Defibrillation is the therapeutic use of electricity in cardiac arrest to depolarize the entire myocardium to eliminate ventricular fibrillation or nonperfusing ventricular tachycardia so that coordinated contractions can resume. It should be performed in close coordination with CPR of the cardiac arrest patient.
Electrical cardioversion is the application of a synchronized electrical impulse to convert a still-perfusing tachydysrhythmia back to a normal sinus rhythm. Cardioversion may also be performed pharmacologically or nonpharmacologically for the stable patient.
The indications for defibrillation include ventricular fibrillation (Figure 23-1) and pulseless ventricular tachycardia (Figure 23-2). Defibrillation is not “jumpstarting the heart” and is thus not indicated for asystole or pulseless electrical activity. It is contraindicated for sinus rhythm, conscious patients with a pulse, or when there is danger to the operator or others (e.g., from a wet patient or wet surroundings).
Electrical cardioversion is indicated for patients with ventricular tachycardia, supraventricular tachycardia, atrial flutter, or atrial fibrillation, who are hemodynamically unstable as a consequence of the rhythm. It may also be considered after unsuccessful pharmacologic therapy for the previously mentioned arrhythmias, even if the patient remains hemodynamically stable. Electrical cardioversion should be synchronized, which means the electric impulse will be timed with the patient’s intrinsic QRS complexes, to minimize the risk of inducing ventricular fibrillation.
The energy used for defibrillation or electrical cardioversion is delivered as a wave and may be monophasic or biphasic. Monophasic waveforms are found in older defibrillators and deliver the energy in a single direction, while biphasic waveforms deliver the energy forward and back in two phases within the same amount of time. The amount of energy required for successful defibrillation is typically lower with biphasic waveforms. Most current defibrillators employ biphasic waveforms, with some manufacturers using their own proprietary waveforms.
Manual defibrillators require a manual analysis of the patient’s cardiac rhythm, as well as manual delivery of the shock through paddles or self-adhesive pads (see below) by the operator.
Automated external defibrillators may be fully or semi-automated. Fully automated external defibrillators will analyze the rhythm automatically, and if indicated, charge and deliver the shock, whereas semi-automated external defibrillators will require an operator to manually deliver the shock after analysis and charging.
Manual shocks may be delivered using paddles or self-adhesive defibrillator pads. Manual paddles are docked in cradles on the defibrillator and need to be removed and applied onto the patient’s chest, with minimal time in transit from one position to the other. To prevent inadvertent discharges, always point the paddles downward (Figure 23-3A...