The following are key points to remember from a state-of-the-art review on angiography-derived and sensor-wire methods to assess coronary microvascular dysfunction (CMD) in patients with acute myocardial infarction:

1. This review provides an overview about conventional and novel methods to assess CMD in patients with ST-segment elevation myocardial infarction (STEMI).
2. Post-ischemic CMD and microvascular obstruction (MVO) injury is observed in up to 40-50% of STEMI cases and is associated with adverse outcomes.
3. Conventional methods to assess CMD in patients with STEMI present some limitations that in part can explain why the assessment of CMD is often confined to the research environment.
4. Post-ischemic CMD is characterized by a complex pathophysiology (ischemia-related injury, reperfusion-related injury, and distal embolization) and portends adverse clinical outcomes.
5. Among the pressure-wire-derived indices, index of microcirculatory resistance (IMR) is the one supported by the largest body of evidence. IMR >40 units predicts myocardial hemorrhage and MVO on cardiac magnetic resonance imaging and is strongly associated with adverse clinical outcomes including mortality and heart failure.
6. Other physiology-based indices include coronary flow reserve, resistive reserve ratio, absolute coronary flow, and microvascular resistance reserve. All come with limitations.
7. Continuous thermodilution technique has the advantage of not requiring pharmacological vasodilatation and removes the operator’s variability bias as no manual injection of saline is required.
8. One of the main limitations of absolute flow and resistance remains the absence of normal reference values and, importantly, a significant interpatient variability. The novel index, the microvascular resistance reserve, offers the advantage of being independent of epicardial resistance and autoregulation. It remains to be validated with limited data on diagnostic and prognostic value.
9. Angiographic only (TIMI flow) evaluation of CMD is substantially limited by low accuracy and sensitivity.
10. Angiography-derived index of microcirculatory resistance (IMR_angio) is obtained from computational fluid dynamics applied to the 3D reconstruction of the coronary artery derived from angiographic views during adenosine-induced steady-state hyperemia. Notably, IMR_angio >40 units was able to detect clinically significant CMD as assessed by IMR.
11. Several other angiography-based computational-flow-dynamics methods may facilitate CMD assessment in clinical practice but require further validation.
12. Eventually CMD assessment can aid to triage the application of novel additional device-based or pharmacological therapies in STEMI.

Clinical Topics: Acute Coronary Syndromes, Cardiac Surgery, Cardiovascular Care Team, Heart Failure and Cardiomyopathies, Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Stable Ischemic Heart Disease, Vascular Medicine, Cardiac Surgery and Heart Failure, Cardiac Surgery and SIHD, Acute Heart Failure, Interventions and ACS, Interventions and Imaging, Interventions and Vascular Medicine, Angiography, Magnetic Resonance Imaging, Nuclear Imaging, Chronic Angina

Keywords: Acute Coronary Syndrome, Adenosine, Angiography, Coronary Angiography, Diagnostic Imaging, Heart Failure, Hyperemia, Microcirculation, Myocardial Infarction, Myocardial Ischemia, Myocardial Revascularization, Magnetic Resonance Imaging, Reperfusion, ST Elevation Myocardial Infarction, Thermodilution, Triage, Vasodilation

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