Don Ho may have sung the praise of “tiny bubbles in the wine,” but to cardiovascular ultrasound expert Robert J. Siegel, MD, microbubbles are a bigger inspiration—and a potentially lifesaving ally in fighting heart disease.
Ultrasound imaging is a powerful diagnostic tool that uses sound waves to obtain pictures of internal structures, including the heart and blood vessels. Very small bubbles can be used as contrast agents, making certain tissues and organs easier to visualize. Microbubbles, as they are known, are smaller than red blood cells, which allow them to flow easily through the circulation as well as the microcirculation. They contain a gas surrounded by a shell made of a biocompatible material such as a lipid or biodegradable polymer. Microbubbles can be injected intravenously, where they float freely through the bloodstream and can be visualized during ultrasound imaging.
What’s In a Name?
A lot, according to these medical acronyms:
computer-assisted pericardial surgery
scanning acoustic microscope
naturally occurring radioactive material
penicillin aluminum monostearate
transthoracic intracardiac monitoring
Dr. Siegel—director of the Cardiac Noninvasive Laboratory at Cedars-Sinai’s Heart Institute and the Rexford S. Kennamer, MD, Chair in Cardiac Ultrasound—has spent the past three decades using ultrasound imaging to assess the heart’s structure and function. A pioneer in the development of therapeutic applications of ultrasound energy, Dr. Siegel and his co-workers were the first to demonstrate through animal tests that a combination of low-frequency ultrasound and drugs led to improved efficacy and success rates when treating blood clots. They also found in animal models that ultrasound and microbubbles could be used to dissolve blood clots in the heart.
Based on his innovative studies, Dr. Siegel was recruited to be part of a multicenter national team focusing on the treatment of acute myocardial infarction (heart attack). The goal of their National Institutes of Health-sponsored study is to develop the optimal ultrasound transducer to help dissolve blood clots in conjunction with microbubbles. This novel approach avoids the use of clot-dissolving agents, which not only show limited efficacy but also carry the risk of excessive bleeding. If successful, this noninvasive approach could lead to a treatment that does not require invasive cardiac catheterization and could be administered to heart attack victims in the ER or even in an ambulance.