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Basic principles and technique of electrical cardioversion and defibrillation

Bradley P Knight, MD, FACC
Section Editor
Richard L Page, MD
Deputy Editor
Brian C Downey, MD, FACC


Electrical cardioversion and defibrillation have become routine procedures in the management of patients with cardiac arrhythmias. Cardioversion is the delivery of energy that is synchronized to the QRS complex, while defibrillation is the nonsynchronized delivery of a shock randomly during the cardiac cycle. In 1956, alternating current (AC) for transthoracic defibrillation was first used to treat ventricular fibrillation in humans [1]. Following this breakthrough, in 1962 direct current (DC) defibrillators were introduced into clinical practice [2]. Subsequent studies in the early 1960s demonstrated that electrical countershock or cardioversion across the closed chest could abolish other cardiac arrhythmias in addition to ventricular fibrillation [3-5].

This topic will review the basic principles and technique of electrical cardioversion and defibrillation. The clinical indications for these procedures, procedural sedation, potential side effects, and the use of the automated external defibrillator (AED) are discussed separately. (See "Cardioversion for specific arrhythmias" and "Procedural sedation in adults outside the operating room" and "Procedural sedation in children outside of the operating room" and "Automated external defibrillators".)


Most defibrillators are energy-based, meaning that the devices charge a capacitor to a selected voltage and then deliver a prespecified amount of energy in joules. The amount of energy that arrives at the myocardium is dependent upon the selected voltage and the transthoracic impedance (which varies by patient).

Two other types of defibrillators are used less frequently in clinical practice:

Impedance-based defibrillators allow selection of transthoracic current based upon the transthoracic impedance; the latter is assessed initially with a test pulse with the capacitor subsequently charged to the appropriate voltage [6].

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Literature review current through: Nov 2017. | This topic last updated: Aug 24, 2017.
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