What are the basic principles in 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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Transient delivery of an electrical current causes a momentary depolarization of most cardiac cells, thereby allowing the sinus node to resume normal pacemaker activity. In the presence of a reentrant-induced arrhythmia, such as paroxysmal supraventricular tachycardia (PSVT) and ventricular tachycardia (VT), electrical cardioversion interrupts the self-perpetuating circuit and restores a sinus rhythm. Electrical cardioversion is much less effective in treating arrhythmia caused by increased automaticity (eg, digitalis-induced tachycardia, catecholamine-induced arrhythmia) because the mechanism of the arrhythmia remains after the arrhythmia is terminated and therefore is likely to recur. [6]

At present, two types of defibrillators are in use for external cardioversion and defibrillation: a monophasic sinusoidal waveform (positive sine wave) and a biphasic truncated waveform. In 1997, a low-energy, impedance-compensating biphasic waveform was evaluated for atrial and ventricular arrhythmia management. This defibrillator automatically adjusted to the patient's transthoracic impedance, which is a feature that the monophasic models lack. Currently, there are several biphasic devices with similar efficacy available on the market.

The more recent use of biphasic cardioversion has shown that less energy is required to convert an arrhythmia to a normal sinus rhythm than with monophasic cardioversion. Consequently, use of biphasic energy results in fewer delivered shocks to the patient and less cumulative energy delivered. Potential benefits include fewer burn wounds, less tissue damage, and reduced damage to the heart muscle than is found with higher voltage shocks.

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