Bicuspid Aortic Valve

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BACKGROUND

The bicuspid aortic valve has been recognized as a common congenital abnormality for centuries. Leonardo da Vinci was one of the first to call attention to the aortic valve with 2 leaflets. He recognized the superior engineering advantages of the normal trileaflet valve. Considering that it is a common abnormality, bicuspid aortic valve is mentioned only briefly in many paediatric and cardiology textbooks.

A bicuspid aortic valve is a heart condition that is usually due to a congenital deformity. A normal aortic valve has three cusps, whereas a bicuspid valve has only two. About 1-2% of the population have bicuspid aortic valves, although the condition is nearly twice as common in males. The majority will cause no problems. However, especially in later life, a bicuspid aortic valve may become calcified, which may lead to varying degrees of severity of aortic stenosis and aortic reguritation, which will manifest as murmurs. If these become severe enough, they may require heart surgery. Most patients with bicuspid aortic valve whose valve becomes dysfunctional will need careful follow-up and potentially valve replacement in their third or fourth decade of life. Bicuspid aortic valve has been found to be a inheritable. Familial clustering as well as isolated valve defects have been documented. The incidence of bicuspid aortic valve can be as high as 10% in families affected with the valve problem. It is estimated to exist in 1 to 2 % of the population, predominating in males. Other congenital heart defects are associated with bicuspid aortic valve at various frequencies.

Another important fact is the aorta of patients with bicuspid aortic valve is not normal. The aorta of a patient with a bicuspid aortic valve does not have the same histological characteristics of a normal aorta. The tensile strength is reduced. These patients are at a higher risk for aortic dissection and aneurysm formation of the ascending aorta. The size of the proximal aorta should be evaluated careful during the work-up. The initial diameter of the aorta should be noted and periodic evaluation with CT scan (every year or sooner if there is a change in aortic diameter) should be recommended. Therefore, if the patient needs surgery, the size of the aorta will determine what type of surgery should be offered to the patient. Additionally, patients with bicuspid aortic valve are at higher risk of aortic coarctation (see previous blog), an abnormal narrowing of the thoracic aorta.
Patients with bicuspid aortic valve should be followed by cardiologist or cardiac surgeon with specific interest in this valve pathology.

DEFINITION

What is a bicuspid aortic valve?

A congenitally bicuspid aortic valve has 2 functional leaflets. Most have 2 complete commissures. Approximately half of cases have a low raphe. Not included are stenotic or partially fused valves caused by inflammatory processes, such as rheumatic fever.

Bicuspid aortic valve occurs when the aortic valve does not develop normally while the baby is in the womb. It is one of the most common congenital heart defect affecting about 20 per 1000 babies born.

HISTORY

Patients with bicuspid aortic valves may be completely asymptomatic. About 30% of individuals with a bicuspid aortic valve develop complications. If symptoms are present, they relate to the development of aortic stenosis, aortic insufficiency, or both. Occasionally, a congenitally bicuspid aortic valve may be the cause of critical aortic stenosis, with symptoms of severe congestive heart failure developing in early infancy. This critical form of stenosis is more frequently associated with a unicommissural valve. In patients in whom a bicuspid aortic valve is observed in association with other types of left heart obstruction (coarctation or interrupted aortic arch), the bicuspid valve generally functions well, and symptoms are usually caused by the associated disorder.

  • Inheritance: Although most cases of bicuspid aortic valve are sporadic, familial clusters have been identified, with incidence as high as 10-17% in first-degree relatives of probands. Increasing evidence suggests an autosomal-dominant inheritance pattern with variable penetrance, encompassing the entire spectrum of left heart obstruction (hypoplastic left heart syndrome, aortic stenosis, coarctation of the aorta).
  • Associated syndromes
    • Coarctation or interrupted aortic arch (bicuspid aortic valve is present in >50% of patients with these lesions)
    • Williams syndrome (bicuspid aortic valve associated with supravalvular aortic stenosis occurs in 11.6% of cases)
    • Patent ductus arteriosus, also associated with hand anomalies
      Erdheim cystic medial necrosis (familial aortic dissection)

