Comparison of Nitroglycerin-Induced Pressure Ratio Drop and Resting Full-Cycle Ratio in a Pressure Wire Study

<b>Background/Objectives</b>: The acute drop in distal coronary pressure (Pd)-to-aortic pressure (Pa) ratio after intracoronary nitroglycerin (NTG-Pd/Pa) administration is an acceptable estimate of fractional flow reserve (FFR). We aimed to compare the diagnostic performance of NTG-Pd/Pa with that of the resting full-cycle ratio (RFR) in predicting the binary results of FFR. <b>Methods</b>: This study included two prospective studies registered under the numbers NCT04700397 and NCT03693157. Altogether, 202 vessels were included. The optimal cutoff of NTG-Pd/Pa for predicting FFR ≤ 0.8 was identified and validated in another prospective registry. We used the McNemar's test and the DeLong method to compare the diagnostic efficiency of NTG-Pd/Pa vs. RFR in predicting FFR ≤ 0.8 in a pooled cohort. <b>Results</b>: NTG-Pd/Pa was strongly correlated with FFR (r = 0.945, <i>p</i> < 0.001). The NTG-Pd/Pa cutoff for predicting FFR ≤ 0.8 was 0.85 in both the derivation and validation cohorts. The area under the receiver-operating characteristic curve (AUC) and accuracy in predicting FFR ≤ 0.8 were higher for NTG-Pd/Pa than for RFR in the pooled cohort (AUC 0.97 vs. 0.91, <i>p</i> < 0.001; accuracy 91% vs. 84%, <i>p</i> < 0.001). The sensitivity and negative predictive values were also higher for NTG-Pd/Pa than for RFR (all <i>p</i> < 0.05). The specificity and positive predictive value were numerically higher for NTG-Pd/Pa than for RFR (all <i>p</i> > 0.05). <b>Conclusions:</b> The diagnostic performance of NTG-Pd/Pa may surpass that of the RFR in predicting the binary results of the FFR.