The mitral valve plays an important role in the normal function of the heart. Damage to the mitral valve affects the flow of blood through the left chambers of the heart and can increase the risk of cardiovascular disease. Some patients can develop an abnormal heart rhythm known as atrial fibrillation.¹ Atrial fibrillation can be dangerous and potentially result in strokes and myocardial infarction, therefore treatment with surgery to fix the underlying issue and/or anti-clotting medication is fundamental.²

Introduction

Mitral valve disorders affect 33 Million people worldwide and are an important risk factor for cardiovascular disease and events.³ Mitral stenosis and regurgitation interfere with the normal passage of blood across the heart chambers. This can cause congestive heart failure, affect the heart rhythm, especially atrial fibrillation (AF) and promote the formation of potentially dangerous blood clots. Mitral defects can be congenital, associated with genetic syndromes or acquired through infectious/autoimmune disorders and exposure to some medications.¹

Atrial fibrillation is a an episodic or continuous heart rhythm abnormality (arrhythmia) which is present in 2% of people, and up to 17% of those aged 60-80 years old and is typically experienced as “palpitations” or sudden racing heart.² Heart valve disease and hypertension are the two most common causes of AF, other aetiologies include congestive heart failure, congenital heart defects, cardiomyopathy and coronary heart disease.⁴ On Electrocardiogram (ECG), AF is characterised by the absence of an electrical wave representing the electrical signal for contraction of the atrium, indicating electrical or contractile dysfunctions due to disease of the heart valves or circulation.⁵

Treatment for atrial fibrillation is typically anticoagulant medication which can reduce the risk of stroke by up to 70%.⁶ Other treatments include catheter ablation surgery to remove the affected atrial tissue and correct the electrical abnormality through cardioversion.⁷ If AF is due to dysfunction of the mitral valve surgery to repair the leaflets may be necessary.⁸ Overall, both heart valve disease and atrial fibrillation, and particularly the combination of the two, greatly affect cardiovascular health and can potentially lead to dangerous clotting events and heart failure. As such monitoring patients at risk, encouraging preventative modifications and providing prompt anticoagulant treatment is crucial to reduce cardiovascular disease burden.⁷

What is mitral valve disease

The human heart is composed of four chambers - the left and right atria, superiorly, and the left and right ventricles, inferiorly. Each atrium is separated from the same-sided ventricle by a fibrous valve that it must pump blood across. The right atrium receives blood that has previously taken in excretion products from cells and has been depleted of oxygen, it then pumps it to the right ventricle which sends it to the lungs to be cleared and oxygenated again. From the lungs, oxygenated blood arrives in the left atrium which passes it onto the left ventricle that then pumps it into the systemic circulation to supply all cells across the body, and the cycle repeats.⁹

The mitral valve separates the left atrium from the left ventricle and is formed of two leaflets which gate the passage of blood. When the atrium contracts and the ventricle relaxes blood flows downwards through the mitral valve which opens in response to the pressure gradient. There are two main types of mitral valve disease. Mitral regurgitation is the most common mitral valve defect, affecting 24 Million people worldwide, it causes an abnormal opening in the mitral leaflets, most often due to a prolapsed valve.³ This causes blood in the left ventricle to flow back into the atrium disturbing the volume of blood that is pumped in each ejection. On the other hand, mitral stenosis occurs when the mitral valve becomes too thick causing it to be harder to pump blood into the left ventricle. These mitral valve dysfunctions can cause turbulent blood flow which can lead to clotting as well as increased risk atrial fibrillation, congestive heart failure, and acute cardiovascular events such as stroke and myocardial infarction.¹

While mitral valve regurgitation, 50-70% of all cases of mitral stenosis are due to rheumatic fever as a result of streptococcal infection, this is particularly prevalent in developing countries and is avoidable with prompt availability of antibiotic treatment for common throat and middle ear infections.¹⁰ Other causes of mitral disease include:

• Congenital defects 
• Connective tissue disorders such as Ehler-Danlos Syndrome and Marfan's syndrome. Inflammation of the heart valves (endocarditis) due to bacteria or autoimmune diseases(e.g. Lupus systemic erythematosus) 
• Trauma
• Radiation therapy
• Advanced ischaemic heart and dilated cardiomyopathy, which can stretch the mitral leaflets resulting in mitral regurgitation^1,11

Mitral valve defects are often asymptomatic. When symptoms become present they are usually similar to congestive heart failure. Patients may have.

