Thallium 201 for detection of viable myocardium: comparison of different reinjection protocols

Comparative accuracy of various Tl-201 reinjection imaging protocols to detect myocardial viability

The conventional exercise-3 hours-redistribution thallium-201 [201Tl] imaging protocol has been recognized to be suboptimal for reliable detection of myocardial viability. Although 201Tl rest-injection after exercise has improved detection of viable myocardium, it is still underestimated in some patients. The present study was designed to compare detection of viable myocardium in five separate imaging steps: step 1: initial-exercise imaging, step 2: delayed-exercise imaging, step 3: Tl-201 reinjection imaging after delayed-exercise imaging, step 4: separate day rest-injection imaging, and step 5: separate day delayed-rest imaging. The study group consisted of 22 patients scheduled for coronary revascularization (either percutaneous transluminal coronary angioplasty or coronary bypass surgery). Pre- and postintervention echocardiographic wall motion and thickness served as independent markers of myocardial viability.

RESULTS

Accuracy in identifying myocardial viability gradually improved incrementally from 201Tl imaging step 1 to step 5. The positive predictive value, negative predictive value and overall accuracy were best for the separate day delayed-rest study (step 5) at 90%, 33% and 78%, respectively. Myocardial segments had fixed defects on separate day delayed-rest 201Tl imaging (step 5), but nevertheless echocardiographic evidence of myocardial viability indicated less severe defects than segments judged nonviable by echocardiography (p = 0.021). The overall accuracy of separate day delayed-rest imaging (step 5) in predicting viability improved to 88% when segments with moderate or mild defects were considered viable. In conclusion, the most reliable predictor of myocardial viability with 201Tl imaging is defect severity on separate day delayed-rest images.