Cardiac Valve Disease
Valves within the heart separate the right atrium and ventricle (tricuspid valve), the left atrium and ventricle (mitral valve), the right ventricle and the pulmonary artery (pulmonic valve), and the left ventricle and aorta (aortic valve) (click here to see cardiac anatomy diagram). The valves ensure that blood flows in a single pathway through the heart by opening and closing in a particular time sequence during the cardiac cycle. Normal valves permit blood to flow in only one direction, for example, from the right atrium into the right ventricle. When heart valves become diseased or damaged, they may not fully open or close. This can seriously impair cardiac function by causing blood to leak back into cardiac chambers or by requiring heart chambers to contract more forcefully to move blood across a narrowed valve.
A chronic disease process is responsible for defective valves in most older individuals. Sometimes, the disease results from a triggering event many years earlier, such as rheumatic fever. Bacterial infection, viral infection and inflammation of valves can trigger changes in valve structure and function. Normally, valve leaflets are very thin and flexible, but they can become thickened and rigid in response to a disease processes. When this occurs to a valve, it may not be able to fully open or to completely close. Valve disease found in younger individuals is usually due to a congenital defect in the embryologic development of the heart. Valve dysfunction can occur secondarily to other cardiac diseases, such as coronary artery disease, cardiac hypertrophy and cardiac dilation. If coronary artery disease progresses to the point where papillary muscles become hypoxic or infarcted, then the impaired contractile function of these muscles can lead to a leaky tricuspid or mitral valve. Cardiac hypertrophy or dilation, by altering cardiac chamber structure and dimensions, can lead to valve dysfunction. Finally, valve dysfunction can also occur if the chordae tendineae that connect the valve leaflet to the papillary muscle ruptures.
There are two general types of cardiac valve defects: stenosis and insufficiency. Some patients, however, may have a combination of stenosis and insufficiency.
Valvular stenosis results from a narrowing of the valve orifice that is usually caused by a thickening and increased rigidity of the valve leaflets, often accompanied by calcification. When this occurs, the valve does not open completely as blood flows across it, thereby resulting in a high resistance to flow and the development of a large pressure gradient across the valve when blood is flowing through the valve.
Valvular insufficiency results from the valve leaflets not completely sealing when the valve is closed so that regurgitation of blood occurs (backward flow of blood) into the proximal chamber.
Valvular stenosis and insufficiency can have serious cardiac consequences, and produce the following clinical symptoms:
- Shortness of breath (dyspnea)
- Reduced exercise capacity
- Light headedness or fainting (syncope)
- Heart failure
- Pulmonary hypertension
- Pulmonary/systemic edema
- Chest pain (angina)
- Blood clots (thromboembolism) which can cause stroke