Introduction

The heart has four valves – pulmonary and tricuspid valves on the right side of the heart, aortic and mitral valves on the left side of the heart. These valves control the direction of blood flow, which is a one-way system of flow with flaps that open and close with every heartbeat to prevent backflow.¹

The mitral valve is the most complex valve and mitral valve disease is a common heart valve condition, affecting 5.1% of the elderly aged 65 and above in the UK. It is also a frequent cause of heart failure, with complications that include arrhythmia, endocarditis, and cardiac arrest, which can even lead to death. Located at the junction between left atrium and left ventricle, the mitral valve acts as a gate – when the left ventricle is relaxed, the valve opens and blood flows. The above image shows the different chambers of the heart, heart valves and the direction of blood flow through the heart. Image from:

From the left atrium into the left ventricle, then closes when the left ventricle contracts to pump out the oxygen-rich blood to the whole body as well as to prevent backflow of blood into the left atrium. Therefore, the mitral valve is crucial for cardiac function, and any abnormalities that affect the functionality of the valve can negatively affect the cardiac function.^2,3

The three most common types of conditions affecting the mitral valve are mitral valve stenosis (obstruction), mitral valve regurgitation (leakage), and mitral valve prolapse (bulging backwards during valve closure). The prevalence of these conditions increase with age, especially in elderly aged 75 and above.⁴ 

Mitral valve stenosis

Mitral valve stenosis is the narrowing or obstruction of the mitral valve, which eventually restricts the oxygenated blood supply from the heart to the whole body. 

Rheumatic fever is the major cause of mitral valve stenosis. Approximately 60% of all patients with mitral stenosis present with rheumatic fever, which is an inflammatory disease following an untreated streptococcal infection, specifically the group A, β-hemolytic streptococcus bacteria. The condition occurs due to an exaggerated immune response as the body’s immune system tries to fight off the infection, but instead it attacks the healthy tissues. As the disease progresses over time, the flaps of the mitral valve harden and thicken causing the obstruction. Although rheumatic fever is mainly associated with mitral stenosis, it usually affects more than one heart valve.

However, not all people with streptococcal infections develop rheumatic fever and mitral valve stenosis.^5,6 Another cause of mitral stenosis is due to hard deposits such as calcium that form around the valve with increase in age. In kidney failure patients, calcium deposits on the valve occur 10–20 years earlier compared to the general population.⁷ In infants and children, congenital defects are usually responsible for the malformation of the valves leading to mitral stenosis.⁸ 

The common symptoms of mitral valve stenosis are:

• Shortness of breath
• Fatigue
• Rapid irregular heartbeats or palpitations
• Dizziness
• Chest pain

There are two definitive modes of treatment for mitral valve stenosis: balloon valvuloplasty and mitral valve surgery. Balloon valvuloplasty is usually recommended for patients whose valves are not calcified too severely. This non-invasive procedure involves inflating a balloon to open the valve, thereby relieving the obstruction.⁹ Mitral valve surgery, on the other hand, is recommended for patients with severely affected valves. Although it is the last resort of treatment options in children, young adults, and women contemplating pregnancy, it is the treatment of choice in older patients with significant calcium deposits and leaky valves.

These patients will have their valves replaced. A non-surgical treatment option would be medications to manage the symptoms. However, this does not affect the progression of the disease. Examples of medications are beta-blockers and calcium channel blockers to control the heart rate, and anticoagulants to prevent stroke, particularly in patients with irregular heart rhythms. Patients with a previous history of rheumatic fever should be put on prophylaxis treatment to prevent its recurrence.^10,11 

Mitral valve regurgitation(MR)

Mitral valve regurgitation occurs when the valve does not close completely during contraction of the left ventricle, causing blood to leak into the left atrium. This happens when the valve becomes too floppy or when the ring of muscle around the valve becomes too wide.

