LABORATORY INVESTIGATION NUCLEAR CARDIOLOGY Effect of glucose-insulin-potassium infusion on thallium myocardial clearance

Factors influencing the rate of 201T1 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 201TI clearance rates from myocardium with and without initial 201T1 loading. Anesthetized open-chest dogs underwent 5 min of left anterior descending coronary artery occlusion and intravenous 201TI was injected and the occlusion released 5 min later. Thirty minutes after 201TI injection, 30 ml of either GIK (nine dogs) or saline (five dogs) was infused intravenously. The clearance rates of 201T1 from the anterior wall (without initial 201TI loading) and from the posterior wall (with initial 201T1 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 201TI from both myocardial regions with and without initial loading. The most marked change induced by GIK infusion was in the myocardial region without initial 201T1 loading; a net increase in 201TI activity (72 + 42 cpm/30 min) was converted into a net loss (594 + 228 cpm/30 min). There was no significant change in 201T1 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 201T1 clearance from myocardial zones with and without initial 201T1 loading. Circulation 68, No. 1, 203-209, 1983. ALTHOUGH previous studies have defined the relationship of initial 201TI distribution in the myocardium to regional myocardial blood flow,' relatively little information is available regarding the factors influencing the rate of 201TI loss in normal and ischemic myocardium. Results of recent studies24 suggest that the rate of 207T1 loss from the myocardium can be used as a criterion for the detection of myocardial ischemia. Approximately 20% of 201TI should be lost by the myocardium over a minimum 4 hr period in normal individuals.2 Some patients have an unusually rapid loss of 201Tl from the myocardium, with a decrease of over 60% in 201Tl activity in normal myocardium in the time between the recording of initial and delayed images (recorded 4 hr later). Preliminary investigations have suggested that rapid loss of 207T1 is associated From the Cardiac Unit and Nuclear Medicine Division, Departments of Medicine and Radiology, Massachusetts General Hospital, Boston. Supported in part by NIH grants HL07416, HL21751, and HL26215. Address for correspondence: H. William Strauss, Nuclear Medicine, Massachusetts General Hospital, Boston, MA 02114. Received Sept. 8, 1982; revision accepted March 24, 1983. Drs. Okada and Pohost are Established Investigators of the American Heart Association. Vol. 68, No. 1, July 1983 with the ingestion of a high-carbohydrate meal between initial and delayed imaging sessions. Since many investigators believe the kinetics of 207T1 in the myocardium are similar to those of potassium,5 6 we investigated the possibility that the myocardial 207T1 clearance time is influenced in part by insulin. Results of previous studies by Weich et al.7 suggested that the initial extraction of 201TI by the myocardium was not influenced by insulin. However, that study did not determine whether the myocardial release rate of 201Tl was influenced by the hormone. Accordingly, our purpose was to define the impact of an intravenous infusion of glucose-insulin-potassium (GIK), with and without initial 201TI loading, on the clearance of 201TI from myocardium in dogs. Methods Fourteen adult mongrel dogs (mean weight 22 kg, range 18 to 27) were anesthetized with chloralose (140 mg/kg) and urethane (1400 mg/kg iv), intubated, and ventilated with a Harvard respirator apparatus with 5 cm of positive end-expiratory pressure. The heart was exposed by a left thoracotomy and was suspended in a pericardial cradle. Supplemental oxygen was used to maintain an arterial Po2 greater than 70 mm Hg. Miniature cadmium 203 by gest on July 5, 2017 http://ciajournals.org/ D ow nladed from