Coronary Aorta Systolic and Diastolic Pressure Indices: Two Novel Indicators for Predicting Significant Coronary Stenosis –– A Validation Against Fractional Flow Reserve

Background: Since most of the coronary flow occurs in diastole, either mean Pd/Pa or iFR has been used to measure the hemodynamic significance of a coronary stenosis. We have observed that a significant pressure gradient exists in coronary stenosis even in systole, which is contrary to general understanding but similar to ankle brachial index. Furthermore, prior studies have evaluated baseline Pd/Pa (mean coronary artery/mean aorta pressure) ratio as well as iFR (instantaneous wave-free ratio obtained during entire period of diastole) to predict fractional flow reserve (FFR) ≤ 0.80. We hypothesized a simple end-systolic and -diastolic pressure measurement in the coronary artery distal to stenosis may perform adequately to predict FFR, obviating a need to measure Pd/Pa or iFR. Purpose: We sought to evaluate systolic and diastolic Pd/Pa, and termed them coronary artery systolic pressure index (CASPI) and coronary artery diastolic pressure index (CADPI), respectively, against FFR ≤ 0.80. Methods: After retrospectively identifying 555 moderate stenotic lesions undergoing FFR measurement at a tertiary care center over a 4-year period, we procured original pressure tracings obtained during the cardiac catheterization and manually measured systolic and diastolic pressures in the aorta and in the coronary artery distal to the stenosis, before and after adenosine infusion. Utilizing FFR ≤ 0.80, operating test characteristics of CASPI and CADPI were measured and compared to those of baseline Pd/Pa. Results: In the 555 lesions, mean CASPI (0.97 ± 0.04) and CADPI (0.95 ± 0.08) were similar to baseline Pd/Pa (0.95 ± 0.05). CASPI correlated well with baseline Pd/Pa (Spearman r = 0.81; P \u3c 0.0001). Similarly, CADPI was strongly correlated with baseline Pd/Pa (0.86; P \u3c 0.0001). The area under the receiver operating curve (AUC) was lower for CASPI and CADPI, as compared to baseline Pd/Pa (0.80 vs. 0.82 vs. 0.89, respectively), for predicting the FFR ≤ 0.80. For a CASPI \u3c 0.88 there were no false positives with 100% specificity, and for a CASPI \u3e 1.02, there were no false negatives with 100% sensitivity. Similarly, for a CADPI \u3c 0.8 there were no false positives with 100% specificity, and for CADPI \u3e 1.16 there were no false negatives with 100% sensitivity. Conclusion: These data demonstrate that contrary to the popular belief, significant systolic and diastolic pressure gradients distal to coronary stenosis exist with a reasonable but lower predictive power towards FFR ≤ 0.80