Thallium-201 (201Tl) uptake and redistribution kinetics were examined in an open-chest canine preparation of occlusion and reperfusion. Seven dogs (group I) underwent 3 hr of sustained occlusion and received 1.5 mCi of 201Tl after 40 min of occlusion of the left anterior descending coronary artery (LAD). Group II (n = 18) underwent 60 min of LAD occlusion followed by sudden and total release of the ligature. Group IIa (n = 8) received intravenous 201Tl during occlusion of the LAD, whereas group IIb (n = 10) received intravenous 201Tl at the time of peak reflow. Group III dogs (n = 26) also underwent 60 min of LAD occlusion that was followed by gradual reflow through a residual critical stenosis. Animals in this group also received 201Tl either before (IIIa; n = 16) or after reflow was established (IIIb; n = 10). In group I, the relative 201Tl gradient (nonischemic minus ischemic activity) decreased from 88 ± 8% (mean ± SEM) to 59 ± 6% during 3 hr of coronary occlusion (p = .034). After rapid and total reperfusion (group IIa), this gradient decreased from 71 ± 6% during occlusion to 26 ± 5% after reflow (p<.001). After slow reperfusion through a residual stenosis (group IIIa), the gradient decreased from 81 ± 5% to 31 ± 5% (p<.001) (p = .56 compared with group IIa). In rapidly reperfused dogs receiving intravenous thallium during peak reflow (IIb), initial 201Tl activity in the ischemic zone was 155 ± 20% of initial normal activity and fell to 93 ± 13% of normal after 2 hr of reperfusion. Similarly, in dogs reperfused slowly through a critical stenosis (IIIb), which received 201Tl during reflow, 201Tl activity soon after reflow was 94 ± 4% of initial normal and decreased to 80 ± 6% at 2 hr of reperfusion (p = .10). Histochemical evidence of necrosis was present in the biopsy region in 80% of the 20 dogs subjected to triphenyl tetrazolium chloride (TTC) staining. Microsphere-determined transmural blood flow was similar in all groups during LAD occlusion and final flows after 2 hr were comparable in all subgroups undergoing reflow. Ischemic zone flow (% normal) was significantly higher at the time of 201Tl administration in groups IIb (192 ± 25%) and IIIb (110 ± 5%), which received 201Tl during reflow, than in groups IIa (31 ± 9%) and IIIa (22 ± 5%), which received 201Tl during occlusion. These differences in flow at the time of administration of 201Tl explain the different thallium uptake patterns observed. These data suggest that after 1 hr of LAD occlusion there is no difference between rapid reperfusion through a totally patent vessel and slow reperfusion through a critical stenosis with regard to ultimate degree of flow restoration or magnitude of 201Tl redistribution in instances in which 201Tl is given before reflow. With both methods of reperfusion a residual 201Tl gradient is seen. Administration of 201Tl during reflow, however, probably overestimates the degree of myocardial salvage as reflected by final 201Tl uptake values. In dogs rapidly reperfused, a relative 'hot spot' of 201Tl activity was observed in the ischemic zone when 201Tl was administered at peak reflow, despite histochemical evidence of necrosis. These results have clinical implications with respect to the timing of 201Tl administration and interpretation of serial 201Tl scintigrams in patients with acute myocardial infarction undergoing thrombolysis.
All Science Journal Classification (ASJC) codes
- Cardiology and Cardiovascular Medicine
- Physiology (medical)