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Chapter 13:
Angiography and Intravascular Ultrasound
Coronary atherosclerosis, or coronary artery disease, is a widespread, chronic and usually progressive disease that affects men at an earlier age than women. There are, for example, more than 7 million Americans with diagnosed coronary artery disease [1]. Risk factors are well known and include modifiable factors, such as hypertension, hyperlipidemia, smoking and lack of exercise, and nonmodifiable factors, such as age and gender. In patients with coronary atherosclerosis, progression of the disease is one of the major factors that determine clinical prognosis. The dynamics of this process, that is, progression and regression of atherosclerotic lesions, the healing of lesions and the development of new ones, has intrigued cardiologists since the time that this process could be followed by repeated coronaryarteriographic x-ray examinations. A complicating factor in the evaluation of the severity and extent of the degree of coronary atherosclerosis is the occurrence of compensatory mechanisms, which is nowadays denoted by the term coronary artery remodeling. Glagov et al. were the first to describe that compensatory enlargement of the human atherosclerotic coronary arteries occurs during the early stages of plaque formation. This compensatory enlargement results in the preservation of a nearly normal lumen cross-sectional area so that an atherosclerotic plaque would have less hemodynamic effects. This "outward" growth process stops at a certain point in time as it reaches the maximal stretching capacities of the vessel, followed by subsequent further "inward" growth of the plaque. Once the lumen of the vessel becomes impaired, it becomes visible by x-ray arteriography, which is a two-dimensional projection technique, allowing only the visualization of the contrast-filled lumen. For this reason, the x-ray arteriogram is sometimes also called a "luminogram." Atherosclerosis usually is present as a focal narrowing with a limited length, superimposed upon a diffuse atherosclerotic process within the entire artery. Since x-ray arteriography only depicts the remaining opening of an artery, it underestimates the presence of diffuse atherosclerosis and is unable to detect the early stages of coronary atherosclerosis. Since the early 1980s, the field of interventional cardiology has been directed at trying to remove the obstructions in the coronary arteries (also called remodeling) through invasive therapeutic procedures, such as percutaneous transluminal coronary angioplasty (PTCA), coronary atherectomy or debulking by various approaches, and stenting. A comprehensive overview of the various interventional procedures can be found in. Unfortunately, after a procedure, restenosis still occurs at frequencies ranging from 10-30%, depending upon the technology used. More than 500,000 Americans and 1,000,000 patients worldwide undergo a nonsurgical coronary artery interventional procedure yearly. In many catheterization laboratories, stents are now used in over 60-70% of the cases. The restenosis process is the Achilles heel of interventional cardiology; all efforts are directed at understanding and influencing the mechanism of coronary remodeling.
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