Purpose: To verify if a third series of images acquired by reinjection thallium-201, 24h after conventional myocardial perfusion with the radioisotope, improves the identification of myocardial viability segments.
Methods: We studied 30 patients, mean age 57.7 +/- 9.4 years, with old myocardial infarction using thallium (Tl)-201 SPECT (single-photon-emission computed tomography), and we obtained 3 series of images (stress, redistribution after 4h and reinjection after 24h. Cardiac images were divided in 5 segments (apical, lateral, anterior, septal and inferior) and each one received a value by a score system according to the Tl-201 myocardial uptake (0 = normal uptake; 1 = mild hypoperfusion; 2 = moderate hypoperfusion; 3 = severe hypoperfusion or no myocardial uptake). We considered viable myocardium when the uptake of Tl-201 in the segment related to the myocardial infarction increased at least 1 point in two different axis of Tl-201 SPECT.
Results: Seven (23.3%) patients demonstrated increase of Tl-201 uptake only at reinjection images, showing a higher efficacy of the method. Nine (30%) patients showed persistent hypoperfusion at all series of images suggesting only fibrosis in the area related to the infarction. Fourteen (46.7%) patients showed increase of Tl-201 concentration at redistribution images; among these patients, six showed improvement of myocardial uptake at reinjection. This condition were interpreted as regional chronic ischemic process: hibernating myocardium.
Conclusion: Tl-201 hypoperfusion at redistribution images without significant changes in relation to the stress images do not represent fibrosis at all. The reinjection technic was better than conventional redistribution in the detection of viable myocardium. This data allows a better therapeutic orientation.