Cardioversion refers to the process of restoring the heart's normal rhythm by applying a controlled electric shock to the exterior of the chest.
Description
Elective cardioversion is usually scheduled ahead of time. After arriving at the hospital, an intravenous (IV) catheter will be placed in the arm and oxygen will be given through a face mask. A short-acting general anesthetic will be administered through the vein. During the two or three minutes of anesthesia, the doctor will apply two paddles to the exterior of the chest and administer the electric shock. It may be necessary to give the shock two or three times to obtain normal rhythm.
Who Performs the Procedure and Where Is It Performed?
Heart doctors (cardiologists) specially trained in cardioversion (called electrophysiologists) should perform this procedure. To find a heart rhythm specialist or an electrophysiologist, patients can contact the North American Society of Pacing and Electrophysiology. Cardioversion usually takes place in the hospital setting in a special lab called the electrophysiology (EP) laboratory. It may also be performed in an intensive care unit, recovery room or other special procedure room.
Questions to Ask the Doctor
Why is this procedure being performed?
What are the potential benefits of the procedure?
What are the risks of the procedure?
Can I take my medications the day of the procedure?
Can I eat or drink the day of the procedure? If not, how long before the procedure should I stop eating or drinking?
When can I drive after the procedure?
What should I wear the day of the procedure?
Will I be awake during the procedure?
What kinds of monitors are used during the procedure to evaluate my condition?
Will I have to stay in the hospital after the procedure?
When can I resume my normal activities?
When will I find out the results?
What if the procedure was not successful?
If I've had the cardioversion procedure once, can I have it again to correct an abnormal heart rhythm, if necessary?
Will I have any pain or discomfort after the procedure? If so, how can I relieve this pain or discomfort?
Are there any medications, foods or activities I should avoid to prevent my symptoms from recurring?
Definition
Cardioversion refers to the process of restoring the heart's normal rhythm by applying a controlled electric shock to the exterior of the chest. Abnormal heart rhythms are called arrhythmias or dysrhythmias.
Purpose
When the heart beats too fast, blood no longer circulates effectively in the body. Cardioversion is used to stop this abnormal beating so that the heart can begin its normal rhythm and pump more efficiently.
Abnormal heart rhythms are slightly more common in men than in women and the prevalence of abnormal heart rhythms, especially atrial fibrillation, increases with age. Atrial fibrillation is relatively uncommon in people under age 20.
Description
Elective cardioversion is usually scheduled ahead of time. After arriving at the hospital, an intravenous (IV) catheter will be placed in the arm to deliver medications and fluids. Oxygen may be given through a face mask.
In some people, a test called a transesophageal echocardiogram (TEE) may need to be performed before the cardioversion to make sure there are no blood clots in the heart.
A short-acting general anesthetic will be given through the IV to put the patient to sleep. During the five or 10 minutes of anesthesia, an electric shock is delivered through paddles or patches placed on the exterior of the chest and sometimes on the back. It may be necessary for the doctor to administer the shock two or three times to stop the abnormal heartbeat and allow the heart to resume a normal rhythm. During the procedure, the patient's breathing, blood pressure, and heart rhythm are continuously monitored.
Diagnosis/Preparation
Diagnosis of Abnormal Heart Rhythms
A doctor may be able to detect an irregular heart beat during a physical exam by taking the patient's pulse. In addition, the diagnosis may be based upon the presence of certain symptoms, including:
palpitations (feeling of skipped heart beats or fluttering in the chest)
nuclear medicine test, such as a MUGA scan (multiple-gated acquisition scanning)
Preparation for Cardioversion
Medication Guidelines.
Medication to thin the blood (blood thinner or anticoagulant) is usually given for at least three weeks before elective cardioversion.
The patient should take all usual medications as prescribed, unless other instructions have been given.
Patients who take diabetes medications or anticoagulants should ask their doctor for specific instructions.
Eating and Drinking Guidelines
The patient should not eat or drink anything for six to eight hours before the procedure.
Other Guidelines
It is advisable to arrange for transportation home, because drowsiness may last several hours and driving is not permitted after the procedure.
Do not apply any lotion or ointments to your chest or back before the procedure.
Aftercare
The patient generally wakes quickly after the procedure. Medical personnel will monitor the patient's heart rhythm for a few hours, after which the patient is usually sent home. The patient should not drive home; driving is not permitted for 24 hours after the procedure.
Medications
The doctor may prescribe anti-arrhythmic medications (such as beta-blockers, digitalis, or calcium channel blockers) to prevent the abnormal heart rhythm from returning.
Some patients may be prescribed anticoagulant medication, such as warfarin and aspirin, to reduce the risk of blood clots.
The medications prescribed may be adjusted over time to determine the best dosage and type of medication so the abnormal heart rhythm is adequately controlled.
Discomfort
Some chest wall discomfort may be present for a few days after the procedure. The doctor may recommend that the patient take an over-the-counter pain reliever such as ibuprofen to relieve discomfort. Skin irritation may also be present after the procedure. Skin lotion or ointment can be used to relieve irritation.
Risks
Cardioverters have been in use for many years and the risks are few. The unlikely risks that remain include those instances when the device delivers greater or lesser power than expected or when the power setting and control knobs are not set correctly. Unfortunately, in about 50% of cases, the heart prefers its abnormal rhythm and reverts to it within one year, despite cardioversion. Cardioversion can be repeated for some patients whose abnormal heart rhythm returns.
Normal Results
About 90% of cardioversions are successful and, at least for a time, restore the normal heart rhythm safely and prevent further symptoms.
