Digital radiofrequency echocardiography in the detection of myocardial contrast following intravenous administration of Albunex(R)

Conventional contrast echo techniques have proved inadequate for the detection of myocardial perfusion using intravenously injected echo contrast agents because of the limitations and relative insensitivity of standard echocardiographic equipment. In order to avoid these problems, we have obtained pure digital radiofrequency ultrasound data from the left ventricle and myocardium during i.v. contrast myocardial perfusion echo studies. In 30 patients, following coronary arteriography, i.v. injections of the echo contrast agent Albunex (sonicated human serum albumin) in two doses of 0.08 and 0.22ml . kg−1 were administered during digital radiofrequency echocardiography sampling of data from the myocardium and left ventricular cavity. Analysis of mean integrated backscatter (MIB, a measure of the total ultrasound energy) was performed before, during and after Albunex injection. The data were also analysed for a shift in frequency spectrum which could be caused by resonance of the Albunex contrast microspheres in the heart, a phenomenon which has been previously demonstrated in vitro. Digital radiofrequency ultrasound data were successfully obtained and analysed in 23 patients. In 31 segments where reasonable resting perfusion was expected, there was a significant increase in MIB from 0.644 to 1.245, P<0.001 and time intensity curves could be constructed showing wash-in and wash-out of contrast from the myocardium. In 10 segments supplied by significantly diseased vessels, MIB intensity increased from 1.044 to 1.874, P=0.054. In myocardial segments supplied by non-diseased vessels, microsphere resonance also caused a drop in mean frequency of 140 KHz, P<0.001 and permitted similar temporal analysis of myocardial perfusion. Frequency changes preceded intensity changes in both the LV and myocardium by 2.3 beats and may represent faster pulmonary transmit of smaller contrast microspheres. In conclusion, digital radiofrequency ultrasound echocardiographic analysis provides a method of detecting myocardial perfusion following i.v. Albunex. It should provide the basis for future methods enabling study of organ tissue perfusion by ultrasound following i.v. injection of ultrasonic contrast agents.