Mitral regurgitation (MR) is defined as an abnormal blood flow into the left atrium in systole as a result of an abnormal closing of the mitral valve. In chronic mitral insufficiency, the LVEF and cavity size may remain preserved for several years. However, LV remodeling eventually occurs, cavity size begins to dilate, ejection fraction becomes reduced, and patients enter a decompensated state. In acute MR, the left atrium and left ventricle have no chance for gradual dilation, and therefore a sudden rise in LV and pulmonary venous pressure occurs, leading to pulmonary edema.
Chronic MR is generally asymptomatic or associated with minimal symptoms of dyspnea or generalized fatigue. When
LV function declines severely, patients can become symptomatic with symptoms and signs of CHF. Patients might provide a history of rheumatic fever, endocarditis, CAD, or CHF. Acute MR needs to be in the differential diagnosis of a patient with sudden-onset pulmonary edema.
On examination, patients will display a systolic murmur, most often holosystolic, high-pitched and present at the apex with radiation to the axilla, left scapula, middle back, or left sternal border, depending on the direction of the regurgitant jet. A midsystolic click is often heard if associated mitral valve prolapse is seen. Occasionally a low-pitched diastolic rumble and an S3 sound can be heard.
The ECG often displays an enlarged left atrium (biphasic P wave in V1), large QRS complex secondary to LV enlargement, possible atrial fibrillation, and in ischemic MR, evidence of old or acute inferior infarcts can be seen. The chest radiograph may show an enlarged cardiac silhouette, calcified mitral valve, or increased pulmonary vascular congestion. Echocardiography provides the diagnosis by assessing the presence of the MR, its severity, and its etiology, such as severe prolapse, endocarditis, calcification, papillary muscle or chordae rupture, or a degenerative valve. Left- and right-sided heart catheterization is indicated before corrective surgery to determine the presence of CAD and confirm the diagnosis of MR with the use of left ventriculography. MR is graded based on the amount of contrast seen in the left atrium in systole: grade I, contrast does not opacify entire left atrium; grade II, contrast opacifies all left atrium but less dense than the contrast in the left ventricle; grade III, contrast equally opacifies left atrium and left ventricle; and grade IV, contrast in the left atrium is darker than the left ventricle with opacification of pulmonary veins (Fig. 27-21). Also, the angiogram can quantitatively determine the regurgitant fraction (RF). An RF greater than 50% generally indicates severe MR that requires corrective surgery.
Patients with a history of mitral insufficiency need to have bacterial endocarditis prophylaxis. Chronic MR benefits from long-term afterload reduction, although this remains controversial. Aggressive treatment of atrial fibrillation with rate control and warfarin anticoagulation is needed. Patients with moderate to severe MR need to be closely monitored for LVEF and LV cavity size. A lower threshold for surgical intervention is generally agreed on when compared to AR. Symptomatic patients (NYHC II-IV) or asymptomatic patients with LV end-systolic dimension approaching 4.5 cm or LVEF of 60% or less should be treated. Patients with lower ejection fraction and a larger cavity size carry a poorer outcome after surgery. However, those with LVEF of 30% to 50% and LV cavity size in systole of 50 to 55 mm also benefit from surgery. Asymptomatic patients with preserved LV function and cavity size but with atrial fibrillation might benefit from surgery.
Acute MR should be treated aggressively with afterload reduction (e.g., sodium nitroprusside). These patients generally require immediate surgery but will do best if they can be initially treated medically and enter a compensated state b efore surgery. Most regurgitant mitral valves can now be repaired instead of replaced. Techniques for percutaneous repair of the mitral valve are now being tested and hold significant promise.
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