Microvascular dysfunction in the spectrum of coronary instability.

The term "coronary instability" commonly refers to the sequence of events that lead from plaque erosion or rupture to the occurrence of acute coronary syndromes (ACS). However, evidence indicates that coronary microvascular dysfunction plays a relevant pathophysiologic and prognostic role in the setting of ACS, both in ST-segment elevation myocardial infarction and in non-ST-segment elevation ACS. Our group have recently demonstrated that Tako-Tsubo syndrome, which clinically mimics ACS, is sustained by a common pathophysiologic mechanism represented by reversible coronary microvascular dysfunction. Given this evidence, we propose a reappraisal of the concept of coronary instability, extending this notion from the dramatic event represented by plaque erosion or rupture to a more diffuse process that can acutely affect each segment of the coronary circulation.