Accumulation of cholesterol and other fatty substances in the walls of arteries, causing them to narrow
Atherosclerosis is a disease that results in the arteries becoming narrowed. The condition can affect arteries in any area of the body and is a major cause of stroke, heart attack (see Myocardial infarction), and poor circulation in the legs (see Lower limb ischaemia). The arteries become narrowed when fatty substances, such as cholesterol, that are carried in the blood accumulate on the inside lining of the arteries and form yellow deposits called atheroma. These deposits restrict the blood flow through the arteries. In addition, the muscle layer of the artery wall becomes thickened, narrowing the artery even more. Platelets (tiny blood cells responsible for clotting) may collect in clumps on the surface of the deposits and initiate the formation of blood clots. A large clot may completely block the artery, resulting in the organ it supplies being deprived of oxygen.
Atherosclerosis is much more common in northern Europe than in developing countries in Africa and Asia. The condition becomes more common with increasing age and tends to run in families. Autopsies on young men who have died in accidents reveal that many have already developed some atheroma in their large arteries, and most people who die in middle age are found to have a degree of atherosclerosis. However, the condition rarely causes symptoms before the age of 45–50, and many people are unaware that they have it until they have a heart attack or a stroke.
The incidence of atherosclerosis is much lower in women before the menopause than in men. However, by the age of 60 a woman’s risk of developing atherosclerosis is the same as a man’s. Although it is likely that the female sex hormone oestrogen contributes to the lower risk in premenopausal women, hormone replacement therapy in postmenopausal women does not reduce the risk of heart disease and may increase the risk of certain cancers.
The risk of developing atherosclerosis is determined largely by the level of cholesterol in the bloodstream, which depends on dietary and genetic factors. Since cholesterol levels are closely linked with diet, atherosclerosis is most common in Western countries where most people eat a diet high in fat. Some disorders, such as diabetes mellitus, can be associated with a high cholesterol level regardless of diet. Certain inherited lipid disorders also result in a high level of fats in the blood (see Inherited hyperlipidaemias).
In addition to high blood cholesterol levels, factors that make atherosclerosis more likely are smoking, lack of regular exercise, having high blood pressure (see Hypertension), and being overweight, especially if there is a concentration of fat around the waist.
There are usually no symptoms in the early stages of atherosclerosis. Later, symptoms are caused by the reduced or total absence of a blood supply to the organs supplied by the affected arteries. If the coronary arteries, which supply the heart muscle, are partially blocked, symptoms may include the chest pain of angina. If there is a complete blockage in a coronary artery, there may be a sudden, often fatal, heart attack. Many strokes are a result of atherosclerosis in the arteries that supply blood to the brain. If atherosclerosis affects the arteries in the legs, the first symptom may be cramping pain when walking caused by poor blood flow to the leg muscles. If atherosclerosis is associated with an inherited lipid disorder, fatty deposits may develop on tendons or under the skin in visible lumps.
Since atherosclerosis has no symptoms until blood flow has been restricted, it is important to screen for the disorder before it becomes advanced and damages organs. Routine medical checkups include screening for the major risk factors of atherosclerosis, particularly raised blood cholesterol levels, high blood pressure, and diabetes mellitus. It is recommended that adults who have cardiovascular disease or are at high risk of developing it, or who have a family history of high blood cholesterol, should have their cholesterol levels checked regularly by their doctor.
If you develop symptoms of atherosclerosis, your doctor may arrange tests to assess the damage both to the arteries and to the organs they supply. Blood flow in affected blood vessels can be imaged by Doppler ultrasound scanning or coronary angiography. If your doctor thinks that the coronary arteries are affected, an ECG may be carried out to monitor the electrical activity of the heart and imaging techniques, such as angiography and radionuclide scanning, may be used to look at the blood supply to the heart. Some of these tests may be done as you exercise to check how the heart functions when it is put under stress (see Exercise testing).
The best treatment is to prevent atherosclerosis from progressing. Preventive measures include following a healthy lifestyle by eating a low-fat diet, not smoking, exercising regularly, and maintaining the recommended weight for your height. These measures lead to a lower than average risk of developing significant atherosclerosis.
If you have been found to have a high blood cholesterol level but are otherwise in good state of health, you will be advised to adopt a low-fat diet. You may also be given drugs that decrease your blood cholesterol level (see Lipid-lowering drugs). For people who have had a heart attack, research has shown that there may be a benefit in lowering blood cholesterol levels, even if the affected person’s cholesterol level is within the average range for healthy people.
If you have atherosclerosis and are experiencing symptoms of the condition, your doctor may prescribe a drug such as aspirin to reduce the risk of blood clots forming on the damaged artery lining (see Drugs that prevent blood clotting). Your doctor may also prescribe drugs to relieve the symptoms, such as drugs used to alleviate angina.
If you are thought to be at high risk of severe complications, your doctor may recommend that you undergo an invasive treatment, such as coronary angioplasty and stenting, in which a balloon is inflated inside the artery to widen it and improve blood flow. In most cases, a stent (a tubular scaffold device) will be inserted in the artery to help keep it open. If blood flow to the heart is severely obstructed (see Coronary artery disease), you may be advised to have a bypass operation (see Coronary artery bypass graft) to restore blood flow.
A healthy diet and lifestyle can slow the progress of atherosclerosis in most people. If you do have a myocardial infarction or a stroke, you can reduce the risk of developing further complications by taking preventive measures (see Life after a heart attack).
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.