Comparison of 201 Tl, 99m Tc-Tetrofosmin, and Dobutamine Magnetic Resonance Imaging for Identifying Hibernating Myocardium

Abstract

Background —Both radionuclide perfusion tracers and contractile response to dobutamine have been used to identify hibernating myocardium. The aim was to compare 201 Tl (thallium) single photon emission CT (SPECT), 99m Tc-tetrofosmin (tetrofosmin) SPECT, and dobutamine cine MRI for identifying regions of reversible myocardial dysfunction. Methods and Results —Thirty patients with 3-vessel coronary artery disease and impaired left ventricular function (mean LVEF, 24.0%; SD, 8.3%) scheduled for coronary bypass grafting were recruited. All underwent rest/dobutamine stress (5 to 10 μg · kg −1 · min −1 ) cine MRI, stress/rest tetrofosmin SPECT, and stress/redistribution and separate-day rest/redistribution thallium SPECT before surgery. Stress/redistribution thallium SPECT and resting MRI were repeated after surgery. In a 9-segment model, SPECT images were scored visually for tracer uptake, which was also measured from a polar plot of myocardial counts. MRI was scored visually for endocardial motion, myocardial thickening, and thickness. Five patients died before follow-up, and 2 declined postoperative investigation. In the remaining 23 patients, mean LVEF increased from 24.0% (SD, 8.3%) to 29.7% (SD, 11.1%) ( P <0.05). Of 207 segments analyzed, 145 had significantly abnormal wall motion before surgery, and 82 of these improved function after revascularization. The criteria for predicting recovery of severely hypokinetic segments on preoperative imaging were tracer uptake graded “moderately reduced” or better, or positive inotropic response on dobutamine MRI. Late-rest thallium images showed the highest sensitivity (76%), compared with stress-redistribution thallium (68%) and rest tetrofosmin (66%) ( P <0.05). All 3 tracer techniques were nonspecific (44%, 51%, and 49%, respectively). Redistribution of thallium after the resting injection was insensitive (18%) but highly specific (83%). Inotropic response to dobutamine was also insensitive (50%) but specific (81%). Conclusions —Radionuclide uptake is a sensitive but nonspecific predictor of myocardial functional recovery, whereas dobutamine MRI is specific but insensitive.