The causes of heart attacks

The most common cause of a heart attack is a blood clot that completely blocks a coronary artery, cutting off blood supply to the heart.

• Scientists now know that so-called "soft" plaque can be the dangerous trigger. Hard plaque contains more calcium and can grow relatively large, narrowing arteries, restricting blood flow and causing chest pain or high blood pressure. By contrast, "soft" plaque, which causes less narrowing but is loaded with fatty deposits, can easily rupture without warning.
• A rupture causes the lipids (blood fats) and other debris to spill out from the artery wall and form a clot which could block vital blood flow to an area of the heart muscle. The rupture of soft plaque is thought to be responsible for about 85 per cent of all heart attacks. Patches of soft plaque are also more difficult to detect because standard tests, such as CT scans, tend to measure calcium deposits that are a sign of hard plaque.

• While clots are the most common cause, a heart attack can also occur if an artery goes into spasm, temporarily stopping the flow of blood. Atherosclerosis (narrowing of the arteries) can cause such a spasm, or it can be a reaction to drugs such as amphetamines or cocaine, viral infection or smoking (particularly in women who also take birth control pills) — even stress. Less common causes of heart attacks include:

• Clots or other "debris" that travel from elsewhere in the body to lodge inside a coronary artery, a process known as coronary embolism.
• Clots that result from trauma following an accident, or conditions in which blood thickens and clots more easily — including, rarely, use of birth control pills in women.
• Congenital abnormalities of the coronary arteries, present since birth.
• Certain rare conditions, such as thrombocytosis, where the "stickiness" of the blood is increased, which can impede its flow and cause clots to form.

• Atherosclerosis can cause other problems, too. The plaque buildup may weaken arterial walls, causing a swelling called an aneurysm. The intense pressure of blood flowing through the artery can cause the arterial wall to balloon out and, in extreme cases, to burst.
• A family history of aneurysms raises the risk, as does smoking and high blood pressure. The most common site for an aneurysm is the aorta, the largest artery, which carries blood down from the heart to the rest of the body. Without urgent treatment, a ruptured abdominal aortic aneurysm could be fatal.
• Blocked arteries in other parts of the body may cause pain and a variety of other damaging effects. They can even result in disorders as serious as gangrene, when tissue dies because it is starved of blood.

• These problems are not only affecting older people. In recent studies, fatty streaks on the inside of artery walls have been found in youngsters, too — a development that worries scientists and health professionals. In a study of 294 adolescents at the Institute of Child Health in the United Kingdom, researchers noted blood vessel changes in teenagers as young as 13, whose artery walls were already losing their crucial elasticity.
• The risk factors in children are the same as they are for adults: abnormal blood fats, high blood pressure, obesity and diabetes. In fact, the evidence that atherosclerosis can begin early in life is so powerful that doctors are being urged to take an active role in its prevention, by encouraging overweight children to modify their diet and do more exercise.