The Effects of a Vasodilator on Transluminal Attenuation Gradient at Coronary Computed Tomography Angiography

Abstract

Objective: To evaluate the effects of vasodilators on contrast enhancement and transluminal attenuation gradient (TAG) of coronary arteries at coronary computed tomography angiography (CCTA).

Materials and methods: We retrospectively reviewed CCTA scans of patients who underwent double-acquisition CCTA; CCTA without a vasodilator, and CCTA during a intravenous (IV) infusion of nitrate. Among them, we enrolled 19 patients who had no significant atherosclerotic lesions or coronary spasms. In the control group, 28 patients were enrolled who showed normal coronary arteries on CCTA, which was acquired by a conventional method (sublingual vasodilator). We measured the TAG and Hounsfield units for each of the three major epicardial coronary arteries (reported as 'ProxHU') and then compared the results between the nitrate administration methods (CT without vasodilator [CT_pre], CT with IV vasodilator [CT_iv], and CT with sublingual vasodilator [CT_sub]).

Results: The mean TAG showed a significant difference between the coronary arteries (right coronary artery [RCA] > left anterior descending artery [LAD] > left circumflex artery [LCX], p < 0.05), while there was no difference in ProxHU of each coronary artery in all three types of nitrate administration methods (p > 0.05). The TAG of CT_pre group showed steeper slope than those of vasodilator groups (CT_iv and CT_sub) on LAD and LCX ([LAD: CT_pre = -22.1 ± 6.66, CT_iv = -16.76 ± 5.78, and CT_sub = -16.47 ± 5.78, p = 0.005], [LCX: CT_pre = -31.26 ± 17.43, CT_iv = -23.74 ± 14.06, and CT_sub = -20.94 ± 12.15, p = 0.051]), while that of RCA showed no significant differences (p = 0.600). When comparing proxHU, CT_iv showed higher proxHU than that of CT_pre or CT_sub, especially on LCX (CT_pre = 426.7 ± 68.3, CT_iv = 467.9 ± 84.9, and CT_sub = 404.9 ± 63.3, p = 0.013). ProxHU showed a negative correlation with TAG on all three of methods (r = -0.280, p < 0.001).

Conclusion: TAG in CCTA was significantly affected by vasodilator administration. Both TAG and ProxHU of coronary arteries tend to increase with vasodilator administration on CCTA.

Keywords: Cardiac imaging techniques; Coronary vessels; Multi-detector computed tomography; Vasodilator agents; Wide area detector.