Aortic Valve Stenosis
Aortic valve stenosis
Aortic valve stenosis, is the narrowing of the aortic valve so that blood flow through the valve is restricted.
The heart consists of two upper chambers (right and left atria), two lower chambers (right and left ventricles), and four valves (tricuspid, pulmonary, mitral, and aortic) that keep blood flowing only in one direction. Blood coming from the body enters the right atrium and then passes through the tricuspid valve into the right ventricle. The right ventricle pumps the blood through the pulmonary valve into the pulmonary artery, which carries it to the lungs. In the lungs, the blood releases carbon dioxide (a waste produce of cellular metabolism) and picks up oxygen. The pulmonary vein returns the oxygen-rich blood to the left atrium of the heart. The blood passes through the mitral valve into the left ventricle.
The left ventricle is the largest and most muscular chamber of the heart. When the left ventricle contracts, blood is forcefully pumped through the aortic valve and into the aorta. The aorta is the largest artery. It distributes this oxygen-rich blood to the rest of the body.
Aortic stenosis occurs when the aortic valve does not open fully or is narrowed through scar tissue build-up or congenital (present at birth) deformity. This narrowing (stenosis) forces the left ventricle to work harder than normal to push the blood through the aortic valve and out into the rest of the body. Over time, the left ventricle becomes more muscular. As it enlarges, the size of the ventricle cavity decreases, so that the left ventricle holds a smaller volume of blood. The heart tries to compensate for these changes. As a result, people can have aortic stenosis for a long time before they show symptoms. Eventually, the amount of blood reaching the body is substantially reduced and serious symptoms develop.
In the United States, between 2% and 9% of the population have aortic stenosis. Congenital valve defects that result in aortic stenosis occur in about one of every 250 live births and are three times more common in males than in females. Except in people born with heart defects, aortic stenosis is usually a disorder of the elderly. It is present in about 3% of individuals older than age 75. Another exception is in people whose heart valves have been damaged by rheumatic fever. These people can develop aortic stenosis considerably earlier, often between the ages of 30 and 50.
Causes and symptoms
Three main causes of aortic stenosis are congenital valve defects, calcium build-up on the valve as the result of aging, and damage to the valve caused by rheumatic fever. There are also a few other rare causes.
Congenital valve defects
The normal aortic valve consists of three triangular flaps called leaflets. About 2% of people are born with a valve made only of two leaflets (a bicuspid aortic valve). Two-leaflet valves do not open as widely as three-leaflet valves. In young people, two-leaflet valves usually open enough to allow adequate blood flow, and these individuals can remain symptom-free for a long time. However, because the size of the valve opening is reduced, blood rushing through it is more turbulent. The turbulence creates excessive wear and tear on the valve, causing scarring and weakening its ability to open. About 10% of people with bicuspid aortic valves develop heart problems related to aortic stenosis. This birth defect is the most common cause of aortic stenosis in people under age 65.
Aging and calcium deposits
As some people age, calcium, a mineral found in bones and blood, is deposited in the leaflets of the aortic valve. This causes the valve to lose flexibility and reduces the degree to which it can open. Once the valve opening has narrowed, blood flow increases in turbulence, accelerating wear and scaring of the valve. The accumulation of calcium and resulting wear and tear is a gradual process. Symptoms often do not occur until people are in their 70s or 80s.
Rheumatic fever is a complication of untreated strep throat. In developed countries where streptococcal infections are routinely treated with antibiotics , rheumatic fever has become rare. In developing countries where medical care is scarce, it is common. Rheumatic fever damages the heart valves and causes formation of scar tissue that narrows the size of the valve opening. It also accelerates calcium deposit build-up. The aortic valve may either fail to fully open (aortic stenosis) or fail to fully close (aortic regurgitation). Stenosis that results from rheumatic fever damage can occur in people as young as age 30.
Radiation therapy for cancer can damage the aortic valve. Although radiation damage is unlikely to be the sole cause of aortic stenosis, it can accelerate the wear and tear process. Likewise, long-term use of some medications used in treating migraine headaches can also damage the aortic valve and accelerate the development of aortic stenosis.
Symptoms of aortic stenosis are similar to other heart and lung conditions. These include:
- chest pain (angina)
- shortness of breath, often first noticed during exercise
- dizziness or fainting, usually during exercise
- rapid, fluttering heartbeat
- heart murmur
Often the first clue to aortic stenosis comes when the doctor listens to the heart with a stethoscope and hears abnormal heart sounds. Heart murmurs are caused by malfunctioning valves opening and closing. Additional tests are then ordered to determine the cause of the heart murmur. These tests include:
- electrocardiogram. This noninvasive test records the electrical activity of the heart and is useful is assessing general heart health. It may indicate that the heart wall is thickened.
- chest x-ray. A chest x-ray may show an enlarged heart or calcium deposits in the valve leaflets.
- echocardiogram. This noninvasive test uses ultrasound waves to visualize soft tissue structures in the chest. Special Doppler electrocardiograms can track the flow of blood through the heart and show whether valves are leaking. A transesophageal echocardiogram, in which a tiny device that emits the sound waves is threaded down the throat while the patient is sedated, may b necessary to obtain a clear picture of the aortic valve.
- cardiac catheterization. An invasive test done under anesthesia in which a catheter (tiny tube) is inserted in a blood vessel at some distance from the heart (often in the elbow or groin) and threaded through the circulatory system into the heart where it measures blood flow and blood pressure on either side of the aortic valve. From this information, the size of the aortic valve opening can be calculated. This is the definitive test for aortic stenosis. Often during cardiac catheterization, a dye is injected into the bloodstream so that the cardiologist can assess the health of the coronary arteries (arteries that supply blood to the heart).
