Mitral Annular Calcification (MAC) is a common degenerative condition where calcium deposits form within the heart’s fibrous structure, specifically at the base of the mitral valve. It is primarily associated with the aging process and is often discovered incidentally during routine cardiac imaging. While frequently benign in its early stages, MAC signals potential underlying health issues. In some cases, the calcification can grow large enough to interfere with normal heart mechanics and electrical signaling.
What Is Mitral Annular Calcification?
MAC involves the deposit of calcium and often lipid within the mitral annulus, the ring-shaped fibrous structure that supports the mitral valve. This annulus anchors the two leaflets of the mitral valve, which separate the heart’s upper left chamber (left atrium) from the lower left chamber (left ventricle). The calcification process is a type of degeneration, gradually turning the normally flexible tissue of the ring into a hardened, shelf-like structure.
This calcification is distinct from the plaque buildup seen in the coronary arteries, although both share underlying biological processes and risk factors. MAC is a chronic, age-related process that results in the deposition of mineralized material. The calcification most commonly begins along the posterior portion of the annulus, but in severe cases, it can extend completely around the ring.
The hardened tissue can appear lumpy and irregular, sometimes extending into the base of the valve leaflets or the adjacent heart muscle. While the exact pathological mechanisms are not fully understood, MAC is not simply a passive accumulation of calcium. It is recognized as an active, regulated process similar to bone formation, involving specialized cells and inflammation.
Who is at Risk for Developing MAC?
Advanced age is the most significant non-modifiable factor contributing to MAC development, with prevalence increasing substantially in elderly populations. The condition is commonly seen in up to 35% of individuals over 65 years old and is observed more frequently in women than in men.
Certain systemic diseases accelerate MAC development by disrupting the body’s mineral balance. Chronic kidney disease is a major factor, as it often leads to disorders in calcium and phosphorus metabolism that promote calcification in soft tissues. Severe hypercalcemia, an abnormally high level of calcium in the blood, can also contribute to the process.
MAC shares many risk factors with general atherosclerosis, suggesting a common susceptibility to vascular damage. Traditional cardiovascular risk factors, such as high blood pressure (hypertension), elevated cholesterol levels, and diabetes, are associated with a higher incidence of MAC. Conditions that increase mechanical stress on the valve, like severe aortic stenosis or hypertrophic cardiomyopathy, may accelerate the annular degeneration.
How MAC Affects Heart Function
The presence of calcium in the annulus can compromise the movement of the mitral valve leaflets, leading to two main mechanical issues. First, the hardening can prevent the valve from opening fully, a condition known as mitral stenosis, which restricts blood flow from the left atrium into the left ventricle. Second, the calcium can distort the shape of the annulus, preventing the valve leaflets from closing tightly during contraction.
This distortion results in mitral regurgitation, where blood leaks backward into the left atrium instead of moving forward into the left ventricle. Moderate or severe forms of mitral valve dysfunction are more than twice as common in patients with MAC compared to those without the condition.
Mild cases are often asymptomatic and have little hemodynamic consequence. However, as the calcification becomes more extensive, it can protrude into the left ventricular outflow tract or involve the leaflets, significantly worsening both stenosis and regurgitation. MAC is also a marker for increased risk of cardiovascular events and all-cause mortality.
Beyond mechanical interference, the calcified tissue can disturb the heart’s electrical conduction system. The mitral annulus sits close to the atrioventricular (AV) node and the Bundle of His, which are pathways that carry electrical signals to coordinate the heart’s rhythm. Calcium deposits can encroach upon these pathways, leading to various conduction blocks and delays.
Patients with MAC have a higher prevalence of arrhythmias, including atrial fibrillation, an irregular and often rapid heart rhythm originating in the upper chambers. They also experience higher rates of atrioventricular block, which slows or entirely blocks the electrical signal from traveling from the atria to the ventricles. These electrical disturbances can lead to symptoms like palpitations, shortness of breath, and fatigue.
Detection and Management Strategies
Mitral Annular Calcification is typically diagnosed using non-invasive cardiac imaging, with echocardiography serving as the initial and most common assessment tool. On an echocardiogram, MAC is visible as an echodense, irregular structure located at the base of the mitral valve, often with associated acoustic shadowing. This imaging allows clinicians to assess the extent of the calcification and determine if it is causing functional issues, such as stenosis or regurgitation.
Computed Tomography (CT) scans offer a more detailed, three-dimensional view and are more sensitive for quantifying the amount and location of the calcium deposit. CT imaging is useful for planning interventions, as it provides a clear map of the hardened tissue. In the majority of cases, MAC is mild, asymptomatic, and discovered incidentally, requiring no immediate specific treatment.
Management for most patients focuses on surveillance, involving monitoring for progression of calcification or valve dysfunction. Long-term care involves aggressive management of associated cardiovascular risk factors, such as optimizing blood pressure and cholesterol levels. This approach aims to reduce the overall cardiac risk associated with MAC.
For the minority of patients who develop severe, symptomatic mitral valve dysfunction due to MAC, intervention may become necessary. Surgical repair or replacement of the mitral valve is technically challenging in the presence of extensive calcification, which increases the procedural risk. Transcatheter mitral valve replacement is an emerging option for high-risk patients, offering a less invasive alternative to address the resulting valve disease.