Comparative Visual Analysis of Coronary Slow Flow and Myocardial Blush Grade in Relation to Invasive Testing for Coronary Microvascular Dysfunction.

Abstract

Background: Angiographic coronary slow flow (CSF) has been correlated with coronary microvascular dysfunction (CMD) and abnormal myocardial blush grade (MBG) has been associated with worse outcomes in acute myocardial infarction. Their validity has not been compared with newer invasive forms of coronary functional CMD testing. Therefore, we aimed to investigate whether angiographic assessment of CSF and MBG correlate with gold-standard invasive assessments of CMD.

Methods: Using the Coronary Microvascular Disease Registry (NCT05960474), we identified patients with angina and non-obstructive coronary arteries (ANOCA) who underwent invasive coronary functional testing (CFT) between August 2021 and August 2024. CMD was defined as coronary flow reserve (CFR) < 2.5 with an index of microcirculatory resistance (IMR) > 25 using invasive bolus thermodilution technique. CSF was defined as > 3 cardiac cycles for distal opacification of vessels with contrast. Slow Thrombolysis in Myocardial Infarction frame count (TFC) was defined as a corrected frame count of > 25. MBG was categorized as abnormal (Grade 0 or 1). Rates of abnormal CSF and MBG were compared between the CMD-positive and negative groups.

Results: A total of 304 patients were included, of whom 81 (26.6%) were CMD positive. Patients were predominantly female (67.9 vs. 63.7%, p = 0.50) and slightly older (64.0 ± 11.3 vs. 60.6 ± 10.8 years, p = 0.02) with a lower BMI (28.5 ± 5.7 vs. 31.6 ± 6.9; p < 0.001) in the CMD positive group. Common comorbidities included hypertension, hyperlipidemia, and diabetes with a similar prevalence in both groups. There was no difference between CMD-positive and negative groups for CSF, (8.6% vs. 4.9%, p = 0.23) or slow cTFC (14.8% vs. 15.7%, p = 0.85). Additionally, the rate of abnormal MBG was similar in both groups (1.3% vs. 3.1%; p = 0.37).

Conclusion: Our findings suggest that, while readily available and previously used for diagnosis, the angiographic findings of CSF and MBG do not reliably indicate the presence of CMD in ANOCA patients. Therefore, dedicated CFT should be pursued if there is clinical suspicion of CMD.