What is synchronized electrical cardioversion?

Updated: Nov 28, 2018
  • Author: Sean C Beinart, MD, MSc, FACC, FHRS; Chief Editor: Jose M Dizon, MD  more...
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Delivery of direct current (DC) shocks to the heart has long been used successfully to convert abnormal heart rhythms back to normal sinus rhythm. In 1775, Abildgaard reported using electricity to both induce and revive a hen from lifelessness. [1] Beck was the first physician to use DC defibrillation on a human to treat ventricular fibrillation (VF, vfib) in a 14-year-old during cardiac surgery in 1947. Fifteen years later, Lown applied synchronized DC shocks to the heart to convert atrial fibrillation (AF, afib) and ventricular tachycardia (VT, vtach) to normal sinus rhythm. [2]

Cardioversion is defined as a “synchronized DC discharge, and … does not apply to ventricular defibrillation or to the pharmacologic reversion of arrhythmias.” [3, 4]  It is typically used to terminate life-threatening or unstable tachycardic arrhythmia (unstable ventricular and supraventricular rhythms) in patients who still have a pulse but who are hemodynamically unstable. [5] The DC electrical discharge is synchronized with the R or S wave of the QRS complex. Synchronization in the early part of the QRS complex avoids energy delivery near the apex of the T wave in the surface electrocardiogram (ECG), which coincides with a vulnerable period for induction of ventricular fibrillation. The peak of the T wave represents the terminal portion of the refractory state when adjacent heart fibers are in differing states of repolarization.

Defibrillation refers to an unsynchronized discharge of energy and is only recommended for ventricular fibrillation. It is used in patients who are in cardiac arrest. [5]

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