Myocardial contrast enhancement after intravenous injection of sonicated albumin microbubbles. a transesophageal echocardiography dipyridamole study

Myocardial opacification after intravenous injection of an echo-contrast agent is a major end point in contrast echocardiography, but it has not yet been obtained in human beings. We propose transesophageal contrast echocardiography as a clinical tool for the study of myocardial perfusion in human beings. Sonicated albumin microbubbles are bright ultrasound reflectors that cross the pulmonary vasculature after intravenous injection and show physiologic transit times through tissues. Transesophageal echocardiography uses ideal transducer frequency and acoustic window for in vivo detection of sonicated albumin microbubbles. We have studied 11 patients receiving peripheral vein bolus injection of sonicated albumin microbubbles during transesophageal echocardiography at baseline and during dipyridamole infusion. Images were recorded on videotape and digitized off-line. Quantitative measurements were made on 11 normally perfused myocardial segments by tracing a region of interest of greater than 100 pixels on frozen end-systolic frames, at baseline, and during dipyridamole infusion. Transpulmonary passage with full left ventricular cavity opacification was obtained in all injections. In 8 of 22 injections there was also transient left ventricular cavity attenuation. In all patients there was a marked opacification of the left ventricular outflow tract and aortic root. At baseline, mean signal intensity in the myocardium increased from 80 +/- 37 to 117 +/- 49 IU (p < 0.05) and during dipyridamole infusion increased from 84 +/- 28 to 146 +/- 36 IU (p < 0.001). The analysis of background-subtracted data showed that mean pixel intensity increased from baseline to dipyridamole contrast injection (from 37 +/- 15 to 62 +/- 19 IU; p < 0.01). The opacification of normally perfused left ventricular myocardium is feasible during transesophageal echocardiography because there is a significant increase in signal intensity versus background intensity. During dipyridamole infusion there is a further increase in signal intensity that probably reflects pharmacologically induced increase in myocardial blood flow.