Definition and Overview
Electric cardioversion is a procedure that uses electric energy to normalise abnormal or irregular cardiac rhythm. It is different from a defibrillation in that electrical cardioversion is synchronised, which means that electric current is delivered at a specific time in the cardiac cycle. Doing so prevents the delivery of shock during the refractory period, which can make the heart vulnerable to other kinds of arrhythmia, specifically ventricular fibrillation.
Who Should Undergo and Expected Results
An arrhythmia is a term used to describe an abnormal cardiac rhythm. The sinus node, which is the pacemaker of the heart, sends electrical signals that run through the atria and ventricles to produce coordinated beats, ensuring optimal delivery of blood to the lungs and the rest of the body. In a patient with an arrhythmia, there is a problem in the signalling process or in one of the components of the conduction system.
Patients with arrhythmias usually manifest with a fast heart rate or skipped beats, with symptoms of shortness of breath and weakness with some also experiencing lightheadedness and even loss of consciousness. Some may also develop blood clots in the heart; if these clots become dislodged, they can travel to certain areas of the body and may cause serious complications. For instance, if the embolus (dislodged clot) becomes lodged in the brain, it can cause a stroke.
There are different kinds of arrhythmia and the one that is most commonly managed with electric cardioversion is atrial fibrillation. Other arrhythmias that may be treated with this procedure include atrial flutter, sinus tachycardia, and some forms of ventricular tachycardia, among others.
Guidelines on advanced cardiac life support state that unstable patients, especially those who are hypotensive with a specific kind of tachycardia, should immediately undergo synchronised electric cardioversion.
Electric cardioversion usually results in successful outcomes for patients with atrial fibrillation, especially if the condition has been present for less than a year. After the procedure, the patient will continue to receive certain medications including anticoagulants to minimise the risk of stroke, and anti-arrhythmic to prevent the recurrence of the arrhythmia.
How is the Procedure Performed?
Electrical cardioversion may be performed either in an elective or emergency setting. Prior to the procedure, intravenous access is secured and precautions for complications are prepared. A transesophageal echocardiogram may also be requested before the procedure to check for the presence of a thrombus. If there is no thrombus, the patient may proceed with cardioversion.
If the patient is conscious during the procedure, he is sedated to make the cardioversion tolerable. Pain medications are also provided.
Two pads, which serve as electrodes, are lined with a conductive gel and placed either both on the chest or one on the chest and the other at the back. The pads are attached to an equipment, which serves to function both as an electrocardiograph and a defibrillator, via cables. Before the procedure, the machine is set on synchronised mode and the amount of electric current is decided on. The machine basically delivers a shock of electrical current to the heart at a specific time in the cardiac cycle (synchronised). Delivery of a direct current to the heart results in the depolarisation of the cells, in a way resetting the pacemaker of the heart. The patient may need more than one shock to restore the rhythm to normal.
After electrical cardioversion, patient monitoring is continued to make sure that sinus rhythm is attained and maintained.
Possible Risks and Complications
When performed by trained and experienced personnel, electric cardioversion is generally a safe procedure. Minor complications include burns, most of which are superficial and usually managed with anti-bacterial ointments.
The most serious complication that can occur with this procedure is the induction of an arrhythmia. Atrioventricular blocks or bradycardia may be induced in patients with acute myocardial infarction who undergo electric cardioversion. These patients may eventually require the insertion of a pacemaker. Patients are also at risk of developing ventricular fibrillation. In these cases, post-cardioversion ventricular fibrillation is treated with defibrillation.
Electric cardioversion does not always result in successful outcomes. In cases wherein the heart rhythm still does not return to normal after the procedure, an implantable cardioverter defibrillator or a pacemaker may have to be inserted. In some patients, cardioversion may initially be successful, but the arrhythmia may recur at a later time. In these cases, a repeat cardioversion may be necessary, as well as intake of anti-arrhythmic medications.
Smith G, Taylor DM, Morgans A, Cameron P. Prehospital Synchronized Electrical Cardioversion of a Poorly Perfused SVT Patient by Paramedics. Prehosp Disaster Med. 2013 Jun. 28(3):301-4. [Medline].
[Guideline] Part 5: Electrical Therapies. Automated External Defibrillators, Defibrillation, Cardioversion, and Pacing. Circulation. 2005. 112:IV-35-IV-46.