Section 3. Heart and Blood Vessel Disorders

Chapter 28. Heart Valve Disorders

Topics: Introduction | Mitral Regurgitation | Mitral Valve Prolapse | Mitral Stenosis | Aortic Regurgitation | Aortic Stenosis | Tricuspid Regurgitation | Tricuspid Stenosis | Pulmonary Stenosis

Aortic Regurgitation

Aortic regurgitation (aortic incompetence, aortic insufficiency) is leakage of the aortic valve each time the left ventricle relaxes.

As the left ventricle relaxes to fill with blood from the left atrium, blood leaks backward from the aorta, increasing the volume and pressure of blood in the left ventricle. As a result, the amount of work the heart has to do increases. To compensate, the muscular walls of the ventricles thicken (hypertrophy), and the chambers of the ventricles enlarge (dilate). Eventually, despite this compensation, the heart may be unable to meet the body's need for blood, leading to heart failure.

Rheumatic fever and syphilis used to be the most common causes of aortic regurgitation in North America, Australasia, and Western Europe, where both disorders are now rare because of the widespread use of antibiotics. In regions in which antibiotics are not widely used, aortic regurgitation due to rheumatic fever or syphilis is still common. Aside from these infections, the most common causes of severe aortic regurgitation are weakening of the valve's usually tough, fibrous tissue due to myxomatous degeneration (a hereditary disorder in which the valve gradually becomes floppy); degeneration of the valve due to unknown factors; aortic aneurysms; and aortic dissection. Common causes of mild aortic regurgitation are severe high blood pressure and a birth defect in which the aortic valve consists of two cusps (bicuspid valve) instead of the usual three (tricuspid valve) (see Section 23, Chapter 265). About 2% of boys and 1% of girls are born with this defect. Other causes of aortic regurgitation include bacterial infection of a heart valve (infective endocarditis) and injury.

Symptoms and Diagnosis

Mild aortic regurgitation produces no symptoms other than a characteristic heart murmur that can be heard with a stethoscope each time the left ventricle relaxes. People with severe regurgitation may have palpitations (awareness of heartbeats) because the left ventricle enlarges and contracts more forcefully. It enlarges as the volume of blood it contains increases. Eventually, heart failure with fluid accumulation in the lungs results. Heart failure causes shortness of breath during exertion. Lying flat, especially at night, makes breathing difficult. Sitting up allows backed-up fluid to drain out of the upper part of the lungs, restoring normal breathing. About 5% of people with aortic regurgitation have chest pain due to an inadequate blood supply to the heart muscle (angina), especially at night.

The pulse, sometimes called a collapsing pulse, is momentarily strong, then disappears quickly because the blood leaks backward through the aortic valve, causing blood pressure to decrease sharply.

Doctors usually suspect the diagnosis based on the results of a physical examination (such as the collapsing pulse and characteristic heart murmur) and an enlarged heart seen on an x-ray. Electrocardiography (ECG) may show signs of an enlarged left ventricle. Echocardiography can show the faulty valve and help doctors determine how severe regurgitation is and whether heart valve replacement surgery is needed. Coronary angiography is performed before surgery because about 20% of people with aortic regurgitation also have coronary artery disease.

Treatment

Heart failure due to aortic regurgitation can initially be treated with drugs. Unless aortic regurgitation is mild, surgery is ultimately almost always required. In the weeks before surgery, heart failure is treated with digoxin, diuretics, and a drug that dilates blood vessels and thus reduces the work of the heart, such as a calcium blocker, an angiotensin-converting enzyme (ACE) inhibitor, or hydralazine plus a nitrate (see Section 3, Chapter 25). An angiotensin II receptor blocker may be used when an ACE inhibitor cannot be used. Use of a pacemaker (see Section 3, Chapter 27) to increase the heart rate can sometimes help reduce the severity of heart failure.

The damaged valve should be surgically replaced with an artificial valve before the left ventricle becomes irreversibly damaged and heart failure becomes too severe. Usually, echocardiography is performed periodically to determine how rapidly the left ventricle is enlarging, so that surgery can be scheduled at an appropriate time.

People with aortic regurgitation, even when mild, are given antibiotics before surgical, dental, or medical procedures (see Section 3, Chapter 29) to reduce the risk of infection of the damaged heart valve.