Prevalence of Impaired Flow-Mediated Epicardial Vasodilation among Different Types of Coronary Flow Regulation

Background To assess the prevalence of impairment of flow-mediated epicardial vasodilation (IEV) in the presence of normal and abnormal coronary microvascular function. Methods In 332 consecutive symptomatic patients, global and longitudinal myocardial blood flow (MBF) at rest and during pharmacologically stimulated hyperemia was evaluated with ¹³ N-ammonia positron emission tomography/computed tomography (PET/CT). Normal coronary microvascular function (nCMF) was defined by a myocardial flow reserve (MFR = MBFstress/MBFrest) of ≥ 2.0 (group 1; n = 210 (G1)), while an abnormal MFR of < 2.0 (predominantly due to decreases in hyperemic MBF) denoted classical CMD (group 2; n = 83 (G2)) or (predominantly related to increases in resting MBF ≥ 1.0mL/g/min) signified endogen CMD (group 3; n = 39 (G3)), respectively. Furthermore, normal flow-mediated epicardial vasodilation (NEV) was defined as longitudinal hyperemic MBF gradient < -0.10 mL/g/min, whereas a value ≥ -0.10 mL/g/min signified IEV. Results In the entire study population, IEV was present in 34.6.% (115/332). IEV was highest in group 1 (46.2%), while there was a comparable low prevalence between group 2 and group 3 (13.3% vs. 17.9%; p = 559). The hyperemic longitudinal MBF gradient was significantly higher in G1 compared to G2 (-0.28 ± 0.10 vs. -0.19 ± 0.08 mL/g/min; p ≤ 0.008), but comparable between group 1 and group 3 (-0.28 ± 0.10 and − 0.27 ± 0.10 mL/g/min; p = 0.795). The hyperemic longitudinal MBF gradient and ΔMBF Gradient correlated inversely with the global hyperemic MBF, respectively (r = 0.41, SEE = 0.09 and r = 0.34, SEE = 0.09, both p ≤ 0.001). Conclusions Nearly half of symptomatic patients with normal global MFR had IEV. As IEV carries important diagnostic and prognostic information, it may further optimize prognostication on cardiovascular individuals deserving further clinical testing.