Bicuspid aortic valve
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 pediatric and cardiology textbooks.
Definition
A congenitally bicuspid aortic valve has 2 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.
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 will lead to the development of a
bicuspid valve, often through incomplete separation (or fusion) of valve tissue.
Bicuspid aortic valve often is seen with either coarctation of the aorta or
interrupted aortic arch, suggesting a common developmental mechanism.
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 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. Anterior-posterior 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
seen in 30-45% of cases. The conjunction is of tissue which 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
seen more commonly with bicuspid aortic valve. The left main coronary artery may
be up to 50% shorter in patients with bicuspid aortic valve.
The aortic root may be dilated. This has been attributed to "poststenotic"
dilatation. However, the aortic root may be inherently abnormal (e.g., it may
have decreased connective tissue).
Pathophysiology: With degeneration of aging valves, sclerosis and
calcification can occur. The bicuspid valve also may be completely competent,
producing no regurgitant flow. However, redundancy and prolapse of cusp tissue
can lead to valve regurgitation. Although bicuspid aortic valve is a common
abnormality, complications may arise in as many as one third of patients over
their lifetimes; this disorder, therefore, deserves close attention and medical
follow-up.
Frequency:
In the US: Bicuspid aortic valves may be present in up to 1-2% of the
population. Since the bicuspid valve may be entirely "silent" during
infancy, childhood, and adolescence, these incidence figures generally are not
included in the overall incidence of congenital heart disease.
Internationally: Incidence does not appear to be affected by race or
geography.
Sex: Male-to-female ratio is 2:1 or greater. Sex is not a predictive
variable in the natural history of bicuspid aortic valve.
Age: Bicuspid aortic valve may be identified at any age from birth
through the 11th decade; it also 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 will be diagnosed after a patient has
developed infective endocarditis with systemic embolization. Infective
endocarditis, when it occurs, is usually seen in children or young adults.
Stenosis of the 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.
Younger individuals who develop pathologic changes in the bicuspid aortic valve
are more likely to develop "pure" valve regurgitation than stenosis.
Clinical
History: Patients with bicuspid aortic valves may be
completely asymptomatic. 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 presenting in early infancy. This
critical form of stenosis is associated more frequently with a unicommissural
valve. In patients in whom a bicuspid aortic valve is seen in association with
other types of left heart obstruction (coarctation or interrupted aortic arch),
the bicuspid valve generally functions well, and symptoms usually are caused by
the associated disorder.
Inheritance: Although bicuspid aortic valve is generally sporadic,
familial clusters have been identified, with incidence as high as 10-17% in
first-degree relatives of probands.
Associated syndromes
Coarctation or interrupted aortic arch (bicuspid aortic valve present in >50%
of patients with these lesions).
Williams syndrome (bicuspid aortic valve, associated with supravalvular aortic
stenosis in 11.6%)
Patent ductus arteriosus, also associated with hand anomalies
Erdheim cystic medial necrosis (familial aortic dissection)
Turner syndrome (bicuspid aortic valve in 30% of patients)
Physical: Since the bicuspid aortic valve is frequently a clinically
"silent" condition, findings of a general examination are usually
normal.
Typical features of Turner syndrome (short stature in females with webbed neck
and broad chest) or Williams syndrome ("elfin" facies, mild
retardation) may suggest the possibility of bicuspid aortic valve.
Cardiac examination
The precordium is usually normal to palpation, and there is no evidence of
cardiomegaly.
The first heart sound is unaffected. The second heart sound splits normally with
inspiration, with absent or minimal outflow gradient. With increasing aortic
stenosis gradient, the splitting of the second sound will be less apparent or
may be absent. With severe stenosis, the second sound will be split
"paradoxically" (ie, with expiration). This splitting differs from
normal splitting of the first heart sound (ie, with tricuspid and mitral valve
closures) in that normal splitting is best appreciated at the lower left sternal
border and is a softer, lower-pitched sound than the click of a bicuspid aortic
valve.
