Assessment of left anterior descending artery stenosis of intermediate severity by fractional flow reserve, instantaneous wave-free ratio and non-invasive coronary flow reserve

Assessment of the functional significance of left anterior descending coronary artery (LAD) stenosis of intermediate severity is challenging and often based on fractional flow reserve (FFR). The instantaneous wave-free ratio (IFR), a new vasodilator-free index of coronary stenosis severity, and non-invasive coronary flow reserve (CFR) by transthoracic Doppler echocardiography are also potentially useful. A direct comparison of FFR, IFR, and non-invasive CFR has never been performed. Our objective was to test the usefulness of non-invasive CFR by comparison to invasive FFR and IFR in patients with LAD stenosis of angiographic intermediate severity and stable coronary artery disease. Methods Ninety-four stable consecutive patients (mean age, 68 ± 10 years; 19 women) with angiographic proximal or mid LAD stenosis of intermediate severity (40–70% diameter stenosis on quantitative coronary angiography), were prospectively studied. They underwent IFR that was calculated as a trans-lesion pressure ratio during a specific period of baseline diastole, FFR with intracoronary bolus adenosine (180 μg), and CFR using intravenous adenosine (140 μg/kg/min over 2 min) in the distal part of the LAD, the same day. CFR was defined as hyperemic peak diastolic LAD flow velocity divided by baseline flow velocity and FFR as distal pressure divided by mean aortic pressure during maximal hyperemia. Results The mean values of IFR, FFR, and CFR were 0.88 ± 0.07, 0.81 ± 0.09 , and 2.4 ± 0.6 respectively. A significant correlation was found between CFR and FFR ( R  = 0.63, curvilinear relationship), FFR and IFR ( R  = 0.6, linear relationship), and between CFR and IFR ( R  = 0.5) (all, P N  = 31) was IFR ≤ 0.88 with a sensitivity (Se) of 74%, specificity (Sp) of 73%, AUC 0.81 ± 0.04; and CFR ≤ 2 with a Se = 77%, Sp = 89%, AUC 0.88 ± 0.04, (all, P ( agreement 85%), between CFR and IFR in 26 cases (agreement 72%), and between IFR and FFR in 26 cases ( agreement 72%). Conclusion In stable patients with LAD stenosis of intermediate severity, non-invasive CFR is a useful tool to detect a significant lesion based on FFR. Furthermore, there was a better correlation and agreement between CFR and FFR than with IFR.