The interpretation of thallium-201 cardiac scintigrams. Studies in experimental ischemic heart disease in dogs.

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Abstract
Anesthetized and thoracotamized dogs (21) were studied. Scintigrams of the heart were recorded using a continuous infusion of 81mKr into the aortic sinuses and i.v. injections of 201Tl. A gamma camera linked to a digital computer was used to record the myocardial distribution of these tracers. The distribution of 201Tl was similar to that of 81mKr when myocardial blood flow was normal (7 dogs). In 14 dogs, the left anterior descending coronary artery (LAD) was narrowed to produce a regional decrease in myocardial blood flow. Blood flow changes were measured with an electromagnetic flowprobe. When the epicardial ECG was normal in 7 dogs, the 201Tl scintigram showed no regional decreases in activity when the tracer was delivered after LAD narrowing. A decrease in the activity of 81mKr was observed in the region supplied by the LAD. When the decrease in blood flow was associated with ECG signs of ischemia in 7 dogs, both 81mKr and 201Tl scintigrams showed decreased activity in the ischemic area. The cardiac distribution of 201Tl was determined in 5 dogs while myocardial blood flow and metabolism were normal. LAD narrowing then produced 24 h of severe myocardial ischemia. The distribution of creatine kinase activity in the left ventricle (U/mg DNA) was similar to the distribution of 201Tl (counts/mg DNA), r = 0.83; P = < 0.001. 201Tl scintigraphy of the heart can demonstrate decreases in regional myocardial perfusion only when metabolism is disturbed.