Diagnostic Performance of Resting and Hyperemic Invasive Physiological Indices to Define Myocardial Ischemia: Validation With N-Ammonia Positron Emission Tomography.

Objectives: The authors sought to compare the diagnostic performance of fractional flow reserve (FFR), instantaneous wave-free ratio (iFR), and resting distal coronary artery pressure/aortic pressure (Pd/Pa) using N-ammonia positron emission tomography (PET).

Background: The diagnostic performance of invasive physiological indices was reported to be different according to the reference to define the presence of myocardial ischemia.

Methods: A total of 115 consecutive patients with left anterior descending artery stenosis who underwent both N-ammonia PET and invasive physiological measurement were included. Optimal cutoff values and diagnostic performance of FFR, iFR, and resting Pd/Pa were assessed using PET-derived coronary flow reserve (CFR) and relative flow reserve (RFR) as references. To compare discrimination and reclassification ability, each index was compared with integrated discrimination improvement (IDI) and category-free net reclassification index (NRI).

Results: All invasive physiological indices correlated with CFR and RFR (all p values <0.001). The overall diagnostic accuracies of FFR, iFR, and resting Pd/Pa were not different for CFR <2.0 (FFR 69.6%, iFR 73.9%, and resting Pd/Pa 70.4%) and RFR <0.75 (FFR 73.9%, iFR 71.3%, and resting Pd/Pa 74.8%). Discrimination and reclassification abilities of invasive physiological indices were comparable for CFR. For RFR, FFR showed better discrimination and reclassification ability than resting indices (IDI = 0.170 and category-free NRI = 0.971 for iFR; IDI = 0.183 and category-free NRI = 1.058 for resting Pd/Pa; all p values <0.001).

Conclusions: The diagnostic performance of invasive physiological indices showed no differences in the prediction of myocardial ischemia defined by CFR. Using RFR as a reference, FFR showed a better discrimination and reclassification ability than resting indices.