Multicenter Core Laboratory Comparison of the Instantaneous Wave-Free Ratio and Resting Pd/Pa With Fractional Flow Reserve

Objectives This study sought to examine the diagnostic accuracy of the instantaneous wave-free ratio (iFR) and resting distal coronary artery pressure/aortic pressure (P-d/P-a) with respect to hyperemic fractional flow reserve (FFR) in a core laboratory-based multicenter collaborative study. Background FFR is an index of the severity of coronary stenosis that has been clinically validated in 3 prospective randomized trials. iFR and P-d/P-a are nonhyperemic pressure-derived indices of the severity of stenosis with discordant reports regarding their accuracy with respect to FFR. Methods iFR, resting P-d/P-a, and FFR were measured in 1,768 patients from 15 clinical sites. An independent physiology core laboratory performed blinded off-line analysis of all raw data. The primary objectives were to determine specific iFR and P-d/P-a thresholds with >= 90% accuracy in predicting ischemic versus nonischemic FFR (on the basis of an FFR cut point of 0.80) and the proportion of patients falling beyond those thresholds. Results Of 1,974 submitted lesions, 381 (19.3%) were excluded because of suboptimal acquisition, leaving 1,593 for final analysis. On receiver-operating characteristic analysis, the optimal iFR cut point for FFR <= 0.80 was 0.90 (C statistic: 0.81 [95% confidence interval: 0.79 to 0.83]; overall accuracy: 80.4%) and for P-d/P-a was 0.92 (C statistic: 0.82 [95% confidence interval: 0.80 to 0.84]; overall accuracy: 81.5%), with no significant difference between these resting measures. iFR and P-d/P-a had >= 90% accuracy to predict a positive or negative FFR in 64.9% (62.6% to 67.3%) and 48.3% (45.6% to 50.5%) of lesions, respectively. Conclusions This comprehensive core laboratory analysis comparing iFR and P-d/P-a with FFR demonstrated an overall accuracy of similar to 80% for both nonhyperemic indices, which can be improved to >= 90% in a subset of lesions. Clinical outcome studies are required to determine whether the use of iFR or P-d/P-a might obviate the need for hyperemia in selected patients. (C) 2014 by the American College of Cardiology Foundation