A 69-year-old man comes to the clinic due to a squeezing pressure in his midline chest and neck that occurs when walking. He has a history of hypertension and type 2 diabetes mellitus. The patient is an ex-smoker with a 20-pack-year history. Coronary angiography shows extensive atherosclerosis and near-total occlusion of the left anterior descending artery. Further testing shows normal resting left ventricular ejection fraction with no regional wall motion abnormalities. The absence of myocardial necrosis and scarring despite vessel occlusion in this patient can be best explained by which of the following features of the occluding plaque?

Question

A 69-year-old man comes to the clinic due to a squeezing pressure in his midline chest and neck that occurs when walking.  He has a history of hypertension and type 2 diabetes mellitus.  The patient is an ex-smoker with a 20-pack-year history.  Coronary angiography shows extensive atherosclerosis and near-total occlusion of the left anterior descending artery.  Further testing shows normal resting left ventricular ejection fraction with no regional wall motion abnormalities.  The absence of myocardial necrosis and scarring despite vessel occlusion in this patient can be best explained by which of the following features of the occluding plaque?

Quizplus · Accepted Answer

11ec160b_38be_4e17_9249_dfdab03dbdfe_MD0001_00 In response to progressive reductions in blood flow caused by atherosclerotic coronary artery disease, ischemic myocardium may release growth factors (eg, vascular endothelial growth factor) to stimulate the formation and maturation of collateral vessels. In this patient, the slow development of a stable atherosclerotic plaque in the left anterior descending artery (LAD) likely allowed collateral vessels from the right coronary artery to supply the ischemic myocardium located distal to the LAD occlusion. Because there is low hydrostatic pressure distal to the LAD occlusion, a pressure gradient is created that facilitates blood flow through the small collateral vessels. An unstable atherosclerotic plaque is less likely to allow the development of viable collateral vessels, as it is more likely to rupture before it becomes large enough to cause significant chronic ischemia; rupture leads to overlying thrombus and abrupt arterial occlusion with acute myocardial ischemia/infarction and cellular necrosis. The rapid development of ischemia allows insufficient time for collateral vessels to develop and mature. (Choices A, B, and F) Atherosclerotic plaques with active inflammation (containing activated macrophages that secrete metalloproteinases and degrade collagen), high core concentration of lipids, and/or a thin fibrous cap are unstable and more likely to rupture. All of these properties are less likely in an atherosclerotic lesion that has grown to create near-total occlusion without rupturing. (Choice C) A patient's total coronary artery calcium content correlates with the total atherosclerotic plaque burden, and calcium scoring by cardiac CT scan is sometimes used to estimate the severity of coronary artery disease. However, low calcium content (or immature calcification) within an individual plaque may decrease stability of that plaque and increase the likelihood of rupture. (Choice D) Ostial atherosclerotic plaques (those located at a branch point of 2 arteries) are more likely to occlude blood flow to multiple areas of myocardium, thereby limiting the availability of nearby well-perfused arteries from which viable collateral vessels can develop. Educational objective: Gradually developing myocardial ischemia encourages the formation and maturation of collateral vessels and is most likely to occur in the setting of a slow-growing, stable atherosclerotic plaque. An unstable atherosclerotic plaque (eg, that with active inflammation, a lipid-rich core, and/or a thin fibrous cap) is more likely to rupture, resulting in the abrupt onset of ischemia/infarction that precludes the development of viable collateral vessels. __________ References: Importance of angina for development of collateral circulation. (http://www.ncbi.nlm.nih.gov/pubmed/3814448)

A 69-Year-Old Man Comes to the Clinic Due to a Squeezing