Multicenter core laboratory comparison of the instantaneous wave-free ratio and resting Pd/Pa with fractional flow reserve: the RESOLVE study

This study sought to examine the diagnostic accuracy of the instantaneous wave-free ratio (iFR) and resting distal coronary artery pressure/aortic pressure (Pd/Pa) with respect to hyperemic fractional flow reserve (FFR) in a core laboratory-based multicenter collaborative study. FFR is an index of the severity of coronary stenosis that has been clinically validated in 3 prospective randomized trials. iFR and Pd/Pa are nonhyperemic pressure-derived indices of the severity of stenosis with discordant reports regarding their accuracy with respect to FFR. iFR, resting Pd/Pa, 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 Pd/Pa 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. 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 Pd/Pa 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 Pd/Pa 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. This comprehensive core laboratory analysis comparing iFR and Pd/Pa with FFR demonstrated an overall accuracy of ~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 Pd/Pa might obviate the need for hyperemia in selected patients