PET-measured responses of MBF to cold pressor testing correlate with indices of coronary vasomotion on quantitative coronary angiography

The aims of this study were to determine whether responses in myocardial blood flow (MBF) to the cold pressor testing (CPT) method noninvasively with PET correlate with an established and validated index of flow-dependent coronary vasomotion on quantitative angiography. Methods: Fifty-six patients (57 ± 6 y; 16 with hypertension, 10 with hypercholesterolemia, 8 smokers, and 22 without coronary risk factors) with normal coronary angiograms were studied. Biplanar end-diastolic images of a selected proximal segment of the left anterior descending artery (LAD) (n = 27) or left circumflex artery (LCx) (n = 29) were evaluated with quantitative coronary angiography in order to determine the CPT-induced changes of epicardial luminal area (LA, mm²). Within 20 d of coronary angiography, MBF in the LAD, LCx, and right coronary artery territory was measured with ¹³N-ammonia and PET at baseline and during CPT. Results: CPT induced on both study days comparable percent changes in the rate x pressure product (%ΔRPP, 37% ± 13% and 40% ± 17%; P = not significant [NS]). For the entire study group, the epicardial LA decreased from 5.07 ± 1.02 to 4.88 ± 1.04 mm² (ΔLA, - 0.20 ± 0.89 mm²) or by -2.19% ± 17%, while MBF in the corresponding epicardial vessel segment increased from 0.76 ± 0.16 to 1.03 ± 0.33 mL·min^-1·g ^-1 (ΔMBF, 0.27 ± 0.25 mL·min ^-1·g^-1) or 36% ± 31% (P < 0.0001). However, in normal controls without coronary risk factors (n = 22), the epicardial LA increased from 5.01 ± 1.07 to 5.88 ± 0.89 mm ² (19.06% ± 8.9%) and MBF increased from 0.77 ± 0.16 to 1.34 ± 0.34 mL·min^-1·g^-1 (74.08% ± 23.5%) during CPT, whereas patients with coronary risk factors (n = 34) revealed a decrease of epicardial LA from 5.13 ± 1.48 to 4.24 ± 1.12 mm² (-15.94% ± 12.2%) and a diminished MBF increase (from 0.76 ± 0.20 to 0.83 ± 0.25 mL·min ^-1·g^-1 or 10.91% ± 19.8%) as compared with controls (P < 0.0001, respectively), despite comparable changes in the RPP (P = NS). In addition, there was a significant correlation (r = 0.87; P ≤ 0.0001) between CPT-related percent changes in LA on quantitative angiography and in MBF as measured with PET. Conclusion: The observed close correlation between an angiographically established parameter of flow-dependent and, most likely, endothelium-mediated coronary vasomotion and PET-measured MBF further supports the validity and value of MBF responses to CPT as a noninvasively available index of coronary circulatory function.