Evaluation of Myocardial Blood Perfusion in Man with Radioactive Potassium or Rubidium and Precordial Counting

The myocardial clearance of potassium may be obtained by precordial counting after a single intravenous injection of K 42 Cl or Rb 86 Cl. The theoretical foundations of the method and the technic developed have been presented and discussed. The distribution of the values obtained in normal subjects and in subjects with coronary insufficiency is in agreement with the clinical expectancy, and changes of the observed MCK after nitroglycerin agree with the results obtained by other investigators who measured coronary blood flow by the indirect Fick method. In agreement with the observations of other investigators in rats and dogs, the amount of K 42 or Rb 86 in the myocardium was found to change very little for an appreciable time interval after the first circulation, despite the significant recirculation and the decreasing arterial concentration. This observation and the fact that MCK values in normal subjects closely agree with the accepted values for coronary blood flow confirm Sapirstein's findings in rats and dogs, and support the view that the organ uptake of Rb 86 or K 42 immediately after single intravenous injection reflects the fractional organ blood flow. As obtained with the present technic, and similarly with the indirect Fick method, MCK reflects the flow per gram of myocardium and not the total coronary blood flow. MCK, however, has the advantage that every unit volume of myocardium, no matter how well it is perfused or through which vessels it is drained, contributes to the precordial counting rate in variable proportions determined by the efficiency of the counting method.