Thoracic Imaging 2003 - Society of Thoracic Radiology

MONDAY
104
Valvular Heart Disease
Lynn S. Broderick, M.D.
Objectives
At the completion of this course, the attendee should be able
to:
1. Describe major causes of valvular heart disease
2. Describe the typical radiographic appearance of valvular
heart disease including chest radiography, CT and MR
3. Describe the physiology of valvular heart disease and how it
affects patients’ symptoms
Basic Principles of Valvular Heart Disease
When a cardiac valve is stenotic, the proximal chamber
hypertrophies in order to overcome the increased pressure necessary
to pump blood through the valve. The receiving chamber
is unaffected by the stenotic valve. When a cardiac valve is
regurgitant, both the proximal and receiving chambers dilate;
the delivering chamber because it is receiving additional blood
volume through the regurgitant valve, and the receiving chamber
as it receives this additional blood volume during its filling
phase. Echocardiography is the study of choice in evaluation
of valvular heart disease. However, the diagnosis may be first
suggested on chest radiograph. Patients with known valvular
heart disease may also demonstrate typical findings on crosssectional
imaging. MR imaging may be performed in cases
where echocardiography is unable to fully evaluate the heart.
Gated 2D fiesta images will demonstrate the signal void of the
jet of blood being forced through a stenotic valve or the retrograde
jet of blood through a regurgitant valve. Phase contrast
sequences can be performed to quantitate the peak velocity.
Aortic Stenosis
Aortic stenosis may result from a congenital abnormality, a
sequela of rheumatic heart disease or may be due to age-related
degeneration. The stenotic aortic valve results in pressure overload
for the left ventricle, which must hypertrophy in order to
maintain cardiac output. The hypertrophied left ventricle
requires an increased supply of oxygen due to the increased
muscle mass as well as the increased work that is being performed.
This can result in an oxygen imbalance that leads to
angina, even in the presence of normal coronary arteries.
During periods of exercise, there is increase in peripheral capacitance.
In the normal person, the left ventricle responds to this
by increasing the cardiac output. In aortic stenosis, the left ventricle
may be responding maximally at rest and will be unable to
increase cardiac output. This can lead to decreased blood flow
to the brain resulting in syncope. Decreased blood flow to the
left ventricle can also result in ventricular arrhythmias leading
to syncope or sudden death. If the left ventricle fails, dyspnea
and signs of heart failure may be the dominant symptoms.
Congenital bicuspid aortic valve occurs in 1-2% of the population.
The two cusps can be oriented in an anterior and posterior
position, with the right and left coronary arteries arising from
the anterior leaflet or they may be oriented in a left and right
position with one coronary artery arising from each leaflet. The
anterior or right leaflets have a raphe, the site where the commissure
should have formed. Complications of bicuspid aortic
valve include valvular stenosis, valvular regurgitation and bacterial
endocarditis. Patients with aortic malformations have a high
incidence of bicuspid aortic valve. For example, approximately
50% of patients with aortic coarctation will also have a bicuspid
aortic valve. Turbulent blood being ejected through the abnormal
valve is thought to result in wear and tear causing thickening
of the leaflets. Calcification of the valve begins during the
4th decade of life. As with all causes of aortic stenosis, the
amount of valvular calcification correlates with the severity of
the stenosis. The diagnosis of a bicuspid aortic valve can be
made on chest radiograph when the valve and raphe are calcified.
As the valve becomes stenotic, the blood is pumped
through at increased pressure and forms a jet. This jet of blood
can, over time, cause dilatation of the ascending aorta. Patients
with aortic stenosis secondary to a bicuspid aortic valve tend to
present earlier in life than patients with aortic stenosis from
other causes.
Rheumatic fever occurs following beta-hemolytic streptococcal
pharyngitis. Valvular disease secondary to rheumatic fever
almost always involves the mitral valve. Mitral valve disease
occurs 7-10 years following rheumatic endocarditis with aortic
stenosis developing approximately seven years following the
onset of mitral valve disease. As the endocarditis heals, the
commissures thicken and fuse resulting in stenosis. Asymmetry
of the fused commissures may result in the appearance of a
bicuspid valve. However, there is greater asymmetry of the
leaflet size in rheumatic aortic stenosis than in congenital bicuspid
aortic valve.
Age-related degeneration of the aortic valve can occur in
patients over the age of 65 and affects women more than men.
The leaflets thicken and eventually calcify, resulting in a stenotic
valve. In contrast to rheumatic aortic stenosis, the commissures
are not fused in age-related degenerative aortic stenosis.
The chest radiograph and cross-sectional imaging will show
normal vascularity and may show evidence of left ventricular
hypertrophy. Calcification of the aortic valve may be present
and is seen best on the lateral view as it is obscured by the spine
on the PA radiograph. It should be noted that patients might
have aortic stenosis without evidence of valvular calcification
on the chest radiograph. However, visible calcification of the
aortic valve on the chest radiograph implies aortic stenosis. In
patients with bicuspid aortic stenosis, prominence of the ascending
aorta secondary to post-stenotic dilatation may be identified.
This is due to the jet effect of blood being pumped through the
narrowed valve, which is directed toward the lateral wall of the
aorta. The aortic arch and descending aorta will be normal.
Aortic Regurgitation
Aortic regurgitation can occur secondary to an abnormal aortic
valve or from an abnormality of the aortic root. Congenital
bicuspid aortic valve can result in aortic regurgitation if the larger
of the two cusps does not appose the smaller cusp.
Degenerative and rheumatic aortic stenosis may result in aortic
regurgitation due to shortening of the leaflets as they thicken.
Bacterial endocarditis can cause perforation of the valve leaflets