The immune system has several mechanisms to neutralize invading microorganisms, limit the damage to the body and totally eradicate the infection. This immune response is a carefully coordinated sequence of events that ensures that the invaders are specifically targeted and the body’s tissues are spared. However, sometimes this process is disrupted and the immune system causes damage of otherwise healthy tissue. Rheumatic fever is one example of this inappropriate response and tends to arise several weeks after a certain type of bacterial throat infection. Inflammation is widespread and involves many systems of the body, including the heart. It is an acute reaction that can last several weeks and usually does not cause any permanent damage to any part of the body, except for the heart valves in some cases.
What is rheumatic heart disease?
Rheumatic heart disease is the inflammation of the heart that arises with a post-infective immunologically mediated response known as rheumatic fever. Various organs and systems of the body are affected in acute rheumatic fever including the heart, skin, joints and nerves. While the heart is not the only organ affected in rheumatic fever, the chronic effects usually involving its valves, can severely impair normal cardiac function in the long term.
Causes of Rheumatic Heart Disease
The immune system forms antibodies against specific proteins present on the surface of microorganisms (antigens). These antibodies bind with the antigens and helps the immune cells to accurately identify the invading organisms and elicit a rapid response against it. In a certain type of sore throat caused by streptococcal bacteria known as group A streptococcal pharyngitis, the body produces antibodies against the M proteins on the bacteria.
However, the antibodies cross react with normal tissue antigens in the heart. The immune response is then directed towards the heart tissue causing injury, inflammation and even structural damage of heart in the long term. Refer to strep throat for more information on the causes, method of transmission and contagiousness of streptococcal pharyngitis.
The Heart and Its Valves
The heart is the central organ of the cardiovascular system. Although similar to blood vessels, particularly arteries, it is more specialized and vital for sustaining life. As a muscular pump, the heart is responsible for circulating deoxygenated (oxygen deficient) blood to the lungs and oxygenated blood to the rest of the body. There are four chambers in the heart – two atria and two ventricles.
Between the atrium and ventricle on each side lies the atrioventricular (AV) valves – tricuspid valve on the right and bicuspid valve (mitral valve) on the left. Blood leaves the heart through the ventricles and passes into the large arteries – pulmonary artery on the right and aorta on the left. Between the ventricles and the arteries are another set of valves known as the semilunar valves. On the right, this is the pulmonary or pulmonic valve while on the left it is the aortic valve.
Heart valves prevent the backward flow of blood (regurgitation). In this way blood travels in only one direction through the heart – into the atrium, then the ventricle and out through the respective large artery. These valves must also be able to open fully and allow blood to flow freely when necessary.
Carditis in Acute Rheumatic Fever
In rheumatic fever, all three layers of the heart may be inflamed to varying degrees and this is known as pancarditis. This includes the inner endocardium (endocarditis), middle muscular myocardium (myocarditis) and outer pericardial lining (pericarditis). Most of this inflammation may resolve but the heart valves are at risk of chronic damage. The mitral and aortic valves are more commonly affected. Nodules tend to develop on the leaflets of the mitral valves and permanently affect its functioning.
Chronic Rheumatic Heart Disease
Chronic heart disease arises in about half of patients who experience carditis with rheumatic fever. This chronic disease is associated with damage of the heart valves that do not resolve spontaneously. It is not uncommon for rheumatic fever to be undiagnosed or even forgotten in childhood only for the valvular damage to be detected in adulthood.
Over time, there is progressive fibrosis of the heart valves with insufficiency of varying degrees. Most cases affect the mitral valve and then the aortic valve. Involvement of the pulmonary and tricuspid valves are uncommon. Fibrosis causes the valve to stiffen and for certain parts to fuse together. This causes narrowing of the channel regulated by the respective valve and also allows for backward flow of blood (regurgitation). These changes cause turbulence of blood flow which further damages the heart valves and contributes to even greater fibrosis. With time there is extensive calcification of the heart valves, particularly the mitral and aortic valves, leading to an almost complete loss of flexiblity and excessive narrowing.
The myocardium and pericardium of the heart may also be affected in the chronic stages. This can lead to various other pathologies including heart failure and disruption of the electrical conduction system of the heart. After the initial attack of rheumatic fever, there is a geater risk of reactivation with future group A streptococcal throat infections. This further damages the heart and may speed up the progression of severe heart disease.
Signs and Symptoms
In acute rheumatic fever, carditis may vary in intensity and can present with signs and symptoms such as :
- Rapid heart rate (tachycardia)
- Irregular heart beat (arrhythmia)
- Heart murmurs
- Pericardial friction rub
- Chest pain
These same clinical features may be present in chronic rheumatic heart disease. Additional features associated with long term inflammation, fibrosis and specifically heart valve disease includes :
- Enlargement of the heart (cardiomegaly)
- Swelling of the legs, hands and/or abdomen (edema)
- Breathlessness (dyspnea)
- Abnormal breathing sounds (crepitations/crackles)
- Fluid in the lungs (pulmonary edema)
- Coughing up of blood stained sputum (hemoptysis)
Patients are also at greater risk of thromboembolic conditions like an ischemic stroke, infections of the inner heart wall (infective endocarditis) and permanent arrhythmias. Heart failure is the more common complication that arises and may lead to death. However, early diagnosis of heart valve disease and surgical replacement of the valve may be prevent these complications.