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Thallium-201 accumulation during reperfusion of ischemic myocardium: dependence on regional blood flow rather than
Insights
Thallium-201 (TI-201) uptake after coronary thrombus lysis is linked to blood flow, not just heart muscle viability. Caution is advised when using TI-201 to assess myocardial salvage in early reperfusion phases.
Area of Science:
- Cardiology
- Nuclear Medicine
- Experimental Pathology
Background:
- Assessing myocardial viability after reperfusion is crucial for treatment efficacy.
- Thallium-201 (TI-201) is used to evaluate myocardial perfusion and viability.
- Streptokinase lysis aims to restore blood flow after coronary thrombus formation.
Purpose of the Study:
- To determine if TI-201 accumulation during reperfusion reflects coronary blood flow or myocardial viability.
- To investigate the relationship between TI-201 uptake and regional myocardial blood flow (MBF) after thrombolysis.
Main Methods:
- Experiments were conducted in open-chest dogs with induced left anterior descending coronary artery occlusion.
- TI-201 accumulation and regional MBF (using microspheres) were measured at 10 minutes and 24 hours post-reperfusion.
- Subendocardial MBF reduction during ischemia was quantified to infer myocardial necrosis.
Main Results:
- Significant subendocardial MBF reduction occurred during ischemia in both groups.
- The ratio of TI-201 accumulation to MBF in ischemic tissue was similar to normal tissue.
- TI-201 distribution correlated with MBF, even when MBF was in the normal range post-reperfusion.
Conclusions:
- Immediate TI-201 distribution after streptokinase lysis is primarily dependent on regional blood flow.
- Using TI-201 to assess myocardial salvage in the early reperfusion phase requires caution.
- Intramyocardial TI-201 accumulation appears to be a passive process, independent of Na-K ATPase activity.
Abstract:
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.