C h a p t e r 1 9
Disorders of Cardiac Function
461
The effects of valvular heart disease depend on the
valve involved, the degree of involvement, the rapidity
of onset, and the rate and adequacy of compensatory
mechanisms. For example, sudden destruction of an
aortic valve cusp by infection can cause massive regurgi-
tation and rapid heart failure, whereas rheumatic mitral
stenosis usually develops over years without obvious
symptoms. Abnormal turbulent flow through diseased
valves typically produces abnormal heart sounds called
murmurs
.
Mitral Valve Disorders
The mitral or left atrioventricular (AV) valve controls
the directional flow of blood between the left atrium and
the left ventricle. The edges or cusps of both AV valves,
which are thinner than those of the semilunar (i.e., pul-
monic and aortic) valves, are anchored to the papillary
muscles by the chordae tendineae. During much of sys-
tole, the mitral valve is subjected to the high pressure
generated by the left ventricle as it pumps blood into
the systemic circulation. During this period of increased
pressure, the chordae tendineae prevent the eversion of
the valve leaflets into the left atrium.
Mitral Valve Stenosis.
Mitral valve stenosis represents
the incomplete opening of the mitral valve during dias-
tole, with left atrial distension and impaired filling of
the left ventricle (see Fig. 19-15). Mitral valve stenosis
is most commonly the result of rheumatic fever.
37,38
Less
frequently, the defect is congenital and manifests dur-
ing infancy or early childhood or calcification in elderly
patients. Mitral valve stenosis is a continuous, progres-
sive, lifelong disorder consisting of a slow, stable course
in the early years and progressive acceleration in later
years.
Mitral valve stenosis is characterized by fibrous
replacement of valvular tissue, along with stiffness and
fusion of the valve apparatus (see Fig. 19-14). Typically,
the mitral cusps fuse at the edges and the chordinae ten-
dinae thicken and shorten pulling the valvular structures
into the ventricles. As the resistance to flow through the
valve increases, the left atrium dilates and left atrial
pressure increases. The increased left atrial pressure
eventually is transmitted to the pulmonary venous sys-
tem, causing pulmonary congestion. A characteristic
auscultatory finding in mitral stenosis is an opening
snap following the second heart sound, which is caused
by the stiff mitral valve. As the stenosis worsens, there is
a localized low-pitched diastolic murmur that increases
in duration with the severity of the stenosis.
The clinical presentation of mitral valve stenosis
depends on the severity of the obstruction or the
degree of reduction in the valve area—the more severe
the stenosis, the greater the symptoms. Manifestations
are related to the elevation in left atrial pressure and
pulmonary congestion such as dyspnea with exer-
tion, decreased cardiac output owing to impaired left
ventricular filling, and left atrial enlargement with the
development of atrial arrhythmias and mural thrombi.
More severe stenosis is associated with symptoms of
pulmonary congestion, including paroxysmal noctur-
nal dyspnea (PND) and orthopnea. Palpitations, chest
pain, weakness, and fatigue are common complaints.
Aortic valve stenosis
Mitral valve regurgitation
Mitral valve stenosis
Aortic valve regurgitation
Pulmonary veins
Aortic valve
Mitral valve
Systole
Diastole
Left atrium
Left ventricle
FIGURE 19-15.
Alterations in
hemodynamic function that
accompany aortic valve stenosis,
mitral valve regurgitation, mitral
valve stenosis, and aortic valve
regurgitation.The thin arrows
indicate direction of normal flow,
and thick arrows the direction of
abnormal flow. Expand description.
