Saturday, June 5, 2010

Biphasic Defibrillators

By Thomas Morva

A defibrillator is an instrument that carries out defibrillation on the chambers of the heart. When the device is implanted in the user, it is known as an implantable cardioverter or internal cardiac defibrillator (ICD). Traditionally, monophasic waveforms were used in these implements but research studies have shown that biphasic waveforms are better suited for such equipments.

In monophasic defibrillators, electrical pulses are sent rapidly from one electrode to the other, in a single direction. In case of biphasic defibrillation, the direction of the pulses alternates, completing one cycle in approximately 10 milliseconds. Biphasic defibrillation was originally developed and used for implantable cardioverter-defibrillators. They use a different waveform technology than the monophasic ones. It uses either a biphasic truncated exponential (BTE) waveform or a rectilinear biphasic waveform. In the first phase, the current moves from one paddle to the other as with monophasic defibrillators. During the second phase, the current flow reverses direction, thus lowering the electrical threshold for successful defibrillation.

The American Health Association has a different opinion about low-energy biphasic defibrillation. As per them, biphasic defibrillation is now a part of advanced cardiac life support guidelines. Biphasic shocks at energy levels of 200 joules or less are at least as safe and effective as monophasic shocks with traditional energies between 200 and 360 joules. Biphasic shocks of 200 joules or less are now classified as a Class II-A recommendation.

The biphasic defibrillation process varies depending on the specific biphasic waveform used. External biphasic defibrillation offers equal or better value at lower energies than traditional monophasic waveform defibrillators .It has less risk of post -shock myocardial dysfunction and skin burns. There is a significant cost and size saving which helps in the proliferation of the automated external defibrillators.

When low-energy biphasic shocks were used, the left ventricular ejection fraction and mean arterial pressure returned to baseline more quickly.
In conclusion, based on all the research studies carried out till date, biphasic cardioversion is more effective than monophasic cardioversion in patients with acute atrial fibrillation

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