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.
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.
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).
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®).
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.