Cardioversion is a medical procedure by which an abnormally fast heart rate (tachycardia) or other cardiac arrhythmia is converted to a normal rhythm using electricity or drugs.

[2] To perform synchronized electrical cardioversion, two electrode pads are used (or, alternatively, the traditional hand-held "paddles"), each comprising a metallic plate which is faced with a saline based conductive gel.

A synchronizing function (either manually operated or automatic) allows the cardioverter to deliver a reversion shock, by way of the pads, of a selected amount of electric current over a predefined number of milliseconds at the optimal moment in the cardiac cycle which corresponds to the R wave of the QRS complex on the ECG.

[3] Pharmacological cardioversion is an especially good option in patients with atrial fibrillation of recent onset.

Class I agents are sodium (Na) channel blockers (which slow conduction by blocking the Na+ channel) and are divided into 3 subclasses a, b and c. Class Ia slows phase 0 depolarization in the ventricles and increases the absolute refractory period.

Class Ic greatly slow phase 0 depolarization in the ventricles (however unlike 1a have no effect on the refractory period).

[4] Class II agents are beta blockers which inhibit SA and AV node depolarization and slow heart rate.

Ibutilide is another Class III agent but has a different mechanism of action (acts to promote influx of sodium through slow-sodium channels).

In addition to cardiology, anesthesiology is also usually involved to ensure comfort of the patient for the duration of the shock therapy.

[5] Once this is complete, the medical team will adhere the pads to the patient using a rolling motion to ensure the absence of air pockets.

The anesthesiology team will then administer a general anesthetic (e.g., Propofol) in order to ensure patient comfort and amnesia during the procedure.

Opioid analgesics (e.g., Fentanyl) may be combined with Propofol, although anesthesiology must weight the benefits against adverse effects including apnea.

The pads are connected to a machine that can interpret the patient's cardiac rate and rhythm and deliver a shock at the appropriate time.

If sinus rhythm is restored, the pads may be disconnected, and any other medical equipment is removed from the patients (e.g., bite blocks, restraints, etc.).

However, if the arrhythmia is persistent, the machine may be re-charged to a higher energy level, and the cardioversion attempt may be repeated.

It is recommended to wait 60 seconds between subsequent cardioversion attempts, but this amount of time may be adjusted based on the patient and/or provider.