Aetiology And Risk Factors For Mitral Valve Disease

Introduction

The mitral valve, a vital component of the heart's machinery, is a dynamic gateway between the left atrium and left ventricle.¹ Like a well-timed conductor, it opens and closes in perfect rhythm, ensuring that blood flows seamlessly in one direction. As blood enters the heart from the lungs, it passes through the mitral valve into the left ventricle, from where it's pumped out to nourish the rest of the body.

However, when the mitral valve falters, known as Mitral Valve Disease (MVD), this essential flow is disrupted, leading to potentially serious complications. Understanding the causes and risk factors behind MVD is crucial for prevention and early intervention. In this article, we explore the key factors contributing to MVD and how proactive measures can make all the difference.

MVD types

MVD is generally divided into two main categories: Mitral Valve Stenosis and Mitral Valve Regurgitation.

Mitral valve stenosis occurs when the valve’s opening becomes abnormally narrow, restricting blood flow from the left atrium to the left ventricle. While Rheumatic Fever is the leading cause of this condition, several other factors can contribute to its development, such as:²

• Calcification 
• Infective endocarditis 
• Systemic lupus erythematosus 

Mitral valve regurgitation is the most common type of valvular disease, occurring when the mitral valve fails to close fully during the heart’s contraction (systole). This incomplete closure allows blood to leak backwards into the left atrium instead of moving forward into the left ventricle, disrupting the heart’s efficient blood flow.³ 

Aetiology (causes)

Congenital causes

Congenital mitral valve abnormalities are present at birth and can manifest in various ways, including:

• Thickened or stiffened flaps (otherwise known as leaflets)
• Deformed flaps or flaps that are joined
• Issues with the cords that support the flaps. They could be missing, too short or too thick
• Multiple openings at the mitral valve (otherwise known as a double-orifice valve)

Acquired cases

Unlike congenital abnormalities, acquired mitral valve issues develop later in life due to various factors, such as ageing or underlying health conditions.

Rheumatic heart disease

Rheumatic heart disease is an autoimmune disease that occurs as a complication of rheumatic fever.⁴ It is caused by an infection of Group A Streptococcus spp.⁵ Rheumatic fever can lead to:⁶ 

• Joint pain and swelling 
• Mitral valve regurgitation
• Chorea

Rheumatic heart disease affects an estimated 15 million people worldwide, contributing to approximately 233,000 deaths each year.⁷

Degenerative mitral valve disease

Degenerative mitral valve disease is characterised by direct damage to the mitral valve, which can lead to mitral valve prolapse. In this condition, the valve flaps become floppy and fail to close properly, potentially resulting in:⁸

• Enlargement
• Elongation
• Dilation
• Thickening of the flaps

The primary causes of degenerative mitral valve disease are myxomatous infiltration and fibroelastic deficiency.⁹ These conditions relate to the amount of connective tissue in the area, impacting the structural integrity of the valves.

Infective endocarditis

Infective endocarditis occurs when the inner lining of the heart, known as the endocardium, becomes infected, potentially affecting the heart valves.¹⁰ Approximately 80% of cases are attributed to two groups of bacteria: Streptococci and Staphylococci.¹¹

These bacteria can proliferate within the heart, spreading to the valves and impairing their function by producing toxins and enzymes that break down tissue.¹⁰ While infective endocarditis is relatively rare, with an incidence of 3 to 10 cases per 100,000 people annually, it remains a significant concern. The condition is increasingly observed in individuals over the age of 65, largely due to the presence of other health conditions such as diabetes, the need for haemodialysis, and the use of cardiac devices and prosthetic valves.¹⁰

Heart attack

Myocardial infarction, commonly known as a heart attack, can also contribute to the development of MVD. A heart attack occurs when a blood vessel supplying blood to the heart becomes narrowed or blocked, severely reducing or completely obstructing blood flow to a specific area of the heart. This can lead to muscle damage or even irreversible muscle death.¹² 

Mitral regurgitation, a common form of MVD, occurs in up to 39% of individuals who have experienced a heart attack. The likelihood of developing MVD is higher in those who suffer a heart attack on the right or inferior side of the heart compared to those affected on the left or anterior side.¹³

Risk factors

There are a range of factors that can increase your risk of developing MVD. This may include but is not limited to:

Demographic factors

• Older age can increase your risk of developing MVD
• Those assigned male at birth are more likely to develop heart conditions, including MVD, than those assigned female at birth

Lifestyle factors

Lifestyle habits such as smoking, poor diet, obesity, and lack of physical activity can increase your risk of a range of heart conditions including MVD.

Medical history

Having other medical conditions can also increase your risk of developing MVD, particularly if you:¹⁴

• Have an overactive thyroid (hyperthyroidism) 
• Are pregnant 
• Have high blood pressure
• Have diabetes

If you have Marfan Syndrome you could also be at a higher risk of developing MVD. Autoimmune disorders, such as Rheumatoid Arthritis or Systemic Lupus Erythematosus, are also linked to an increased risk of developing MVD.

Genetics

A family history of MVD may elevate your risk of developing the condition, suggesting a potential genetic predisposition.

Summary

Mitral Valve Disease (MVD) is a serious yet treatable condition that affects the mitral valve, which plays a crucial role in regulating blood flow within the heart. The two primary types of MVD are Mitral Valve Stenosis and Mitral Valve Regurgitation.

Numerous factors can contribute to the development of MVD, including congenital abnormalities, rheumatic heart disease, infective endocarditis, and heart attacks. Additionally, various demographic, lifestyle, and medical factors can increase the risk of developing this condition.