Mitral annular calcification (MAC) is a common degenerative process involving the fibrous annulus of the mitral valve. It is generally an incidental finding associated with aging although it is occasionally associated with significant mitral regurgitation and can rarely cause symptomatic mitral stenosis. In addition, MAC is associated with atrial fibrillation, conduction system disease, atherosclerotic disease and adverse cardiovascular events, including stroke and mortality.
The diagnosis, clinical significance, and associated cardiovascular risk of MAC and management of MAC-related disorders are discussed here.
Echocardiography of the mitral valve, mitral valve disease, and conduction system disease are discussed separately. (See "Echocardiographic evaluation of the mitral valve" and "Etiology, clinical features, and evaluation of chronic mitral regurgitation" and "Medical management and indications for intervention in mitral stenosis" and "Etiology of atrioventricular block".)
ANATOMY AND PATHOLOGY
Normal anatomy — The mitral valve annulus is the C-shaped segment of the fibrous skeleton at the base of the left ventricle at its junction with the left atrium. The leaflets of the mitral valve are attached to and suspended from the mitral annulus, which provides structural support to the valve apparatus along the medial, posterior, and lateral aspects of the valve. Anteriorly, the mid-section of the anterior mitral leaflet is in fibrous continuity (via the intervalvular fibrosa) with the posterior aortic root without intervening annular tissue.
Mitral annular calcification — Mitral annular calcification (MAC) develops from progressive calcium deposition along and beneath the mitral valve annulus . MAC generally follows the C-shape of the mitral annulus, so the base of the anterior mitral leaflet is generally (but not always ) spared. MAC is most commonly identified by echocardiography as an echodense shelf-like structure involving the mitral valve annulus with associated acoustic shadowing (image 1 and image 2). The calcification frequently has an irregular, lumpy appearance. Although mitral valve leaflets and chordae tendinae are generally not involved, calcification may progressively accumulate in the subvalvular region beneath the posterior leaflet with encroachment on the leaflet. Usual sparing of the leaflet commissures and anterior leaflet distinguishes MAC from rheumatic mitral involvement.