Myocardial kinetics of thallium and potassium in man.

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Abstract
Myocardial and blood kinetics of 201Tl and 42K were studied in 5 patients with normal coronary angiography. A mixture of 400 .mu.Ci of 201Tl, 400 .mu.Ci of 42K, 50 .mu.Ci of 125I radioiodinated human serum albumin as intravascular indicator, and 400 .mu.Ci of H3O (THO) as extravascular indicator was injected as a bolus into the pulmonary artery, and blood time-concentration curves were obtained from the aortic root and coronary sinus. These curves were numerically deconvoluted to obtain the frequency function of transit times (FFTT) of the 4 isotopes through the coronary system. Initial maximal myocardial extraction of the 2 tracers were similar. The net maximal myocardial uptake of 201Tl per 100 g of tissue ranged from 1.0-2.7% of the injected dose and was positively related to myocardial blood flow (MBF) calculated from THO and to the ratio MBF/cardiac output (CO), while net uptake of 42K ranged from 1.4-2.4%, but was not correlated with MBF nor with MBF/CO. The analysis of the FFTT indicates that 42K, but not 201Tl, is washed out from the myocardium more rapidly when MBF and the heart rate are higher. Tl appears to be a much more suitable agent than K isotopes for myocardial perfusion studies.