BACKGROUND: Normal endothelial function is a measure of vascular health and dysfunction is a predictor of coronary events. Nitric oxide-mediated coronary artery endothelial function, as assessed by vasomotor reactivity during isometric handgrip exercise (IHE), was recently quantified noninvasively with magnetic resonance imaging (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 and blood flow in the right coronary artery and the IMA in 25 patients with coronary artery disease and 26 healthy subjects during IHE were assessed using 3T MRI. In 8 healthy subjects, a nitric oxide synthase inhibitor was infused to evaluate the role of nitric oxide in the IMA-IHE response. Interobserver IMA-IHE reproducibility was good for cross-sectional area (R=0.91) and blood flow (R=0.91). In healthy subjects, cross-sectional area and blood flow of the IMA increased during IHE, and these responses were significantly attenuated by monomethyl-l-arginine (P<0.01 versus placebo). In patients with coronary artery disease, the right coronary artery did not dilate with IHE, and dilation of the IMA was less than that of the healthy subjects (P=0.01). The blood flow responses of both the right coronary artery and IMA to IHE were also significantly reduced in patients with coronary artery disease.
CONCLUSIONS: MRI-detected IMA responses to IHE primarily reflect nitric oxide-dependent endothelial function and are reproducible and reduced in patients with coronary artery disease. 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.