MYOCARDIAL TECHNETIUM-99M-TEBOROXIME UPTAKE DURING ADENOSINE-INDUCED HYPEREMIA IN DOGS WITH EITHER A CRITICAL OR MILD CORONARY STENOSIS - COMPARISON TO TL-201 AND REGIONAL BLOOD-FLOW

Experimental studies have shown Tc-99m-teboroxime to have a higher first-pass myocardial extraction, exceeding that of Tl-201 with nearly linear initial myocardial uptake over a wide range of coronary flows. The goal of this study was to quantitatively compare teboroxime with Tl-201 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 mu g/kg/min). When LCx flow was maximal, Tl-201, teboroxime and microspheres were simultaneously injected and the dogs were killed either 2 or 4 min later. Regional Tl-201, teboroxime activities and myocardial blood flow were determined by gamma well counting and ex vivo imaging of Tc-99m-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 Tl-201 (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 less than or equal to 0.01), but the degree of underestimation was greater for teboroxime compared with TI (p less than or equal to 0.05). Conclusion: In dogs with either critical or mild LAD stenoses, as early as 2 min after tracer injection, the Tl-201 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.