Predictive value of thrombolysis in myocardial infarction frame count for coronary microvascular dysfunction evaluated with an angiography-derived index of microcirculatory resistance in patients with coronary slow flow

Background: The association between coronary slow flow (CSF) and coronary microvascular dysfunction (CMD) remains unclear. The objective of this study was to evaluate the correlation between the corrected thrombolysis in myocardial infarction (TIMI) frame count (CTFC) and the index of microcirculatory resistance (IMR). Methods: We consecutively enrolled patients with CSF from January 2017 to March 2018. Concurrently, we randomly selected control participants with normal flow arteries at a ratio of 3:1. Two cardiologists performed the measurements of CTFC. Coronary angiography-derived IMR (caIMR) was used to assess CMD. The caIMR was analyzed by an independent agency, with CMD being defined as caIMR >40 U. Results: 67.7%; P=0.042). Additionally, the CSF group had higher CTFC, coronary angiography-derived fractional flow reserve (caFFR), and caIMR regardless of left anterior descending artery (LAD), left circumflex artery (LCX), and right coronary artery (RCA) (all P values <0.001). A strong correlation between CTFC and caIMR was observed for all arteries (all P values <0.001). In the univariate analysis, male sex [hazard ratio (HR) =2.63, 95% CI: 1.30-5.31], E/e' (HR =0.88, 95% CI: 0.78-0.99), CTFC (HR =1.12, 95% CI: 1.09-1.16), and caFFR (HR =1.81, 95% CI: 1.50-2.17) were significantly correlated with CMD. After adjusting for covariates, male sex (HR =2.72, 95% CI: 1.22-6.06), CTFC (HR =1.10, 95% CI: 1.07-1.14), and caFFR (HR =1.22, 95% CI: 1.00-1.50) were independent predictors for CMD. Additionally, the best cutoff value of CTFC of all arteries for predicting CMD was 38 frames, with an area under the curve of 0.873, a sensitivity of 92.8%, and a specificity of 63.8% (P<0.001). Moreover, the best cutoff value of CTFC of LAD, LCX, and RCA to identify CMD was 35 frames, 52 frames, and 50 frames, respectively (all P values <0.001). Conclusions: CTFC correlated well with caIMR and had a strong predictive power to identify CMD.