There are two types of defibrillators: monophasic and the newer biphasic.
Monophasic defibrillators deliver a single current of electricity that travels in one direction between the two pads or paddles on the patient's chest. To be effective, a large amount of electrical current is required for monophasic defibrillation.
Biphasic defibrillators have recently been introduced into hospitals. Pad or paddle placement is the same as with the monophasic defibrillator. The difference is that during biphasic defibrillation, the electrical current discharged from the pads or paddles travels in a positive direction for a specified duration and then reverses and flows in a negative direction for the remaining time of the electrical discharge.
The biphasic defibrillator delivers two currents of electricity and lowers the defibrillation threshold of the heart muscle, making it possible to successfully defibrillate VF with smaller amounts of energy.
The biphasic defibrillator can adjust for differences in impedance or resistance of the current through the chest. This reduces the number of shocks needed to terminate VF.
Because the biphasic defibrillator requires lower energy levels and fewer shocks, damage to the myocardial muscle is reduced. Biphasic defibrillators used at the clinically appropriate energy level may be used for defibrillation and, in the synchronized mode, for synchronized cardioversion.