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Myocardial technetium-99m-teboroxime uptake during adenosine-induced hyperemia in dogs with either a critical or mild coronary stenosis: comparison to thallium-201 and regional blood flow.

UNLABELLED
Experimental studies have shown 99mTc-teboroxime to have a higher first-pass myocardial extraction, exceeding that of 201Tl with nearly linear initial myocardial uptake over a wide range of coronary flows. The goal of this study was to quantitatively compare teboroxime with 201Tl for the assessment of a regional coronary flow imbalance when administered during adenosine vasodilation in dogs with either critical or mild LAD stenoses.


METHODS
Twenty-four anesthetized dogs with either critical (n = 10) or mild (n = 14) LAD stenoses were given an i.v. infusion of adenosine (300 micrograms/kg/min). When LCx flow was maximal, 201Tl, teboroxime and microspheres were simultaneously injected and the dogs were killed either 2 or 4 min later. Regional 201Tl, teboroxime activities and myocardial blood flow were determined by gamma well counting and ex vivo imaging of 99mTc-teboroxime activity in myocardial heart slices was performed.


RESULTS
In both the critical and mild stenosis groups, the LAD/LCx zone ratios in dogs killed 2 min after tracer injection for both 201Tl (0.31 +/- 0.07, 0.63 +/- 0.05) and teboroxime (0.38 +/- 0.09, 0.72 +/- 0.04) significantly underestimated the microsphere flow ratio (0.18 +/- 0.05, 0.43 +/- 0.05) (p < or = 0.01), but the degree of underestimation was greater for teboroxime compared with Tl (p < or = 0.05).


CONCLUSION
In dogs with either critical or mild LAD stenoses, as early as 2 min after tracer injection, the 201Tl activity ratio more accurately assessed the adenosine-induced regional flow heterogeneity than did teboroxime. These results highlight the importance of an ultra-fast imaging protocol when using teboroxime with pharmacologic stress.