Effect of glucose-insulin-potassium infusion on thallium myocardial clearance

Factors influencing the rate of 201Tl clearance from the myocardium have not been clearly defined. This study determined the effect of an intravenous infusion of glucose-insulin-potassium (GIK) on the net 201Tl clearance rates from myocardium with and without initial 201Tl loading. Anesthetized open-chest dogs underwent 5 min of left anterior descending coronary artery occlusion and intravenous 201Tl was injected and the occlusion released 5 min later. Thirty minutes after 201Tl injection, 30 ml of either GIK (nine dogs) or saline (five dogs) was infused intravenously. The clearance rates of 201Tl from the anterior wall (without initial 201Tl loading) and from the posterior wall (with initial 201Tl loading) were monitored with miniaturized cadmium telluride detectors placed on the myocardium. Calculation of net myocardial clearance rates was performed by linear regression analysis from serial 1 min counts. Compared with saline infusion, GIK increased the net clearance of 201Tl from both myocardial regions with and without initial loading. The most marked change induced by GIK infusion was in the myocardial region without initial 201Tl loading; a net increase in 201Tl activity (72 +/- 42 cpm/30 min) was converted into a net loss (-594 +/- 228 cpm/30 min). There was no significant change in 201Tl clearance after the saline infusion. Heart rate, aortic and left atrial pressure, sonomicrometer-measured transmural myocardial wall thickness, microsphere-determined myocardial blood flow, and blood glucose and potassium concentrations did not change significantly during GIK or saline infusions. Thus, GIK infusion appears to increase net 201Tl clearance from myocardial zones with and without initial 201Tl loading.