Cardioversion is a corrective procedure where an electrical shock is delivered to the heart to convert, or change, an abnormal heart rhythm back to a normal heart rhythm. Most elective or "non-emergency" cardioversions are performed to treat atrial fibrillation (AFib) or atrial flutter (AFL), non-life threatening abnormal heart rhythms. Cardioversion is 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 atria). The sinus node sends organized electrical signals through the heart resulting in a perfectly timed, rhythmic heartbeat. In people with AFib, 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 a normal rhythm.

 Types of Cardioversion

• Chemical cardioversion – Antiarrhythmia medications are used to restore the heart's normal rhythm. Antiarrhythmia medications work by altering the heart's electrical impulses to reduce the frequency of abnormal heart rhythms and to help restore a normal rhythm. Depending on symptoms, underlying heart disease and the specific medication to be used, the chemical conversion may be done on an outpatient basis, or in the hospital where the heart rhythm can be monitored.

• 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 to restore a normal heart beat. The shock causes all the heart cells to contract at the same time, interrupting and stopping the abnormal electrical rhythm (typically fibrillation of the atria) without damaging the heart. 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  breathing, blood pressure, and heart rhythm can be closely monitored. Special pads are placed on the chest and back (or alternatively, both pads can be placed on the front of the chest). The pads are connected to an external defibrillator by a cable. The defibrillator allows the medical team to 1) continuously monitor the heart’s rhythm, and 2) to deliver the electrical shock to restore the heart's rhythm back to normal.

A normal heart rhythm can be restored more than 90 percent of the time, although abnormal rhythms may recur in about half the patients within one year. The success of electrical cardioversion often depends on the duration of atrial fibrillation and the underlying cause (heart disease).

Blod clots and Anticoagulation

Because the upper chambers of the heart are fibrillating (quivering) and do not squeeze uniformly in people with atrial fibrillation, there is a potential risk that blood clots may form. The process of restoring a normal rhythm could potentially dislodge a blood clot from the heart resulting in a heart attack or a stroke.

To help prevent blood clots and reduce the potential for stroke, the blood is thinned prior to cardioversion with a process called anticoagulation. Anticoagulant medications include aspirin, heparin, or warfarin (Coumadin®).

• Heparin is a blood thinner that can be given as an intravenous solution or as a shot. It acts more quickly and its effects are reversed more rapidly than Coumadin®. Frequently, patients are placed on heparin until Coumadin® becomes effective, as this may take several days.

• Warfarin is a pill taken daily and dosed according to the results of regularly scheduled blood tests. This test, referred to as the International Normalized Ratio (INR), monitors the "thinness" or "thickness" of the blood and should be in the 2.0-3.0 range (a normal INR in someone who is not on warfarin is typically around 1.0). If the INR is too low, there may be at an increased risk of forming a blood clot. If the INR is too high, there may be at an increased risk for bleeding.

The appropriate anticoagulation medication is determined based on the risk of blood clot formation. In a patient with AFib or AFL that has been present for a while, the blood must be adequately thinned for at least 3-4 weeks prior to the procedure.

Because it takes many hours for blood clots to form, cardioversion can be safely performed without blood-thinning medication in patients who have had their heart rhythm problem for less than 48 hours.

Occasionally, your doctor may recommend a special ultrasound of the heart called a transesophageal echocardiogram (TEE). During a TEE, a special probe is placed in the esophagus. It allows your doctor to directly visualize the atria to scan for potential blood clots. Typically, anticoagulation is continued after the cardioversion for an additional 4 weeks to 6 months, even if the cardioversion is successful.