Noninvasive quantification of regional myocardial flow reserve in patients with coronary atherosclerosis using nitrogen-13 ammoni positron emission tomography: Determination of extent of altered vascular reactivity

Objectives. The aim of this study was to evaluate patients with coronary artery disease to 1) determine the relation between flow reserve measured by nitrogen-13 (N-13) ammoni kinetic modeling and stenosis severity assessed by quantitative angiography, and 2) examine whether flow reserve is impaired in regions supplied by vessels without significant angiographic disease. Background. With the advent of new therapeutic approaches for coronary disease, an accurate noninvasive approach for absolute quantification of flow and flow reserve is needed to evaluate functional severity and extent of atherosclerosis. Nitrogen-13 ammoni kinetic modeling may permit such evaluation. Methods. Twenty-seven subjects were classified into three groups: group 1 = 5 young volunteers; group 2 = 7 middle-aged volunteers; and group 3 = 15 patients with coronary artery disease. Dynamic N-13 ammoni positron emission tomographic imaging was performed at rest and during adenosine infusion. three-compartment model was fit to regional N-13 ammoni kinetic dat to determine myocardial flow. Group 3 patients underwent quantitative coronary angiography. Results. The regional blood flow results in patients with coronary disease were classified into four subgroups: no significant detectable disease and mild (50% to 69.9% are stenosis), moderate (70% to 94.9% are stenosis) or severe (95% to 100% are stenosis) coronary disease. Flow reserve was 2.95 ± 0.65; 2.09 ± 0.47; 2.02 ± 0.51; 1.3 ± 0.32, respectively (p ≤ 0.01 except mild vs. moderate). Flow reserve was correlated with percent are stenosis (r = −0.56) and minimal lumen diameter (r = 0.75). In volunteers (groups 1 and 2), flow reserves were greater than in segments without detectable disease in group 3 patients (4.10 ± 0.71 and 3.79 ± 0.42, respectively, vs. 2.88 ± 0.56, p ≤ 0.02). Conclusions. The functional severity of coronary disease measured by N-13 ammoni positron emission tomography varied for given stenosis but was significantly related to angiographic severity. Among patients with coronary disease, myocardial regions without significant angiographic stenoses displayed reduced flow reserve than did regions in control subjects, indicating that vascular reactivity was more diffusely impaired in group 3 than was suggested by angiography. Noninvasive quantification of myocardial flow reserve using dynamic N-13 ammoni positron emission tomography yields important functional dat that permit definition of the extent of disease even when disease is not apparent by angiography.