Comparison of reinjection thallium 201 and resting technetium 99m sestamibi tomographic images for the quantification of infarct size after acute myocardial infarction.

BACKGROUND

Both thallium 201 and technetium 99m sestamibi have been used to quantitate infarct size at rest. Exercise 201Tl scintigraphy has been shown to have powerful prognostic information after myocardial infarction. A single study using these agents that could provide data on infarct size and prognosis would be of value. The purpose of this study was to compare estimates of infarct size by use of 201Tl and 99mTc sestamibi and to correlate these measurements with left ventricular ejection fraction in patients after acute myocardial infarction.

METHODS AND RESULTS

The study group consisted of 20 patients who underwent low-level 201Tl stress studies with reinjection and 99mTc sestamibi resting studies within 4 days. Acute reperfusion was attempted in 18 of 20 patients. For 99mTc sestamibi tomographic imaging, infarct size was quantitated with 60% of maximal counts per slice for five short-axis slices as described in multiple previous studies. The postreinjection delayed 201Tl images acquired 4 hours after stress were quantitated according to the same threshold method. 201Tl patient images were also quantitated with a commercially available polar map program and compared with sex-matched control subjects. Ejection fraction was determined for each patient by radionuclide ventriculography 6 weeks later. Ejection fraction was well preserved for the group: mean 0.53 +/- 0.10. Infarct size with 99mTc sestamibi was 12% +/- 13% of the left ventricle, which was significantly smaller than either method with 201Tl: threshold method, 29% +/- 18% of left ventricle; polar map method, 25% +/- 17% of left ventricle (both 201Tl estimates, p < 0.0001 vs 99mTc sestamibi; 201Tl, 70% threshold vs 201Tl polar map, p = 0.04). There was a significant correlation between infarct size with 99mTc sestamibi and that with 201Tl (r = 0.72 to 0.73; p < 0.001). Infarct size with 99mTc sestamibi, however, provided the closest correlation with ejection fraction (r = 0.81; p < 0.001), with the two 201Tl quantitative methods providing very similar correlations (r = 0.69; p < 0.001).

CONCLUSIONS

Infarct size with reinjection 201Tl imaging correlates significantly with resting infarct size with 99mTc sestamibi, although it provides significantly larger estimates. Although both approaches can be combined with a same-day exercise protocol, the closer correlation of infarct size with ejection fraction at 6 weeks suggests that resting infarct size with 99mTc sestamibi may be slightly more accurate.