The most common abnormal sound heard with bicuspid aortic valve has been
described as a systolic ejection "click." This sound is actually a
less distinct, medium-pitched sound heard well at the apex with the diaphragm of
the stethoscope. It is heard in all phases of respiration just after the first
heart sound, and its timing does not vary with maneuvers (eg, hand-grip,
Valsalva, squatting). The ejection sound also may be heard in the aortic area
(upper right sternal border), where it takes on a brighter and sharper quality.
In contrast, the click of pulmonary valvular stenosis is intermittent (heard
best during expiration) and located closer to the left sternal border. It is a
bit less distinct than the aortic valve click. The click of mitral valve
prolapse also may be heard at the apex but is softer, occurs later, and is less
distinct than the bicuspid aortic valve click. The mitral prolapse click often
will vary in timing with changes in position or isometric handgrip and may be
followed by the murmur of mitral regurgitation. Multiple showers of clicks are
common, and the sound has been likened to crinkling cellophane.
Minimal or mild stenosis may produce a soft and fairly harsh ejection murmur at
the upper right sternal border with possible radiation into the carotids.
Increasing severity of stenosis produces a longer, louder, and harsher murmur
with definite radiation into the carotids and possibly into the posterior
shoulder. With more severe stenosis, a thrill may be felt in the suprasternal
notch.
In the presence of a typical opening sound or click, the high-pitched sound of
subtle aortic valve insufficiency may be heard at the third left intercostal
space with the diaphragm of the stethoscope. A variety of maneuvers may be
helpful in auscultation, including isometric handgrip, having patients lean
forward in a seated position (to bring the aortic area closer to the chest
wall), and having patients hold their breath in expiration (also decreases the
distance between the stethoscope and the left ventricle).
Differentials
Aortic Stenosis, Subaortic
Aortic Stenosis, Supravalvar
Aortic Stenosis, Valvar
Aortic Valve Insufficiency
Cardiomyopathy, Hypertrophic
Mitral Valve Prolapse
Pulmonary Stenosis, Valvar
Rheumatic Heart Disease
Work-up
Lab Studies:
Total and high-density lipoprotein (HDL) cholesterol or fasting lipid profile
should be measured in children older than 3 years.
Elevated low-density lipoprotein (LDL) cholesterol may accelerate sclerosis of
the bicuspid aortic valve.
In the case of a child with bicuspid aortic valve and family history of
hypercholesterolemia or early coronary artery disease, baseline cholesterol may
be helpful in recommending dietary modification.
Imaging Studies:
Chest x-ray may show mild prominence of the ascending aorta in the
posteroanterior projection along the superior right heart border; this is due to
"poststenotic" dilation. Left ventricular enlargement would imply
progressive aortic valve insufficiency.
Two-dimensional echocardiography provides accurate confirmation of a bicuspid
aortic valve.
Imaging can show the bicuspid aortic valve in multiple planes. Most important
information is obtained from the parasternal long- and short-axis views.
Long-axis view shows the typical systolic "doming" due to limited
valve opening. An approximation of valve orifice diameter can be obtained at
peak systole. This view is also important for sizing the sinus of Valsalva,
sinotubular junction, and ascending aorta.
Short-axis view is used to examine commissures, leaflet morphology, mobility,
and presence or absence of a low raphe. Diameter or area of valve opening
generally is overestimated in this view, since the true orifice usually lies
above this plane.
Doppler measurements of peak and mean systolic velocities and gradients can be
recorded from the apical "5-chamber," the suprasternal, or the high
right parasternal views. Doppler signal should be lined up as closely as
possible and parallel to the "jet" to provide accurate estimates of
flow velocities. Estimates of flow velocity from the apical view sometimes can
be improved by moving the transducer more medially toward the sternum.
Parasternal long- and short-axis views also can be used for color Doppler
studies, which evaluate for aortic insufficiency. The severity of aortic valve
insufficiency can be assessed by several methods. One of the simplest and most
reliable is to measure the insufficiency jet diameter at the aortic valve
annulus and compare this diameter to the annulus diameter.
False-positive diagnosis of bicuspid aortic valve may arise from incomplete
demonstration of all 3-valve closure lines. The typical normal (trileaflet)
aortic valve shows a rotated "Mercedes sign" on closure. The bicuspid
valve may not be recognized if there is a high raphe seen with valve closure.
