Download The Washington Manual of Medicine 2nd Edition

The Washington Manual of Medicine 2nd Edition
Valvular heart disease
A. Pathophysiology and clinical presentation
1. Aortic stenosis (AS). Left ventricular outflow obstruction can occur at the subvalvular, the supravalvular,
or (most commonly) the valvular level. Aortic valvular stenosis is usually the result of degeneration and
calcification of a normal or congenitally bicuspid aortic valve. Less frequently, AS develops many years
after an episode of acute rheumatic fever. AS places a pressure overload on the left ventricle. Adequate
cardiac output is usually maintained until late in the course of AS but at the expense of left ventricular
hypertrophy. Physical signs include a systolic ejection murmur, diminished carotid pulses, and a sustained,
forceful, nondisplaced apical impulse. Symptoms often develop when the valve area decreases to 1.0 cm2 or
less.
2. Angina pectoris develops in approximately 65% of patients with severe AS and results from ventricular
hypertrophy (e.g., increased myocardial oxygen demand and reduced coronary perfusion) and the high
incidence of concomitant CAD. Syncope (25% incidence) probably results from fixed cardiac output and
decreased cerebral perfusion during systemic vasodilatation. Dyspnea usually represents the development of
congestive heart failure. The development of symptoms is associated with a 50% 2-year mortality (Am Heart
J 99:419, 1980).
3. Aortic insufficiency (AI) is usually the result of valve leaflet pathology from rheumatic heart disease
(often associated with mitral valve disease) or myxomatous degeneration. AI may also result from other
causes of leaflet dysfunction or aortic root dilatation, including endocarditis, syphilis, connective tissue
diseases (e.g., Marfan's syndrome), inflammatory disease (e.g., ankylosing spondylitis), hypertension, and
aortic dissection. Chronic AI results in volume overload of the left ventricle, causing chamber enlargement
and wall thickening (although a relatively normal ratio of wall thickness to volume is usually maintained).
Gradual myocardial decompensation often progresses either without symptoms or with subtle symptoms
(e.g., weakness, fatigue, or dyspnea on exertion). Physical signs include a hyperdynamic circulation with
markedly increased systemic arterial pulse pressure, known as Corrigan's water-hammer pulse; forceful and
laterally displaced apical impulse; and a decrescendo diastolic murmur. Acute AI is not well tolerated
because of the lack of compensatory chamber enlargement and thus often results in fulminant pulmonary
edema, myocardial ischemia, and cardiovascular collapse.
4. Mitral stenosis (MS) is caused by rheumatic fever in almost all cases. Other less common causes include
collagen vascular diseases, amyloidosis, and congenital stenosis. MS places a pressure overload on the left
atrium with relative sparing of ventricular function. Left atrial dilatation to more than 45 mm is associated
with a high incidence of atrial fibrillation and subsequent thromboembolism. A transvalvular pressure
gradient is present with a valve area of less than 2 cm2, and critical MS occurs when the valve area is 1 cm2
or less. Physical signs include an apical diastolic murmur, an opening snap, and a loud S1. Symptoms usually
develop late and reflect pulmonary congestion (e.g., dyspnea), reduced left ventricular preload (e.g., low–
cardiac-output syndrome), or atrial fibrillation (e.g., thromboembolism).
5. MR results from abnormalities of the leaflets (e.g., rheumatic disease, myxomatous degeneration,
endocarditis), annulus (e.g., calcification, dilatation, or destruction), chordae tendineae (e.g., rupture from
endocarditis or MI, fusion, or elongation), or ischemic papillary muscle dysfunction or rupture. The most
common cause of MR in the United States is myxomatous degeneration. MR places a volume overload on
the left ventricle and atrium, causing chamber enlargement and wall thickening, although a relatively normal
ratio of wall thickness to volume is usually maintained. Systolic unloading into the compliant left atrium
allows enhanced emptying of the left ventricle during systole with only slight increases in oxygen
consumption. Atrial fibrillation often develops because of left atrial dilatation. Physical signs include a
hyperdynamic circulation with a brisk laterally displaced apical impulse, a holosystolic murmur, and a
widely split S2. Gradual myocardial decompensation often progresses in the absence of symptoms (e.g.,
dyspnea on exertion, fatigue). In acute MR, adaptation is not possible, and fulminant cardiac decompensation
often ensues.
6. Tricuspid insufficiency (TI) most often results from a functional dilatation of the valve annulus caused
by pulmonary hypertension, which, in turn, may be caused by intrinsic mitral or aortic valve disease. Causes
of primary TI include rheumatic heart disease, bacterial endocarditis (usually in intravenous drug users),
carcinoid tumors, and blunt trauma. Patients have a systolic murmur, a prominent jugular venous pulse, and a
pulsatile liver. Mild to moderate TI usually is well tolerated.
B. Diagnostic tests. Cardiac catheterization or echocardiography can be used to estimate valve areas,
transvalvular pressure gradients, and the degree of regurgitant flow in patients with valvular heart disease.
C. Indications for operation
1. Aortic valve replacement is usually indicated for AS in symptomatic patients and in asymptomatic patients
with critical AS (e.g., a valve area <1.0 cm2 or a transvalvular pressure gradient ³50 mm Hg). Timing of
surgery for AI is critical because irreversible myocardial dysfunction often precedes the development of
symptoms. Indications for operation include symptoms or objective evidence of ventricular decompensation
(e.g., ejection fraction <50%, increased left ventricular end-diastolic volume and end-systolic left ventricular
diameter >55 mm). If there is coexistent CAD documented by coronary arteriography, patients should
undergo concomitant CABG.
2. Mitral valve replacement or repair is indicated for patients with symptomatic MR, new-onset atrial
fibrillation, or objective evidence of left ventricular dysfunction (same as for AI). Operation is indicated in
symptomatic MS or asymptomatic patients with critical MS (valve orifice <1 cm2). With the advent of mitral
valve repair, operation is often undertaken earlier if the valvular anatomy suggests that the valve can be
repaired rather than replaced.
3. Tricuspid valve. Significant tricuspid regurgitation may be repaired at the time of surgery for other cardiac
anomalies. Intervention for isolated TI is uncommon. The majority of tricuspid valves can be repaired with
simple annuloplasty techniques rather than replaced. Patients with endocarditis and TI can undergo simple
valve excision.
4. Endocarditis. The main indications for operation include hemodynamic instability, recurrent septic emboli,
and persistent evidence of infection despite appropriate antibiotic therapy. Relative indications include
severe acute mitral or aortic valvular insufficiency, heart block, and intracardiac fistulas.
D. Selection of a prosthetic valve must be individualized for each patient. Despite years of research, there
still is no ideal prosthetic valve for all patients. The general considerations for selecting an appropriate
prosthetic valve are summarized in Table 36-1.
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