Abstract 17163: The Relationship Between TIMI Frame Count, Microvascular Resistance, and Coronary Flow Reserve in Patients With Ischemia and Nonobstructive Coronary Arteries

Abstract

Introduction: Ischemia and nonobstructive coronary artery disease (INOCA) may be caused by coronary microvascular dysfunction (CMD), but coronary function testing for CMD is not routinely performed. Consensus statements include coronary flow reserve (CFR), an index of microcirculatory resistance (IMR), or coronary slow flow by corrected TIMI frame count (cTFC) >25 as diagnostic for CMD. However, correlations between cTFC and invasive parameters of CMD are uncertain. Methods: Adults age ≥ 18 with INOCA (<50% stenosis by invasive coronary angiography in all major epicardial coronary arteries) were prospectively enrolled. cTFC was measured from baseline angiography of the left anterior descending artery. Invasive coronary function testing using thermodilution techniques was performed to identify CMD, defined by IMR≥25 and/or CFR<2.5. Relationships between cTFC and invasively derived CMD were evaluated. Results: Ninety-seven patients (mean age 60.4 ± 11 years; 80% female) underwent assessment; coronary slow flow was present in 46%. Coronary slow flow (cTFC>25) had a sensitivity of 50%, a specificity of 57%, a positive predictive value of 53%, and a negative predictive value of 54% to identify CMD defined by IMR and/or CFR. cTFC weakly correlated with IMR (r=0.40, p<0.001) and was not correlated with CFR (Pearson r=-0.03, p=0.73). Areas under the receiver operating characteristic curves were calculated for cTFC to identify abnormal IMR (AUC = 0.64), CFR (AUC = 0.55), CMD (AUC = 0.59), and CMD endotypes of abnormal IMR with normal CFR (AUC = 0.65), abnormal CFR with normal IMR (AUC = 0.58), abnormal IMR and CFR (AUC = 0.54). Conclusions: Coronary slow flow by angiography was not a reliable indicator of CMD defined by abnormal IMR and/or CFR. Correlations between cTFC and IMR were poor and no correlation with CFR was observed. These findings raise questions regarding the relevance of coronary slow flow at baseline to assess microvascular pathology causing INOCA.