Electrical Cardioversion

How to Cite This Chapter: Al Duhailib Z, Trusz-Gluza M, Jankowski M. Electrical Cardioversion. McMaster Textbook of Internal Medicine. Kraków: Medycyna Praktyczna. https://empendium.com/mcmtextbook/chapter/B31.IV.24.63.?utm_source=nieznany&utm_medium=referral&utm_campaign=social-chapter-link Accessed May 30, 2024.
Last Updated: March 21, 2020
Last Reviewed: June 18, 2021
Chapter Information

Electrical cardioversion involves synchronizing the electrical shock with the electrocardiographic R wave.


1. Emergency cardioversion: Supraventricular and ventricular tachyarrhythmia causing hemodynamic abnormalities with pulse (ventricular tachycardia [VT] with pulse, including ventricular flutter: see Defibrillation).

2. Elective cardioversion: Tachyarrhythmia (primarily atrial fibrillation [AF] or atrial flutter [AFL]) causing no hemodynamic abnormalities and refractory to pharmacologic treatment, or when pharmacologic treatment is not feasible.


Ventricular fibrillation (VF) (due to an inappropriate technique of cardioversion resulting in the R-on-T phenomenon), asystole, skin burns at electrode placement sites, and arterial embolism (atrial thrombus, particularly in patients in whom no anticoagulant treatment was used prior to the procedure despite existing indications [see below]).

The R-on-T phenomenon happens during the relative refractory period, which is when the heart is irritable and could respond to a strong stimulus, leading to malignant ventricular arrhythmia. Caution should be practiced in case of digitalis toxicity, as the heart is sensitized to electrical activity. A lower starting energy is suggested to avoid degeneration of VT to VF due to the potential R-on-T phenomenon.

Patient PreparationTop

Obtain informed consent (if possible) and use short-term procedural sedation (see Procedural Sedation and Analgesia). In the case of elective cardioversion, the patient should remain fasting on the day of the procedure. Correct electrolyte disturbances when appropriate. There is no need to discontinue digitalis before the procedure unless digitalis poisoning is suspected. Anticoagulation is indicated for ≥4 weeks before the procedure in patients with AFL or AF lasting >48 hours. If urgent cardioversion is needed, transesophageal echocardiography (TEE) may be done prior to the procedure to document the absence of clots in the left atrial appendage.


The same as in manual defibrillation (see Defibrillation) and short-term general anesthesia (see Procedural Sedation and Analgesia).


1. Apply the adhesive pads using an anterior-lateral approach as well as the electrocardiography (ECG) leads and other monitors (typically pulse oximetry and noninvasive blood pressure monitoring).

2. As in manual defibrillation, but after turning the defibrillator on and obtaining an ECG recording switch the synchronization option on. Synchronization markers should be visible on the cardiac monitor, over the peaks of each R wave or immediately after them. Select the ECG lead where markers appear at the appropriate position with every R wave.

3. Select your initial shock setting (see below). Press “charge” on the ECG to prepare the machine for cardioversion. Most machines produce a sustained ringing tone to indicate they are ready. Press the “shock” or “discharge” button once everyone is clear (there is no physical contact between the personnel and the patient/bed). Wait for the defibrillator to deliver the shock (unlike in defibrillation, this may not occur immediately).

4. If tachyarrhythmia persists, before the next shock make sure that the synchronization option is still on (most modern defibrillators automatically switch to defibrillation mode). The energy settings for subsequent shocks recommended for stopping AF or unstable VT are 100 J, 200 J, 300 J, and 360 J; lower initial settings of 50 J and even 25 J are optional in patients with supraventricular tachycardia, AFL, stable ventricular tachycardia, or digitalis toxicity. Starting energy is usually slightly higher when using monophasic devices as opposed to biphasic ones.

5. Monitor the heart rate (with a cardiac monitor) and hemoglobin oxygen saturation in arterial blood (SaO2) (with pulse oximetry) throughout the procedure and until the patient awakes from general anesthesia. Airway and breathing should be monitored until the patient makes complete recovery, and support must be provided as needed.

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