Introduction
The mitral annulus or mitral ring is a circular structure that separates the left side top and bottom chambers of the heart (the left atrium and ventricle). While the upper atrium receives oxygenated blood from the lungs, the lower ventricle pumps the same into the body through the aorta. The mitral ring sits between these chambers and contains the mitral valve. One may define this as the supportive ring of the bicuspid valve. The valve is also responsible for the prevention of the backflow of blood from the ventricle to the atrium. Mitral ring calcification is a result of long-standing etiology.
What Is Mitral Ring Calcification?
First discovered and described by M. Bonninger in 1908, mitral ring calcification, or Mitral annular calcification (MAC), is a chronic degenerative pathology of the mitral valve that results in a gradual deposition of calcium and lipids over the annular fibrosa ring that supports the mitral valve. The role of this ring is to provide structural support to the valve and also maintain its proper shape and function. Deposition of calcium makes the ring lose its flexibility, become stiff, and narrow, which then hampers the blood flow and significantly increases the risk of other cardiac disorders. The posterior part of the annulus is most commonly affected. Mild calcification offers no significant hindrance to one’s health, but the degree of calcification may increase if there is any increase in stress on the annulus or the valve.
Who Is Susceptible to Mitral Ring Calcification?
The prevalence of MAC greatly varies among populations and is influenced by age and the presence of comorbidities. Some studies present a prevalence of about 14 percent in the elderly tribe, while some studies claim to have identified annular calcification in 35 percent of the elderly under study. One study that studies elderly people with a mean age of 76 years found the prevalence of MAC to be about 42 percent, along with a strong association with cardiovascular diseases. As the age of the cohort increases, so does the prevalence, with evidence of a 60 percent prevalence in elderly people above 85 years. There is approximately a 3.7-fold increase in MAC prevalence with a ten-year age jump.
Similar scouting was also conducted to find a gender prevalence. This found a male predominance in prevalence with 4.6 percent versus 5.6 in a mean age cohort of 59 years. But as the age increases, the prevalence increases with an increasing difference in predominance in percentage. However, studies including multiple ethnicities found a 12 percent prevalence in women and over eight percent in males. The prevalence is usually highest among the white population, followed by Hispanics, Blacks, and Chinese, with the lowest rates.
What Causes Mitral Ring Calcification?
MAC is strongly associated with atherosclerosis, and some evidence claims that MAC and calcific aortic stenosis belong to a spectrum of atherosclerotic diseases. The point of the attachment of the mitral valve is subjected to turbulent blood flow and is susceptible to endothelial injury, which increases the risk of atherosclerosis. The valve has certain sites of lipid accumulation from where the calcification begins. Endothelial injury promotes the recruitment of T-cell infiltrates and macrophages. Caseous calcification of the mitral valve is a rare form of MAC that typically affects the posterior annulus.
Some of the factors that increase the risk of developing MAC are as follows:
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Advanced age.
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Systemic hypertension.
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Hypercholesterolemia (high levels of bad cholesterol).
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Diabetes mellitus.
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Secondary hyperparathyroidism.
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Conditions that increase annular stress (like mitral valve prolapse).
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Genetic abnormalities of the fibrous skeleton.
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Aortic stenosis (narrowing of the aorta).
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Hypertrophic cardiomyopathy (thickening of the heart muscles).
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Chronic kidney disease.
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Atherosclerosis (buildup of fats, cholesterol, and other substances in and on the artery walls).
What Are the Clinical Features of Mitral Ring Calcification?
Mild MAC does not greatly hamper general health, and the heart is able to compensate. The patients may be completely asymptomatic. But as the calcification progresses, the valve opening gets constricted, which can then precipitate several symptoms like:
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Shortness of breath.
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Fatigues.
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Heart palpitations.
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Chest pains.
How to Diagnose Mitral Ring Calcification?
MAC is usually an incidental finding during regular health checks involving cardiac imaging. Cardiac echo, chest X-ray, and cardiac catheterization provide sufficient diagnostic information to reach a final interpretation.
What Is the Outcome of Echocardiogram Studies on Mitral Ring Calcification?
With transthoracic echo (on parasternal or apical views), an echo-dense band or mass can be visualized in the atrioventricular groove and may be seen all the way through the systole-diastole cycle. These are evidence of MAC. These calcifications are seen affecting the posterior part of the ring and may just occasionally extend to the anterior annulus or the inner annular fibrosa.
The echo may show calcification extension from the ring to the leafless, sometimes completely encasing their mobility and gradually reducing the mobility till they are completely immobilized. Caseous calcifications are comparatively less echo-dense, have a central echo-lucent zone, and have an absence of acoustic shadowing on echocardiogram images.
Cardiac magnetic resonance imaging and computed tomography may be used for evaluation. However, they are particularly useful in differentiating MAC from caseous MAC, cardiac tumor, and thrombus when the echo images are of poor resolution.
How to Treat Mitral Ring Calcification?
Medical therapy does not affect MAC directly. However, pharmacotherapeutic management for possible risk factors is recommended due to its association with atherosclerosis and other cardiac conditions. Hospitalization may not be necessary for MAC patients, but regular follow-ups are necessary post-diagnosis, as the patients are at an increased risk of major cardiovascular mishaps.
Surgery may be required to manage mitral stenosis or mitral regurgitation. The risk and complexity of surgery increase with the progression of MAC. A valvular replacement may be considered in patients undergoing recurrent calcific emboli or thromboembolism. Percutaneous mitral valve repair is contraindicated in the case of existing MAC; hence transcatheter methods are usually preferred owing to their greater prognosis.
What Is the Prognosis of Mitral Ring Calcification?
According to studies, every one-millimeter increase in calcification increases the risk of death by ten percent. However, the primary cause of death was due to cardiovascular events, which are a complication of MAC. MAC also makes one susceptible to the development and fatalities associated with these cardiovascular events.
What Is the Differential Diagnosis of Mitral Ring Calcification?
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Atrial myxoma (non-neoplastic cardiac tumor).
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Benign cardiac tumors
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Thrombus (clots).
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Vegetation (infections in the heart).
What Are the Complications of Mitral Ring Calcification?
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Stroke.
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Myocardial infarction.
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Atherosclerosis.
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Mitral regurgitation (backflow of blood from the left ventricle to the atrium).
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Mitral stenosis.
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Arrhythmias.
Conclusion
Mitral ring calcification is an age-associated progressive disorder and is closely associated with atherosclerosis. Although it usually remains hidden, the calcifications may be discovered during regular checkups or when the patient complains of breathing issues, palpitations, and fatigue. It is important to introduce lifestyle changes, including a healthy diet, smoking cessation, exercises, management of underlying health conditions, and, most importantly, regular follow-ups to track and predict the progression of MAC and associated complications, respectively.
