of such fibrillation or tachychardia, the ICD will deliver a biphasic current, similar to an external defibrillator, in an attempt to stop the abnormal rhythm.

External Defibrillators

• With the growing body of evidence that biphasic defibrillators deliver higher levels of success at restoring normal heart rhythms, their use is becoming more widespread. The biphasic waveform has been the standard in Automatic External Defibrillators (AED) for some time. These are types found in emergency service vehicles and also in some corporate and public settings. Increasingly, the biphasic waveform model has been in Manual External Defibrillators which are mostly seen in medical settings like hospitals.