[Detection of viability by percent thallium uptake with conventional thallium scintigraphy]

Thallium myocardial scintigraphy (TMS) is used for diagnosis of viability in infarcted myocardium before coronary revascularization. Underestimation of viability by TMS has been reported by many investigators. To evaluate viability precisely, thallium re-injection method or 24 hour delayed imaging is performed. However these techniques are not convenient and are difficult to perform in clinical practice. Percent Tl-uptake method was developed for predicting myocardial viability. To evaluate usefulness of this method, TMS was performed before and after PTCA in 23 patients with myocardial infarction. Left ventricle was divided into 3 layers, then each layer was divided into 4 segments (12 segments in total). Forth three segments showed recovery of perfusion on TMS after PTCA. Viability in infarcted myocardium is predicted by 1) redistribution (RD), 2) %Tl-uptake > or = 45% on the image immediately after exercise (TE), and 3) %Tl-uptake > or = 45% on delayed image (TD). Sensitivity was RD: 60%, TE: 90% and TD: 95% (p < 0.001 vs. RD). Specificity was RD: 74%, TE: 68%, and TD: 60% (NS). Predictive accuracy (PA) was RD: 69%, TE: 77%, TD: 73% (NS). Compared with RD, %Tl-uptake, either TE or TD, increased sensitivity with slightly improved PA, but decreased specificity slightly. Therefore %Tl-uptake would be a sensitive and useful predictor to find patients who are most likely to benefit from re-vascularization.