Myocardial uptake of Tc-99m-N-NOET and (TI)-T-201 during dobutamine infusion - Comparison with adenosine stress

Background-The myocardial uptake of Tc-99m-sestamibi is attenuated by dobut amine stress, resulting in underestimation of ischemia. N-Ethyl-N-ethoxy-di thiocarbamato-N-Tc-99m (Tc-99m-N-NOET) is a new Tc-99m-labeled perfusion ag ent that is highly extracted by the myocardium by a mechanism different fro m that defined for Tc-99m-sestamibi. We therefore hypothesized that Tc-99m- N-NOET uptake would not be attenuated by dobutamine and that Tc-99m-N-NOET uptake would be comparable to Tl-201 uptake during dobutamine stress. Methods and Results-In 28 open-chest dogs, after placement of a stenosis in the left anterior descending coronary artery that reduced flow reserve by >50%, adenosine (300 mu g . kg(-1) . min(-1); n = 15) or dobutamine (2.5 to 30 mu g . kg(-1) . min(-1); n = 13) was infused. During adenosine stress, the stenotic-to-normal activity ratio for Tc-99m-N-NOET was 0.55+/-0.05. Th e stenotic-to-normal flow ratio was 0.33+/-0.04 at the time of Tc-99m-N-NOE T injection. During dobutamine stress, the stenotic-to-normal Tc-99m-N-NOET activity ratio was 0.63+/-0.04, comparable to the Tl-201 activity ratio of 0.59+/-0.04. The stenotic-to-normal flow ratio was 0.47+/-0.04 at the time of Tc-99m-N-NOET and Tl-201 injection. The relationship between Tc-99m-N-N OET uptake and blood flow was comparable for adenosine and dobutamine stres s, with no evidence of attenuation of Tc-99m-N-NOET extraction by dobutamin e. Conclusions-in the presence of coronary stenoses that reduced regional flow reserve, the myocardial uptake of Tc-99m-N-NOET and Tl-201 are closely pro portional to blood flow during both adenosine and dobutamine stress, sugges ting that the adverse effect of dobutamine on Tc-99m-sestamibi uptake is a tracer-specific phenomenon rather than a generalized effect. The clinical i mplication of this finding is that Tc-99m-N-NOET might be preferable to Tc- 99m-sestamibi when used with dobutamine stress for detection of coronary st enoses.