The mitral annulus is a ring-like structure that separates the top and bottom chambers of the left side of the heart

The mitral annulus is a ring-like structure that separates the top and bottom chambers of the left side of the heart. Mitral annular calcification (MAC) is a chronic degenerative process within the cardiac fibrous skeleton that bears similarities to valvular and vascular calcification (Pressman, Rodriguez, and Gartman, et al., 2017). It appears as a whiter and brighter area on the mitral annulus when performing an echocardiogram. As shown in illustration 1 (cover page) and 2, MAC will appear as a bright band behind the posterior mitral valve leaflet (Ahmed, 2015) (Brinkman, 2016). Mild MAC commonly occurs on the left ventricular side of the posterior annulus, near the base of the posterior mitral valve leaflet. Though, in more severe cases of MAC, the entire posterior annulus has increased echogenicity (Otto, 2013). It is more common in people with renal dysfunction, as well as the elderly. It is associated with cardiovascular disease, including coronary disease and stroke (Pressman et al., 2017).
Illustration 2

Pressman et al.’s (2017) article details a study performed on mitral vegetation echocardiographic cases. Researchers specifically searched for patients with reported mitral valve vegetations. The goal was to see whether MAC would be prevalent in patients with mitral valve vegetations and whether these vegetations would frequently occur on calcific nodules. Also, examination was done to see if there were any bacteriological differences between vegetations attached to the calcified annulus and the vegetations attached to the leaflet (Pressman et al., 2017). A study such as this, if correlation is proven true, allows cardiologists to take preventative measures for endocarditis in patients with MAC. If patients with MAC are more prone to developing endocarditis due to disruption of the endocardial surface from MAC, then routine lab work or diagnostic studies and preventative treatment may be beneficial for the patient.
Collected Data
Pressman et al.’s (2017) study put a focus on bacteriological differences in the setting of endocarditis and MAC. In this study, many echocardiographic studies were examined by a single reader for patients with a confirmed presence of MAC. Patients with a coexisting case of infective endocarditis were noted as well. It was then examined to see which specific type of bacteria was causing the endocarditis and if there were any correlation between the bacteria causing the endocarditis and the presence of MAC. It was found that there was a higher incidence of patients having a vegetation caused by the bacteria staphylococcus aureus. The study consisted of a total of 56 patients with mitral valve endocarditis. As shown in Table 1, out of the 56 patients, 28 patients had endocarditis associated with S. aureus (Pressman et al, 2017). Of these 28 patients, 16 patients had the vegetation on the MAC location (shown in table 2) (Pressman et al, 2017). Therefore, the incidence of S. aureus with a MAC location is a little over a fourth of the study’s population. S. aureus appears almost twice as much as any other organism found in the study. In comparison to the bacterias found with MAC, S. aureus was the bacteria which dominated the other bacterias observed in the study, appearing 10 times more than any other bacteria in this study.
Table 1
Bacteriology
Organisms Number of subjects
S. aureus 28
Streptococcal species (enterococcus) 17 (11 enterococcus)
Klebsiella species 1
Staphylococcus coagulase negative 1
Hemophilus parainfluenza 1
Eikinella corrodens 1
Candida albicans 1
No growth 6
Total 56

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Table 2

Vegetation characteristics by organism (all 56 subjects)
Organism On MAC Not on MAC (vegetation attached to leaflets or to the noncalcified annulus) Stippled mass Complications (Perforation, abscess, fistula)
S. aureus 16 12 12 10
Streptococcal species 1 16 3 1
Others 5 6 5 3
Total 22 34 18 14

