Microcirculation Function in Non-ST-Elevation Myocardial Infarction After the Index Event and at Follow-Up Assessment

The assessment of coronary physiology is seldom considered in cases of non-ST-elevation myocardial infarction (NSTEMI). This study aimed to characterize coronary physiology and determine the incidence of microvascular dysfunction in the myocardial infarction (MI) culprit coronary artery during the acute phase of NSTEMI and subsequent follow-up evaluation.

This study included 30 patients hospitalized for NSTEMI. A physiological assessment of the MI culprit coronary artery was performed using fractional flow reserve, coronary flow reserve (CFR), and index of microcirculatory resistance (IMR). At a median of 7 months after MI, patients underwent repeated physiological assessment of the same coronary artery.

Microvascular dysfunction identified using CFR (< 2.0) was frequently present (60%) during the acute phase of NSTEMI, whereas severe microcirculatory dysfunction (IMR > 40) was uncommon (17%). Over time, a significant reduction occurred in the prevalence of abnormal CFR values (< 2.0; 60% vs 26%, P = 0.013) and extensive microvascular resistance (IMR > 40; 17% vs 4%, P = 0.03) at the follow-up evaluation. Patients were categorized according to their CFR and IMR results. In patients with abnormal CFR (< 2.0) and normal IMR (< 25), reduced CFR is attributable to elevated resting coronary blood flow rather than diminished hyperemic flow.

In the acute phase of NSTEMI, reduced CFR was commonly observed in the MI culprit coronary artery, whereas severe microcirculatory dysfunction was infrequent.