A cardioversion is a procedure used to convert an abnormal heart rhythm (usually atrial fibrillation or atrial flutter) back to a normal heart rhythm.
It is usually performed when the arrhythmia is not expected to stop on its own. There are two methods of cardioversion: chemical and electrical. Typically, the chemical cardioversion is attempted first. If it fails, the electrical cardioversion is then performed.
The Procedure
The cardioversion procedure requires the patient to be without food for at least six hours. It is usually recommended to eat nothing after midnight the day before the procedure. Any medications should be taken the morning of the procedure with a small sip of water. The cardioversion can be performed in an electrophysiology laboratory or in a telemetry unit. Medications are administered through an intravenous line. The patient's vital signs are monitored continuously during the procedure.
Checking for Blood Clots
Prior to the procedure, it is important that the physician is certain no blood clots are inside the upper chambers of the heart (atria). A blood clot in the atria at the time of the cardioversion increases the risk of a stroke or heart attack, usually forcing postponement of the procedures until the patient is treated adequately with blood thinners. If your arrhythmia started within the past 24 to 48 hours, however, it's highly unlikely a blood clot has formed in your heart. In that case, the cardioversion would likely proceed.
When the duration of the arrhythmia is unknown there are two options:
- A special type of echocardiogram called a transesophageal echocardiogram, a long tube (feeding tube) placed in the esophagus to look for blood clots in the atria. If blood clots are found, then the cardioversion will likely be postponed and blood thinners will be continued for 4-6 weeks.
- Blood thinners. This is initially done using an intravenous blood thinner called heparin. At the same time, an oral blood thinner (warfarin, or brand-name Coumadin, is also started). After 4-6 weeks on the oral blood thinner, the cardioversion can be performed safely.
Chemical vs. Electrical
Chemical Cardioversion: If a chemical cardioversion is to be attempted first, the intravenous drug (usually procainamide or ibutilide) and the heart's rhythm is monitored continuously. The success rate of a chemical cardioversion depends on many factors, one of the most important being the duration that the patient is in the arrhythmia. For patients who have been in the arrhythmia for less than 48 hours, success rate in converting (changing) the heart rhythm back to normal can be as high as 50 percent to 60 percent. (The average conversion rate typically quoted is about 30 percent.) If the chemical cardioversion is successful, the patient is monitored for at least a few hours, if not overnight, to watch the rhythm.
Electrical Cardioversion: If the chemical cardioversion fails to restore a normal rhythm or, if the physician feels that a chemical cardioversion is unwarranted, an electrical cardioversion will be performed. Special pads are placed on the chest and back and attached to a defibrillator. The patient is sedated with medication via the intravenous line. The defibrillator then delivers an electrical shock via the pads through the heart muscle to restore a normal rhythm. The initial success rate of electrical cardioversion is about 95 percent.
Afterward
After the cardioversion, the physician will likely initiate or continue medications in an attempt to maintain a normal rhythm. Among the medications used for this purpose: beta-blockers (ie. atenolol, metoprolol, propranolol), calcium channel blockers (verapamil, diltiazem) or other antiarrhythmic medications (ie. procainamide, quinidine, sotalol, or amiodarone). Your physician will want to see you back for an electrocardiogram within the next few weeks to ensure that the rhythm is normal.