Defects on SPECT "perfusion" images can occur due to abnormal segmental contraction.

Abstract

Technetium-99m-sestamibi images reflect tracer distribution at the time of injection. This "stay put" indicator allowed us to separate the effects of segmental left ventricular dysfunction per se versus myocardial blood flow on SPECT "perfusion" images in ten dogs. An electromagnetic flow probe and hydraulic occluder were placed on the LAD coronary artery. Sonomicrometry was used to measure segmental wall shortening. At peak myocardial blood flow induced by adenosine, 35-45 mCi 99mTc-sestamibi were injected without occlusion. At 1 hr postinjection, during normal contraction, 40-50 msec end-diastolic and end-systolic SPECT images (#1) were acquired to reflect normal myocardial blood flow distribution. Later, during total LAD occlusion, and without reinjection of isotope, another gated scan (#2) was acquired. Coincident with abnormal contraction, large severe systolic defects [(28 +/- 5)% more severe compared to the baseline-scan #1; p < 0.01], and milder diastolic defects [(12 +/- 8)% more severe compared to the baseline-scan #1; p < 0.01] were observed during scan #2. Thus, abnormal contraction alone produced defects on SPECT images. Accordingly, defects in myocardial perfusion images must be interpreted as representing the integrated result of the combination of blood flow and segmental contraction heterogeneity.