Mitral stenosis Causes
The most common causes of Mitral stenosis is rheumatic fever and chronic rheumatic heart valve disease. Other mitral stenosis causes are congenital mitral ring calcification, mitral valve dysplasia, connective tissue lesions, serious aortic insufficiency and left atrial myxoma.
The normal mitral valve is Soft texture, valve area is about 4 ~ 6cm2. When the valve area decreases to 1.5 ~ 2.0cm2 is mild stenosis; 1.0 ~ 1.5cm2 for moderate stenosis; <1.0cm2 for severe stenosis; the main pathologic changes of mitral stenosis is that diastolic blood from the left atrium flow into left ventricular inflow is limited, making abnormally high left atrial pressure, increased between left atrial and left ventricular pressure gradient to maintain normal cardiac output. Increased left atrial pressure can cause pulmonary venous and pulmonary capillary pressure increased, followed by expansion and congestion. Patients can rest at this time no obvious symptoms, but physical activity, the result of faster blood flow, pulmonary venous and pulmonary capillary pressure increased further, immediate difficulties, coughing, cyanosis, or acute pulmonary edema. Long-term volume overload of pulmonary circulation, can lead to increased pulmonary arterial pressure. Long-term pulmonary hypertension, so that the pulmonary artery spasm and hardening, and cause right ventricular hypertrophy and expansion, followed by right ventricular failure can occur. At this point lower pulmonary artery pressure, pulmonary blood flow decreased, pulmonary congestion can be eased.
When simple mitral stenosis, in the left ventricular diastolic telophase, the pressure and volume is normal. The majority of patients with mitral stenosis increases left ventricular ejection fraction, reduce volume in diastolic telophase. About a quarter of the mitral stenosis have severe left ventricular dysfunction, expressed as ejection fraction and other indices of reduced systolic function, which result in reduced the chronic load. Most of the patients with mitral stenosis resting cardiac output is in the normal range, exercise cardiac output increase lower than normal; a small number of severe stenosis were resting below normal cardiac output, cardiac output during exercise is not reduced rather than an increase, mainly because of mitral stenosis in addition, there are left and right ventricular function has been impaired. In addition, as a result of the expansion of the left atrium and difficult to maintain normal electrical activity of the heart, so often occur atrial fibrillation. Rapid ventricular rate in rapid atrial fibrillation can increase pulmonary capillary pressure, easy cause increased pulmonary congestion or pulmonary edema.