Impact of Microvascular Spasm on Coronary Physiological Assessment　- Insights From Angiography-Derived Index of...

Microvascular spasm (MVS), a phenotype of microvascular dysfunction in patients with angina with non-obstructive coronary arteries (ANOCA), involves transient microvascular constriction. The angiography-derived index of microcirculatory resistance (A-IMR) is a less invasive method for assessing microcirculatory resistance. We aimed to evaluate MVS characteristics using A-IMR.

We retrospectively studied ANOCA patients who underwent acetylcholine spasm provocation tests (SPT). Patients were classified into no-spasm, epicardial spasm (ECS), or MVS groups. A-IMR was measured before and after SPT. Of 109 patients, 21 (19.3%) had MVS. The MVS group had more women (76.2% vs. 42.0%; P=0.01) than the other 2 groups combined. While pre-SPT A-IMR values were similar, post-SPT A-IMR after nitroglycerin was significantly higher in the MVS group than the no-spasm group, especially in the left anterior descending (LAD) artery (44.60 vs. 33.54; P=0.007). ∆A-IMR (post- minus pre-SPT) was significantly greater in the MVS group for both the LAD (9.89 vs. -9.26; P=0.001) and right coronary artery (RCA; 3.22 vs. -6.83; P=0.001). Multivariable analysis showed ∆A-IMR in the LAD and RCA were independently associated with MVS.

Serial A-IMR assessment during SPT reveals sustained nitrate-resistant microvascular constriction in patients with MVS, which may confound standard post-SPT physiological assessments such as coronary flow reserve or IMR. These findings underscore the need for careful interpretation of physiological data in the presence of MVS.