The application of electricity to the heart induces depolarization of the myocardial cells in a uniform fashion. This may interrupt reentry circuits that are inducing an arrhythmia. Once depolarization of the myocardium has been achieved, the sinus node may then resume its normal pacing function. This is accomplished with the transthoracic application of a direct-current electrical shock.
The techniques of cardioversion and defibrillation are relatively straightforward and practically identical. The main differences are the indications and use of synchronization with cardioversion. The purpose of cardioversion is to deliver a precisely timed electrical current to the heart to convert an organized rhythm to a more hemodynamically stable rhythm. The purpose of defibrillation is to deliver a randomly timed high-energy electrical current to the heart to restore a normal sinus rhythm. These techniques are currently performed by emergency medical technicians, nurses, paramedics, physicians, and a variety of other healthcare workers on a daily basis. This chapter discusses the techniques of manual cardioversion and defibrillation. A discussion of Advanced Cardiac Life Support (ACLS), cardiac rhythms, chemical cardioversion, and Pediatric Advanced Life Support is beyond the scope of this work. The technique of automatic external defibrillation is not discussed.
In general, electrical cardioversion is performed either electively or emergently. In the Emergency Department, the role of electrical cardioversion is usually limited to urgent or emergent situations or when medical therapy has failed.1,2 This includes symptomatic reentry tachycardias (e.g., supraventricular tachycardia, atrial fibrillation, atrial flutter, and Wolff–Parkinson–White syndrome) and hemodynamically stable ventricular tachycardia associated with acute myocardial infarctions, altered levels of consciousness, chest pain, congestive heart failure, dizziness, dyspnea, hypotension, presyncope, pulmonary edema, shock, or syncope.
In the Emergency Department, electrical cardioversion is often preferred to chemical cardioversion for many reasons. Electrical cardioversion is simple and quick to perform. It is effective—in most cases almost immediately. It may be more successful than chemical cardioversion. The complications are usually minimal. Potential allergic reactions and toxic effects are nonexistent with electrical cardioversion.
Defibrillation is indicated when ventricular fibrillation or ventricular tachycardia has not spontaneously converted to an organized rhythm. Ventricular fibrillation and ventricular tachycardia are rarely spontaneously reversible and are not compatible with life. Defibrillation must be performed immediately if the patient is found pulseless, unconscious and apneic, or during the ACLS protocol. “Fine” ventricular fibrillation can be present and may be confused with asystole. It may be secondary to low gain amplitude or improper lead positioning. If “quick-look” paddles are being used, they may be rotated 90°. If a monitor is being used, select a different lead and/or increase the gain to determine if the cardiac rhythm is fine ventricular fibrillation or asystole. Ventricular fibrillation or ventricular tachycardia secondary to myocardial ischemia or infarct, electrolyte abnormalities, long-QT syndromes, hypothermia, or drug toxicity (e.g., digoxin, tricyclic antidepressants, antiarrhythmics, antihistamine, and macrolide antibiotic combinations) may convert to a ...