Abstract
This study was designed to assess the sensitivity of the monocationic 99mTc-hexakis-2-methoxy, 2-methylpropylisonitrile (99mTc-sestamibi) as compared to 201T1 in the detection of regional myocardial blood flow deficits in dogs with different degrees of stenosis with or without dipyridamole. Regional myocardial distribution of 99mTc-sestamibi and 201Tl was determined in mongrel dogs under different levels of left arterial descending coronary artery (LAD) stenosis (30-45, 60-70 and 100% flow reduction) as monitored with electromagnetic flow probes and radiolabeled microspheres. Both 99mTc-sestamibi and 201Tl distribute in direct proportion to blood flow at all levels of stenosis (r2 = 0.90-0.99). Quantitatively, both tracers underestimate the resting flow stenosis. The regional myocardial distribution for both 99mTc and 201Tl was also determined in subcritically stenosed mongrel dogs. This was produced by placing a balloon cuff around the LAD, infusing dipyridamole to peak hyperemic flow and immediately stenosing the LAD to basal flow. Stenosed to normal zone flow ratios were 0.68 +/- 0.01 compared to 99mTc and 201Tl ratios of 0.73 +/- 0.04 and 0.80 +/- 0.05, respectively. These data suggest that 99mTc is at least as sensitive as 201Tl in the detection of different degrees of critical and subcritical coronary artery stenosis.
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