Coronary Artery Disease
The pathological processes that impair the patency of coronary arteries resulting in reduced blood flow to the heart muscle is the definition of Coronary Artery Disease. Coronary atherosclerosis is the most frequent process involved in impaired myocardial perfusion. Disorders of the coronary arteries are the most common cause of death in affluent countries, affecting more than one million Americans each year. Almost half of these people die from cardiac arrest; of that number, 95% die within two hours after the onset of symptoms and before medical care is reached. This is known as sudden cardiac death.
Coronary artery disease usually exists for many years before it has any adverse effects upon the myocardium. Myocardial ischemia, reduction of blood flow, develops when the coronary circulation is inadequate to supply myocardial oxygen demands.
The development of ischemia depends upon the:
- Location and severity of the stenosis or stenoses
- Presence of collateral vessels
- Demands of the myocardium
- Coexistence of various risk factors
The three major clinical manifestations of myocardial ischemia are: angina pectoris, myocardial infarction, and sudden cardiac death. Angina pectoris (chest pain) is a clinical syndrome resulting from transient and reversible ischemia.
Myocardial infarction results from total coronary occlusion and loss of blood flow. The affected area of the myocardium dies and no longer contributes to the ventricle’s pumping action. Thus, a greater burden of work falls to the remaining viable myocardium.
Watch atherosclerosis develop in this animation
Video source:The Heart of Nuclear Cardiology, An Interactive Primer; © 2002 Bristol-Myers Squibb Imaging. Inc.
Evidence obtained at autopsy in young adults suggests that the pathologic process in the coronary arteries that leads to atherosclerosis appears to begin at birth. As the process of cholesterol deposit continues, fatty deposits accumulate in the lumen of the artery, interfering with the smooth flow of blood through the vessel. Fibrin and platelets are deposited, further increasing the size of roughened deposits. Gradually, calcium and other substances may be deposited, forming plaque. Coronary arteries which have been invaded by plaque deposits are no longer elastic, and may severely limit the process of vasodilation in the delivery of oxygen to the muscle during periods of increased demand.