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Defibrillation is the therapeutic use of electricity to depolarize the myocardium and thus allow more coordinated contractions to occur. The term defibrillation is usually applied to an attempt to terminate a nonperfusing cardiac arrest rhythm [e.g., ventricular fibrillation (Vfib) or pulseless ventricular tachycardia (Vtach)], allowing normal electrical activity to occur.

Cardioversion, by contrast, is the application of electricity to attempt to terminate a still perfusing rhythm (e.g., Vtach with a pulse, supraventricular tachycardias, including atrial arrhythmias), hopefully to allow a normal sinus rhythm to restart. By this definition, cardioversion is a less urgent procedure compared to defibrillation, although the patient may be hypotensive or hemodynamically unstable, rather than in cardiac arrest.

Indications for defibrillation include Vfib (Figure 36-1) and pulseless Vtach (Figure 36-2). Defibrillation is contraindicated for asystole, pulseless electrical activity, sinus rhythm, a conscious patient with a pulse, or where there is danger to the operator or others (e.g., from a wet patient or surroundings).

Cardioversion is indicated for a hemodynamically unstable patient with Vtach, 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.

Electrical energy can terminate an abnormal rhythm, but if inappropriately delivered, it can also induce Vfib. This can happen if the electric shock occurs during the relative refractory portion of cardiac electrical activity.1 This coincides with the middle and terminal phases of the T wave and is also referred to as the vulnerable period.

When performing defibrillation, check the patient and rhythm to ensure that a shock is truly indicated. Movement artifacts or loose leads may lead to a misinterpretation of the rhythm. When using automated external defibrillators (AEDs), it is important to stop all movement (e.g., during transport) and confirm cardiac arrest before initiating analysis mode.

Make sure that no rescuer is inadvertently in contact with the patient when a shock is delivered—thus the emphasis on “stand clear” drills during defibrillator training. 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, always make sure that the paddles are either on the defibrillator cradle or on the patient’s chest, with minimal time in transit. Always point the paddles downward and never wave the paddles around or face them toward each other, especially when paddles are charged. This is to prevent inadvertent discharges. Sparking can occur when the paddles are in close proximity to each other.

During cardioversion, there is a possibility that the patient can deteriorate or ...

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