Abstract

Microcirculation Function in Non-ST-elevation Myocardial Infarction after the Index Event and at Follow-Up

Author(s): Luis Manuel Vilardouro Paiva

Research on coronary physiology in acute coronary syndromes has predominantly focused on patients with ST-Segment Elevation Myocardial Infarction (STEMI) and the significance of Fractional Flow Reserve (FFR), often disregarding the prevalence of microvascular dysfunction following Non-ST-Elevation Myocardial Infarction (NSTEMI). Paiva, et al. made a significant contribution to the understanding of coronary microvascular function following NSTEMI. This study evaluated a cohort of patients with NSTEMI using a combination of invasive physiological indices: FFR, Coronary Flow Reserve (CFR), and Index of Microcirculatory Resistance (IMR) in the MI culprit coronary artery. These assessments were conducted at the time of the index ischemic event and during the follow-up period, with a median duration of 7 months after MI. The key findings included a high prevalence of abnormal CFR during the acute phase of MI, whereas extensive microcirculatory dysfunction (IMR>40) was uncommon. Over the follow-up period, there was a significant reduction in the prevalence of abnormal CFR values (<2.0) and extensive microcirculatory resistance (IMR<40). In patients presenting a CFR below 2.0 and an IMR under 25, the observed decrease in CFR was attributed to an increase in resting coronary blood flow rather than a reduction in hyperemic flow. During the acute phase of NSTEMI, an abnormal CFR was frequently observed in the MI culprit coronary artery, whereas extensive microcirculatory resistance was infrequent in this cohort. Microvascular dysfunction in the MI culprit coronary artery improved during the follow-up period. Patients with low CFR and low IMR did not experience compromised microvascular vasodilation following ischemic injury.