Quantitative analysis of defect reversibility after immediate and standard 201Tl reinjection.

Immediate reinjection of 201Tl after exercise imaging has been proposed as a time-saving approach for the accurate distinction between ischaemic and scarred myocardium. However, with this procedure, defect reversibility may be underestimated due to the high level of residual 201Tl activity in normally perfused myocardium at the time of reinjection. The aim of this study was to determine whether the detection of defect reversibility is hampered by a shortening of the time interval between exercise and reinjection. In 53 patients, 201Tl was injected, at the point of maximal exercise. In 26 patients, 201Tl was reinjected immediately after exercise imaging (Group I); in 27 patients, 201Tl was reinjected after 3 h redistribution imaging (Group II). In all patients (424 myocardial segments), three-view planar images were analysed quantitatively. Changes in myocardial activity after 3 h redistribution and reinjection were compared with the post-exercise images. In normal segments, the relative change in 201Tl activity after reinjection was 8.8 +/- 19.9% in Group I and -19.7 +/- 19.5% in Group II (P < 0.05). In Group I, persistent defects showed a relative change of 14.3 +/- 25.1% and reversible defects a relative change of 36.3 +/- 41.6% (P < 0.05). In Group II, persistent defects showed a relative change of -15.1 +/- 18.3% and reversible defects a relative change of 2.4 +/- 25.2% (P < 0.05). Our results indicate that shortening the time interval between exercise and reinjection has no effect on the detection of ischaemia.