Mitral annular calcification (MAC)

Mitral annular calcification (MAC)

Mitral annular calcification is more likely in those with chronic kidney disease because of the deranged calcium and phosphorus metabolism. Products of calcium and phosphorus metabolism cause soft tissue calcification. MAC is also a marker of atherosclerotic burden. MAC is associated with higher incidence of atrial arrhythmias, stroke and cardiovascular mortality. MAC is more common in females, elderly and in those with hypertension and diabetes.

Mechanism of mitral regurgitation in MAC

MAC is more likely to cause mitral regurgitation than stenosis. Three reasons could contribute to this:

1. The normal sphincter like mechanism of mitral annulus during systole is prevented by calcification.
2. Dense calcification may lift the base of the posterior mitral leaflet, causing improper coaptation with the anterior leaflet.
3. Elevation of the base of posterior leaflet also causes chordal elongation which can lead on to chordal rupture and worsening of mitral regurgitation.

Degenerative mitral stenosis due to MAC

Mitral stenosis due to MAC is quite rare and occurs only with very severe forms. Unlike in rheumatic mitral stenosis, in which the smallest orifice is at the tip of the leaflets, the level of stenosis in mitral stenosis due to mitral annular calcification, the limiting orifice is at the base of the leaflets.