Tissue edema and loss of tracer microspheres in infarcted myocardium

Microsphere loss from the ischemic myocardium was studied in a canine model after 2 and 7 days coronary occlusion. 10 million tracer microspheres (TM) of 7-10 micrograms diameter were injected into the left atrium before and 15 minutes after left anterior descending coronary artery (LAD) occlusion. To determine the tissue water content, dried tissue weight was measured after desiccation. TM content in the nonoccluded left circumflex coronary artery (LCX) area was unchanged before and after coronary occlusion. In the infarcted area, microsphere loss was maximum at the low flow endocardial region averaging 27% and 42% in 2 and 7 days occlusion, respectively. An inverse linear correlation between TM loss and regional blood flow in 2 (r = -0.82, p less than 0.05) and 7 (r = -0.96, p less than 0.01) days coronary occlusion was noted. Water content was increased in the ischemic endocardium by 4.1 and 5.7% in 2 and 7 days occlusion, thus approximately 17% of TM loss was attributed to tissue edema. These results suggest that there is an ischemia-dependent reduction of TM in the ischemic myocardium and that microsphere migration participates in the major part of TM loss. Thus flow measurements by TM may be invalid when this compound is injected during the active phase of microsphere migration or during water content alterations.