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Impaired coronary flow reserve (CFR) has a prognostic value in CAD patients with intermediate coronary stenosis (50-70%). Peripheral arterial tonometry after reactive hyperemia (RH-PAT) is a method to assess peripheral microvascular endothelial function and is linked to coronary microvascular endothelial dysfunction. We investigated the value of RH-PAT as a noninvasive tool to identify CAD patients with reduced coronary flow reserve (CFR)Methods: Using RH-PAT (EndoPat, Itamar), digital pulse volume changes during reactive hyperemia were assessed in 89 patients with angiographically documented CAD and <70% stenosis of LAD. The PAT device consists of two finger-mounted probes, which include a system of inflatable latex air-cushions within a rigid external case. A blood pressure cuff is placed on one upper arm (study arm), while the contralateral arm serves as a control (control arm) RH-PAT index was calculated as the ratio of the digital pulse volume during reactive hyperemia divided by that at baseline using the Endo-PAT apparatus. Coronary flow reserve (CFR) of the LAD after adenosine infusion was assessed using Doppler echocardiography Patients were categorised to those with either normal (≥2.5) or impaired (<2.5) CFR.Results: A decreasing CFR was related with decreasing RH-PAT index (r=0.45 p=0.003). RH-PAT index was lower in patients with CFR<2.5 compared with those with CFR>2.5 (1.4± 0.3 vs. 1.85± 0.4, p = 0.006). By ROC analysis, an RH-PAT index >1.5 was found to have a sensitivity of 75 % and a specificity of 77% to identify patients with CFR<2.5Conclusions: Digital hyperemic response, as measured by RH-PAT, is attenuated in patients with impaired CFR suggesting a role for RH-PAT as a noninvasive test to identify CAD patients with significant coronary endothelial dysfunction and thus adverse prognosis.