Background .– To assess the functional significance of left anterior descending artery (LAD) stenosis of intermediate severity (IS) (50–70% diameter stenosis) is challenging.

Objective .– To compare the value of non-invasive coronary flow reserve (CFR) to the invasive fractional flow reserve (FFR) in the setting of LAD stenosis of angiographic IS.

Methods .– Fifty stable consecutive patients (pts) (mean age 63 ± 13 years, 11 females, mean left ventricular ejection fraction 61 ± 10%) with an angiographic proximal LAD stenosis of IS (55.5 ± 5% diameter stenosis, QCA), no previous anterior myocardial infarction, and with various vascular risk factors, were prospectively studied. They underwent FFR with intracoronary bolus adenosine (150 μg), and CFR using intravenous adenosine (140 μg/kg per minute over 2 min), in the distal part of the LAD, the same day in nearly all cases. CFR was defined as hyperemic peak diastolic LAD flow velocity divided by baseline flow velocity (normal value > 2) and FFR was defined as distal pressure divided by mean aortic pressure during maximal hyperemia (normal value > 0.8).

Results .– The mean FFR and CFR were 0.84 ± 0.07 and 2.7 ± 0.75 respectively, in the whole population. Concordant results between FFR and CFR were seen in 44 cases (88%) and discordant results in six cases (12%). There was a significant correlation between CFR and FFR ( r = 0.59, P < 0.01). A better correlation was found between FFR and % LAD diameter stenosis, and lesion length (all, P < 0.05), than between CFR and the same anatomic markers of stenosis severity (all, P = NS).The sensitivity, specificity, positive and negative predictive values of CFR more than 2 to detect a non significant lesion defined by a normal FFR were 95, 69, 90, and 82%, respectively.

Conclusion .– In pts with LAD stenosis of IS, discordant results between non-invasive CFR and FFR were not unusual, and the anatomic determinants of the stenosis are better correlated to FFR than to CFR. However, CFR which is a global evaluation of the coronary tree has a very high sensitivity to detect a non significant lesion, despite the high prevalence of vascular risk factors.