Mitral Valve Regurgitation

Mitral Valve Regurgitation

This patient is a forty-eight-year-old plumber. His general practitioner referred him following an insurance medical exam during which a systolic murmur was identified. He was noticed to have a heart murmur when examined for an inguinal hernia repair ten years previously but has not had any recent follow-up. He is a non- smoker that only drinks socially. During the physical exam, the patient does not report any symptoms, and he is fit and well. Cardiovascular examination reveals: pulse sixty beats per minute, regular, with a normal character; blood pressure 160/70 mmHg. Jugular venous pressure was not elevated. His heart sounds are normal. There is a pansystolic murmur heard in all areas and radiating to the axilla. The apex beat is displaced two centimeters laterally. There are no other abnormal findings. The electrocardiogram results came back normal, and the echocardiogram shows a mildly dilated left ventricle with normal function and normal left atrial dimensions. This patient is experiencing chronic mitral regurgitation (Lilly, 2015). This paper will discuss clinical manifestations, normal physiology, pathophysiology, medical management, and current research regarding mitral regurgitation.

Clinical Manifestations

The patient presented with a systolic murmur heard in all areas and radiating to the axilla and elevated blood pressure. The result of the echocardiogram is that there is a mildly dilated left ventricle and the electrocardiogram is normal.

The clinical manifestations of mitral regurgitation differ depending on if the problem is acute or chronic (Lilly, 2016).  As the degree of the regurgitation increases the severity of the symptoms that the patient experiences also increase. The symptoms often experienced with mitral regurgitation are dyspnea, especially when laying down, increased fatigue, heart palpitations, and edema in the lower extremities. Mitral regurgitation is often mild and progresses slowly; therefore, it is possible to have it for years and never experience any symptoms (Mayoclinic, 2019). When the disease has progressed, it is common to hear a murmur when auscultating over the heart that radiates to the axilla. This murmur reflects the continues pressure gradient between the left ventricle and the left atria (Lilly, 2016). This sound can be increased, thereby supporting the cause of the murmur, by having the patient clench their fist and forearm. Chronic mitral regurgitation may be caused by degeneration of the valve, rheumatic deformity, congenital valve defects, or extensive calcification of the mitral valve (Lilly, 2016).

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There are a few different tests that may be performed to diagnose mitral regurgitation. Echocardiogram results that would indicate mitral regurgitation are systolic flow from the left ventricle into the left atrium, and in cases of a chronic issue it would show enlarged left atrial and ventricle (Lily, 2016). In the case study presented, the patient’s echocardiogram demonstrated a mildly enlarged left ventricle. Chest radiographs in a patient with mitral regurgitation would also show dilation of the left atrial and ventricle as well as signs of pulmonary venous congestion. In a cardiac catheterization, mitral regurgitation will cause an increase in the pulmonary artery wedge pressure (Lilly, 2016).

Normal Physiology

Mitral regurgitation is the backflow of blood in the heart from the left ventricle to the left atrium. This process affects the body by causing increased pressure in the heart and decreasing the blood flow to the body. The result of increased pressure in the heart chronically is that the left atrial and ventricle become enlarged and the increased pressure can start building and affect the pulmonary system (Lee, et al., 2015). Having a decreased blood flow in the systemic system increases fatigue and dyspnea in the patient when it is a chronic issue. The cause of mitral regurgitation is that the mitral valve is experiencing degeneration of the collagen fiber network and myxomatous degeneration (Deborde, et al., 2016).

The collagen fiber network that makes up the mitral valve is composed of molecules consisting of triple helix amino acid chains stabilized by hydrogen bonds. The structural characteristic of the collagen structure and the mechanical properties of the collagen at the molecular level are the base of the kinetics of the biaxial stretch of the mitral valve (Lee, et al., 2015)

On a cellular level, there are three structural layers that make up the leaflets of the mitral valve. The fibrosa is the stiff layer on the ventricular surface that is made up of collagen fiber; the atrials are a thin layer on the atrial surface that is more compliant and is composed of elastic fibers and the spongiosa, which is composed of glycosaminoglycans and proteoglycans. Mitral valve regurgitation is often caused by mitral valve prolapse, which is characterized by thickened leaflets (Deborde, et al., 2016).

Homeostasis of the valve itself is maintained by valvular interstitial cells that can sense pressure and respond to environmental changes, remodeling, and are able to maintain the strength and durability of the valve. The mechanical stress of the valve is transmitted to the cells through their interactions with the extracellular matrix. The surface of the mitral valve is covered with endothelial cells that maintain the integrity of the valves and also regulates the leaflets’ mechanical properties (Deborde et all, 2016).

In mild and acute mitral regurgitation, there is usually not much or any effect on the heart. Problems arise when mitral regurgitation is a chronic problem that is left untreated. The heart itself is affected by mitral regurgitation by experiencing increased pressure from the backflow of the blood that leads to cardiac and pulmonary congestion. Both the left atrial and ventricles become dilated when this pressure is increased in a chronic manner (Lee, et al., 2015).

Pathophysiology

Molecularly, when there is a disruption of the collagen bonds of the mitral valve, it affects the mitral valve’s ability to stretch and keep a proper seal, preventing backflow of blood into the left atrium. When the kinetics of the collagen bonds are disrupted, it has a negative effect on the valve and therefore, the heart (Deborde, et al., 2016).

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Mitral valve regurgitation is mainly due to myxomatous degeneration, leading to altered mechanical stress and turbulent flow near the mitral valve leaflets. The mitral valve is a structure in the heart that opens, allowing blood flow to the left ventricle, during diastole and closes, preventing blood flow to the left ventricle, during systole. The valve prevents the backflow of blood into the left ventricle. Cellular changes are mainly in the spongiosa and then extend to the other layers resulting in disruption of the collagen organization in the fibrosa (Deborde, et al., 2016).

