Microvascular resistance reserve (MRR), as a measure of coronary microvascular dysfunction (CMD), can be a strong predictor of major adverse cardiovascular and cerebrovascular events (MACCE) at 12 months in patients with STEMI, according to a study by Tsung-Ying Tsai, MD; Patrick W. Serruys, MD, PhD, FACC; et al., presented at EuroPCR 2024 and simultaneously published in JACC: Cardiovascular Interventions.

The prospective cohort study, conducted in a single center in Lithuania, examined the prevalence of CMD in 210 patients with STEMI (median age, 65 years; 59.5% men) with multivessel disease who underwent successful revascularization and were followed for 12 months.

Results, taken from coronary physiology assessments with bolus thermodilution, showed that at three-month follow-up, 56 patients (26.7%) had CMD, defined as an MRR <3.0. Median MRR of the entire group was 3.46 (Q1-Q3: 3.00-3.9). The median coronary flow reserve (CFR) and index of microvascular resistance (IMR) were 2.81 (Q1-Q3: 2.59-3.03) and 20.00 (Q1-Q3: 13.00-27.00), respectively. Their median fractional flow reserve was 0.92 (Q1-Q3: 0.87-0.97).

At 12 months, 48.2% of patients with CMD had experienced an MACCE vs. 11.0% in patients without CMD (p<0.001). MRR was independently associated with 12-month MACCE (hazard ratio, 0.45 per unit increase; 95% CI, 0.31-0.67; p<0.001), as well as with stroke, heart failure and poorer recovery in left ventricular systolic function. Two patients developed stent thrombosis during follow-up, one with CMD (MRR=2.14) and one without (MRR=3.87).

MRR performed similarly to, but not better than, CFR and IMR for predicting clinical events in the post-STEMI population. "Future studies should investigate the integration of MRR into clinical practice for STEMI patients, examining how it can guide therapeutic decisions and potentially improve outcomes," write the authors.

"Whether MRR has a similar incremental value over IMR in STEMI patients cannot be determined from the present study," Morton J. Kern, MD, FACC, and Arnold H. Seto, MD, FACC, write in an accompanying editorial comment."For now, IMR remains the most studied index for microvascular resistance."

However, they add, "Whether MRR becomes the test of choice in clinical practice remains to be seen, but it certainly puts a sharper point on the pencil for CFR and IMR calculations."

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