Most coronary artery disease leading to heart attack results from the process of atherosclerosis, the stiffening and narrowing of arteries. Early changes are seen in people as young as their twenties. A healthy artery is highly elastic, responding readily to changes in the amount or pressure of the blood ?owing through it. As you age, the walls of your arteries tend to become somewhat thicker and stiffer, causing some resistance to the pumping action of the heart. This loss of ?exibility in the arteries, which tends to accelerate as you get older, is the cause of higher blood pressure in older people and con- tributes to several forms of heart disease.
Apart from or in addition to these effects of aging, atherosclerosis is a disease process affecting the interior walls of the major arteries, including the coronary arteries that supply the heart. The inner walls of the arteries become in?amed and irregular and begin to accumulate fatty materials, cholesterol, and other debris that together form plaque. The plaque gradually builds up until it sig- nificantly narrows the channel through which blood is ?owing. This unhealthy process of athero- sclerosis is not fully understood, although a high- fat diet, high levels of cholesterol, smoking, and other known risk factors (see pages 19–22), along with genetic background, are major contributing causes. As plaque builds up, it can form accumulations (called athero- mas or plaques) that ultimately shut off the blood ?ow. A blood clot traveling through the bloodstream can lodge on an accumulation of plaque and block the already narrowed channel altogether.
When a coronary artery is temporarily blocked, it can deprive some portion of the heart of oxygen and nutrients, resulting in a condition called myocardial ischemia. Prolonged ischemia can damage or destroy tissue anywhere in the heart, leading to an infarction (or death of tis- sue), depending on what part of the heart the affected artery supplies. Extensive damage to the left ventricle, the main pumping chamber of the heart, will affect a person’s long-term health and activity level.