Cardioversion

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General Description

A cardioversion is a procedure which is used to convert an abnormal heart rhythm (usually atrial fibrillation or atrial flutter) back to a normal heart rhythm (normal sinus rhythm). It is usually performed when the arrhythmia is not expected to stop on its own. There are two methods of cardioversion available: chemical and electrical. Typically, the chemical cardioversion is attempted first, and if it fails, the electrical cardioversion is then performed. A description of both types of cardioversion is detailed below.

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Checking for Blood Clots

Prior to the procedure it is important that the physician be sure there are no blood clots inside the upper chambers of the heart (atria). If there is a blood clot in the atria at the time of the cardioversion than the risk of a stroke or heart attack is considerably higher and the procedure is usually postponed until an adequate course of blood thinning can be performed. If it is determined that your arrhythmia started within the past 24-48 hours, the likelihood of a blood clot having formed in the heart is extremely small. It is therefore common practice to proceed with the cardioversion without any further investigation for blood clots.

If the duration of the arrhythmia is unknown, then there are two options:

1) perform a special type of echocardiogram called a transesophageal echocardiogram (TEE). This test involves placing a long tube into the esophagus (feeding tube) to look in the atria for the presence of blood clots. If blood clots are present then the cardioversion will likely be postponed and blood thinners will be continued for a period off 4-6 weeks. The cardioversion can be safely performed at this time. If the TEE does not show any blood clots then the cardioversion can be safely performed. The cardioversion is typically performed as soon as is possible after the negative TEE.

2) initiate blood thinners. This is initially done using an intravenous blood thinner called heparin. At the same time, an oral blood thinner (warfarin [Coumadin®]) is also started. After 4-6 weeks on the oral blood thinner the cardioversion can safely be performed.

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The Procedure

The cardioversion procedure requires the patient to be without food for at least 6 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. An intravenous (IV) line is placed to administer medications. The patient's vital signs are monitored continuously throughout the procedure.

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Chemical Cardioversion:

If a chemical cardioversion is to be attempted first, the intravenous drug (usually procainamide or ibutilide) is infused via the IV and the rhythm is continuously monitored. 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, the conversion rates can be as high as 50-60%. The average conversion rate that is typically quoted is ~ 30%. If the chemical cardioversion is successful, the patient is typically monitored for at least a few hours, if not overnight, to watch the rhythm.

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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 rates of electrical cardioversion are very high (~95%). At Lenox Hill Hospital we use a newer defibrillator called a biphasic defibrillator for all of our cardioversions. These biphasic defibrillators have even higher success rates then the defibrillators that are commonly used (monophasic) at other institutions and also leave less of a burn on the skin.

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Afterwards:

After the cardioversion, the physician will likely want to initiate or continue medications in an attempt to maintain a normal rhythm. Some of the medications that are used for this purpose are: beta-blockers (ie. atenolol, metoprolol, propranolol), calcium channel blockers (verapamil, diltiazem), or other antiarrhythmic medications (ie. procainamide, quinidine, sotalol, or amiodarone). Your physician will likely want to see you back for an electrocardiogram within the next few weeks to ensure that the rhythm is normal.

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