Aortic Stenosis refers to a condition that causes obstruction to blood flow between the left ventricle and the aorta.
There are a variety of causes, including muscular obstruction below the aortic valve, obstruction at the valve itself, or aortic narrowing immediately above the valve. The most common form of aortic stenosis is obstruction at the valve itself, referred to as aortic valvar stenosis, which is the subject of this article.
The normal aortic valve consists of three thin and pliable valve leaflets. When the left ventricle ejects blood into the aorta, normal aortic valve leaflets spread apart easily and cause no obstruction to outflow of the blood from the heart. Aortic stenosis occurs when abnormalities of the aortic valve lead to narrowing and obstruction between the left ventricle and the aorta.
The most common abnormality occurs when the aortic valve has only two (instead of three) leaflets. This is called a bicuspid aortic valve (or BAV). Often the valve leaflets are thickened and less pliable than normal, and the lines of separation between them (or "commissures") are fused together to a variable degree. When the aortic valve does not open freely, the left ventricle must work harder to eject blood into the aorta.
To compensate for this additional workload, the muscle of the left ventricle (the myocardium) gradually thickens to provide additional strength to left ventricular ejection. The increased left ventricular muscle, also known as hypertrophy, is rarely a problem itself. Instead, hypertrophy is an indication of significant valve obstruction.
When the aortic valve is severely obstructed, the left ventricular muscle may not be able to compensate satisfactorily. In these very severe, but fortunately rare, instances the left ventricle may fail to pump blood effectively and the patient may develop cardiac failure.
Children with mild-to-moderate degrees of aortic valve stenosis will have easily detectable heart murmurs, and typically have no symptoms at all. Symptoms occur only with severe aortic stenosis.
A newborn with critical aortic valve stenosis develops heart failure in the first days of life. This is an emergency situation that requires immediate treatment, either balloon dilation of the valve or surgery. In an older child, severe aortic stenosis causes the child to experience chest pain, lightheadedness or fainting spells particularly associated with exercise. In rare, but well-documented cases, severe aortic valve stenosis is the cause of sudden death during strenuous sports activities.
Children with mild aortic stenosis rarely require treatment. However, it is important to note that aortic stenosis may be progressive, and that children with mild disease may eventually require treatment later in life. It is also important to understand that all treatment for aortic valve stenosis is palliative (that is, it does not return the valve to a normal condition). Therefore, before and after successful treatment it is important that all children with aortic stenosis be followed carefully by a qualified cardiologist.
The type of treatment required depends on the type of valve abnormality present. Most commonly, the stenotic aortic valve is of normal size, is bicuspid (that is, two leaflets instead of three), and has a variable degree of fusion along the commissures (or lines of leaflet opening). This "typical" form of aortic valvar stenosis responds very nicely to balloon dilation procedures. Balloon dilation valvuloplasty is performed at the time of cardiac catheterization and does not require open-heart surgery. In the newborn, it can be performed through the umbilical artery, thus sparing the use of a small infant's femoral arteries.
Surgical valvotomy is an open-heart procedure during which the surgeon opens the valve along the lines of commissural fusion. In many centers this open-heart procedure has been replaced by the less invasive balloon dilation valvuloplasty technique.
Open-heart surgical procedures are required for more complex valves, where simple balloon dilation does not suffice. These valves may be obstructed by severe calcium deposits in their leaflets, or because the valve ring itself is small and underdeveloped. For these conditions surgical aortic valve replacement will be necessary.
Long-term follow-up, with regular evaluations by a qualified cardiologist, is essential to helping provide the highest quality outcome for patients with aortic stenosis.