The incremental diagnostic value of microvascular resistance reserve in the assessment of coronary microvascular dysfunction.

Background: Patients with coronary microvascular dysfunction (CMD) are at increased risk of major adverse cardiovascular events. The index of microcirculatory resistance (IMR) is more specific than coronary flow reserve (CFR) for CMD diagnosis, but the microvascular resistance reserve (MRR) shows potential due to its hemodynamic adjustments. Our study evaluated the diagnostic utility of IMR, MRR, and their combination in CMD diagnosis for patients experiencing angina and non-obstructive coronary arteries (ANOCA).

Methods: This observational study analyzed data from the Coronary Microvascular Disease Registry (CMDR) of ANOCA patients at two tertiary care centers from 2021 to 2024. Demographics, lab results, and microvascular testing outcomes using bolus thermodilution were evaluated. Participants were grouped by MRR and IMR levels to evaluate CMD prevalence.

Results: Between December 3, 2021, and July 31, 2024, 279 patients with ANOCA underwent invasive microvascular function assessment. Most were female (67.4 %), with an average age of 61.6 ± 11.0 years. CMD prevalence varied by group: 100 % in low MRR/high IMR, 92.3 % in high MRR/high IMR, 13.9 % in low MRR/low IMR, and 2.8 % in high MRR/low IMR (P < 0.001). IMR showed high diagnostic accuracy (81.6 % sensitivity, 99.5 % specificity), while MRR had 79 % sensitivity and 69.5 % specificity. Combining high IMR and low MRR improved specificity to 100 % but reduced sensitivity (65.8 %). ROC analysis showed AUCs of 0.80 (MRR), 0.97 (IMR), and 0.98 (IMR + MRR).

Conclusions: The combination of IMR and MRR enhanced diagnostic specificity for CMD in patients with ANOCA, highlighting their complementary value. Future studies should focus on larger cohorts to validate these findings.