Background
Normal endothelial function is a measure of vascular health and dysfunction a predictor of coronary events. Nitric Oxide (NO)-mediated coronary artery endothelial function (CEF), as assessed by vasomotor reactivity during isometric handgrip exercise (IHE), was recently quantified noninvasively with MRI. Because the internal mammary artery (IMA) is often visualized during coronary MRI we propose the strategy of simultaneously assessing systemic and coronary endothelial function noninvasively by MRI during IHE.
Methods and Results
Changes in cross-sectional area (CSA) and blood flow (BF) in the right coronary artery (RCA) and the IMA in 25 CAD patients and 26 healthy subjects during IHE were assessed using 3T MRI. In 8 healthy subjects a NO synthase inhibitor was infused to evaluate the role of NO in the IMA-IHE response. Inter-observer IMA-IHE reproducibility was good for CSA (R=0.91) and BF (R=0.91). In healthy subjects, CSA and BF of the IMA increased during IHE and these responses were significantly attenuated by L-NMMA (p<0.01 vs. placebo). In CAD patients, the RCA did not dilate with IHE and dilation of the IMA was less than that of the healthy subjects (p=0.01). The BF responses of both the RCA and IMA to IHE were also significantly reduced in CAD patients.
Conclusions
MRI-detected IMA responses to IHE primarily reflect NO-dependent endothelial function, are reproducible and reduced in CAD patients. Endothelial function in both coronary and systemic (IMA) arteries can now be measured noninvasively with the same imaging technique and promises novel insights into systemic and local factors affecting vascular health.
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