Cardiac ablation is a procedure that uses a targeted energy source to destroy small pieces of heart tissue in order to correct a persistent irregular heartbeat.
The purpose of cardiac ablation is to restore a normal heartbeat when an abnormal heartbeat, or arrhythmia, cannot be controlled by drug therapy or electrical cardioversion .
The heart is a muscle containing four compartments or chambers that separate oxygen-poor blood from oxygen-rich blood. The atria are the top chambers. They receive blood from the body. The ventricles are the bottom chambers. They pump blood out to the body. Oxygen-poor blood enters the right atrium, then moves through a valve to the right ventricle from which it is pumped out of the right ventricle to the lungs where it picks up oxygen. The oxygen-rich blood then returns to the left atrium of the heart, flows through a valve to the left ventricle, and is then pumped out to the body. This sequence occurs with every heartbeat.
The frequency and coordination of heart contractions is controlled by electrical signals within the heart. A group of cells called the sinoatrial (SA) node is located in the top of the right atrium. The SA node acts as a natural pacemaker for the heart. It creates a regular electrical impulse that travels to a spot at the center of the heart between the atria and the ventricles called the atrioventricular (AV) node. After passing through the AV node, the electrical signal travels to the bottom of the ventricles, causing them to contract beginning at the bottom, so that blood is forced out into either the pulmonary artery (right ventricle) or the aorta (left ventricle). The timing of the contraction of each chamber of the heart must be tightly coordinated in order for each chamber to empty efficiently and completely. If the electrical signals that cause heart contraction are triggered at improper time intervals or if their transmission through the heart is blocked or diverted, an arrhythmia, or irregular heartbeat, develops.
The arrhythmias that are most often treated by cardiac ablation are:
- atrial fibrillation. Atrial fibrillation is a common arrhythmia experienced by about 2.2 million Americans. With atrial fibrillation, the contractions of the atria are chaotic and uncoordinated, so that less blood is pumped out of the chamber.
- atrial flutter. In this disorder, the atria contract in an organized way, but a “short circuit” causes contractions to occur much faster and out of synchronization with the ventricles.
- atrial tachycardia. Tachycardia is a fast heart rate of above 100 beats per minute. In this case, rapid contractions occur in the atria and can reach rates of 160–200 beats per minute.
- AV node reentry tachycardia. Normally the electrical impulse passes through only one spot in the AV node. In this disorder, it passes through two or more places giving rise to rapid contractions.
- accessory pathways. Normally the electrical impulse travels along a single path. If it travels along multiple divergent pathways, an abnormal rhythm develops.
Cardiac ablation is usually performed after lifestyle changes, medication, and cardioversion (where appropriate) have failed. Individuals must be free of infection and in good enough general health to with-stand the procedure.
Cardiac ablation can be done either by nonsurgical catheter ablation or surgical ablation. Catheter ablation is the most common type of cardiac ablation procedure.
Catheter ablation is often performed at the same time as electrophysiologic mapping. The patient is sedated but awake. A catheter (very thin tube) is inserted through a vein, usually in the groin, shoulder, or neck. The catheter is threaded through the veins until it reaches the heart. An imaging technique called fluoroscopy allows the surgeon to see the catheter on a monitor throughout the procedure. The tip of the catheter contains electrodes that can measure and map the pattern of electrical activity in the heart. The electrodes also can stimulate the heart so that the physician can see what causes or stops an arrhythmia. From this information, the surgeon can locate the cause of the arrhythmia and determine which spots in the heart should be ablated (destroyed). Destruction of tissue is done through radiofrequency energy administered through the catheter. The scar tissue that will form in this spot will not transmit electrical impulses and the abnormal heartbeat should stop. Once the procedure is complete, the catheter is removed and the entry point cleansed and closed. The patient must remain still for several hours following the procedure. The whole process can take anywhere from two to eight hours.
QUESTIONS TO ASK YOUR DOCTOR
- What kind of arrhythmia do I have?
- Can this arrhythmia be treated with catheter ablation?
- If catheter ablation is not an option, what kind of surgery can I expect?
- How many of these procedures have you done in the past year?
- How many of these procedures are done in this hospital in a year? (This is especially important for those having open-heart surgery.)
- How urgent is my condition? I would like to get a second opinion.
- If I am having open-heart surgery, can you refer me to social services that can assist me and my family during my recovery?
A maze procedure is a surgical ablation procedure performed to treat arrhythmias. Traditionally it has been performed as open-heart surgery. The patient is anesthetized, and the surgeon breaks the breastbone (sternum) to gain access to the heart. The patient is put on a heart-lung (cardiopulmonary bypass) machine. The surgeon then creates a series of carefully placed scars in the heart in order to block abnormal electrical pathways. The tissue is scarred using either radiofrequency energy or extreme cold administered by a cryoprobe. Drains are inserted, the breastbone is wired back together, the chest is closed, and when the patient is stable, the heart-lung support is removed. This operation is a complex open-heart procedure with significant risks.
