Supravalvular aortic stenosis

December 31, 2014

Synonyms

Overview

Supravalvular aortic stenosis (SVAS) is a type of heart defect that develops before birth. A normal aortic valve, when open, allows the free flow of blood from the left ventricle to the aorta. When the valve narrows, as it does with stenosis, blood flow is impeded. Because it is more difficult for blood to flow through the valve, there is increased strain on the heart.

It is characterized by a narrowing (stenosis) of the section of the aorta just above the valve that connects the aorta to the heart (aortic valve). The severity of SVAS varies from person to person; some individuals may die in infancy while others never experience symptoms. If symptoms develop, they may include shortness of breath, chest pain, murmur, and/or eventual heart failure. Some affected individuals also have defects in other blood vessels, such as the pulmonary artery.

SVAS can also be associated with Williams syndrome.

Symptoms

The most common symptoms, depending on the severity of the disease, are chest pain, blackouts, and difficulty breathing.

Symptoms related to aortic stenosis depend on the degree of stenosis. Most people with mild to moderate aortic stenosis do not have symptoms. Symptoms usually present in individuals with severe aortic stenosis, though they may occur in those with mild to moderate aortic stenosis as well. The three main symptoms of aortic stenosis are loss of consciousness, anginal chest pain and shortness of breath with activity or other symptoms of heart failure such as shortness of breath while lying flat, episodes of shortness of breath at night, or swollen legs and feet. It may also be accompanied by the characteristic "Dresden china" appearance of pallor with a light flush.

Angina:
Angina in setting of heart failure also increases the risk of death. In people with angina, the 5 year mortality rate is 50% if the aortic valve is not replaced.

Angina in the setting of AS occurs due to left ventricular hypertrophy (LVH) that is caused by the constant production of increased pressure required to overcome the pressure gradient caused by the AS. While the muscular layer of the left ventricle thickens, the arteries that supply the muscle do not get significantly longer or bigger, so the muscle may not receive enough blood supply to meet its oxygen requirement. This ischemia may first be evident during exercise, when the heart muscle requires increased blood supply to compensate for the increased workload. The individual may complain of anginal chest pain with exertion. At this stage, a cardiac stress test with imaging may be suggestive of ischemia.

Eventually, however, the heart muscle will require more blood supply at rest than can be supplied by the coronary artery branches. At this point there may be signs of ventricular strain pattern (ST segment depression and T wave inversion) on the EKG, suggesting subendocardial ischemia. The subendocardium is the region that is most susceptible to ischemia because it is the most distant from the epicardial coronary arteries.

Syncope:
Syncope (fainting spells) from aortic valve stenosis is usually exertional. In the setting of heart failure it increases the risk of death. In people with syncope, the 3 year mortality rate is 50%, if the aortic valve is not replaced.

It is unclear why aortic stenosis causes syncope. One popular theory is that severe AS produces a nearly fixed cardiac output. When a person with aortic stenosis exercises, their peripheral vascular resistance will decrease as the blood vessels of the skeletal muscles dilate to allow the muscles to receive more blood to allow them to do more work. This decrease in peripheral vascular resistance is normally compensated for by an increase in the cardiac output. Since people with severe AS cannot increase their cardiac output, the blood pressure falls and the person will faint due to decreased blood perfusion to the brain.

A second theory as to why syncope may occur in AS is that during exercise, the high pressures generated in the hypertrophied left ventricle cause a vasodepressor response, which causes a secondary peripheral vasodilation that, in turn, causes decreased blood flow to the brain resulting in loss of consciousness. Indeed, in aortic stenosis, because of the fixed obstruction to bloodflow out from the heart, it may be impossible for the heart to increase its output to offset peripheral vasodilation.

A third mechanism may sometimes be operative. Due to the hypertrophy of the left ventricle in aortic stenosis, including the consequent inability of the coronary arteries to adequately supply blood to the myocardium (see "Angina" below), abnormal heart rhythms may develop. These can lead to syncope.

