Loss of microspheres from ischemic canine cardiac tissue: an important technical limitation.

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Abstract
Radionuclide-labeled tracer microspheres are used frequently to map the time-course of coronary collateral flow development. The stability of microspheres in ischemic tissue, over time, is unknown. To test how long microspheres can remain after infarction and yield a reliable measure of myocardial flow, tracer microspheres (15 .mu.m) were injected prior to left anterior descending coronary artery occlusion in 25 closed-chest, sedated dogs. The occlusion was released at 13 min in 5 dogs (control) or maintained in 6 dogs that were killed at 24 h, 6 at 48 h and 8 at 8 days. Control dogs were killed at 48 h after occlusion release. In control dogs, preocclusion central ischemic zone flow/normal zone flow (CZ/NZ) was not significantly different from unity: 0.97 .+-. 0.04 (mean .+-. SE) in the endocardium and 0.94 .+-. 0.02 in the epicardium. In dogs with sustained occlusion, preocclusion endocardial CZ/NZ was 0.66 .+-. 0.05 (P < 0.01 from control) at 24 h after occlusion. The magnitude of the apparent discrepancy in endocardial flow in the CZ was the same at 24 h, 48 h and 8 days. Preocclusion epicardial CZ/NZ was significantly lower in dogs with sustained occlusion killed at 48 h (0.66 .+-. 0.05; P < 0.05 from control) and at 8 days (0.70 .+-. 0.05; P < 0.05 from control), but not at 24 h. Significant loss of tracer microsphere radioactivity from the ischemic endocardium occurred as early as 24 h after occlusion, and from the epicardium by 48 h after occlusion. Microsphere estimates of collateral flow soon after sustained occlusion may be inaccurate when .gtoreq. 24 h elapse prior to tissue sampling.