Experimental study of thallium 201 redistribution in transient myocardial ischemia

The influence of differential washout on the redistribution phenomenon of thallium 201 chloride deposited in ischemic myocardium was investigated. Two groups of dogs had serial scintigraphic images and tissue counting performed. The first group had ischemia produced prior to the injection of the thallium and, following the control image after production of ischemia, the occlusion was released and serial images obtained over a three-hour period. The second group received thallium initially and after a control scintigraph was taken, ischemia was created and maintained for three hours via transthoracic ligature. Activity distribution was followed by serial images. Thallium content of ischemic areas was compared to the normal area by computer assisted data analysis. Tissues from the ischemic and normal areas from both groups were obtained after the serial images and counted. In the first group, prompt redistribution of activity into the ischemic areas was seen within 30 minutes of releasing the occlusion and was verified by tissue counting. Neither scintigraphic image changes nor tissue uptake differences were observed in the second group. The restoration of blood flow and consequently increased avidity for thallium probably accounted for the redistribution seen in the first group as there appeared to be no differential washout of activity in the second group from either the ischemic or normal areas to contribute to the redistribution phenomenon.