Thallium-201 accumulation during reperfusion of ischemic myocardium: dependence on regional blood flow rather than viability.

These experiments in dogs were designed to determine whether the use of thallium 201 (TI-201) accumulation in patients during the reperfusion phase after streptokinase lysis of an intracoronary thrombus is a function of coronary blood flow or a function of myocardial viability. The left anterior descending coronary artery was occluded for 60 minutes in open-chest dogs, and the immediate TI-201 accumulation and regional blood flow (MBF) using microspheres was measured in 2 groups: 10 minutes after reperfusion in 9 dogs (group A) and 24 hours after reperfusion in 6 dogs (group B). There was an 80% or greater reduction in MBF in the subendocardium during ischemia in both groups of dogs, and it was inferred that the subendocardium was destined to become necrotic in group A and had become necrotic in group B dogs. The ratio of TI-201 accumulation to MBF in the tissue that had been ischemic was not significantly different from the ratio in normal tissue despite MBF being in the normal range in group A (n = 7, 2 dogs excluded because of reactive hyperemia) and being markedly decreased in group B. Thus, the immediate TI-201 distribution was related to MBF, and caution is recommended in its use to assess myocardial salvage in the early reperfusion phase after streptokinase lysis of intracoronary thrombi. These data suggest that the intramyocardial accumulation of TI-201 is predominantly a passive process and independent of Na-K ATPase.