DETECTING HIBERNATED MYOCARDIUM WITH SPECT AND THALLIUM-GLUCOSE-INSULIN INFUSION

Because thallium kinetics, like potassium kinetics, may be affected by serum insulin levels, we performed two pilot studies to identify seve rely ischemic myocardium using different protocols based on the infusi on of a thallium, insulin, potassium and glucose solution. Results wer e compared with those obtained with two currently used protocols based on rest injection or reinjection of Tl-201. Methods: In the first stu dy (Protocol 1) of 15 men with a previous large myocardial infarction, perfusion was evaluated by SPECT in 20 segments after a 30-min infusi on of Tl-201 (1 1 1 MBq), insulin (5 U) and potassium (10 mEq) in 10% glucose solution (250 ml). Imaging was repeated 30 min later and the r esults were compared with those obtained from stress and 3-hr reinject ion images. In the second study (Protocol 2), 15 patients were evaluat ed randomly at rest and 3 hr later (rest-redistribution). On a separat e day, the patients were then re-evaluated after infusion of Tl-201 (1 1 1 MBq), potassium (10 mEq) and insulin (5 U) in 5% glucose (250 ml) ; images were obtained 90 and 180 min postinjection. Results: In Proto col 1, radiotracer activity in segments with no uptake during stress w as detected in 35% with the reinjection technique and 58% with the ins ulin solution protocol. In Protocol 2, 31% of segments revealed thalli um activity after insulin infusion but not at rest or rest-redistribut ion. Serum measurements showed high insulin levels (444 +/- 138 in Pro tocol 1, 125 +/- 33 mU/ml in Protocol 2), although glucose levels were not significantly altered (149 +/- 32 versus 71 +/- 20 mg/dl, respect ively). Potassemia was not affected and the patients tolerated the tes ts satisfactorily. Conclusion: These results confirm that continuous i nfusion of Tl-201 with a low dose of insulin in a glucose/potassium ch loride solution is safe and may enhance cellular uptake of the radiotr acer in severe ischemic regions, thereby improving viable myocardium d etection.