Related narrative: Calcific Aortic Stenosis
Aortic stenosis (AS) is a narrowing of the aortic heart valve, causing it to not open properly and to obstruct the flow of blood from the left ventricle to the aorta. Obstruction to left ventricular outflow is localized most commonly at the aortic valve; however, obstruction may also occur above or below the valve. AS is caused by many disorders, including rheumatic fever, calcification of the valve, and congenital abnormalities.
Epidemiology and Risk Factors
AS occurs in approximately 5 out of 10,000 people. It is more common among men and is usually either congenital or degenerative (senile) in origin. Generally, a congenitally bicuspid valve is not stenotic at birth, and the changes that cause stenosis occur over time like degenerative stenosis except they occur in the fifth and sixth decades of life rather than the seventh through ninth decades of life. In degenerative calcific AS, a deposit of calcium along the valve bases immobilizes the cusps. This is the most common cause of AS in adults and appears to result from years of normal stress on the valve. Besides age, the following factors are associated with the incidence of aortic valve disease: male gender, lipoprotein(a), height, hypertension, smoking, cholesterol, and diabetes. There are no studies investigating how the modification of these risk factors could alter the course of or prevent the development of aortic valve obstruction.
In the natural course of adults with AS, a long latent period exists during which there is gradually increasing obstruction and an increase in the pressure load on the myocardium, while the patient remains asymptomatic. While the condition is still asymptomatic, the prognosis is similar to that of age-matched healthy adults. In patients in whom the obstruction is not relieved, once the symptoms occur, survival curves indicate that the onset of death is about two years in patients with heart failure, three years in those with syncope, and five years in those with angina.
In asymptomatic patients, the multivariate predictors of symptom onset are baseline aortic jet velocity and functional status score and the rate of increase in jet velocity over time. Neither age, gender, nor etiology of aortic stenosis has been shown predictive of clinical outcome in adults. Although severe AS is a potentially lethal disease, death usually occurs in symptomatic patients. Sudden death is extremely rare in asymptomatic patients with critical AS.
The main manifestations of AS include syncope, angina pectoris, dyspnea, and congestive heart failure. Once these symptoms develop, the prognosis is poor. Examination shows a palpable chest thrill or heave. There is usually a heart murmur, click, or other abnormal sounds on auscultation. There may be faint pulses or changes in the quality of the pulse in the neck. Some patients with apparently severe stenosis are asymptomatic, while others who appear to have only moderate obstruction have significant symptoms. There is no single value that defines "severe" aortic stenosis; it is the degree of obstruction that is associated with symptoms in each patient. Sometimes, however, symptoms thought to be due to AS are instead caused by coronary artery disease or arrhythmia.
A peak systolic pressure gradient over 50 mm Hg in the presence of a normal cardiac output or an aortic orifice less than 0.8 cm2 in an average-sized adult is generally considered to represent critical obstruction to left ventricular outflow. On average, the aortic valve area decreases by 0.1 cm2/year, and the peak instantaneous gradient increases by 10 mm Hg/year.
Diagnosis and Treatment
Many patients are diagnosed when they are still asymptomatic. They are frequently identified based on the finding of a systolic murmur or an abnormal aortic valve on an echocardiogram performed for other reasons; however, routine radiological examination may be normal, even with the presence of critical AS. When diagnosing AS, the principal electrocardiographic change is left ventricular hypertrophy, which is found in about 85% of patients with severe AS. Angiographic studies of the valve make it possible to demonstrate doming of a thickened valve and a systolic jet. Two-dimensional thoracic echocardiography is useful in the detection of valvular calcification, in defining the number of aortic valve leaflets, and sometimes in determining the severity of the stenosis, by imaging the orifice. Transesophageal echocardiography is more useful, however.
The routine use of cardiac catheterization and the availability of Doppler echocardiography make the diagnosis of AS easier. Therefore, patients who have no symptoms but have significant AS are being identified, and what to do about them is an ongoing dilemma. The ability to predict the rate of progression in an individual patient is not adequate. Available evidence tends to support a conservative approach by deferral of surgery until the onset of symptoms, and surgical intervention in the asymptomatic patient is not recommended. However, if a patient is undergoing coronary artery bypass, and has mild-to-moderate stenosis, a prophylactic valve replacement saves the patient from an additional surgery within the next 4-5 years.
There are no known approaches to altering the disease progression in adults with asymptomatic AS without surgery. Medical therapy is usually directed towards preventing complications, such as using endocarditis prophylaxis for dental procedures, etc. Surgical therapy should be considered as soon as the patient develops symptoms.
In most adults with calcific AS, valvular function cannot be restored nonsurgically, so valve replacement in the treatment of choice. Balloon valvuloplasty may be effective in children and adolescents with congenital AS, but there is no effect on outcome in adults. The choice of valve type is based on the patient's expected longevity after surgery. A mechanical valve is durable, but long-term warfarin anticoagulation is needed, which raises the risk of thrombosis and bleeding. On average, the risk of a serious complication is 1-2% a year. Newer valves that are under evaluation, like the stentless porcine valves, may be durable without the need for anticoagulation.
In adults less than 70 years old, operative mortality is 3-5%. Risk factors for surgical mortality include age, female gender, emergency surgery, coexisting coronary artery disease, hypertension, left ventricular dysfunction, renal failure, and concurrent mitral valve surgery. Although there is a higher risk in older patients, surgery significantly improves clinical outcome, so age in not a contraindication to valve replacement. Coexisting diseases, though, should be considered in the decision process.
After valve replacement, symptoms secondary to elevation of left atrial pressure and myocardial ischemia are relieved in almost every patient. Left ventricular hypertrophy regresses, and ventricular systolic performance improves. The hypertrophy may take up to eight years to resolve fully, but the majority of the regression occurs in the first two years after surgery. Exercise and functional status improves, too, but patients often still have exercise limitations.
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