Cardioversion is a corrective procedure where an electrical shock is delivered to the heart to convert, or change, an abnormal heart rhythm back to normal sinus rhythm. Most elective or "non-emergency" cardioversions are performed to treat atrial fibrillation (A Fib) or atrial flutter (AFL), non-life threatening abnormal rhythms in the top of the heart. Cardioversion is also used in emergency situations to correct an abnormal rhythm when it is accompanied by faintness, low blood pressure, chest pain, difficulty breathing, or loss of consciousness.
What is Cardioversion?
Each normal heartbeat starts in an area of the heart known as the sinus node, located in the upper right chamber of the heart (right atrium). The sinus node sends organized electrical signals through the heart resulting in a perfectly timed, rhythmic heartbeat. In people with atrial fibrillation however, this electrical signal is chaotic, causing the atria to fibrillate (or "quiver"). This typically results in a fast and irregular heartbeat. While some people have no symptoms, others may experience shortness of breath, lightheadedness and fatigue. Depending on your specific medical history and symptoms, your doctor may recommend a cardioversion to return your heart to normal sinus rhythm.
Types of Cardioversion
- Chemical cardioversion – Antiarrhythmic medications can be used to restore the heart's normal rhythm. Antiarrhythmic medications work by altering the flow of electricity through the heart. Depending on severity of symptoms, underlying heart disease and the specific medication to be used, the chemical conversion may be done as an outpatient, or in the hospital under monitoring.
- Electrical cardioversion– Also known as "direct-current" or DC cardioversion, a synchronized (perfectly timed) electrical shock is delivered through the chest wall to the heart through special electrodes or paddles that are applied to the skin of the chest and back. The goal of the procedure is to disrupt the abnormal electrical circuit(s) in the heart and thereby to reset the heart to normal rhythm. This split second interruption of the abnormal beat allows the heart's electrical system to regain control and restore a normal heartbeat. Electrical cardioversion is performed in a hospital setting where oxygen levels, blood pressure and heart rhythm are closely monitored.
Normal sinus rhythm can be restored more than 90 percent of the time, however the atrial fibrillation or other abnormal rhythms may recur in over time. Your doctor may prescribe medications or recommend catheter ablation to reduce the risk of atrial fibrillation recurrence.
Blood clots and Anticoagulation
Because the upper chambers of the heart are fibrillating (quivering) rather than squeezing in people with atrial fibrillation, there is a risk that blood clots may form. The process of restoring a normal rhythm could dislodge a blood clot from the heart resulting in a stroke.
To help prevent blood clots and reduce the potential for stroke, the blood is thinned with medications called anticoagulants. Anticoagulant medications include aspirin, heparin, and warfarin.
In a patient with A Fib or A flutter that has been present for more than 48 hours, the blood must be adequately thinned for at least 3-4 weeks prior to the procedure. Alternatively a transesophageal echocardiogram (TEE) can be performed to make sure there is no blood clot in the atrium. During a TEE, a special probe is placed in the esophagus which allows your doctor to directly visualize the atria. Because it takes many hours for blood clots to form, cardioversion can be safely performed without blood-thinning medication in patients who have been in an atrial arrhythmia for less than 48 hours.
Typically, anticoagulation is continued after the cardioversion for a minimum of 4 weeks, often longer.