Characterization of Different Phenotypes of Microvascular Dysfunction and Their Impact on Angina Severity in Patients With Chronic Angina in the Absence of Obstructive Coronary Artery Disease

After administration of unfractionated heparin (100UI/Kg), a special pressure guide (Pressure Wire X, Abbott), equipped with a distal sensor capable of measuring pressure and temperature, will be introduced inside the anterior descending branch (IVA) of the left coronary artery and hyperemia will be induced by intravenous infusion of adenosine. The IMR will be calculated using the thermodilution technique, and is given by the product between the mean distal pressure, in the left anterior descending coronary artery, and the mean transit time (Tmn) during maximal hyperemia.

During the procedure, additional coronary physiological indices will be calculated such as:

• Quiescent full cycle flow ratio (RFR), - Fractional flow reserve (FFR),
• Coronary flow reserve (CFR)

In order to identify different phenotypes of microvascular dysfunction, as follows:

• Phenotype A: Patients with IMR>25, CFR <2 and FFR>0.80 (concordant pure-microvascular pathological results)
• Phenotype B: patients with IMR>25, CFR>2 and FFR>0.80 (increased microvascular hyperemic resistance, maintenance of microvascular reactivity)
• Phenotype C: Patients with IMR 25, CFR 2 and FFR>0.80 (normal hyperemic resistance and reduced reactivity) All these phenotypes can also be combined with pathological FFR measures (<0.80) (phenotypes A1, B1, C1).