Recently, the maze procedure is being performed in some hospitals using a minimally invasive technique. The sternum is not broken and the patient does not require the assistance of a heart-lung machine. To reach the heart, one lung is deflated. The patient will continue to breathe using the other lung, but will be put on a ventilator to assist in breathing. Recovery time for a minimally invasive maze procedure is much less than for an open-heart procedure, and there is less pain because the breastbone is not broken and a smaller risk of infection.
Before cardiac ablation is performed, the individual will have undergone various cardiac tests to diagnose arrhythmia. These tests often include an electrocardiogram (EKG), ambulatory (Holter) monitoring, and a stress test . Catheter ablation is often performed during electrophysiologic mapping. If surgical ablation is performed, electrophysiologic mapping will be done before the procedure.
The physician may instruct the patient to stop taking certain medications up to a week before the procedure. Beginning the night before the procedure, patients should not eat or drink. People who undergo surgical ablation will also have standard preoperative blood tests and meet with an anesthesiologist before the procedure.
After catheter ablation, the catheter is removed and pressure is applied to the entry point to prevent bleeding. The patient must stay very still for several hours. Most often, the patient is kept overnight in the hospital so that heart function can be monitored. After returning home, heavy physical exercise (e.g. lifting, vigorous exercise) should be avoided until approved by the doctor. The patient may need to take medications, such as anticoagulants and antibiotics , for a period after the procedure. It is important to take medications exactly as prescribed.
Recovery from surgical ablation is more complex, with patients undergoing minimally invasive surgical ablation recovering more quickly than those who receive open-heart maze surgery. Following surgery, patients receive continued cardiac monitoring in the intensive care unit and usually remain in intensive care for 24–48 hours after surgery. After that, the patient is transferred to a special cardiac unit where monitoring is continued. Open-heart patients may stay in the hospital two weeks, with full recovery at home taking several months. These patients will also take medication for a period following the surgery.
Ambulatory monitoring —EKG recording over a prolonged period during which the patient can move around.
Aorta —The main artery that carries blood from the heart to the rest of the body. The aorta is the largest artery in the body.
Artery —A vessel that carries oxygen-rich blood to the body.
Atrium (plural Atria) —The right or left upper chamber of the heart.
Cardioversion —Application of an electric pulse to the chest to shock the heart back into a normal rhythm. Used in the treatment of atrial fibrillation and atrial tachycardia.
Catheter —A long, thin, flexible tube that can be inserted into a vein and moved through the cardiovascular system.
Electrophysiologic mapping —Diagramming the electrical activity by using a catheter that measures the heart's electrical activity at many different spots.
Stent —A device made of expandable, metal mesh that is placed (by using a balloon catheter) at the site of a narrowing artery; the stent stays in place to keep the artery open.
Stress test —A test that involves an electrocardiogram during rest and exercise to determine how the heart responds to stress.
Ventricle —A lower pumping chamber of the heart. There are two ventricles, right and left. The right ventricle pumps oxygen-poor blood to the lungs to be re-oxygenated. The left ventricle pumps oxygen-rich blood to the body.
When catheters are inserted into the circulatory system, there is always a chance of infection, damage to the blood vessels or heart, and the development of blood clots . Bleeding, bruising , and swelling may occur where the catheter is inserted. A serious but uncommon complication is that of damage to the heart's pacemaker system. In this case, an artificial pacemaker may be inserted in the heart. Death during the procedure is possible, but rare.
Successful cardiac ablation can permanently cure a heart arrhythmia.
Catheter ablation is normally performed in an electrophysiologic laboratory, often within a hospital, with specially trained personnel assisting a cardiac surgeon who also has specialized training in catheter ablation. Surgical ablation is performed in a hospital operating room that is equipped for open-heart surgery. Present will be an anesthesiologist, at least one cardiac surgeon, operating room nurses, and technicians with special training in cardiac procedures such as heart-lung machine operation. Recovery will be monitored in an intensive care unit or special cardiac unit by nurses with training in these areas.
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American Heart Association, 7272 Greenville Avenue, Dallas, TX, 75231, (800) 242-8721, http://www.americanheart.org.
National Heart Lung and Blood Institute Health Information Center, P.O. Box 30105, Bethesda, MD, 20824-0105, (301) 592 8573; TTY: (240) 629 3255, (240) 629 3246,:[email protected], http://www.nhlbi.nih.gov.
Tish Davidson A. M.