Coronary slow flow as measured by corrected TIMI frame counts is associated with impaired microvascular resistance

Abstract Background The Coronary Slow Flow Phenomenon (CSFP) reflects an increased resting microvascular resistance and has been defined as a corrected thrombolysis in myocardial infarction frame count (cTFC) >27 in the in the absence of obstructive coronary artery disease (CAD). However, there is limited and conflicting data on the diagnostic utility of CTFC with respect to gold standard coronary haemodynamic parameters; namely coronary flow reserve (CFR) and hyperaemic microvascular resistance (hMR). Purpose To evaluate the relationship between angiography-derived cTFC and the coronary haemodynamic parameters (CFR and hMR). Methods Patients with angina and non-obstructive CAD (< 50% epicardial stenosis; ANOCA) underwent comprehensive functional coronary angiography utilising a dual sensor-tipped pressure-doppler flow wire during adenosine infusion for investigation of coronary microvascular impairment, and acetylcholine provocative testing for the diagnosis of coronary artery spasm. Results In 103 patients who underwent functional coronary angiography, 60 patients had CSFP and this was associated with low flow velocity and higher microvascular resistance at rest as compared with patients without CSFP (19.2 ± 7.3 versus 22.6 ± 6.7, p=0.024; and 5.9 ± 2.0 versus 4.6 ± 1.7, p=0.009, respectively). Whilst cTFC was poorly associated with CFR (r= 0.058, p= 0.564), there was a relatively strong, positive correlation with hMR (r=0.258, p=0.008). Furthermore, receiver operating characteristic analyses demonstrated that CTFC poorly predicts an impaired CFR <2.5 (AUC, 0.479 [0.36-0.59]) but does predict an impaired hMR >2.5 (AUC, 0.623 [0.51-0.74] p=0.037). Conclusion In patients with ANOCA, cTFC is associated with coronary microvascular dysfunction as measured by microvascular resistance during hyperaemia. This data suggests the cTFC may be a surrogate marker for impaired microvascular resistance.cTFC versus hMR