When aortic stenosis is mild, physicians often take a watch and wait approach, taking no immediate action, but having the patient return for regular check-ups to determine if the condition is worsening. They may supplement watchful waiting with medications to treat mild symptoms, antibiotics to prevent heart infection (endocarditis), and restrictions on strenuous exercise such as weightlifting.
Many people with aortic stenosis are not diagnosed until symptoms are moderate to severe. For these patients, aortic valve replacement (AVR) surgery is the most common treatment. AVR is usually major open heart surgery and requires a 2–3 day postoperative stay in an intensive care unit (ICU), a 2–3 week stay in the hospital, and several months of cardiac rehabilitation therapy. Occasionally patients are eligible for minimally invasive procedures that shorten the recovery time substantially. Additional details on the valve replacement procedure can be found in the entry on cardiac valve surgery .
QUESTIONS TO ASK YOUR DOCTOR
- If you are recommending a watch and wait approach, what are the warning signs that my aortic stenosis is worsening and how often should I have routine check-ups?
- If I need surgery, am I a candidate for a minimally invasive procedure?
- What type of valve will I receive and why do you think that type is best for me?
- Can you explain the advantages and disadvantages of this type of valve?
- How many AVR surgeries have you done in the past three years?
- How many AVR surgeries are done at this hospital annually?
- Can you refer me to social services that may help me and my care givers during my recovery?
The aortic valve can be replaced with either a mechanical metal and treated carbon valve or a tissue valve. Mechanical valves have the advantage of longevity; they rarely need replacement during the patient's lifetime. Their main disadvantage is that the patient must take anticoagulant (blood-thinning) drugs such as warfarin (Coumadin) for the rest of their life to prevent blood clots from forming in the valve. Anticoagulant drugs can have serious side effects and must be kept within a tightly regulated range. Mechanical valves also make a clicking sound as they close that some patients can hear and find annoying.
Tissue valves, also called biologic valves, come from either pigs (porcine valves) cows (bovine valves) or human cadaver donors (homografts or allografts). Human valves are in very short supply. All tissue valves are treated chemically so that the patient's immune system will not reject them. The main advantage of tissue valves is that the patient only needs to take anticoagulation drugs for a few months after the surgery. The main disadvantage is that tissue valves tend to wear out and often need replacement in 7–12 years. The age and health of the patient usually determine the type of valve used. People who receive either type of valve must take antibiotics before having dental work, surgery, or certain invasive tests. This is to reduce the chance of endocarditis.
In some patients, the aortic valve opening can be widened with balloon angioplasty . In this procedure, a soft-tipped catheter is threaded through a blood vessel until it reaches the aortic valve. The tip of the catheter is then inflated, forcefully widening the opening of the valve. The catheter is then deflated and withdrawn. This procedure is used most often in children. In adults, although the initial effect is to widen the aortic valve opening, the opening usually re-narrows within a short time.
As of 2008, there was no direct correlation between diet and the development of aortic stenosis. Nevertheless, eating a healthy diet low in animal fats (saturated fats) and high in fresh fruits, fresh vegetables, and whole grains, as well as maintaining a healthy weight, benefits the whole circulatory system and promotes good health.
Following AVR, the individual will participate in a supervised cardiac rehabilitation program.
Sudden death occurs in about 4% of people who have aortic stenosis but no symptoms. The incidence of sudden death in people with moderate to severe symptoms of aortic stenosis is 15–20% with an average survival time of less than 5 years. Survival of patients with AVR surgery depends heavily on the patient's age and general health.
In most cases, such as congenital valve defects and normal aging, aortic stenosis cannot e prevented. Scientists do not know why some people develop calcium deposits in their valve leaflets and others do not. As of 2008, some preliminary evidence suggests that cholesterol-lowering drugs can help slow or prevent aortic stenosis, but more investigation needs to be done to verify this link.
Recovery from AVR surgery is a slow process that can stretch to six months or more depending on the age and health of the patient. Initially care givers will need to be continuously available, with the need for assistance in the routine self-care decreasing as the patient becomes stronger. Care givers can also assist the patient by seeing that they begin antibiotic therapy as directed by their doctor before any dental or surgical procedures. Individuals who have had a mechanical valve replacement should keep identification with them (ID card, Medic Alert bracelet) that indicates that they have an artificial valve and are taking anticoagulants. The presence of a mechanical valve may prevent the patient from having certain routine tests such as a chest MRI (an MRI mkes the metal in the valve heat up). Rarely a metal valve may set off an airport or similar metal detector.
Balloon angioplasty —a surgical procedure is done to stretch and widen the opening of a valve or to reopen a partially blocked artery so that blood can flow through it again at a normal rate. A tiny tube (catheter) is threaded through blood vessels to the point of the blockage. The catheter contains a balloon that is then expanded to stretch and open the artery.
Cardiac rehabilitation —A structured program of education and activity offered by hospitals and other organizations.
Doppler echocardiography —A testing technique that uses Doppler ultrasound technology to evaluate the pattern and direction of blood flow in the heart.
Echocardiogram —A non-invasive imaging procedure used to create a picture of the heart's movement, valves, and chambers.
Endocarditis —Infection of the heart endocardium tissue, the inner most tissue and structures of the heart.
Transesophageal echocardiography —A diagnostic test using an ultrasound device that is passed into the esophagus of the patient to create a clear image of the heart muscle and other parts of the heart.
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“Aortic Valve Stenosis.” Mayo Clinic. September 24, 2007 [cited February 28, 2008]. http://www.mayoclinic.com/health/aortic-valve-stenosis/DS00418.
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.