Background: The purposes of this study were to determine (1) whether perfusion defects and differential teboroxime clearance observed on serial postdipyridamole planar gamma camera images have utility in differentiating severity of coronary stenosis in canine myocardium and (2) whether single-zone (99mTc activity in one zone over time) or dual-zone (99mTc activity ratio in two zones over time) quantitative analysis provides the most useful characterization of teboroxime clearance kinetics.
Methods and results: Accordingly, eight dogs received a mild coronary stenosis (microsphere-determined, post-dipyridamole flow > or = 0.4 ml/min/gm) and 10 dogs received a severe coronary stenosis (flow < or = 0.3 ml/min/gm). In three control dogs there was no coronary stenosis. Teboroxime (5 mCi) was injected after dipyridamole (0.8 mg/kg/min), and gamma camera imaging was begun immediately and continued for 60 minutes. Quantitative analysis of single-zone clearance curves indicated that teboroxime retention for both zones of stenosis (mild = 66.3% +/- 2.8%, SEM; severe = 69.5% +/- 3.7%) was significantly greater than control zone retention (54.5% +/- 3.0%; p < 0.05) at 10 minutes. Retention in mild (37.2% +/- 1.9%, SEM) and severe (42.3% +/- 1.5%) zones of stenosis was significantly different from each other at 60 minutes (p < 0.05). There was a significant direct, linear correlation of flow with teboroxime clearance at 20 minutes (r = +0.74, normal and ischemic zones). Quantitative analysis with dual-zone count ratios (stenosed/normal) demonstrated significant differences among control (0.93 +/- 0.04, SEM), mild stenoses (0.54 +/- 0.04), and severe stenoses (0.39 +/- 0.03) as early as 2 minutes after administration of 99mTc-labeled teboroxime. The correlation coefficient for flow ratio versus dual-zone counts/pixel ratio at 20 minutes was r = +0.74.
Conclusion: Thus in this canine stenosis model with dipyridamole, gamma camera imaging could distinguish mild from severe coronary stenoses by either single- or dual-zone analysis.