Turner syndrome (bicuspid aortic valve occurs in 30% of patients)

ANATOMY

The bicuspid valve is composed of 2 leaflets or cusps, usually of unequal size. The larger leaflet is referred to as the conjoined leaflet. Two commissures (or hinge points) are present; usually neither is partially fused. The presence of a partially fused commissure, which has also been called a high raphe, probably predisposes toward eventual stenosis. At least half of all congenitally bicuspid valves have a low raphe, which never attains the plane of the attachments of the two commissures and which never extends to the free margin of the conjoined cusp. Redundancy of a conjoined leaflet may lead to prolapse and insufficiency.

Valve leaflet orientation can vary. Anteroposterior orientation of the commissures, with right (conjoined) and left leaflets, occurs in approximately 50-65% of cases. The conjunction is of tissue that would normally form the right noncoronary commissure. Horizontal (left-right) orientation of the commissures, with anterior (conjoined) and posterior leaflets is observed in 30-45% of cases. The conjunction is of tissue that would normally form the left-right commissure. For unclear reasons, conjunction of tissue normally destined to form the left noncoronary commissure is rare.

Coronary arteries may be abnormal. A left-dominant coronary system (ie, posterior descending coronary artery arising from the left coronary artery) is more commonly observed with bicuspid aortic valve. Rarely, the left coronary artery may arise anomalously from the pulmonary artery. The left main coronary artery may be up to 50% shorter in patients with a bicuspid aortic valve. Occasionally, the coronary ostium may be congenitally stenotic in association with bicuspid aortic valve.

The aortic root may be dilated. This has been attributed to poststenotic dilatation in association with aortic stenosis. However, the aortic root may be inherently abnormal (eg, it may have abnormal connective tissue with cystic medial necrosis changes indistinguishable from other disorders such as Marfan syndrome).

The aortic valve (1) is one of four valves in the normal heart. It sits between the left ventricle (2) and the aorta (3). Heart valves are thin flaps of tissue anchored in a fibrous ring. The normal aortic valve has 3 leaflets (4) that open to allow blood to move forward and close to prevent backward blood flow. In bicuspid aortic valve (5), there are only 2 leaflets instead of three and the valve leaflets are often thickened. This can result in obstruction of blood flow across the valve, a condition called aortic stenosis and/or valve leakage, a condition called aortic valve regurgitation. The natural course of bicuspid aortic valve varies widely. There can be severe aortic stenosis at birth, due to incomplete opening of the valve leaflets. Aortic stenosis can also develop during childhood, during adulthood, peaking around the fourth decade of life, or it may never develop. Aortic valve leakage (called aortic regurgitation or aortic insufficiency) is less common during early childhood but can also develop over time.

The normal aortic valve, as shown in the drawing, has three leaflets (flaps, cusps) that move flexibly, opening and closing to control the flow of blood into the aorta from the left ventricle of the heart as it beats. When the cusps come together as the valve closes, the shape is that of a trisected circle

In contrast, a BAV has only two leaflets, also shown in the diagram on the left. It is sometimes described as resembling the mouth of a fish as it opens and closes. Depending on the degree of malformation and associated malfunction, blood flowing through the valve may make an abnormal sound, called a murmur. While some bicuspid aortic valves are silent, the detection of a murmur may be the first indication of abnormality of the aortic valve. Over time a bicuspid valve may lose its ability to open widely, close properly or both. As previously described, a murmur may develop. Regardless of how the valve is failing, it should be monitored and a surgical solution planned appropriately before any lasting damage is done to the heart.

EMBRYOLOGY

The embryonic truncus arteriosus is divided by the spiral conotruncal septum during development. The normal right and left aortic leaflets form at the junction of the ventricular and arterial ends of the conotruncal channel. The nonseptal leaflet (posterior) cusp normally forms from additional conotruncal channel tissue. Abnormalities in this area lead to the development of a bicuspid valve, often through incomplete separation (or fusion) of valve tissue.

