Almost all mitral stenosis is due to rheumatic heart disease:
• At least 50% of sufferers have a history of rheumatic fever or chorea.
• The single most common valve lesion due to rheumatic fever is pure mitral stenosis (50%).
• The mitral valve is affected in over 90% of those with rheumatic valvular heart disease.
• Rheumatic mitral stenosis is much more common in women.
• The pathological process results after some years in valve thickening, cusp fusion, calcium deposition, a narrowed (stenotic) valve orifice and progressive immobility of the valve cusps.
• Lutembacher’s syndrome is the combination of acquired mitral stenosis and an atrial septal defect.
• A rare form of congenital mitral stenosis can occur.
• In the elderly a syndrome similar to mitral stenosis can develop because of calcification and fibrosis of the valve, valve ring and subvalvular apparatus (chordae tendineae).
When the normal valve orifice area of 5 ern” is reduced to approximately 1 em”, severe mitral stenosis is present. In order that sufficient cardiac output will be maintained, the left atrial pressure increases and left atrial hypertrophy and dilatation occurs. Consequently, pulmonary venous, pulmonary arterial and right heart pressures also increase. The increase in pulmonary capillary pressure is followed by the development of pulmonary oedema. This is partially prevented by alveolar and capillary thickening and pulmonary arterial vasoconstriction (reactive pulmonary hypertension). Pulmonary hypertension leads to right ventricular hypertrophy, dilatation and failure. Right ventricular dilatation results in tricuspid regurgitation. The complications of mitral stenosis are frequent.
Usually there are no symptoms until the valve orifice is moderately stenosed, i.e. has an area of 2 em”. In Europe this does not usually occur until several decades after the first attack of rheumatic fever, but in the Midclle or Far East, children of 10-20 years of age may have severe calcific mitral stenosis.
Because of pulmonary venous hypertension and recurrent bronchitis, progressively severe dyspnoea develops. A cough productive of blood-tinged, frothy sputum is quite common, and occasionally frank haemoptysis may occur. The development of pulmonary hypertension eventually leads to right heart failure and its symptoms of weakness, fatigue and abdominal or lower limb swelling. The large left atrium favours atrial fibrillation, giving rise to symptoms such as palpitations. Atrial fibrillation may result in systemic and pulmonary emboli, which give rise to cerebral, mesenteric, renal and pulmonary infarcts.
Severe mitral stenosis with pulmonary hypertension is associated with the so-called mitral facies or malar flush. This is a bilateral, cyanotic or dusky pink discoloration over the upper cheeks that is due to arteriovenous anastomoses and vascular stasis.
At first the pulse is regular (sinus rhythm) but later the irregular pulse of atrial fibrillation usually develops. The onset of atrial fibrillation often causes a dramatic clinical deterioration.
Jugular veins If right heart failure develops there is obvious distension of the jugular veins. If pulmonary hypertension or tricuspid stenosis is present, the a wave will be prominent provided that atrial fibrillation has not supervened.
The apex beat is ‘tapping’ in quality. This is the result of a palpable first heart sound combined with left ventricular backward displacement produced by an enlarging right ventricle. A parasternal heave due to right ventricular hypertrophy may also be felt.
Auscultation reveals a loud first heart sound because the cusps are kept open until the beginning of ventricular systole. In early diastole a sound is produced when the mitral valve opens (opening snap). This is followed by a diastolic rumbling murmur due to turbulent blood flow through the narrowed valve. If the patient is in sinus rhythm the murmur becomes louder when atrial systole occurs. This is called presystolic accentuation. The severity of mitral stenosis is judged by the time between the closure of the aortic valve and the opening of the mitral valve. Thus the shorter the A2-OS time the more severe the stenosis. This is because it takes less time for the left ventricular pressure to fall to the high left atrial pressure which occurs in severe mitral stenosis. As the valve cusps become immobile, the loud first heart sound softens and the opening snap disappears. When pulmonary hypertension occurs, the pulmonary component of the second sound is increased in ntensity and the mitral diastolic murmur may become quieter because of the reduction of cardiac output.