Morbidity and Mortality Rates
The 2002 Rate Control vs. Electrical Cardioversion for Persistent Atrial Fibrillation (RACE) study, published in The New England Journal of Medicine indicated that controlling a patient's heart rate is as important as controlling the patient's heart rhythm to prevent death and complications from cardiovascular causes. The study also concluded that anticoagulant therapy is important to reduce the risk of stroke and is appropriate therapy for patients who have recurring, persistent atrial fibrillation even after they were treated with cardioversion. In patients who did not receive anticoagulant therapy after cardioversion, there was a 2.4% increase of embolic events (such as stroke or blood clots), even though there were no signs of these events prior to the procedure.
Alternatives
Atrial fibrillation and atrial flutter often revert to normal rhythms without the need for cardioversion. Healthcare providers usually try to correct the heart rhythm with medication or recommend lifestyle changes before recommending cardioversion.
Lifestyle changes often recommended to treat abnormal heart rhythms include:
quitting smoking
avoiding activities that prompt the symptoms of abnormal heart rhythms
limiting alcohol intake
limiting or not using caffeine (Caffeine products may produce more symptoms in some people with abnormal heart rhythms.)
avoiding medications containing stimulants, such as some cough and cold remedies (These medications contain ingredients that may cause abnormal heart rhythms. Read all medication labels and ask a doctor or pharmacist for specific recommendations.)
If cardioversion is not successful in restoring the normal heart rhythm, other treatments for abnormal heart rhythms include:
McGoon, Michael D., ed., and Bernard J. Gersh, MD. MayoClinic Heart Book: The Ultimate Guide to Heart Health, Second Edition. New York: William Morrow and Co., Inc., 2000.
Topol, Eric J., MD. Cleveland Clinic Heart Book: The Definitive Guide for the Entire Family from the Nation's Leading Heart Center. New York: Hyperion, 2000.
Trout, Darrell, and Ellen Welch. Surviving with Heart: TakingCharge of Your Heart Care. Colorado: Fulcrum Publishing, 2002.
Periodicals
The New England Journal of Medicine 347, no. 23 (December 5, 2002): 1834–1840.
Organizations
American College of Cardiology. Heart House. 9111 Old Georgetown Rd., Bethesda, MD 20814-1699. (800) 253-4636 ext. 694 or (301) 897-5400. http://www.acc.org.
American Heart Association. 7272 Greenville Ave. Dallas, TX 75231. (800) 242-8721 or (214) 373-6300. http://www.americanheart.org.
The Cleveland Clinic Heart Center, The Cleveland Clinic Foundation. 9500 Euclid Avenue, F25, Cleveland, Ohio, 44195. (800) 223-2273 ext. 46697 or (216) 444-6697. http://www.clevelandclinic.org/heartcenter.
National Heart, Lung and Blood Institute. National Institutes of Health. Building 1. 1 Center Dr., Bethesda, MD 20892. E-mail: NHLBIinfo@rover.nhlbi. http://www.nhlbi.nih.gov.
North American Society of Pacing and Electrophysiology. 6 Strathmore Rd., Natick, MA 01760-2499. (508) 647-0100. http://www.naspe.org .
The delivery of a direct current shock synchronized with the qrs complex to the myocardium as an elective treatment to end tachydysrhythmias; called also countershock and precordial shock. Used in humans, it has also been effectively used in dogs with atrial fibrillation and ventricular tachycardias.
To perform synchronized electrical cardioversion two electrode pads are used, each comprising a metallic plate which is faced with a saline based conductive gel. The pads are placed on the chest of the patient, or one is placed on the chest and one on the back. These are connected by cables to a machine which has the combined functions of an ECG display screen and the electrical function of a defibrillator. A synchronizing function (either manually operated or automatic) allows the cardioverter to deliver a reversion shock, by way of the pads, of a selected amount of electric current over a predefined number of milliseconds at the optimal moment in the cardiac cycle which corresponds to the R wave of the QRS complex on the ECG. Timing the shock to the R wave prevents the delivery of the shock during the vulnerable period (or relative refractory period) of the cardiac cycle, which could induce ventricular fibrillation. If the patient is conscious, various drugs are often used to help sedate the patient and make the procedure more tolerable. However, if the patient is haemodynamically unstable or unconscious, the shock is given immediately upon confirmation of the arrhythmia. When synchronized electrical cardioversion is performed as an elective procedure, the shocks can be performed in conjunction with drug therapy until sinus rhythm is attained. After the procedure, the patient is monitored to ensure stability of the sinus rhythm.
Various antiarrhythmic agents can be used to return the heart to normal sinus rhythm. Pharmacological cardioversion is an especially good option in patients with fibrillation of recent onset. Drugs that are effective at maintaining normal rhythm after electric cardioversion, can also be used for pharmacological cardioversion. Drugs like amiodarone, diltiazem, verapamil and metoprolol are frequently given before cardioversion to decrease the heart rate, stabilize the patient and increase the chance that cardioversion is successful. There are two classes of agents that are most effective for pharmacological cardioversion.
Class I agents (slow conduction by blocking the Na+ channel): Procainamide, quinidine and disopyramide are Class Ia agents, while flecainide and propafenone are Class Ic agents.
Class III agents (prolong repolarization by blocking outward K+ current): Amiodarone and sotalol are effective Class III agents. Ibutilide is another Class III agent but has a different mechanism of action (acts to promote influx of sodium through slow-sodium channels). It has been shown to be effective in acute cardioversion of recent-onset atrial fibrillation and atrial flutter.
If the patient is stable, adenosine may be administered first, as the medicine performs a sort of "chemical cardioversion" and may stabilize the heart and let it resume normal function on its own without using electricity.
