15.8
Sténose Mitrale I : Introduction
La sténose de la valve mitrale (SVM) est une affection cardiaque caractérisée par un rétrécissement de la valve mitrale, entravant la circulation sang…
La sténose mitrale est une condition médicale dans laquelle la valve mitrale devient étroite, limitant le flux sanguin de l’oreillette gauche vers le ventricule gauche, le plus souvent causée par une endocardite rhumatismale.
Les causes moins fréquentes comprennent les malformations congénitales, les maladies auto-immunes, la radiothérapie et la calcification annulaire mitrale sévère.
La physiopathologie implique une endocardite rhumatismale, qui provoque une inflammation et des cicatrices.
Cela conduit à l’épaississement, à la calcification et à la fusion des feuillets de la valve mitrale et des chordes tendineuses, rétrécissant l’orifice de la valve et obstruant la circulation sanguine de l’oreillette gauche au ventricule gauche pendant la diastole.
En conséquence, le volume sanguin résiduel dans l’oreillette gauche augmente, provoquant une hypertrophie et une dilatation de l’oreillette gauche au fil du temps.
Une pression élevée continue dans l’oreillette gauche peut provoquer une congestion pulmonaire et un œdème et rendre l’oreillette sujette à des arythmies comme la fibrillation auriculaire, ce qui diminue l’efficacité cardiaque.
Il peut également provoquer une hypertension pulmonaire et une tension sur le ventricule droit, entraînant potentiellement une hypertrophie ventriculaire droite et une insuffisance cardiaque.
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Q1: What causes mitral stenosis?
Mitral stenosis is most commonly caused by rheumatic endocarditis, which results from inadequately treated streptococcal infections. Less common causes include congenital malformations, autoimmune disorders like rheumatoid arthritis, radiation therapy to the chest, and severe mitral annular calcification in older adults.
Q2: How does rheumatic endocarditis damage the mitral valve?
Rheumatic endocarditis causes inflammation and scarring of the mitral valve leaflets and chordae tendineae. This leads to thickening, calcification, and fusion of valve structures, creating a characteristic fish-mouth appearance. These deformities narrow the valve orifice and obstruct blood flow from the left atrium to the left ventricle during diastole.
Q3: What happens to the left atrium when the mitral valve narrows?
When the mitral valve narrows, blood backs up in the left atrium, increasing residual blood volume. Over time, this elevated pressure causes left atrial hypertrophy and dilation. The enlarged atrium becomes prone to arrhythmias like atrial fibrillation, which decreases cardiac efficiency and further compromises blood circulation.
Q4: How does mitral stenosis affect the pulmonary circulation?
Mitral stenosis causes blood to back up into the pulmonary veins, leading to pulmonary congestion and edema. The increased pressure in the pulmonary circulation can cause pulmonary hypertension and place excessive strain on the right ventricle, potentially leading to right ventricular hypertrophy and eventual heart failure.
Q5: Why does increased heart rate worsen mitral stenosis symptoms?
An increased heart rate shortens the diastolic phase, reducing the time available for blood to flow from the left atrium into the left ventricle. This causes more blood to back up into the pulmonary veins, further reducing cardiac output and increasing pulmonary pressures, exacerbating the condition's hemodynamic effects.
Q6: What is the relationship between mitral stenosis and cardiac output?
Mitral stenosis reduces cardiac output through two mechanisms: decreased ventricular filling due to the narrowed valve orifice, and reduced forward blood flow into the left ventricle. This decreased cardiac output compromises the heart's ability to deliver oxygen-rich blood to body tissues, affecting overall cardiovascular function.
Q7: How do structural changes in mitral stenosis create a pressure gradient?
The thickened, fused, and calcified mitral valve leaflets create an obstruction that prevents normal blood flow during diastole. This obstruction generates a significant pressure differential between the left atrium and left ventricle, forcing the atrium to work harder to push blood through the narrowed valve opening.