Angiography
The bicuspid aortic valve is viewed best in the anterior-posterior 30 degree
right anterior oblique (RAO) projection. Injection is into the left ventricle
and also into the aortic root.
Typical finding is systolic "doming" of the valve margins due to
incomplete opening.
Aortic insufficiency can be looked for on the aortic root injection.
Magnetic resonance imaging: MRI generally is not helpful for the
diagnosis of bicuspid aortic valve alone, but may be helpful for complete
assessment of the thoracic aorta in cases of coarctation, Turner syndrome, or
Williams syndrome.
Other Tests:
Electrocardiogram
ECG generally is normal for an isolated bicuspid aortic valve without stenosis
or insufficiency.
Progression of stenosis or insufficiency will lead to left atrial enlargement
and left ventricular hypertrophy.
Procedures:
Transesophageal echocardiography may be necessary to define valve commissures
and vegetations in adolescents or young adults in whom bicuspid aortic valve is
suspected on clinical grounds (particularly those with symptoms or findings that
suggest infective endocarditis).
Treatment
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.
Surgical Care: Surgery specifically for bicuspid aortic valve is not
necessary unless progressive complications ensue.
The patient with known bicuspid aortic valve will require 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.
Diet: Since 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.
Strenuous isometric activity, such as weight lifting, rope climbing, and
pull-ups, should be avoided by patients with aortic valve insufficiency.
Follow-up
Complications:
Overall complication rates are variable. In general, bicuspid aortic valve may
be a common reason for acceleration of "normal" aging process (eg,
valve sclerosis and calcification). Four specific complications are related to
the congenitally bicuspid aortic valve.
Aortic stenosis
Sclerosis of the bicuspid aortic valve generally begins in the second decade of
life, and calcification becomes more concerning from the fourth decade. The
presence of coronary risk factors (eg, smoking, hypercholesterolemia) may
accelerate these processes.
Approximately 50% of adults with severe aortic stenosis have a congenitally
bicuspid valve.
Historically, rheumatic fever was the most common cause of aortic stenosis. With
significantly decreasing incidence of rheumatic fever in "developed"
nations, bicuspid aortic valve is the most common cause of aortic stenosis in
adults and is probably the most common etiology of valve insufficiency, as well.
Acute rheumatic fever and its recurrences are still a major problem in
"developing" countries, and in these areas chronic effects of
rheumatic fever still are more significant than bicuspid valve in the etiology
of aortic stenosis and insufficiency. Rheumatic aortic valve damage can be
confirmed only at surgery or autopsy by the presence of Aschoff bodies.
Aortic insufficiency
The majority of cases of severe aortic insufficiency are related, either
directly or indirectly, to a congenitally bicuspid valve.
A number of factors may contribute to development of aortic valve insufficiency.
These include cusp prolapse, erosion of irregular commissure lines, aortic root
dilatation (particularly at the sinotubular junction or supra-aortic ridge),
infective endocarditis, and systemic hypertension (particularly with coarctation).
Bacterial (eg, infective) endocarditis
The risk of developing infective endocarditis on a bicuspid aortic valve is
10-30% over a lifetime.
Bicuspid aortic valve is the second most common congenital etiology for
infective endocarditis in infants and children; and overall, approximately 25%
of endocarditis infections develop on a bicuspid valve.
Aortic root dissection
Findings of histologic studies on the aortic root in individuals with bicuspid
aortic valve are controversial. Enlargement of the root is often attributed to
poststenotic dilatation. However, the root may dilate without significant valve
stenosis.
The risk of aortic root dissection is much higher for individuals with Marfan
syndrome (approximately 40%) than for those with bicuspid aortic valve
(approximately 5%). Since bicuspid valve is a much more prevalent disorder,
dissection of the ascending aortic root more commonly is associated with the
valve abnormality.
Prognosis:
Overall 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."
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 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.
The majority of young individuals with bicuspid aortic valve should not require
restrictions in physical activity or sports participation, unless they have
stenosis or insufficiency.
Medical/Legal Pitfalls:
The bicuspid aortic valve may fail to be recognized as a source for emboli in
cases of unexplained fever and focal central nervous system deficits.