Bicuspid aortic valve is often observed with other left-sided obstructive lesions such as coarctation of the aorta or interrupted aortic arch, suggesting a common developmental mechanism.

AGE

Bicuspid aortic valve may be identified in patients of any age, from birth through the 11th decade of life. It may be only an incidental finding at autopsy. Bicuspid aortic valve may remain silent and be discovered as an incidental finding on echocardiographic examination of the heart.

  • Critical aortic stenosis and infective endocarditis may be considered relatively early sources of morbidity for patients with bicuspid aortic valve. Critical aortic stenosis may occur in infancy and may be associated with a bicuspid valve.
  • Occasionally, bicuspid aortic valve is diagnosed after a patient has developed infective endocarditis with systemic embolization.
  • Stenosis of a bicuspid aortic valve is more likely to develop in persons older than 20 years and is caused by progressive sclerosis and calcification. High levels of serum cholesterol have been associated with more rapidly progressive sclerosis of the congenitally bicuspid aortic valve.
  • Children who develop early progressive, pathologic changes in the bicuspid aortic valve are more likely to develop valve regurgitation than stenosis. Bicuspid aortic valve was identified in 167 (0.8%) of 20,946 young Italian military conscripts. Of these, 110 were found to have either mild or moderate aortic insufficiency.

TESTS

How is the problem diagnosed?

Medical tests:
Medical tests that are carried out:

Imaging Studies:

  • Chest radiography
  • Two-dimensional echocardiography provides accurate confirmation of a bicuspid aortic valve.
  • Angiography
  • Magnetic resonance imaging: MRI is generally not helpful for the diagnosis of bicuspid aortic valve alone, but it may be helpful for complete assessment of the thoracic aorta, particularly in cases of coarctation, Turner syndrome, or Williams syndrome.
  • Transesophageal echocardiography

Other Tests:

  • Electrocardiography
  • Testing in family members

Physical:
Because the bicuspid aortic valve is frequently a clinically silent condition, general examination findings are usually normal.

  • Typical features of Turner syndrome (eg, short stature in females with webbed neck and broad chest) or Williams syndrome (eg, elfin facies, mild retardation) may suggest the possibility of bicuspid aortic valve.

Cardiac examination

TREATMENT.

How is the defect treated?
Treatment is needed only if the valve becomes obstructed or leaky. See page on Aortic Stenosis for more information.

Medical Care: No specific medical care is required for individuals with bicuspid aortic valve, unless they have progressive deterioration or infection. Serial follow-up evaluations are important for early recognition of potential complications (valve insufficency, valve stenosis, progressive aortic root dilation) and the prevention of possible bacterial endocarditis.

Surgical Care: Surgery specifically for bicuspid aortic valve is not necessary unless progressive complications ensue (valve insufficiency, valve stenosis, progressive aortic root dilation, possible bacterial endocarditis).

  • The patient with known bicuspid aortic valve requires antibiotic prophylaxis for invasive dental or noncardiac surgical procedures.
  • For noncardiac procedures, preoperative cardiac evaluation may be appropriate, particularly for patients with aortic stenosis or insufficiency. The patient with simple, uncomplicated bicuspid aortic valve should not require special anesthetic precautions, other than bacterial endocarditis prophylaxis, when appropriate.

Diet: Because hypercholesterolemia and other coronary artery disease risk factors may accelerate the sclerosis and deterioration of a congenitally bicuspid aortic valve, a heart-healthy diet is recommended for all patients, not only those with recognized risk factors. This diet should limit fat calories to no more than 30% of total calories. Calories from saturated fats should be limited to no more than 10% of total.

Activity: Patients with normally functioning bicuspid aortic valves (ie, no stenosis or insufficiency) do not require activity restrictions. They may participate in organized competitive sports activities.

