INTRACORONARY AIR-FILLED ALBUMIN MICROSPHERES FOR MYOCARDIAL BLOOD-FLOW MEASUREMENT

Objectives. The aim of this study was to explore the possibility of qu antifying coronary blood Bow by myocardial contrast echocardiography w ith air-filled serum albumin microspheres (Albunex). Background. Air-f illed albumin microspheres have been proposed as an intravascular trac er for the study of myocardial perfusion by contrast echocardiography. Methods. In six anesthetized open chest dogs, the left circumflex cor onary artery was cannulated and perfused by a roller pump with blood f rom the femoral artery. Both air-filled albumin microspheres (0.4 mi, 2 x 10(8) spheres/ml) and technetium-99m-labeled albumin were injected as a bolus into the coronary cannula at baseline and after treatment with dipyridamole (0.56 mg/kg body weight intravenously for 4 min). Tw o-dimensional echographic images of the left ventricular short axis we re digitized to generate myocardial time-intensity curves; myocardial radioactivity was measured by an external detector to generate radionu clide time-activity curves. Results. After dipyridamole, left circumfl ex coronary artery blood Bow (as measured by both the pump and an elec tromagnetic Bow meter) significantly increased (from 1.06 +/- 0.28 to 3.61 +/- 1.43 ml/min per g of myocardium). Peak intensity and rise tim e of contrast echo curves were able to differentiate baseline myocardi al perfusion from coronary hyperemia but did not show any significant correlation with coronary blood Bow. A weak inverse correlation with c oronary blood Bow was provided by myocardial mean transit time of air- filled albumin microspheres (r = 0.33). Conversely, a close inverse co rrelation with coronary blood how was obtained by myocardial mean tran sit time of technetium-99m-labeled albumin (r = 0.95). Myocardial tran sit time of air-filled albumin microspheres (1.95 +/- 0.60 s) was also markedly shorter than that of labeled albumin (5.35 +/- 3.43 s, p < 0 .001) and the measurements were less reproducible. Conclusions. In thi s experimental study, coronary blood how was not adequately quantified by myocardial contrast echocardiography with intracoronary injection of air filled albumin microspheres.