DEFECTS ON SPECT PERFUSION IMAGES CAN OCCUR DUE TO ABNORMAL SEGMENTALCONTRACTION

Technetium-99m-sestamibi images reflect tracer distribution at the tim e of injection. This ''stay put'' indicator allowed us to separate the effects of segmental left ventricular dysfunction per se versus myoca rdial blood flow on SPECT ''perfusion'' images in ten dogs. Methods: A n electromagnetic flow probe and hydraulic occluder were placed on the LAD coronary artery. Sonomicrometry was used to measure segmental wal l shortening. At peak myocardial blood flow induced by adenosine, 35-4 5 mCi Tc-99m-sestamibi were injected without occlusion. A 1 hr postinj ection, during normal contraction, 40-50 msec end-diastolic and end-sy stolic SPECT images (#1) were acquired to reflect normal myocardial bl ood flow distribution. Later, during total LAD occlusion, and without reinjection of isotope, another gated scan (#2) was acquired. Results: Coincident with abnormal contraction, large severe systolic;defects [ (28 +/- 5)% more severe compared to the baseline-scan #1; p < 0.01], a nd milder diastolic defects [(12 +/- 8)% more severe compared to the b aseline-scan #1; p < 0.01] were observed during scan #2. Thus, abnorma l contraction alone produced defects on SPECT images. Conclusion: Acco rdingly, defects in myocardial perfusion images must be interpreted as representing the integrated result of the combination of blood flow a nd segmental contraction heterogeneity.