Mitral Annular Calcification, a Not So Marginal and Relatively Benign Finding as Many of Us Think: A Review

Abstract

Mitral annular calcification (MAC) is usually considered an incidental, benign, age-related finding without serious complications in patients evaluated for cardiovascular or pulmonary disease with imaging studies that may result in mitral regurgitation or stenosis when severe. Therefore, it is usually not considered a significant alteration. However, there is accumulating evidence that it is associated with a higher risk of cardiovascular events, such as atherosclerotic coronary artery disease, aortic artery disease, carotid artery disease, peripheral artery disease, stroke, atrial fibrillation, atrioventricular and/or intraventricular conduction disturbance, systemic embolization, infective endocarditis, heart failure and mortality. The presence of MAC also significantly influences the outcome of mitral valve transcatheter and surgical interventions. Several conditions may predispose to MAC. MAC is strongly related to cardiovascular risk factors, such as hypertension, diabetes, smoking and cardiovascular atherosclerosis, and inflammation may also play a role in the pathogenesis of MAC. Also, conditions that increase mitral valve stress, such as hypertension, aortic stenosis and hypertrophic cardiomyopathy, predispose to accelerated degenerative calcification of the mitral annulus area. Congenital disorders, e.g., Marfan syndrome and Hurler syndrome, are also associated with MAC, due to an intrinsic abnormality of the connective tissue composing the annulus.

Keywords: atrioventricular conduction disturbance; electrocardiography; mitral annular calcification.

Figure 1

Three-dimensional transesophageal echocardiographic en face “surgical view” visualizing the atrial aspect of the mitral valve in a patient with significant mitral annular calcification (MAC), showing a more pronounced calcification of the posterior mitral annulus.

Figure 2

Cardiac computed tomography (CT) images of a patient with significant mitral annular calcification. Panel (A): three-dimenstional maximum intensity projection reconstruction overview of the heart and mediastinal great vessels. Panels (B,C): four-chamber and short axis double oblique reconstructions of the cardiac CT images and Panel (D): double oblique reformation of the heart, showing “en face” view of mitral annulus, demonstrating a more pronounced posterior and moderate anterior mitral annular calcification (yellow arrows) and the estimated location of the atrioventricular (AV) node (blue asterisks). AoV: aortic valve, LAA: left atrial appendage, LA: left atrium, LV: left ventricle, MV: mitral valve, RA: right atrium, RV: right ventricle.

Figure 3

New mitral annular calcification severity grading system by cardiac CT and echocardiography proposed by the Heart Valve Collaboratory working group. CT: computed tomography, MAC: mitral annular calcification, TEE: transesophageal echocardiography, TTE: transthoracic echocardiography. Modified from Table 1 and Figure 1 of Ref. [11].

Figure 4

ECGs recorded at the initial presentation. Panel (A) (initial ECG): 68 bpm sinus rhythm, significant left axis deviation with a frontal plane QRS axis of approximately −40°, PR interval: 520 ms [first-degree atrioventricular (AV) block]. Fragmented QRS complexes are present in leads III, aVL and aVF, positive–negative P waves are seen in the inferior leads corresponding to third-degree interatrial block predisposing to atrial fibrillation. Mildly elevated ST segments in leads V_1–2. Panel (B): ECG recorded 24 days after the initial presentation showing Mobitz type I second-degree AV block (AV Wenckebach periodicity) with blocked, non-conducted P waves. The PR interval of the first QRS complex after the pause was still significantly prolonged: 360 ms. Otherwise, the ECG was identical to the initial ECG.

Figure 5

Echocardiographic examination of the patient. Panels (A–D): parasternal long axis and short axis, apical 4-chamber and 2-chamber views showing the conspicuous posterior and mild anterior mitral annular calcification and mild calcification and thickening of the aortic valve. Panel (B): parasternal short axis view at the level of mitral annulus reveals a posterior mitral annular calcification of 8 mm, which exceeds the significant level (>4 mm).

Figure 6

Cine movie cardiac MR images in transversal planes. Arrows show the mitral annular calcification. Suspected area of the AV node is indicated by asterisk, showing its proximity to MAC.

Figure 7

ECGs recorded 18 months after the initial presentation before pacemaker implantation. Panel (A): sinus rhythm with second-degree Mobitz type I AV block with 2:1 AV conduction and a 34 bpm ventricular rate. Panel (B): sinus rhythm with second-degree Mobitz type I AV block with 3:2 AV conduction and a 44 bpm ventricular rate.