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Etiologies
By far the number one cause of MS is rheumatic valvular disease (RVD). This accounts for approximately
98% of all MS. RVD is more common in females than in males and up to 50% of the time, a person with
newly diagnosed MS will not report a history of rheumatic fever as a child. The incidence of MS has been
drastically reduced in the United States since the advent of antibiotics and the aggressive treatment of
Streptococcus pyogenes pharyngitis, the primary cause of rheumatic heart disease.
Many other causes of impaired left ventricular filling exist and they can mimic mitral stenosis in both
hemodynamics and symptoms. Left atrial myxomas (see cardiac tumors section) are relatively common and
can occur as a part of the Carney complex. These slow growing tumors obstruct the mitral valve causing MS.
Pulmonary vein stenosis after attempted radiofrequency ablation of atrial fibrillation is becoming more
common and this may mimic MS. The anterior leaflet of the mitral valve is the most common spot for a
vegetation to form in patients with bacterial endocarditis. If the vegetation grows to a large enough size, as
often occurs in fungal endocarditis, obstruction of LV filling may occur and symptoms of MS may develop.
Some other rare causes of true MS include congenital mitral stenosis, severe mitral annular calcification, and
prosthetic valve dysfunction. A complete list of causes of MS including those that mimic MS is below. The
rest of this review focuses on MS due to rheumatic heart disease.
Pathophysiology
In rheumatic valvular disease (RVD), and autoimmune attack on the mitral valve produces thickening of the
valve leaflets. The mitral valve is often described as having a “fish-mouth” appearance. Whether the
worsening of MS over time is secondary to a smoldering rheumatic process or simply mitral valve damage
due to high pressures and turbulence is unknown. Both most likely contribute to the progressive nature of
MS.
Over time as the MS worsens and the mitral valve area decreases, a pressure gradient develops between
the LA and the LV to help assist diastole. The elevated LA pressures are transmitted to the pulmonary veins
and the right side of the heart. On exertion as cardiac output increases and the velocity of flow trough the
mitral valve increases, the transmitral pressure gradient becomes exponentially larger. This is explained by
the modified Bernoulli equation:
Pressure gradient = 4v^2
Thus if the velocity of flow is doubled, the transmitral pressure gradient increases by 4 times. The resultant
large increase in LA pressure is primarily responsible for the exertional symptoms seen in MS.
Signs and Symptoms
Mitral stenosis is often asymptomatic early in disease until the mitral valve area decreases enough to cause
a large increase in LA pressure. The first symptoms of MS occur on exertion as explained above. This occurs
since the mitral valve area is fixed, the cardiac output in unable to increase a great deal above resting (low
cardiac reserve), and high pressures are transmitted to the pulmonary vasculature since LA pressures
increase exponentially on exertion. This transmission of pressures results in exertional dyspnea. Fatigue and
inability to exercise are also common complaints. Signs of heart failure such as PND and orthopnea can
occur. Symptoms also occur in other situations that require an increased cardiac output for the same reason
such as pregnancy, anemia, and thyrotoxicosis.
Most patients with moderate to severe MS will have some degree of left atrial enlargement (LAE) due to the
chronic increased LA pressures, predisposing them to atrial fibrillation. Since people with MS rely on atrial
contraction for about 20% of their cardiac output and tachycardia decreases diastolic filling time, the onset
of atrial fibrillation with a rapid ventricular rate and loss of atrial contraction results in significant symptoms
of low cardiac output and heart failure. These include fatigue, dyspnea, lightheadedness and even syncope.
Even in the absence of atrial fibrillation, patients with MS have an increased risk of thrombus formation in
their LA due to stagnation of blood. This may lead embolic events including stroke, acute myocardial
infarction, acute mesenteric ischemia, or
”Blue toe syndrome”.
Hemoptysis may occur due to sudden rupture of a broncial vein. This phenomenon is termed “pulmonary
apoplexy”. Ortner syndrome may occur when a massively enlarged LA compresses on the left recurrent
laryngeal nerve leading to a horse voice. Chest pain from right sided heart strain may occur due to severe
pulmonary hypertension. Other signs of right heart failure such as right upper quadrant pain (due to hepatic
congestion) and peripheral edema may occur.
Physical Examination
Inspection of the jugular venous pulsations may reveal a prominent a wave due to vigorous atrial
contraction or a prominent v wave due to tricuspid regurgitation that develops due to pulmonary
hypertension. The presence of “mitral facies” refers to a pinkish-purple discoloration of the cheeks
produced by a chronic low cardiac output state combined with systemic vasoconstriction. This sign is rare
and non-specific.
Palpation may reveal a palpable S1 over the apex. This finding is pathognomonic for MS. A diastolic thrill
may rarely be appreciated at the apex with the patient in the left lateral decubitus position.
Auscultation of heart sounds will reveal an accentuated S1 early in MS and a soft S1 in severe MS (see heart
sounds). This occurs since the increased LA pressures in early MS forces the leaflets of the mitral valve far
apart. At the onset of ventricular systole, they are forced closed from a relatively far distance resulting in a
loud S1. When MS becomes more severe and the mitral valve leaflets become significantly calcified, the
mobility of the leaflets decline and they are unable to be separated a great deal, resulting in a soft or even
absent S1. When pulmonary hypertension develops, the S2 heart sound will be accentuated. A left
ventricular S3 is always absent in pure MS since LV early diastolic filling is impaired. The significantly
increased opening snap causes an opening snap (OS) to occur when the mitral valve leaflets suddenly tense
and dome into the LV. This high frequency sound is best heard at the apex.
