What is valvular heart disease?
Valvular heart disease is a heterogenous group of disorders of the heart in which various heart valves are diseased. The valves could be abnormal by birth (congenital valvular abnormalities) or the abnormality could be acquired in the course of life (acquired valvular heart disease). Important congenital valvular heart diseases are bicuspid aortic valve (aortic valve having two cusps instead of the normal three), congenital aortic stenosis (narrowing of the orifice of the aortic valve) and congenital pulmonary stenosis (narrowing of the orifice of pulmonary valve). Rarely the mitral valve could also be narrowed by birth (congenital mitral stenosis).
What are the important acquired causes of valvular heart disease?
In the developing world, the most common cause of valvular heart disease is rheumatic fever and its sequelae (rheumatic heart disease). In the developed world, more common would be degenerative valvular heart disease. Reduced blood supply to the heart muscle (ischemic heart disease) can also damage the function of the heart valve. Other causes are infections (infective endocarditis), carcinoid heart disease, heart disease induced by medications used for obesity and traumatic damage to the heart valves.
How do valvular heart disease manifest?
Manifestation of the valvular heart disease depends on the valve involved, severity of involvement and the rapidity of progression. Valvular damage could produce leakage of the valve (regurgitation) or narrowing of the orifice (stenosis). Leakage of the heart valve produces volume overloading of the chambers involved. For example, leakage of the mitral valve (mitral regurgitation) between left atrium and left ventricle causes enlargement of both these chambers. Narrowing of mitral valve (mitral stenosis) produces enlargement of the left atrium which is before the valve, but not the left ventricle, which is after the valve in the blood flow sequence.
Our heart has four chambers and four valves. The valves are named as mitral valve, tricuspid valve, aortic valve and pulmonary valve. They prevent backflow of blood and allow the functioning of the heart and circulatory system in perfect harmony.
Mitral valve is the valve between the left sided upper and lower chambers of the heart, between the left atrium and left ventricle. Its shape resembles the headwear of a bishop (mitre) and hence the name. Mitral valve has two leaflets and is called a bicuspid valve. It closes when the left ventricle contracts, so that blood from the left ventricle does not flow back into the left atrium. Tips of the valve leaflets are held taut by string like structures (chordae tendinae) which connect the valve to small muscles in the left ventricle (papillary muscles).
Tricuspid valve is between the right upper and lower chambers – right atrium and right ventricle. It has three leaflets and hence the name. It closes when the right ventricle contracts thereby preventing leakage of blood from the right ventricle into the right atrium. Like the mitral valve, it is also kept taut by chordae tendinae and papillary muscles. Tricuspid valve has the largest orifice area among the four heart valves.
Aortic valve lies between the left ventricle and the aorta, the largest blood vessel supplying blood to the whole body. It has three semilunar cusps and it is mentioned as a semilunar valve. Aortic valve closes when the left ventricle relaxes after a contraction. Hence the blood pumped into the aorta when the ventricle contracts does not flow back into the left ventricle. This enables the forward flow of blood into the aorta and its branches, reaching all parts of the body, where it is required for various functions.
Pulmonary valve is between the right ventricle and the pulmonary artery. Pulmonary artery is a large blood vessel which carries deoxygenated blood to the lungs for oxygenation. Pulmonary valve closes when the right ventricle relaxes after contraction, preventing backflow of blood from the pulmonary artery to the right ventricle. Like the aortic valve, pulmonary valve also has three semilunar cusps and is known as a semilunar valve.