Finally, in calcific aortic stenosis at least, the calcification in and around the aortic valve can progress and extend to involve the electrical conduction system of the heart. If that occurs, the result may be heart block - a potentially lethal condition of which syncope may be a symptom.

Congestive heart failure:

Congestive heart failure (CHF) carries a grave prognosis in people with AS. People with CHF attributable to AS have a 2-year mortality rate of 50% if the aortic valve is not replaced.[citation needed] CHF in the setting of AS is due to a combination of left ventricular hypertrophy with fibrosis, systolic dysfunction (a decrease in the ejection fraction) and diastolic dysfunction (elevated filling pressure of the LV).

Associated symptoms:
In Heyde's syndrome, aortic stenosis is associated with gastrointestinal bleeding due to angiodysplasia of the colon. Recent research has shown that the stenosis causes a form of von Willebrand disease by breaking down its associated coagulation factor (factor VIII-associated antigen, also called von Willebrand factor), due to increased turbulence around the stenosed valve.

Causes

SVAS can be caused by mutations in the ELN gene and be inherited in an autosomal dominant manner, although some individuals that inherit the mutated gene never develop features of the condition (called reduced penetrance).

Aortic valve stenosis can occur because of a birth defect in the formation of the valve. Calcium deposits may form on the valve with aging, causing the valve to become stiff and narrow. Stenosis can also occur as a result of rheumatic fever.

Prevention

There is no way to prevent aortic stenosis.

Diagnosis

Aortic stenosis is most often diagnosed when it is asymptomatic and can sometimes be detected during routine examination of the heart and circulatory system. Good evidence exists to demonstrate that certain characteristics of the peripheral pulse can rule in the diagnosis. In particular, there may be a slow and/or sustained upstroke of the arterial pulse, and the pulse may be of low volume. This is sometimes referred to as pulsus parvus et tardus. There may also be a noticeable delay between the first heart sound (on auscultation) and the corresponding pulse in the carotid artery (so-called 'apical-carotid delay'). In similar manner, there may be a delay between the appearance of each pulse in the brachial artery (in the arm) and the radial artery (in the wrist).

The first heart sound may be followed by a sharp ejection sound ("ejection click") best heard at the lower left sternal border and the apex, and, thus, appear to be "split". The ejection sound, caused by the impact of left ventricular outflow against the partially fused aortic valve leaflets, is more commonly associated with a mobile bicuspid aortic valve than an immobile calcified aortic valve. The intensity of this sound does not vary with respiration, which helps distinguish it from the ejection click produced by a stenotic pulmonary valve, which will diminish slightly in intensity during inspiration.

An easily heard systolic, crescendo-decrescendo (i.e., 'ejection') murmur is heard loudest at the upper right sternal border, at the 2nd right intercostal space, and radiates to the carotid arteries bilaterally. The murmur increases with squatting and decreases with standing and isometric muscular contraction such as the Valsalva maneuver, which helps distinguish it from hypertrophic obstructive cardiomyopathy (HOCM). The murmur is louder during expiration, but is also easily heard during inspiration. The more severe the degree of the stenosis, the later the peak occurs in the crescendo-decrescendo of the murmur.

The second heart sound (A2) tends to become decreased and softer as the aortic stenosis becomes more severe. This is a result of the increasing calcification of the valve preventing it from "snapping" shut and producing a sharp, loud sound. Due to increases in left ventricular pressure from the stenotic aortic valve, over time the ventricle may hypertrophy, resulting in a diastolic dysfunction. As a result, one may hear a fourth heart sound due to the stiff ventricle. With continued increases in ventricular pressure, dilatation of the ventricle will occur, and a third heart sound may be manifest.

