Etiologies and Mechanisms of Mitral Valve Dysfunction

Causes of Mitral Valve Disease

MV disease is caused by either primary (direct) abnormalities of the MV apparatus or secondary (indirect) causes due to cardiac disease not involving the valve. Examples of diseases that directly affect the MV include congenital malformations such as valve clefts, rheumatic disease, infective endocarditis, trauma, MV annular calcification, valvular tumors, and degenerative diseases. Cardiac diseases that indirectly affect the MV include ischemic and nonischemic dilated cardiomyopathy, hypertrophic cardiomyopathy, and myocardial infiltrative diseases.

Rheumatic MV disease is uncommon in developed countries but continues to be a significant cause of MV disease worldwide. Rheumatic heart disease accounts for about a quarter of all patients with heart failure in endemic countries. Chronic valve disease occurs after one or more episodes of acute rheumatic fever and tends to affect females more than males. Although the MV is involved in almost every case, the aortic and tricuspid valves can also be affected. Younger patients tend to develop pure mitral regurgitation (MR), middle-aged patients more frequently develop mitral stenosis, and older patients usually develop a combination of stenosis and regurgitation.

Degenerative MR, usually associated with mitral valve prolapse (MVP), is the most common cause of MR in developed countries. MVP is an abnormal systolic valve motion of the mitral leaflet into the left atrium (≥2 mm beyond the annulus). Three-dimensional echocardiography (3DE) technology has considerably improved the ability of physicians to both diagnose and treat MVP, which results primarily from two distinctive types of degenerative diseases: Barlow disease and fibroelastic deficiency.

Ischemic MR is the pathophysiologic outcome of ventricular remodeling arising from ischemic heart disease and is also a very common cause of MR in developed countries. Ischemic MR occurs in approximately 20% to 25% of patients with myocardial infarction even in the era of reperfusion, and these patients have significantly worse outcomes irrespective of the degree or MR. The resultant volume overload caused by MR worsens myocardial contractility, which in turn worsens ventricular dysfunction, eventually leading to heart failure and death.