When there is mitral valve regurgitation, the entire heart is affected. In chronic mitral valve regurgitation, there is dilation of both the left atrium and ventricle as a result of the increased blood pressure in the heart. This increased pressure can build and subsequently affects the pulmonary and systemic system if left untreated (Lilly, 2016).

Medical Management

The management of mitral regurgitation depends on the cause but most commonly requires surgical intervention. While there are medications that may be prescribed to decreases blood pressure as well as vasodilators that would potentially decrease arterial resistance thereby decreases pressure in the heart and decrease the amount of regurgitation, these are only used to stabilize a patient until surgery can take place (Lilly, 2016).

Surgical intervention is necessary when the patient’s ejection fraction is less than sixty percent or as soon as a patient begins to have symptoms of mitral regurgitation. The surgical options are to either repair or replace the mitral valve. Repairing the valve is the optimum choice when possible. Repair is an option when the leaflet becomes perforated, and it can be patched or when it is possible to reattach ruptured chordae (Lilli, 2016). When repair is possible, it eliminates later issues that can arise later on when artificial vales are used because the native valve tissue can be preserved (Mayoclinic, 2019). A newer option for repairing mitral valves in patients who are at high surgical risk is to repair the mitral valve with the use of a catheter through the femoral vein as opposed to percutaneously repairing the valve (Muller, et al., 2017). Although, in cases of severe mitral regurgitation, percutaneous repair is the most effective method of repair.  (Lilly, 2016)

When replacement of the mitral valve is necessary, there are options in both the type of surgery and the type of replacement valve. While many mitral valve replacement surgeries require a sternotomy, there are some cases where the repair can be made through a few incisions in the sternum. Mechanical valves are the most common and will last a lifetime, although they require the patient to take anticoagulants. Tissue valves are made of bovine or porcine tissue and often last for ten to twenty years. Biological tissue valves are the least common type of valve used in replacements and also last for only ten to twenty years (Muller, et al., 2017).

Repairing or replacing the valve is the only way to treat the disease long term. Mitral regurgitation is classified as primary if the regurgitation is due to a structural defect or secondary if it results from left ventricular enlargement (Lilly, 2016). The mortality rate after mitral valve repair is only two percent compared to a five to seven percent mortality rate when the valve is replaced. Some degree of prevention of mitral regurgitation can be made with a healthy lifestyle, but no guarantee having a healthy diet and exercising will prevent mitral regurgitation. The prognosis of mitral valve regurgitation is dependent on the degree of regurgitation and if the patient seeks treatment. In an acute and severe situation, even when surgery is performed, there is a thirty-day mortality rate of twenty to twenty-five percent (Lilly, 2016).

Current Research

There is research being conducted currently comparing the long-term results of mitral valve repair to replacement. In a randomized trial comparing the left ventricular end-diastolic index, there was no significant difference seen when comparing mitral valve repair and replacement during the first two years. This was also the case for survival rates and left ventricular remodeling. However, mitral regurgitation did reoccur more often in the patients that had their mitral valves repaired. The reoccurrence mitral regurgitation led to more cardiovascular hospital admissions as well as more heart-failure related adverse events (Goldstein, et al., 2016).

Further research is being conducted to determine if transcatheter mitral valve repair may improve the clinical outcome in patients with heart failure in conjunction with mitral regurgitation. Six-hundred and fourteen patients were enrolled in the study with three hundred of them being in the device group who underwent transcatheter mitral valve repair. In the patients in the device group, there was a lower mortality rate within two years as well as a lower rate of hospitalization for heart failure (Stone, et al., 2018).

References

• Deborde, C., Simionescu, D. T., Wright, C., Liao, J., Sierad, L. N., & Simionescu, A. (2016, November 01). Stabilized Collagen and Elastin-Based Scaffolds for Mitral Valve Tissue Engineering. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5107718/
• Goldstein, D., Moskowitz, A., Gelijns, A., Ailawada, G., Parides, M., Perrault, L., . . . Argenziano, M. (2016, January 28). Two-Year Outcomes of Surgical Treatment of Severe Ischemic Mitral Regurgitation: NEJM. Retrieved from https://www.nejm.org/doi/full/10.1056/NEJMoa1512913
• Lee, C., Amini, R., Sakamoto, Y., Carruthers, C., Aggarwal, A., Gorman, R., . . . Sacks, M. (n.d.). Mitral Valves: A Computational Framework. In , Multiscale Modeling in Biomechanics and Mechanobiology(pp. 223-255). London: Springer-Verlag. doi:10.1007/978-1-4471-6599-6_10
• Lilly, L. S. (2016). Pathophysiology of heart disease: A collaborative project of medical students and faculty. Wolters Kluwer.
• Mitral valve regurgitation. (2019, May 17). Retrieved from https://www.mayoclinic.org/diseases-conditions/mitral-valve-regurgitation/symptoms-causes/syc-20350178
• Muller, D. W., Farivar, R. S., Jansz, P., Bae, R., Walters, D., Clarke, A., . . . Sorajja, P. (2017, January 23). Transcatheter Mitral Valve Replacement for Patients With Symptomatic Mitral Regurgitation. Retrieved from http://www.onlinejacc.org/content/69/4/381
• Stone, G., Lindenfeld, J., Abraham, W., Kar, S., Lim, S., Mishell, J., . . . Sarembock, I. (2018, December 13). Transcatheter Mitral-Valve Repair in Patients with Heart Failure: NEJM. Retrieved from https://www.nejm.org/doi/full/10.1056/NEJMoa1806640