Quantitative flow ratio for the functional assessment of extracranial internal carotid artery stenosis

Background: In asymptomatic patients presenting with significant internal carotid artery (ICA) stenoses undergoing endovascular revascularization, a selective angiography before stenting (CAS) is required. Sometimes, angiographic findings could be discordant from non-invasive assessment and a tool able to evaluate functional relevance of the stenosis could be of value. We sought to evaluate the usefulness of quantitative flow ratio (QFR) as angiography-based tool for functional assessment of ICA stenoses. Methods: We prospectively enrolled 50 asymptomatic patients undergoing CAS. Peak systolic velocity (PSV, cm/s) assessed at color Doppler echocardiography was used to identify significant stenoses (PSV >125 cm/s). At angiography, assessment of ICA stenosis was obtained visually (%DSVISUAL) and according NASCET criteria (%DSNASCET). Stenoses were considered significant if >60%. After exclusion of 20 vessels, QFR, area stenosis (AS, %) and minimal lumen area (MLA, mm2) were obtained in the remaining 80 vessels. Results: At linear regression analysis, QFR significantly correlated with PSV (r2=0.52, P<0.001) as well as with %DSNASCET (r2=0.68, P<0.001) and %DSVISUAL (r2=0.71, P<0.001). Using PSV as reference, QFR showed good accuracy to predict functionally significant stenosis (AUC=0.98, P<0.001) with a cut-off value of 0.93. As compared with %DSNASCET and %DSVISUAL, QFR showed a significantly higher accuracy (61% vs. 73% vs. 94%, respectively; P<0.05), sensitivity (43% vs. 61% vs. 93%, respectively; P<0.05) and negative predictive value (46% vs. 51% vs. 85%, respectively; P<0.05) for detecting hemodynamically significant ICA stenoses. Conclusions: This study suggest the potential benefit of adopting QFR for functional assessment of extracranial ICA stenoses. These data should be validated in larger studies.