Coronary Artery Disease
The coronary arteries supply blood flow to the heart, and when functioning normally, they ensure adequate oxygenation of the myocardium at all levels of cardiac activity. Constriction and dilation of the coronary arteries, governed primarily by local regulatory mechanisms,regulate the amount of blood flow to the myocardium in a manner that matches the amount of oxygen delivered to the myocardium with the myocardial demand for oxygen.
Coronary artery disease (CAD) causes changes in both structure and function of the blood vessels. Atherosclerotic processes cause an abnormal deposition of lipids in the vessel wall, leukocyte infiltration and vascular inflammation, plaque formation and thickening of the vessel wall. These changes lead to a narrowing of the lumen (i.e., stenosis), which restricts blood flow. There are also subtle, yet functionally important changes that can occur before overt changes in structure are observed. Early in the disease process, the endothelial cells that line the coronary arteries become dysfunctional. Because the endothelium produces important substances such as nitric oxide and prostacyclin that are required for normal coronary function, endothelial dysfunction can lead to coronary vasospasm, impaired relaxation, and formation of blood clots that can partially or completely occlude the vessel.
When CAD restricts blood flow to the myocardium (ischemia) there is an imbalance between oxygen supply and oxygen demand. When the oxygen supply is insufficient to meet the oxygen demand (reduced oxygen supply/demand ratio), the myocardium becomes hypoxic. This is often associated with chest pain (angina) and other clinical symptoms. Severe ischemia can lead to anoxia and infarction of the tissue. Furthermore, acute or chronic ischemia caused by CAD can impair cardiac mechanical and electrical activities leading to heart failure and arrhythmias.
About 13 million Americans (~7% of population) have coronary artery disease. About half of all deaths related to cardiovascular disease result from coronary artery disease. Coronary artery disease is the leading cause of death among American men and women, and represents about 20% of all deaths.
As described above, CAD results in myocardial ischemia, which leads to chest pain (angina) and cardiac mechanical and electrical dysfunction. The goal in treating CAD is to restore normal coronary perfusion, or if that is not possible, then to reduce the oxygen demand by the heart (i.e., normalize the oxygen supply/demand ratio) so as to minimize myocardial hypoxia. In severe CAD in which one or more coronary arteries is very stenotic, some patients will have a stent implanted within the coronary artery to open up the lumen and restore blood flow. Other patients may undergo coronary artery bypass grafts in which the diseased segment is bypassed using an artery or vein harvested from elsewhere in their body (i.e., internal mammary artery). If the coronary is occluded by a blood clot, a thrombolytic drug may be administered to dissolve the clot. Anti-platelet drugs and anticoagulants are also given to patients with CAD. However, the vast majority of CAD patients are treated with antianginal drugs that reduce the myocardial oxygen demand by decreasing heart rate, contractility, afterload or preload (e.g., beta-blockers, calcium-channel blockers, nitrodilators), or they are treated with drugs that many prevent or reverse coronary vasospasm in patients with variant angina. Click here for more information on drug treatment for CAD and angina.