Stress-reinjection 201TI scintigraphy without redistribution imaging

Abstract

Reinjection of thallium-201 (201Tl) improves the detection of myocardial ischaemia in approximately 50% of irreversible defects present on 3 h redistribution images. Additional reinjection studies, however, may limit the capacity of the nuclear laboratory and they are not patient-friendly Previous studies have suggested that only severe persistent defects with less than 50% of maximal 201Tl uptake are irreversibly damaged, with little chance of recovery following coronary artery bypass grafting (CABG). We examined the ability of a modified stress-reinjection protocol without redistribution imaging to predict subsequent improvement in myocardial perfusion post-CABG. Thirty-seven patients underwent quantitative planar stress/3 h reinjection 201Tl scintigraphy before and after uncomplicated CABG. After stress, segments were classified as normal (> or = 75% maximum 201Tl uptake), moderate defect (50-75%) or severe defect (< 50%). After reinjection, they were classified as completely normalizing (> or = 75%), partially improving moderate defect (increase > or = 10% but < 75%), partially improving severe defect (increase > or = 10% but < 50%), persistent moderate defect (< 10% increase) or persistent severe defect (< 50% initial uptake with < 10% increase). Scintigraphic classification was compared with left ventricular wall motion and post-operative classification. Of 336 initial stress defects, 264 (79%) were moderate defects and 72 (21%) were severe defects. After reinjection, 146 (55%) moderate defects normalized, 25 (9%) improved partially and 93 (35%) persisted. Nineteen (26%) severe defects normalized, 33 (46%) improved to become moderate defects, 7 (10%) improved only slightly and 13 (18%) persisted. Post-CABG, 201T1 uptake was normal in 123 of 146 (84%) completely normalizing moderate defects, 15 of 25 (60%) partially improving moderate defects, 53 of 93 (57%) persistent moderate defects, 11 of 19 (58%) completely normalizing severe defects and 13 of 33 (39%) partially improving moderate defects. None of the partially improving severe defects or persistent severe defects normalized. The sensitivity and specificity of detection of viability with pre-CABG stress-injection scintigraphy were 66% and 72% respectively, with pre-CABG wall motion 80% and 40% respectively, whereas in combination they resulted in a sensitivity and specificity of 94% and 70% respectively. We conclude that stress/3 h reinjection without redistribution imaging is a clinically feasible method for predicting myocardial 201T1 uptake post-CABG. The severity of defects and the pattern of change of uptake after stress-injection are related to the likelihood of normal 201T1 uptake post-CABG. Severe defects after reinjection are very unlikely to recover.