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[de- + fibrillation]

1. Termination of ventricular fibrillation (vfib) with electrical countershock(s). This is the single most important intervention a rescuer can take in patients who have suffered cardiac arrest due to vfib or pulseless ventricular tachycardia.

Traditional defibrillation uses a monophasic waveform: a single energy pulse. Monophasic electrical current travels in one direction from one electrode or paddle through the heart to the other electrode. In a successful attempt the energy converts the lethal rhythm to a rhythm with a pulse, and to be successful, this type of defibrillation must deliver high energy (200 or more joules).

The biphasic defibrillator delivers current through the heart in two directions, flowing through the heart and back again to the first electrode. Biphasic defibrillation uses lower levels of electrical current than monophasic techniques. Advantages for the patient include lower risk of skin burns, less myocardial injury and dysfunction following defibrillation, and more rapid return of ejection fraction and mean arterial pressure to baseline. In addition, the lower energy levels permit the equipment to be smaller, lighter, less demanding on batteries, and easier to maintain than monophasic models. Biphasic defibrillation usually is initiated at 120 to 150 joules, with the level increased as needed. In cardioversion, only 30 joules is typically required. Health care professionals should become familiar with the type of defibrillator in their facility so that they can safely and rapidly operate defibrillators in an emergency. Staff-development sessions should be provided by the agency to ensure competency.

2. A term formerly used to signify termination of atrial fibrillation. The contemporary terms are conversion or cardioversion.

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