Aortic stenosis is abnormal narrowing of the aortic valve. A number of conditions cause disease resulting in narrowing of the aortic valve. When the degree of narrowing becomes significant enough to impede the flow of blood from the left ventricle to the arteries, heart problems develop. The basic mechanism is as follows:
The heart is a muscular pump with four chambers and four heart valves.
The upper chambers, the right atrium and left atrium (atria -- plural for atrium), are thin walled filling chambers.
Blood flows from the right and left atria across the tricuspid and mitral valves into the lower chambers (right and left ventricles).
The right and left ventricles have thick muscular walls for pumping blood across the pulmonic and aortic valves into the circulation.
Heart valves are thin leaflets of tissue which open and close at the proper time during each heart beat cycle.
The main function of these heart valves is to prevent blood from flowing backwards. Blood circulates through the arteries to provide oxygen and other nutrients to the body, and then returns with carbon dioxide waste through the veins to the right atrium; when the ventricles relax, blood from the right atrium passes through the tricuspid valve into the right ventricle.
When the ventricles contract, blood from the right ventricle is pumped through the pulmonic valve into the lungs to reload on oxygen and remove carbon dioxide.
The oxygenated blood then returns to the left atrium and passes through the mitral valve into the left ventricle.
Blood is pumped by the left ventricle across the aortic valve into the aorta and the arteries of the body.
The flow of blood to the arteries of the body is impaired when aortic stenosis exists. Ultimately, this can lead to heart failure. Aortic stenosis occurs three times more commonly in men than women.
In adults, three conditions are known to cause aortic stenosis.
Bicuspid aortic valve is the most common cause of aortic stenosis in patients under age 65. Normal aortic valves have three thin leaflets called cusps. About 2% of people are born with aortic valves that have only two cusps (bicuspid valves). Although bicuspid valves usually do not impede blood flow when the patients are young, they do not open as widely as normal valves with three cusps. Therefore, blood flow across the bicuspid valves is more turbulent, causing increased wear and tear on the valve leaflets. Over time, excessive wear and tear leads to calcification, scarring, and reduced mobility of the valve leaflets. About 10% of bicuspid valves become significantly narrowed, resulting in the symptoms and heart problems of aortic stenosis
The most common cause of aortic stenosis in patients 65 years of age and over is called "senile calcific aortic stenosis." With ageing, protein collagen of the valve leaflets is destroyed, and calcium is deposited on the leaflets. Turbulence across the valve increases causing scarring, thickening, and stenosis of the valve once valve leaflet mobility is reduced by calcification. Why this ageing process progresses to cause significant aortic stenosis in some patients but not in others is unknown. The progressive disease causing aortic calcification and stenosis has nothing to with healthy lifestyle choices, unlike the calcium that can deposit in the coronary artery to cause heart attack.
Rheumatic fever is a condition resulting from untreated infection by group A streptococcal bacteria. Damage to valve leaflets from rheumatic fever causes increased turbulence across the valve and more damage. The narrowing from rheumatic fever occurs from the fusion (melting together) of the edges (commissures) of the valve leaflets. Rheumatic aortic stenosis usually occurs with some degree of aortic regurgitation. Under normal circumstances, the aortic valve closes to prevent blood in the aorta from flowing back into the left ventricle. In aortic regurgitation, the diseased valve allows leakage of blood back into the left ventricle as the ventricular muscles relax after pumping. These patients also have some degree of rheumatic damage to the mitral valve. Rheumatic heart disease is a relatively uncommon occurrence in the United States, except in people who have immigrated from underdeveloped countries.
The carotid arteries carry blood from the aorta to the brain and are the closest arteries to the aortic valve that can be felt by the doctor examining the neck. Patients with significant aortic stenosis have a delayed upstroke and lower intensity of the carotid pulse which correlates with the severity of narrowing. Aortic valve stenosis causes significant turbulence to blood flowing during contraction of the left ventricle resulting in a loud murmur. The loudness of the murmur does not, however, correlate with the severity of stenosis. Patients with mild stenosis can have loud murmurs, while patients with severe stenosis and heart failure may not pump enough blood to cause much of a murmur.
How is aortic stenosis diagnosed?
Electrocardiogram (EKG): An EKG is a recording of the heart's electrical activity. Abnormal patterns on the EKG can reflect a thickened heart muscle and suggest the diagnosis of aortic stenosis. In rare instances, electrical conduction abnormality can also been seen.
Chest X-ray: A chest X-ray usually shows a normal heart shadow. The aorta above the aortic valve is often enlarged (dilated). If heart failure is present, fluid in the lung tissue and larger blood vessels in the upper lung regions are often seen. A careful inspection of the chest X-ray sometimes reveals calcification of the aortic valve.
Echocardiography: Echocardiography uses ultrasound waves to obtain images of the heart chambers, valves, and surrounding structures. It is a useful non-invasive tool, which helps doctors diagnose aortic valve disease. An echocardiogram can show a thickened, calcified aortic valve which opens poorly. It can also show the size and functioning of the heart chambers. A technique called Doppler can be used to determine the pressure difference on either side of the aortic valve and to estimate the aortic valve area.
Cardiac catheterization: Cardiac catheterization is the gold standard in evaluating aortic stenosis. Small hollow plastic tubes (catheters) are advanced under X-ray guidance to the aortic valve and into the left ventricle. Simultaneous pressures are measured on both sides of the aortic valve. The rate of blood flow across the aortic valve can also be measured using a special catheter. Using these data, the aortic valve area can be calculated. A normal aortic valve area is 3 square centimeters. Symptoms usually occur when the aortic valve area narrows to less than 1 square centimeter. Critical aortic stenosis is present when the valve area