Agreement of the Resting Distal to Aortic Coronary Pressure With the Instantaneous Wave-Free Ratio

Background: Recently, 2 randomized controlled trials showed that the instantaneous wave-free ratio (iFR), a resting coronary physiological index, is noninferior to fractional flow reserve for guiding revascularization. The resting distal to aortic coronary pressure (P_d/P_a) measured at rest is another adenosine-free index widely available in the cardiac catheterization laboratory; however, little is known about the agreement of P_d/P_a using iFR as a reference standard. Objectives: The goal of this study was to investigate the agreement of P_d/P_a with iFR. Methods: A total of 763 patients were prospectively enrolled from 12 institutions. iFR and P_d/P_a were measured under resting conditions. Using iFR ≤0.89 as a reference standard, the agreement of P_d/P_a and its best cutoff value were assessed. Results: According to the independent core laboratory analysis, iFR and P_d/P_a were analyzable in 627 and 733 patients (82.2% vs. 96.1%; p < 0.001), respectively. The median iFR and P_d/P_a were 0.90 (interquartile range: 0.85 to 0.94) and 0.92 (interquartile range: 0.88 to 0.95), and the 2 indices were highly correlated (R² = 0.93; p < 0.001; iFR = 1.31 * P_d/P_a –0.31). According to the receiver-operating characteristic curve analysis, P_d/P_a showed excellent agreement (area under the curve: 0.98; 95% confidence interval: 0.97 to 0.99; p < 0.001) with a best cutoff value of P_d/P_a ≤0.91. The diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value were 93.0%, 91.4%, 94.4%, 93.3%, and 92.7%, respectively. These results were similar in patients with acute coronary syndrome and stable angina. Conclusions: P_d/P_a was analyzable in a significantly higher number of patients than iFR. P_d/P_a showed excellent agreement with iFR, suggesting that it could be applied clinically in a similar fashion.