How does a heart attack develop?
A heart attack occurs when some part of the heart muscle stops getting blood and oxygen. This is usually caused by a clog in one or more of the arteries that carry blood and oxygen to the heart, as a result of coronary artery disease. The arteries become choked with fatty deposits called plaque over the course of many years. This process is called atherosclerosis. The name comes from the Greek words athero, meaning gruel or paste, and sclerosis, meaning hardness. The buildup of fatty deposits, including cholesterol and other lipids, gradually narrows the artery, allowing less blood to flow through. Eventually the fatty plaque may rupture (see below). Atherosclerosis is the main cause of a group of diseases called cardiovascular diseases -- diseases of the heart and blood vessels.
How does atherosclerosis develop?
Atherosclerosis develops when the normally smooth, muscular lining of the artery is damaged. This damage may be caused by smoking, high cholesterol, high blood pressure, or other heart disease risk factors . Fatty materials build up at the site of the injury creating a plaque. When the body's immune system tries to repair the damage, it ends up doing more harm than good: the white blood cells that move in to repair the damaged artery make the lining sticky, more fatty deposits adhere, and the plaque gets bigger. Stable plaques are plaques that develop a hard, thick covering usually made up of calcium. They are the most common cause of hardened, narrowed arteries. Unstable plaques have a thinner, softer coating (a bit like a soft-boiled egg) that can be dislodged more easily.
Why does the gradual buildup of fatty plaque suddenly cause a heart attack?
Sometimes, the plaques that have built up in the arteries break off and cause a blockage. Plaque rupture occurs when the thin covering over the fat deposit is torn – similar to the popping of a pimple. Stress or heavy exertion can rupture a plaque. The body sees this burst plaque and, in the same way it would heal a cut finger, tries to repair the damage by forming a blood clot. This blood clot may block off the already narrow artery (coronary thrombus) causing a heart attack, or a piece of the clot may break away (embolus) and lodge in a different artery (causing an embolism). For example, if the embolus blocks an artery in the brain, this causes a stroke.
Plaques that lack a fatty center may also become disrupted, a process known as plaque erosion. It is not fully understood why or how these plaques begin to erode, but it occurs more frequently in women than in men. Smokers are also at greater risk for plaque erosion. Diagnostic tests can see how much fatty plaque buildup there is in your arteries, but it is hard to tell which plaques are likely to erode or rupture.4, 5
