Defibrillation is the therapeutic use of electricity to depolarize the myocardium so coordinated contractions can occur. The term defibrillation is usually applied to an attempt to terminate a nonperfusing rhythm (e.g., ventricular fibrillation or pulseless ventricular tachycardia).
Cardioversion is the application of electricity to terminate a still perfusing rhythm (e.g., ventricular tachycardia with a pulse, supraventricular tachycardias including atrial arrhythmias) to allow a normal sinus rhythm to restart. By this definition, cardioversion is a less urgent procedure compared to defibrillation, although the patient requiring cardioversion may be hypotensive or hemodynamically unstable, rather than in cardiac arrest.
Indications for defibrillation include ventricular fibrillation (VF) (Figure 13A-1) and pulseless ventricular tachycardia (VT) (Figure 13A-2). Defibrillation is not indicated for asystole and pulseless electrical activity and is contraindicated for sinus rhythm, a conscious patient with a pulse, or when there is danger to the operator or others (e.g., from a wet patient or wet surroundings).
Cardioversion is indicated for a hemodynamically unstable patient with VT, supraventricular tachycardia, atrial flutter, or atrial fibrillation. It is also possibly indicated after failed pharmacologic therapy for the previously mentioned arrhythmias, especially if the patient becomes hemodynamically unstable. Cardioversion should be synchronized, which means the electric current will be timed with the patient's intrinsic QRS complexes, to minimize the risk of inducing VF.
Electrical energy can terminate an abnormal rhythm, but if inappropriately delivered, it can also induce VF. This can happen if the electric shock is delivered during the relative refractory portion of the cardiac electrical activity.1
When preparing for defibrillation, check the patient and rhythm to ensure that a shock is truly indicated. Movement artifacts or loose leads may look like VF. New defibrillator technology is available that can filter compression or movement artifacts to "see through" the underlying rhythm. However, when using automated external defibrillators (AEDs), all manufacturers currently still recommend stopping all compressions and patient movement (e.g., during transport) before initiating analysis mode.
Make sure that no rescuer is inadvertently in contact with the patient when a shock is delivered. Neither single nor double gloves provide the rescuer with complete safety from current,2 so we still recommend "stand clear" drills during defibrillator training, "stand clear" practice during actual defibrillation, and minimizing rather than eliminating the pause in compressions for defibrillation. If the patient is on a wet or conducting surface, move the patient to a safe area and dry the body before delivering the shock. When using manual defibrillation paddles, make sure that the paddles are either on the defibrillator cradle or on the patient's chest, with minimal time in transit from one position to the other. To ...