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. Depolarization of the myocardium allows the sinus node to resume its normal pacing function. This is accomplished with the transthoracic application of a direct-current electrical shock.
A large amount of literature exists on the application of electricity for medical applications and dates back to the 17th century. Peter Abildgaard shocked hens in 1775. He found the application of electricity to the body and head renders the animal lifeless and electrical shocks to the chest revived the heart. Claude S. Beck made the first defibrillator that used AC current from a wall socket (Figure 40-1). It was devised for exposed hearts and used in the Operating Room. Naum L. Gurvich developed the world’s first commercially available transthoracic DC defibrillator in the USSR in 1952 (Figure 40-2).
Beck’s defibrillator. (Used with permission of Dittrick Medical History Center.)
Gurvich’s defibrillator. (Used with permission from Dittrick Medical History Center.)
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 health care 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 (Chapter 38), automatic external defibrillation (Chapter 39), and Pediatric Advanced Life Support is beyond the scope of this chapter.
Electrical cardioversion is performed either electively or emergently. The Emergency Department 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 (i.e., supraventricular tachycardia, atrial fibrillation, atrial flutter, and Wolf-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.
Electrical cardioversion is often preferred in the Emergency Department to chemical cardioversion for many reasons. Electrical cardioversion is simple and quick to perform. It is immediately effective in most cases. It may be more successful than chemical cardioversion. The complications are usually minimal. Potential ...