SPONTANEOUS REDISTRIBUTION AFTER REPERFUSION - A UNIQUE PROPERTY OF AIP-201, AN ULTRASOUND CONTRAST AGENT

Objectives. We sought to determine the mechanism of spontaneous redist ribution of AIP 201 microbubbles after reperfusion from a single left heart injection performed during coronary occlusion. Background. AIP 2 01, an ultrasound contrast agent consisting of 10-mu m sized microbubb les, has demonstrated spontaneous myocardial redistribution in prelimi nary studies. Methods. Myocardial video intensity (VI) and radiolabele d microsphere-derived myocardial blood flow (MBF) were measured serial ly after reperfusion in seven dogs undergoing an AIP 201 injection dur ing coronary occlusion. The behavior of these bubbles was also assesse d in the fat spinotrapezius muscle using intravital microscopy (IM), b oth with and without ultrasound. The effect of ultrasound on these bub bles was also determined in vitro. Results. A spontaneous and gradual increase in myocardial VI was noted after reperfusion, which was relat ed to the magnitude of increase in MBF to that region (r = 0.82, p < 0 .001), On IM, most of the microbubbles were seen entrapped in small ar terioles. Some larger arterioles had aggregates of microbubbles that p eriodically became dislodged and moved downstream. This behavior was n ot affected in vivo by ultrasound. In vitro, however, microbubble aggr egation was noted only during ultrasound exposure. Conclusions. The ma gnitude of redistribution of AIP 201 microbubbles to the reperfused my ocardium is related to changes in MBF and occurs from their dislodgeme nt from microbubble aggregates entrapped in large arterioles. In vitro microbubble aggregation seen during ultrasound exposure was not repro duced in vivo. These results may have important implications for study ing the effects of interventions in acute coronary syndromes and after coronary artery bypass graft surgery. (J Am Coll Cardiol 1998;32:1765 -72) (C) 1998 by the American College of Cardiology.