Association Between Physiological Stenosis Severity and Angina-Limited Exercise Time in Patients With Stable Coronary Artery Disease.

IMPORTANCE Physiological stenosis assessment is recommended to guide percutaneous coronary intervention (PCI) in patients with stable angina. OBJECTIVE To determine the association between all commonly used indices of physiological stenosis severity and angina-limited exercise time in patients with stable angina. DESIGN, SETTING, AND PARTICIPANTS This cohort study included data (without follow-up) collected over 1 year from 2 cardiac hospitals. Selected patients with stable angina and physiologically severe single-vessel coronary artery disease presenting for clinically driven elective PCI were included. EXPOSURES Fractional flow reserve (FFR), instantaneous wave-free ratio (iFR), hyperemic stenosis resistance (HSR), and coronary flow reserve (CFR) were measured invasively. Immediately after this, patients maximally exercised on a catheter-table-mounted supine ergometer until they developed rate-limiting angina. Subsequent PCI was performed in most patients, followed by repeat maximal supine exercise testing. MAIN OUTCOMES AND MEASURES Associations between FFR, iFR, HSR, CFR, and angina-limited exercise time were assessed using linear regression and Pearson correlation coefficients. Additionally, the associations between the post-PCI increment in exercise time and baseline FFR, iFR, HSR, and CFR were assessed. RESULTS Twenty-three patients (21 [91.3%] of whom were male; mean [SD] age, 60.6 [8.1] years) completed the pre-PCI component of the study protocol. Mean (SD) stenosis diameter was 74.6%(10.4%). Median (interquartile range [IQR]) values were 0.54 (0.44-0.72) for FFR, 0.53 (0.38-0.83) for iFR, 1.67 (0.84-3.16) for HSR, and 1.35 (1.11-1.63) for CFR. Mean (SD) angina-limited exercise time was 144 (77) seconds. Anatomical stenosis characteristics were not significantly associated with angina-limited exercise time. Conversely, FFR (R-2=0.27; P=.01), iFR (R-2=0.46; P<.001), HSR (R-2=0.39; P<.01), and CFR (R-2=0.16; P<.05) were all associated with angina-limited exercise time. Twenty-one patients (19 [90.5%] of whom were male; mean [SD] age, 60.1 [8.2] years) competed the full protocol of PCI, post-PCI physiological assessment, and post-PCI maximal exercise. After PCI, the median (IQR) FFR rose to 0.91 (0.85-0.96), median (IQR) iFR to 0.98 (0.94-0.99), and median (IQR) CFR to 2.73 (2.50-3.12), while the median (IQR) HSR fell to 0.16 (0.06-0.37) (P<.001 for all). The post-PCI increment in exercise time was most significantly associated with baseline iFR (R-2=0.26; P=.02). CONCLUSIONS AND RELEVANCE In a selected group of patients with severe, single-vessel stable angina, FFR, iFR, HSR, and CFR were all modestly correlated with angina-limited exercise time to varying degrees. Notwithstanding the limited sample size, no clear association was demonstrated between anatomical stenosis severity and angina-limited exercise time.