The murmur of MS is low frequency and is referred to as a “rumble”. The first part of the murmur of MS
reflects the pressure gradient between the LA and the LV. It begins after S2 with the OS and then
decrescendos (see picture below) ending in mid diastole. The second part of the murmur occurs just before
S1 in a crescendo fashion. This part of the murmur is due to the increased flow of blood through the mitral
valve that occurs during atrial contraction. It then makes sense that this aspect of the murmur would be
absent if the patient is in atrial fibrillation (which is common in MS).
The severity of MS can be estimated on physical exam by the position of the OS in diastole and the length of
the first part of the murmur. An OS that almost immediately follows S2 indicates severe MS while and OS
that occurs later in diastole indicated milder MS. This occurs because in severe MS there is a much higher LA
pressure and transmitral gradient develops immediately after the mitral valve opens. A longer murmur
indicates more severe MS since it takes more time for both blood to pass through the stenotic mitral valve
and for the pressure gradient to dissipate once the mitral valve opens.
Diagnosis
The EKG in MS is often normal early in disease. The most common finding is left atrial enlargement (p-
mitrale), however this finding disappears if the patient enters atrial fibrillation. Right heart strain may
produce findings of right axis deviation and right ventricular hypertrophy on EKG. In pure MS, left
ventricular hypertrophy would be absent.
The chest radiograph will again show left atrial enlargement. This finding is often referred to as a “double
density”. Elevation of the left mainstem bronchus and prominent pulmonary artery may also be seen. Both
the EKG and the chest radiograph, however, are non-specific for MS.
Echocardiography is the primary way to both diagnose and evaluate the severity of MS. Since transmitral
velocities can be determined, the transmitral pressure gradient can be calculated using the modified
Bernoulli equation as described above. The mitral valve area can be found using the continuity equation (see
echocardiography section) and the pulmonary artery pressure can be calculated to assess the severity of
pulmonary hypertension.
Cardiac catheterization can also measure the mitral valve area using the Gorlin equation:
MVA = MVF/37.7(MVG)½
MVA = mitral valve area MVF = mitral valvular flow MVG = mean mitral valvular gradient
Mitral valvular flow is proportional to cardiac output. This equation assumes that no mitral regurgitation is
present and the mitral valve area remains constant. With this equation, it can be seen that if the MVA
remains constant and cardiac output increases, the mitral valve gradient will increase exponentially as
previously described using the modified Bernoulli equation.
Treatment
The treatment of MS relies on the prevention or early recognition of rheumatic heart disease. Prophylactic
penicillin treatment in patients known to have rheumatic heart disease successfully reduces exacerbations
and will limit the damage done to the mitral valve. Anticoagulation is of great importance to prevent the
formation of a left atrial thrombus and embolic events. Even in the absence of atrial fibrillation, patients
with certain risk factors including hypertension or hypercoaguable states should be anticoagulated.
Antibiotic prophylaxis before dental procedures and certain surgeries is currently recommended to prevent
bacterial endocarditis.
Preload reduction with diuretics and salt restriction can relieve symptoms of MS if pulmonary hypertension
is present. Many patients experience symptoms only when the heart rate is elevated, since tachycardia
decreases diastolic filling time significantly. Thus the use of beta-blockers can be beneficial at times,
especially in patients with predominantly exertional symptoms.
Definitive treatment includes Percutaneous Balloon Mitral Valvotomy (PBMV). In this procedure, a catheter
is inserted through the interatrial septum and into the stenotic mitral valve. A balloon is then inflated that
fractures that calcium deposits and relieves the stenosis. Unlike valvuloplasty in the setting of aortic
stenosis, PBMV is highly successful with a low rate of restenosis. Complications include residual mitral
regurgitation, a persistent atrial septal defect, and rarely calcium embolization. PBMV is indicated for
patients who are symptomatic with moderate to severe MS in the absence of pre-existing LA thrombus and
mitral regurgitation. PBMV is also indicated for patients who are asymptomatic with severe MS and an
Abascal echocardiographic score of 8 or less.
Surgical approaches to the management of MS include closed commisurotomy, open commisurotomy, and
mitral valve replacement. Closed commisurotomy is similar to PBMV in that the mitral valve is not directly
visualized and a balloon is used to dilate the stenotic mitral valve. The same criteria that are used for PBMV
are also used to assess which patients may benefit from closed commusurotomy.
Open commisurotomy requires the use of a cardiopulmonary bypass machine which significantly increases
both the cost and the complication rate of the procedure. However the surgeon is able to debride
calcifications on the mitral valve, remove LA thrombi if found, and remove the left atrial appendage, which
is a common site for the formation of thrombi. Open commisurotomy is the treatment of choice in patients
with known LA thrombi or MS with concurrent severe mitral valve calcifications.
Mitral valve replacement is also an option for patients with symptomatic or severe MS requiring definitive
therapy. This is usually reserved for patients that are not a candidate for PBMV or commisurotomy due to
the long-term complications associated with prosthetic valves. Patients with MS along with moderate to
severe mitral regurgitation can benefit greatly from mitral valve replacement.
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