Thallium-201 redistribution after early reinjection in patients with severe stress perfusion defects and ventricular dysfunction

Abstract

Early poststress thallium-201 reinjection to obviate the need for two sets of redistribution images has been proposed as an alternative reinjection protocol although, in a preliminary study, it did not reduce the frequency of late redistribution. The efficacy of the early reinjection protocol was assessed in 102 patients with chronic ischemic heart disease and left ventricular dysfunction who showed severe thallium-201 defects on planar stress images. Thallium-201 was reinjected immediately after the poststress study, and redistribution images were acquired 4 and 24 hours later. By quantitative analysis, a further increase in thallium-201 uptake on 24-hour imaging was documented in only 48 (6%) of 740 segments still abnormal on 4-hour images, 26 (54%) of which were represented by partially reversible or not severe fixed defects. Overall, late thallium-201 uptake was less frequently observed in patients with depressed ejection fraction (p < 0.05). Clinically relevant late reversibility was found in only 3 (3%) of 94 patients. Scans were repeated after revascularization in 20 patients. Tracer uptake improved in 40 (34%) of 118 segments with 4-hour defect: the improvement mainly (85%) involved those segments already showing partial 4-hour reversibility or mild fixed defects on the preoperative study. Thus a negligible late tracer redistribution was found in patients with severe stress thallium-201 defects undergoing early reinjection and 4-hour imaging; no significant 24-hour improvement was observed in those patients with depressed ventricular function and fixed 4-hour defects. This simpler imaging protocol could obviate the need for additional late imaging to detect residual viability.