Bouchiat, Moreau, and Devillard et al. (2015) composed a study to examine genetic differences between strictly defined community-acquired native valve infective endocarditis and bacteremia-related S. aureus. The first set included 126 S. aureus, with 72 infective endocarditis and 54 bacteremia. The second set included 81 community-acquired methicillin-susceptible S. aureus (MSSA) bacteremia and 66 community-acquired MSSA definite infective endocarditis. The results showed that diverse phenotypes like S. aureus ability to bind fibrinogen and fibronectin, resistance to microbicidal peptides, biofilm production, and the formation of platelet-bacteria thrombi on the valve surface have been described as critical in infective endocarditis occurrence (Bouchiat et al., 2015). It determined no difference between the strictly defined community-acquired native valve infective endocarditis and the bacteremia-related S. aureus. Though, the study showed how the bacteria connect to aspects of blood and causes formations on the valvular surfaces. These formations become the bacterial vegetations on the cardiac valves, including the mitral valve. The S. aureus infective endocarditis bacteria have a higher platelet aggregation, fibrinogen binding, and endothelial cell adhesion compared to bacteremia strains, as seen in Table 3 (Bouchiat et al., 2015). MAC intensifies these aspects of aggregation and thrombi formation due to the endocardial inflammation in association with annular calcium (Pressman et al., 2017).
Table 3
Infective Endocarditis (n=14) Bacteremia (n=14)
Fibrinogen binding (% of binding) 51.7 ± 10.22 47.7 ± 10.14
Endothelial cell adhesion (% of binding) 93.9 ± 28.80 90.1 ± 33.12
Platelet aggregation (lag time in minutes) 2.5 ± 2.42 2.2 ± 1.57

Goto, Toda, and Saito et al. (2017) reported a case of an elderly woman who was admitted to a hospital due to sudden cardiovascular collapse associated with bradycardia. Echocardiogram showed a vegetation of 8.0 mm on the anterior mitral valve leaflet and MAC on the medial side. On the follow-up echocardiogram, the patient’s vegetation enlarged to 12 mm and showed a pericardial effusion of 10 mm, despite antibiotic treatment. The patient went into surgery four days after admission, which was unsuccessful due to purulent pericardial effusion and the heart being covered with pus. The next echocardiogram showed continued vegetation enlargement (20 mm). Redo surgery was performed a week later. The vegetation was attached to the medial commissure of the mitral annulus. A vegetectomy and debridement of the mitral annulus was performed. Though, the patient died of sepsis and heart failure weeks later. The autopsy showed anterior mitral leaflet perforation with a vegetation in the A3 segment and an active-phase abscess of the mitral annulus in the MAC area (Goto et al., 2017).
Illustration 3
Illustration 3 demonstrates the locations of the vegetation and the MAC (Goto, et al, 2017). Each are located in closer proximity to the other, both lying on the medial side of the cavities. This may correlate to the previously mentioned study, Pressman et al. (2017), regarding MAC and vegetations. Pressman et al. (2017), aimed to see if there was a connection between presence of MAC and the bacterial vegetation. Being that both the MAC and the vegetation are in close proximity to each other, it may increase the likelihood that the MAC was present first and may have been a factor in the development of the bacterial vegetation.
Conclusion
The goal of Pressman et al.’s (2017) research was to determine a correlation between MAC and infective endocarditis, with a focus on specific bacteria. The conclusion made in Pressman et al.’s (2017) research was a positive finding. With the high prevalence of infective endocarditis in patients with MAC, it would be conclusive that there is a correlation between the infective endocarditis and MAC. The most frequently appearing bacteria in the Pressman et al.’s (2017) study was S. aureus. Thus, there is also a correlation with the presence of S. aureus in association with MAC. This research is complemented by other studies done, such as Bouchiat et al.’s (2017) research, with reference to the specific binding components of S. aureus to valvular surfaces. It is also complemented by case studies involving patients that have coexisting infective endocarditis and MAC, such as the work of Goto et al. (2017). Therefore, patients with MAC may be considered at risk for developing cases of infective endocarditis, especially those caused by the bacteria S. aureus. Precautions may be able to be put in place for those patients to monitor and/or use preventative treatments. Physicians could make treatment options more effective by being able to detect infection sooner or prepare for possible infection. If able to effectively monitor patients with MAC, complete prevention of infective endocarditis may be achievable. This would be especially beneficial to those whom are immunocompromised and that are more susceptible to the dangerous effects of an infection, such as the elderly. Hypothetically, if proper methods for prevention were developed, death rates from infective endocarditis would drop significantly. Further research on the preventative methods, such as a particular lifestyle change, a certain diet for the patient or medications to avoid an infection, would be necessary for this to be attainable.