Coronary microvascular obstruction: the new frontier in cardioprotection.

Cardioprotection aims at infarct size reduction and improvement of clinical outcome from myocardial infarction. The translation of cardioprotection from preclinical and promising proof-of-concept studies to clinical benefit for patients has been largely disappointing. Almost all of these studies which did not translate into clinical benefit had infarct size reduction as the primary endpoint and used protocols selected to achieve infarct size reduction. The present review puts forward the hypothesis that the coronary circulation is a so far neglected target of cardioprotection. Mechanisms of ischemia-reperfusion injury to the coronary circulation are detailed. Clinical methods and measures to assess coronary microvascular impairment in reperfused acute myocardial infarction are presented. A comparison of magnetic resonance imaging data on infarct size vs. coronary microvascular obstruction is made. Finally, the design of studies which are optimized not only for infarct size reduction but also for salvage of the coronary microcirculation is advocated.