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Chapter 34: Coronary Blood Flow and Myocardial Ischemia

Which of the following statements about myocardial ischemia is true?

A. Elective revascularization trials driven by ischemia on diagnostic testing has not yet been shown to reduce myocardial infarction despite relief of angina

B. Revascularization of routinely identified coronary stenoses can improve mortality

C. Revascularization is more effective than medical treatment in preventing myocardial infarction and coronary death in stable CAD

D. Immediate percutaneous coronary intervention (PCI) in acute coronary syndrome (ACS) fails to reduce the risk of subsequent myocardial infarction

E. All of the above

The answer is A. (Hurst’s The Heart, 14th Edition, Chap. 34) Immediate PCI in ACS reduces the risk of recurrent myocardial infarction (option D). However, elective revascularization trials driven by “ischemia” on diagnostic testing has not yet been shown to reduce myocardial infarction or cardiovascular deaths despite relief of angina (option A; not option B). In addition, the failure of randomized revascularization trials to reduce myocardial infarction or coronary deaths compared to medical treatment alone in “stable CAD” has been demonstrated in the Clinical Outcomes Utilizing Revascularization and Aggressive Drug Evaluation (COURAGE) trial1 (option C).

A 66-year-old man undergoes exercise testing with myocardial perfusion imaging. What effect will dipyridamole administration have on this patient in the presence of a 95% diameter stenosis in a coronary artery?

A. It will cause progressive coronary narrowing, reducing coronary flow reserve (CFR) but not resting flow

B. A fall in coronary perfusion pressure due to a steal phenemenon and associated subendocardial ischemia

C. Coronary control mechanisms will be activated and will prevent the invocation of maximal vasodilatory capacity

D. Vasodilator-mediated increased coronary flow will cause a rise in coronary perfusion pressure to the epicardium

E. None of the above are correct

The answer is B. (Hurst’s The Heart, 14th Edition, Chap. 34) Experimentally and clinically, maximal hyperemic flow for determining CFR is achieved pharmacologically by arteriolar vasodilating drugs such dipyridamole, adenosine, and regadenoson. Progressive coronary narrowing reduces CFR with little change in resting flow until an approximately 80% to 90% diameter stenosis. At these levels of severe stenosis, resting blood flow falls (option A), but some residual CFR capacity remains upon pharmacologic vasodilator stimulus. Stenosis severe enough to reduce resting perfusion does not elicit all remaining reserve vasodilator capacity because of a self-regulating mechanism that protects subendocardial perfusion. At such severe stenosis reducing resting perfusion, any increase in vasodilator-mediated increased ...

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