Finally, aortic stenosis often co-exists with some degree of aortic insufficiency (aortic regurgitation). Hence, the physical exam in aortic stenosis may also reveal signs of the latter, for example an early diastolic decrescendo murmur. Indeed, when both valve abnormalities are present, the expected findings of either may be modified or may not even be present. Rather, new signs that reflect the presence of simultaneous aortic stenosis and insufficiency, e.g., pulsus bisferiens, emerge.

According to a meta analysis, the most useful findings for ruling in aortic stenosis in the clinical setting were slow rate of rise of the carotid pulse (positive likelihood ratio ranged 2.8–130 across studies), mid to late peak intensity of the murmur (positive likelihood ratio, 8.0–101), and decreased intensity of the second heart sound (positive likelihood ratio, 3.1–50).

Other peripheral signs include:

Sustained, heaving apex beat, which is not displaced unless systolic dysfunction of the left ventricle has developed
A precordial thrill
Narrowed pulse pressure

Electrocardiogram:

Although aortic stenosis does not lead to any specific findings on the electrocardiogram (ECG), it still often leads to a number of electrocardiographic abnormalities. ECG manifestations of left ventricular hypertrophy (LVH) are common in aortic stenosis and arise as a result of the stenosis having placed a chronically high pressure load on the left ventricle (with LVH being the expected response to chronic pressure loads on the left ventricle no matter what the cause).

As noted above, the calcification process that occurs in aortic stenosis can progress to extend beyond the aortic valve and into the electrical conduction system of the heart. Evidence of this phenomenon may rarely include ECG patterns characteristic of certain types of heart block such as Left bundle branch block.

Heart catheterization:
Cardiac chamber catheterization provides a definitive diagnosis, indicating severe stenosis in valve area of <1.0 cm2 (normally about 3 cm2). It can directly measure the pressure on both sides of the aortic valve. The pressure gradient may be used as a decision point for treatment. It is useful in symptomatic people before surgery. The standard for diagnosis of aortic stenosis is non invasive testing with echocardiography. Cardiac catheterization is reserved for cases in which there is discrepancy between the clinical picture and non-invasive testing, due to risks inherent to crossing the aortic valve such as stroke.

Echocardiogram:

Echocardiogram (heart ultrasound) is the best non-invasive tool / test to evaluate the aortic valve anatomy and function.

The aortic valve area can be calculated non-invasively using echocardiographic flow velocities. Using the velocity of the blood through the valve, the pressure gradient across the valve can be calculated by the continuity equation or using the modified Bernoulli's equation:

Gradient = 4(velocity)² mmHg

A normal aortic valve has a gradient of only a few mmHg. A decreased valvular area causes increased pressure gradient, and these parameters are used to classify and grade the aortic stenosis as mild, moderate or severe. The pressure gradient can be abnormally low in the presence of mitral stenosis, heart failure, co-existent aortic regurgitation and also ischaemic heart disease (disease related to decreased blood supply and oxygen causing ischaemia).

Echocardiogram may also show left ventricular hyperthrophy, thickened and immobile aortic valve and dilated aortic root. However, it may appear deceptively normal in acute cases

Prognosis

The prognosis for aortic valve stenosis depends on the severity of the disease. With surgical repair, the disease is curable. Patients suffering mild stenosis can usually lead a normal life; a minority of the patients progress to severe disease. Anyone with moderate stenosis should avoid vigorous physical activity. Most of these patients end up suffering some kind of coronary heart disease over a 10 year period. Because it is a progressive disease, moderate and severe stenosis will be treated ultimately with surgery. Severe disease, if left untreated, leads to death within 2 to 4 years once the symptoms start.

If untreated, severe symptomatic aortic stenosis carries a poor prognosis with a 2-year mortality rate of 50-60% and a 3-year survival rate of less than 30%..

Treatment

Treatment depends on the symptoms and how the heart's function is affected. The valve can be opened without surgery by using a balloon catheter, but this is often a temporary solution. The procedure involves inserting a deflated balloon at the end of a catheter through the arteries to the valve. It may include surgery to repair the condition in severe cases.