• ST elevation myocardial infarction
• microvascular obstruction
• intracoronary pressure wire

• CAD, coronary artery disease
• CFIp, pressure derived collateral flow index
• CWP, coronary wedge pressure
• IRA, infarct related artery
• MCE, myocardial contrast echocardiography
• MI, myocardial infarction
• PCI, percutaneous coronary intervention
• SPECT, single photon emission computed tomography
• TIMI, thrombolysis in myocardial infarction

A primary goal of therapy in ST elevation myocardial infarction (MI) has been to restore normal blood flow in the occluded epicardial coronary artery as rapidly as possible. The “early open artery hypothesis” is supported by large datasets demonstrating a stepwise association between faster post-reperfusion epicardial blood flow and lower subsequent mortality.¹ A series of studies, using a variety of invasive and non-invasive imaging techniques, has shown that while early and sustained patency of the infarct related artery (IRA) is necessary, it is not sufficient to ensure optimal outcomes after reperfusion therapy: tissue and microvascular perfusion must also be restored.

Using myocardial contrast echocardiography (MCE), a technique that was novel at the time, Ito and colleagues demonstrated microvascular “no reflow” among ~25% of patients with normal epicardial blood flow following primary percutaneous coronary intervention (PCI) for acute MI.² These patients were found to be at high risk for subsequent death and heart failure. Using tools as diverse as intracoronary Doppler, cardiac MRI, nuclear scintigraphy, and contrast angiography, it has been shown that microvascular impairment is associated with an adverse prognosis, even if epicardial blood flow has been restored.³