The influence of left ventricular volume and wall motion in myocardial images.

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Abstract
Dogs (10) were studied to determine if changes in myocardial images could result from alterations in left ventricular (LV) geometry independent of any change in tracer distribution. All dogs received 20 mCi of 99mTc-labeled albumin microspheres (10-45 .mu.) via the left atrium, after which control multigated, gated and ungated myocardial perfusion images were obtained. Next, 5 dogs were sequentially imaged during partial aortic occlusion to increase LV volume; after release of the aortic occlusion; after ligation of the coronary vasculature of the apex of the LV to produce regional dyskinesis; and after nitroprusside-induced hypotension to decrease ventricular volume. Only ligation and nitroprusside studies were done in the remaining 5 dogs. After 1.5 mCi 201Tl was given i.v. to 2 other dogs, sequential ungated control, ligation and nitroprusside images were obtained. At postmortem exam, tracer activity was equivalent at the apex and base for both microspheres and Tl. Partial aortic occlusion caused defects in the apex and anterior wall in 4 of 5 dogs. Coronary ligation caused new defects in 8 of 10 dogs given microspheres and in both dogs given Tl. With nitroprusside, microsphere and Tl defects generally decreased in size. Gated imaged showed that defects caused by ligation tended to be larger in end-systole than in end-diastole, while all partial aortic occlusion-induced defects were equal or greater in size in end-diastole compared with end-systole. Changes in LV geometry or contraction pattern may cause defects on myocardial images without any change in tracer distribution.

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