MITRAL VALVE DISEASE
Mitral stenosis is almost always rheumatic in origin, although in the elderly it can be caused by heavy calcification of the mitral valve apparatus. There is also a rare form of congenital mitral stenosis.
In rheumatic mitral stenosis, the mitral valve orifice is slowly diminished by progressive fibrosis,
calcification of the valve leaflets,
and fusion of the cusps and subvalvular apparatus.
The flow of blood from left atrium to left ventricle is restricted
and left atrial pressure rises,
pulmonary venous congestion
Poor lung compliance
There is dilatation and hypertrophy of the left atrium,
left ventricular filling becomes more dependent on left atrial contraction.
Requires increased cardiac output
Increase in heart rate
Diastole shortens when mitral valve is open
Further rise in left atrial pressure
The mitral valve orifice is normally about 5 cm2 in diastole and may be reduced to 1 cm2 or less in severe mitral stenosis.
Patients usually remain asymptomatic until the stenosis is approximately 2 cm2 or less. At first, symptoms occur only on exercise
In severe stenosis, left atrial pressure is permanently elevated and symptoms may occur at rest. Reduced lung compliance, due to chronic pulmonary venous congestion, contributes to breathlessness and a low cardiac output may cause fatigue. Atrial fibrillation due to progressive dilatation of the left atrium is very common. The onset of atrial fibrillation often precipitates pulmonary oedema because the accompanying tachycardia and loss of atrial contraction frequently lead to marked haemodynamic deterioration with a rapid rise in left atrial pressure.
Progressive dilation of left atrium
Tachycardia and loss of atrial contraction
Marked haemodynamic deterioration
Rapid rise in left atrial pressure
Pulmonary venous congestion
In contrast, a more gradual rise in left atrial pressure tends to cause an increase in pulmonary vascular resistance, which leads to pulmonary artery hypertension that may protect the patient from pulmonary oedema. Pulmonary hypertension may lead to right ventricular hypertrophy and dilatation, tricuspid regurgitation and right heart failure.
Less than 20% of patients remain in sinus rhythm; many of these have a small fibrotic left atrium and severe pulmonary hypertension.
All patients with mitral stenosis, and particularly those with atrial fibrillation, are at risk from left atrial thrombosis and systemic thromboembolism. Prior to the advent of anticoagulant therapy, emboli caused one-quarter of all deaths in this condition.
CLINICAL FEATURES OF MITRAL STENOSIS
Breathlessness (pulmonary congestion)
Fatigue (low cardiac output)
Oedema, ascites (right heart failure)
Palpitation (atrial fibrillation)
Haemoptysis (pulmonary congestion, pulmonary embolism)
Cough (pulmonary congestion)
Chest pain (pulmonary hypertension)
Symptoms of thromboembolic complications (e.g. stroke, ischaemic limb)
Loud first heart sound, opening snap
RV heave, loud P2
Crepitations, pulmonary oedema, effusions
Signs of raised pulmonary capillary pressure
Signs of pulmonary hypertension
Effort-related dyspnoea is usually the dominant symptom.
Exercise tolerance typically diminishes very slowly over many years and patients often do not appreciate the extent of their disability. Eventually symptoms occur at rest.
Acute pulmonary oedema or pulmonary hypertension can lead to haemoptysis. Systemic embolism may be a presenting feature.
The forces that open and close the mitral valve increase as left atrial pressure rises. The first heart sound (S1) is...
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