Uptake of Seven Myocardial Tracers During Increased Myocardial Blood Flow by Dobutamine Infusion

RATIONALE AND OBJECTIVES.Direct comparison of myocardial perfusion tracers has been made difficult by variability in experimental models, and by a virtual absence of data comparing tracer uptake to myocardial blood flow under conditions of increased myocardial oxygen consumption, similar to what occurs with dynamic exercise. METHODS.Tracer uptake versus myocardial blood flow was evaluated for thallium-201 (Tl) and six technetium-99m (Tc) myocardial-imaging agents in 24 open-chest canines with an occluded left-anterior descending coronary artery during dobutamine infusion. Data were fitted to the exponential model y = ax(1 − exp[−PSc/x]), where y is the tissue tracer/g normalized to normal (activity at 1 mL/minute/g) and x is the blood flow measured by the radioactive microsphere method. RESULTS.With dobutamine, myocardial tracer uptake was linear across a wide range of ischemic and hyperemic flows for each tracer. Based on the permeability surface area product, Tl and Tc Q3 provided the best tracer estimate of myocardial blood flow (5.30 ± 0.86 mL/minute/g, r = 0.91; 5.46 ± 0.58 mL/minute/g, r = 0.94, respectively). Correlation coefficient (r) values for other tracers studied were Tc Q4 (r = 0.93), Tc Q12 (r = 0.93), Tc sestamibi (r = 0.90), Tc tetrofosmin (r = 0.96), and Tc-N-Noet (r = 0.82). CONCLUSIONS.Of the Tc tracers examined under conditions of dobutamine-altered myocardial contractility, the myocardial uptake properties of Tc Q3 were most similar to those of Tl.