Focused Ultrasound Technology Improves Myocardial Remodeling after Heart Attack

Tiny gas bubbles are forced to oscillate within the heart using focused ultrasound, which improves microcirculation and decreases the size of the scar tissue. Following myocardial infarction, the findings revealed that the lab mice have improved cardiac output using this technology, as compared to untreated animals.

The study’s findings were published online February 25, 2013, in the journal PLOS ONE. In Germany, about 280,000 people suffer a myocardial infarction per year; more than 52,000 die as a result. Due to an occluded vessel, parts of the heart muscle no longer have sufficient circulation and the tissue dies off. These areas are not replaced by new heart muscle cells but instead by scar tissue—this typically causes the pump function of the heart to decrease after a heart attack. Scientists from the Bonn University Hospital the Bonn University Hospital Bonn University Hospital (Germany) have tested the technology on mice with which scar tissue can be reduced and cardiac output increased.

“There are attempts to treat the scar tissue with gene therapy or stem cells—by contrast, we have chosen a physical approach to treatment,” reported adjunct professor Dr. med. Alexander Ghanem, from the department of cardiology of the Bonn University Hospital Bonn University Hospital. The researchers injected a total of 17 mice that had earlier had a myocardial infarction with microscopically small, gas-filled bubbles in the bloodstream. Once the microbubbles reached the heart, they were made to vibrate there using focused ultrasound. “Through this mechanical stimulation, the circulation of the area of the infarction is improved—and the scar shrinks,” Dr. Ghanem noted.

The scientists compared the findings of the mice treated with the microbubbles to those of a control group. Two weeks after the myocardial infarction, there was predicted worsening of heart function in the control group due to the maturing of the scar tissue. In contrast, the mice treated with the microbubbles did not develop any cardiac insufficiency. Jonas Dörner, the first author of the study, summarized the results, “The pumping function was significantly better in the treated animals as compared to the control group; there was also a significantly smaller amount of decayed heart muscle tissue.”

The scientists searched for the causes of these promising results, which, however, up to now, are unclear. Following ultrasound treatment of the mice, it was shown that the amount of the body’s own growth hormones significantly increased in the heart. “This is evidently the reason why the scar formation decreased as a result of the oscillating microbubbles,” said Dr. Ghanem. The scientists now hope that humans will also be able to ultimately be treated with the microbubble-ultrasound technique; however, additional study is still needed. “Potentially, all patients who have had an acute myocardial infarction are eligible for this follow-up treatment.” explained Dr. Ghanem. Microbubbles are already used as a contrast imaging agent.

The study, conducted with support from the BONFOR funding program of the Medical Faculty of Bonn University and the German Heart Foundation [Deutsche Herzstiftung e.V.], gave rise to a patent application. “Together with the company Philips Medical [Best, The Netherlands], we developed a novel ultrasonic probe which enables a standardized impulse discharge in the heart,” Dr. Ghanem stated.

The two ultrasound sources linked together are contained in one hybrid ultrasonic probe: one with low frequency for the focused stimulation of the microbubbles in the target organ and one with higher frequency for imaging. In this manner, it can be very precisely determined where the scar tissue and the microbubbles are located. “This study demonstrates again that university research inspires technological developments in medicine,” stated Dr. Ghanem.

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Bonn University Hospital
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