• Shortness of breath
• Cough
• Fatigue
• Dizziness/light-headedness and potentially fainting
• Leg swelling
• Palpitations 
• Heart murmur on auscultation¹¹

What is atrial fibrillation 

Atrial fibrillation is an abnormal heart rhythm that can be episodic or become continuous in severe cases which is characterised by abnormal contraction of the atrium, that is seen on ECG as an absence of P waves, which normally represent the electrical activation of the left atrium.⁵ AF can be asymptomatic but can also be accompanied by palpitations described as “missing a beat”, increased heart rate, chest discomfort, shortness of breath and lightheadedness or fainting.⁶ The inability of the atrium to effectively pump blood into the ventricle can promote the formation of clots, hence why AF is associated with an increased risk of ischaemic events.⁵

Atrial fibrillation is most often due to an issue affecting the heart such as heart failure, ischemic heart disease, congenital defects, hypertension or valve disorders. In addition, other health and lifestyle factors can contribute to the development of AF, including:

• Family History
• Infections
• Thyroid Disorders
• Sleep Apnea
• Chronic Lung Diseases:
• Obesity
• Diabetes
• Alcohol Consumption
• Smoking^4,12

How is atrial fibrillation linked to mitral valve defects

Mitral valve disease is one of the most important risk factors for the development of atrial fibrillation, with AF being present in 29% and 16% of patients with mitral stenosis and mitral regurgitation, respectively.13 Researchers believe over time, mitral stenosis can lead to enlargement of the left atrium and thickening of the muscle wall, which can alter the electrical pathways within the heart, promoting the development of  AF.¹⁴ Similarly, in mitral regurgitation, the valve fails to close properly, allowing blood to leak backwards into the left atrium, increasing the volume load on the atrium, causing it to stretch and remodel also predisposing to AF. AF exacerbates the problems associated with mitral valve disease by reducing cardiac efficiency and increasing the risk of blood clots, stroke, and heart failure. The interplay between the two, thus, creates a vicious cycle that can significantly impair heart function.¹⁵

How is atrial fibrillation associated with mitral valve disease treated

The first line approach for AF associated with mitral defects is to focus on prevention through anti-clotting medicines, such as Warfarin and Apixaban. Medications to control heart rhythm and rate such as beta-blockers and calcium channel inhibitors, are also often also used alongside anticoagulants. If AF persists over 48 hours or patients experience recurrent episodes despite pharmacological therapy, cardioversion procedures in which an electrical current is applied on the patient's chest to normalise heart rhythm can be considered. Alternatively, surgical catheter ablation of the damaged atrial tissue is also performed.⁷

In patients with severe mitral stenosis or regurgitation, mitral valve repair or replacement with a prosthetic may be necessary to eliminate AF. On its own, valve repair is only moderately effective, however when combined with catheter ablation it was found to eradicate AF episodes in over 80% of people with valvular AF.¹⁶

Importantly, long-term management of AF requires a coordinated effort between patients and both community and specialist health providers to reduce risk of stroke and other cardiovascular complications. It usually involves lifestyle modifications, adherence to pharmacological therapy as well as managing other frequently present comorbidities such as diabetes and heart failure.¹⁷

Summary

The mitral valve separates the left atrium and ventricle and, under normal circumstances, it responds to pressure gradients to allow blood to pass through its leaflets. Mitral defects such as stenosis and regurgitation are relatively common and can cause a wide range of complications, including the development of an abnormal heart rhythm known as atrial fibrillation. AF is usually episodic, though it can become continuous, and can sometimes be experienced as palpitations, racing heart or lightheadedness. Importantly, both valve disease and AF can greatly increase the risk of stroke, heart attack and congestive heart failure.

Management of AF in valvular heart disease typically involves anticoagulant medication to reduce the risk of ischaemic complications, often alongside drugs that slow down the heart and/or help regulate heart rhythm. Other interventions include cardioversion and catheter ablation, a surgical procedure in which the dysfunctional atrial tissue is removed. In some cases, particularly in severe mitral damage, valve repair or replacement is recommended.

Overall, atrial fibrillation is a common yet potentially dangerous arrhythmia, which can greatly affect cardiovascular health and lead to premature mortality. Mitral valve disease is one possible cause of AF and the combination of the two warrants prompt and long-term management. As such, it is fundamental to empower patients and clinicians to identify it and be aware of the risks and how healthcare teams should manage and monitor it.