Fractional flow reserve (FFR) and index of microcirculatory resistance (IMR) relationship in patients with chronic or stabilized acute coronary syndromes.

Aims: To investigate the influence of index of microcirculatory resistance (IMR) on fractional flow reserve (FFR) and adenosine-induced hyperemia (ΔPd/Pa-FFR) in patients with chronic (CCS) or stabilized acute coronary syndromes (ACS), utilizing various IMR threshold values.

Methods: Data were extracted from two ongoing Italian registries involving patients with CCS or stabilized ACS who underwent a #FullPhysiology approach [Pd/Pa, FFR, IMR, coronary flow reserve (CFR)] by bolus thermodilution technique in the left anterior descending artery. Correlations between IMR and both FFR and ΔPd/Pa-FFR were analyzed both globally and within three IMR-defined groups: Group 1 (IMR <25), Group 2 (25 ≤ IMR <40), and Group 3 (IMR ≥40).