The ECG in mitral stenosis 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 ECG. In pure mitral stenosis, 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 a prominent pulmonary artery may also be seen. Both the ECG and the chest radiograph, however, are non-specific for mitral stenosis.
Echocardiography is the primary means 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 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 x (MVG)½
MVA = mitral valve area
MVF = mitral valve 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 the cardiac output increases, the mitral valve gradient will increase exponentially as previously described using the modified Bernoulli equation.
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