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

The finding fo false fixed 201Tl defects by the conventional stress-redistribution protocol is a well-known phenomenon. The aim of this study was to compare two different 201Tl reinjection protocols to identify viable myocardium in the same group of patients.

Twenty-seven patients with ischemic heart disease and at least one persistent defect on 201Tl uptake redistribution images 3 hours after stress were investigated. In the same-day protocol (R1) patients were reinjected with 1 mCi 201Tl immediately after redistribution images, with imaging starting 15 minutes later; in the different-day protocol the patients were reinjected with 2 mCi 48 to 96 hours later. Two sets of images were obtained, 30 (R2) and 180 (R3) minutes after reinjection. The comparison of redistribution and reinjection versus stress images showed a significant (p < 0.01) frequency distribution. The uptake of 201Tl of the 111 irreversible segments at redistribution was enhanced in 35.1% with R1, 43.2% with R2, and 49.5% with R3. The agreement among the three procedures in classifying the segmental defects was high between R2 and R3 (r = 0.81) and lower between the same- and different-day protocols. Of the 19 patients with a dominant scar pattern demonstrated by the conventional stress-redistribution study, 37%, 47%, and 53% were judged mainly ischemic after R1, R2, and R3, respectively. All but three of the 55 segments-showing an increased 201Tl uptake by R3 had an echocardiographic score of 2 or greater.

The best technique to differentiate scarred from viable myocardium seems to be the reinjection of a second dose of 201Tl on a different day followed by imaging 3 hours later.