Electrical cardioversion is the delivery of a precisely regulated electrical shock to terminate a tachyarrhythmia, and it encompasses both synchronized cardioversion and defibrillation; the key distinction is timing relative to the cardiac cycle, since a shock delivered asynchronously on the T wave during ventricular tachycardia can precipitate ventricular fibrillation, whereas a synchronized shock (timed to the QRS complex) avoids this risk.
Synchronized cardioversion is used for organized tachyarrhythmias such as atrial fibrillation, atrial flutter, paroxysmal supraventricular tachycardia, and hemodynamically compromising ventricular tachycardia, while defibrillation (unsynchronized shock) is reserved for ventricular fibrillation, where urgent reversion to sinus rhythm is required. The rationale for electrical therapy over drugs is that, under monitored conditions, a controlled “dose” of electricity can immediately and safely restore sinus rhythm, obviating slow drug titration and rendering the supraventricular-versus-ventricular distinction less critical. Performance involves sedation (e.g., intravenous midazolam, propofol, or etomidate), routine blood pressure and oximetry monitoring, availability of atropine, isoproterenol, or transcutaneous pacing for post-shock bradycardia, and use of biphasic defibrillators, which are standard due to superior efficacy over monophasic devices.
Electrode position (anterior-posterior vs. antero-lateral) does not affect success, but active compression of the pads lowers defibrillation thresholds and improves success, and maximum fixed-energy shocks outperform low-escalating energy protocols. Note that while cardioversion restores sinus rhythm in up to 95% of patients, long-term maintenance (particularly in persistent AF) remains the greater challenge.