The Queen Elizabeth Hospital, University of Adelaide, Adelaide, Australia
The coronary microvasculature plays a fundamental role in the provision and regulation of myocardial perfusion. Accordingly, coronary microvascular dysfunction may frequently contribute to impaired myocardial perfusion and thus play an important role in the genesis of myocardial ischemia. Thus research into coronary microvascular disorders will not only elaborate new conditions and their mechanisms but also provide insights into the mechanisms by which the microvasculature controls myocardial perfusion.
Syndrome X is the most extensively investigated coronary microvascular disorder and must be delineated from the "metabolic syndrome X." The term was first coined by Kemp in 1973, in an accompanying editorial to a study by Arbogast and Bourassa. This landmark study demonstrated both ST segment depression and myocardial lactate production during rapid atrial pacing in 11 patients with angio-graphic obstructive epicardial coronary artery disease (group C) and also in 10 patients with angina but no epicar-dial coronary disease (group X). Today, syndrome X is broadly defined as chronic angina occurring in the absence of fixed or dynamic flow-limiting epicardial coronary obstructions on angiography. The diagnosis is most frequently made in patients with exertional angina, ST segment depression on exercise stress testing, and angiographically normal epicardial coronary arteries.
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