Diagnostic Criteria for Coronary Microvascular Dysfunction

Guideline-Based Diagnostic Framework

The American Heart Association, American College of Cardiology, American College of Chest Physicians, American Society of Preventive Cardiology, National Lipid Association, and Preventive Cardiovascular Nurses Association guidelines provide definitive criteria for diagnosing coronary microvascular dysfunction, with coronary slow flow phenomenon specifically listed as one of the diagnostic parameters 1, 2, 3, 4
The American College of Cardiology recommends that coronary slow flow phenomenon, defined as TIMI frame count >25, constitutes evidence of impaired coronary microvascular function 1, 2, 3, 4
Impaired coronary flow reserve (CFR ≤2.0 to ≤2.5 depending on methodology) is a marker of microvascular dysfunction 1, 2, 3, 4
Coronary microvascular spasm (reproduction of symptoms with ischemic ECG changes but no epicardial spasm during acetylcholine testing) is a diagnostic parameter for microvascular angina 1, 2, 3, 4
Abnormal coronary microvascular resistance indices (IMR >25) indicate microvascular dysfunction 1, 2, 3, 4

The European Society of Cardiology guidelines recognize coronary microvascular dysfunction as characterized by decreased CFR and increased microvascular resistance (IMR, HMR, MRR) 5, 6
The European Society of Cardiology guidelines specify that a Doppler-derived CFR <2.5 in non-obstructive CAD indicates an abnormal microcirculatory response, corresponding to a thermodilution-derived CFR <2.5 5, 6
An increased IMR (≥25) indicates microvascular dysfunction 5, 6

When evaluating patients with angina and non-obstructive coronary arteries, document TIMI frame count during angiography (>25 suggests slow flow) 1
Perform comprehensive invasive coronary functional testing with pressure and flow measurements when available 5
Measure CFR (abnormal if <2.5) and IMR (abnormal if >25) 6
Consider acetylcholine testing to assess for microvascular spasm 2