Mitral regurgitation is classified into primary and secondary:

• Primary mitral regurgitation is when the actual mitral valve is compromised
• Secondary mitral regurgitation, also known as functional mitral regurgitation, is used when the valve has a normal structure but the left ventricle or left atrium is faulty

Primary mitral regurgitation is usually caused by mitral valve prolapse (another type of mitral valve disease discussed below), rheumatic fever, endocarditis or congenital malformations. Secondary mitral regurgitation is caused by alterations to the left ventricle that negatively affect the function of the mitral valve, such as coronary heart disease, cardiomyopathy or atrial fibrillation.¹² 

The common symptoms of mitral valve regurgitation are:

• Dizziness
• Breathlessness
• Tiredness
• Chest pain
• Heart murmurs

However, some patients do not present with any symptoms, especially when the valve leakage happens gradually over time. This is because when leakage into the left atrium occurs, the heart compensates by increasing the size of the left ventricle. Sudden (acute) mitral regurgitation may occur when the patient has an infection of the heart valve or when the patient has a heart attack that damages that ruptures the muscles connected to the valve.²

Treatment is not necessarily required for asymptomatic patients, but they do require careful and frequent follow-ups.¹³ For symptomatic patients, medications and surgery are some of the treatment options. Medications have a limited role in primary mitral regurgitation patients, compared to secondary mitral regurgitation patients. As there is underlying dysfunction in secondary mitral regurgitation, medications are prescribed to manage the symptoms or conditions associated.

The preferred treatment for primary mitral regurgitation patients is surgery to repair the mitral valve. The surgery, if performed in a timely manner, has good prognosis and can improve the patient’s life expectancy.¹⁴ In contrast, surgery for secondary mitral regurgitation patients has less favourable outcomes with high recurrence rate.¹⁵

There is, however, a newer procedure that is minimally invasive and does not require surgery – a transcatheter correction of mitral regurgitation using MitraClip, whereby a small implanted clip is attached to your mitral valve to help it close more completely. This procedure, however, is reserved for patients who are unsuitable for surgery or with high surgical risk.¹⁶ 

Mitral valve prolapse(MVP)

Mitral valve prolapse is the backward bulging of the mitral valve leaflet into the left atrium during contraction of the left ventricle. It is a common risk factor for MR, in which the worsening of MVP consecutively worsens MR, resulting in congestive heart failure, arrhythmia, and/or sudden death.^17,18 Mitral prolapse is also a risk factor for endocarditis.¹⁹ 

Abnormalities of the valvular or connective tissues and genetic factors are the most common causes of mitral valve prolapse. This is associated with the tissues that join the mitral valve to the heart muscles, with which most of the affected people are born. Several hereditary connective tissue disorders, such as Marfan syndrome, Loeys-Dietz syndrome and Ehlers-Danlos syndrome, have been associated with mitral valve prolapse. There is a 4 to 5-fold risk of mitral valve prolapse in a child when one parent has the disease, compared to parents without the disease. This is because the mutated gene that causes MVP can be passed on from either parent to the child.^20,21 

The common symptoms of mitral valve prolapse are:

• Chest pain
• Palpitations
• Anxiety
• Shortness of breath

The majority of people do not present with symptoms or, at most, have mild MR. They are considered to be low-risk and do not require medical treatment. However, patients are advised on lifestyle modifications such as reducing or avoiding caffeine, smoking, and alcohol intake, which would reduce the burden on the heart and prevent the need for medications in the future. In contrast, symptomatic patients with substantial mitral regurgitation are considered high-risk and often require medical interventions.

These symptomatic patients are at risk for valve infection, thus requiring prophylactic antibiotics.²² A severe MR would require surgical intervention as either mitral valve repair or mitral valve replacement. Other medications such as beta-blockers or anticoagulants are used to manage symptoms associated with atrial fibrillation and heart failure.²³

Summary

The mitral valve is one of the four heart valves, located on the left side of the heart. As it is involved in the flow of blood from the heart to the entire body, any problems associated with the valve would affect the flow. The three most common types of mitral valve conditions are mitral valve stenosis, mitral valve regurgitation and mitral valve prolapse.

The causes that lead to this condition may be interrelated and can be serious, but often treatable. There is currently no cure available, and the treatments are individualised based on the symptoms experienced by the people affected. While more severe cases require surgery, prompt and timely surgery usually results in good prognosis and helps in living a normal life.