  • Patients who develop valve insufficiency or stenosis from a congenitally bicuspid aortic valve may require restrictions from strenuous competitive sports.
  • Patients with aortic valve insufficiency should avoid strenuous isometric activity, such as weight lifting, rope climbing, and pull-ups.

PROGNOSIS

For the individual with bicuspid aortic valve is good. Reviews and reports in the past have emphasized the fairly benign course for patients with bicuspid valves. However, more recent reports on the natural history of these valves suggest a number of more serious problems and an acceleration of normal valvular wear and tear. These problems may not develop until adulthood. Routine and regular follow-up for the child or adolescent with bicuspid aortic valve is recommended.

PATIENT EDUCATION

  • Patient and family education should emphasize the fairly benign course for the child with bicuspid aortic valve.
  • Older children and adolescents should begin to be made aware of the accelerated aging processes (ie, progressive stenosis), with particular attention to coronary risk factors.
  • The importance of bicuspid aortic valve as a potential substrate for infective endocarditis should be emphasized. Good oral and dental hygiene, with appropriate antibiotic prophylaxis for procedures, is important.
  • Most young individuals with bicuspid aortic valve should not require restrictions in physical activity or sports participation, unless they have stenosis or insufficiency.

FREQUENCY

  • In the US: Bicuspid aortic valves may be present in up to 1-2% of the population. Because the bicuspid valve may be entirely silent during infancy, childhood, and adolescence, these incidence figures may be underestimated and are not generally included in the overall incidence of congenital heart disease.
  • Internationally: Incidence does not appear to be affected by race or geography.

Sex: The male-to-female ratio is 2:1 or greater. Sex is not a predictive variable in the natural history of bicuspid aortic valve. A recent prospective echocardiographic study in newborn infants showed a prevalence of bicuspid aortic valve in 7.1 per 1,000 male newborns versus 1.9 per 1,000 female newborns

The remainder of this section refers to patients with bicuspid aortic valve WITHOUT aortic stenosis.

What are the effects of this defect on my child’s health?
Bicuspid aortic valve alone does not cause symptoms unless significant obstruction or leakage develop. Since the narrowing tends to increase over time and can progress during childhood, follow-up by a specialist is needed.

Children with bicuspid valve are at increased risk for subacute bacterial endocarditis (SBE). This is an infection of the heart caused by bacteria in the blood stream. Children with heart defects are more prone to this problem because of the altered flow of blood through the heart. It can occur after dental work or medical procedures on the GI or respiratory tract because these procedures almost always result in some bacteria entering the blood. SBE can usually be prevented by taking an antibiotic before these procedures

How is the problem diagnosed?

Symptoms:
Bicuspid aortic valve without aortic stenosis does not cause any symptoms.

Medical tests:
The suspected diagnosis is confirmed by an echocardiogram. Other tests include an electrocardiogram and chest x-ray.

Physical findings: The presence of an extra heart sound called a “click” and a heart murmur alert the doctor to the possible diagnosis. Since the findings can be quite subtle, the diagnosis may not be made until later childhood or even adulthood

What are the long-term health issues for these children?
SBE prophylaxis: SBE prophylaxis is needed as outlined above.

Exercise guidelines: An individual exercise program is best planned with the doctor so that all factors can be included. Generally, there are no restrictions needed for children with bicuspid aortic valve as long as there is there is no or only slight valve obstruction or leakage.

Disclaimer:

The facts and opinions shown on this blog are as accurate and up to date as possible, but are provided as general “information resources”, which may not be relevant to individual persons. This blog is not a substitute for individual assessment and always take advice from a doctor who is familiar with the particular person.

Consult you or your child’s physician regard the specific outlook for you or your child.

Related Links

American Heart Org
Wikipedia
Emedicine.com
Umich Education
CSMC Education

References

Beppu S, Suzuki S, Matsuda H et al. Rapidity of progression of aortic stenosis in patients with congenital bicuspid aortic valves. Amer J Cardiol 1993;71:322-327. Written by: S. LeRoy RN, MSN, Reviewed by D. Crowley, MD, April, 2003