[Reverse redistribution in dipyridamole-loading thallium-201 images using single photon emission computed tomography].

This study demonstrated the clinical significance of reverse redistribution, i.e., a decrease in the relative Tl activity in the redistribution image compared to that of the stress image after administration of dipyridamole. Dipyridamole was infused intravenously at a rate of 0.142 mg/kg per min for four min, and a stress image was obtained 10 min after the injection of two mCi 201Tl. Each patient returned for redistribution scanning in the identical position three hours after the isotope injection. The myocardial image of Tl was analyzed by single photon emission computed tomography and its washout rate was calculated by the segmental ROI method. Myocardial function and the motion of left ventricular wall were analyzed by 99mTc-RBC-gated cardiac pool imaging. The results were as follows: Reverse redistribution was noted in 27 (21.6%) of 125 consecutive Tl dipyridamole and redistribution myocardial imaging studies. The stress image demonstrated normal perfusion (group 1) and reduced perfusion (group 2) of Tl. Group 1 consisted of 17 patients with diabetes mellitus, supraventricular arrhythmias, hypertension, and others. Group 2 consisted of 10 patients with subendocardial infarction, diabetes mellitus, and hypertension, and others. The percentage prevalence of reverse redistribution among patients with supraventricular arrhythmia was 62.5% (five of eight patients), with subendocardial infarction 60.0% (three of five), with hypertension 42.8% (six of 14), and with diabetes mellitus 40.0% (eight of 20), while in those with transmyocardial infarction and angina pectoris no reverse redistribution percentage was found. The washout rate of Tl in normal perfusion areas was 44.0 +/- 12.8%, the reverse redistribution of group 1 was 47.4 +/- 12.8%, and of group 2 was 51.2 +/- 8.2%. The washout rate of the reverse redistribution of group 2 was significantly greater than that of the normal areas. In gated cardiac pool imaging, patients in group 2 had significantly larger areas showing abnormal contraction of the left ventricular wall and significantly lower ejection fraction than did group 1. In the electrocardiogram ST segment depression was noted more frequently in group 2 than group 1. No Q wave was present in the corresponding reverse redistribution area. These results suggest that reverse redistribution might occur in a region with a combination of scarred and normal myocardium, the metabolically affected myocardium, and an area with relatively increased myocardial blood flow. The patients in group 2 seem to have the more pathological myocardium than do those in group 1.