|
 |
 |
 |
|
What Causes a Heart Attack?
Most heart attacks are caused by a blood clot obstructing blood flow in a coronary artery. The underlying source of an obstructive blood clot is atherosclerosis—
a chronic and progressive disease that narrows and stiffens the coronary arteries.
Atherosclerosis and Plaque Rupture
Atherosclerosis, also called coronary heart disease (CHD), coronary artery disease (CAD), or ischemic heart disease (IHD), is the progressive buildup of plaque along the walls of the coronary arteries. (Plaque is a mixture of fat, cholesterol, cellular waste, calcium, and other substances.) Atherosclerosis is a chronic, progressive disease—it is not curable and may worsen over time. As the plaque thickens, the diameter of the artery narrows, and the artery stiffens, becomes brittle, and loses elasticity.
Plaque buildup is thought to begin by damage to the endothelium—the innermost layer of the coronary arteries. The endothelium may be damaged by high levels of cholesterol (hypercholesterolemia) and triglycerides (hypertriglyceridemia) in the blood, high blood pressure (hypertension), and tobacco smoke.
- Cholesterol: Cholesterol is a soft, fatty, and non-dissolvable substance found in the blood and cells. It is needed to form cell walls, certain hormones, and tissue, but it can be harmful in excess.
- Triglycerides: Triglycerides are the chemical form of fats in foods and the body.
- High blood pressure: High blood pressure results when the heart has to work too hard to pump blood through the arteries, and when the arteries resist blood flow too strongly. An overworked heart, like other muscles, eventually enlarges—but unlike muscles in your arm, which become stronger, an enlarged heart becomes weaker. High blood pressure causes arteries to harden and loss their elasticity.
Narrow, stiff, and brittle coronary arteries are at risk for condition known as plaque rupture. When plaque tears, the endothelial lining of the artery is exposed, and the body
interprets the tear as a wound. The body’s blood coagulation system is then activated, and a blood clot, or thrombus, forms at the site of the tear. The thrombus occludes blood flow through the already narrowed coronary artery.
Heart muscle “downstream” from the blood clot is then
deprived of oxygen. As the duration of the occlusion increases, so does the volume of damaged muscle. This is why seeking medical care as soon as symptoms occur is essential to preventing irreversible damage to the heart muscle and death. As time progresses, more muscle is lost.
Anatomy of a Blood Clot
Blood clots, and the coagulation cascade that gives rise to them, are complex. Understanding the three main components of a blood clot—platelets, thrombin, and fibrin—will help you to understand the preventive, acute, and follow-up treatments that your doctor may prescribe.
- Platelets: Platelets are disclike cells in the blood that clump together to form blood clots.
- Thrombin: Thrombin is a protein active in the coagu-lation of blood. It activates platelets and converts fibrinogen, a type of protein, into fibrin.
- Fibrin: Fibrin is an insoluble protein that forms a stringlike network that binds platelets and other cells together.
Other Causes of Heart Attacks
Rarer causes of heart attacks include:
- Coronary spasm: A coronary spasm can prompt an irregular heartbeat that disrupts blood flow.
- Ventricular hypertrophy: An abnormal increase in the size and mass of a ventricle may impair how blood is pumped into and out of the heart. As a result, the myocardium (as well as other organs) may not receive an adequate supply of oxygenated blood.
- Hypoxia: Hypoxia, or oxygen deprivation, may result from carbon monoxide poisoning or lung disease.
- Coronary artery emboli: A foreign substance (e.g., cholesterol or an air bubble) that travels through the circulatory system is called an embolus (plural emboli). An embolus may become lodged in a coronary artery and obstruct blood flow.
- Drugs: Drugs such as cocaine, amphetamines, and ephedrine may cause a heart attack.
| Acknowledgments & Disclaimer |
