OCE reveals tissue damage caused by heart attacks

29 Jan 2018

University of Houston images biomechanical properties of heart tissue, as an aid to treatment and repair.

A heart attack, or myocardial infarction (MI), can cause considerable damage to the tissues of the heart, and a better understanding of that damage would be a valuable step towards improved treatment and therapy after the attack.

Researchers at the University of Houston have developed a technique based on optical coherence elastography (OCE) that could be used for biomechanical characterization of MI, and be a useful tool to study heart repair. The work was published in Biomedical Optics Express.

"About one million people suffer heart attacks every year, and there is currently no cure for the resulting cardiac tissue scarring," said Kirill Larin of University of Houston, co-leader of the project. "We are working to develop ways to regenerate heart tissue, and our research works to measure the mechanical properties to determine if the heart is healing in response to therapies."

OCE involves loading tissues with either external or internal stimulation, and using an optical coherence tomography-based detection method to measure the corresponding tissue response. In the Houston project, a pulse of low-pressure air acted as the external stimulation.

Tests on ex vivo mice hearts after surgically induced MI used the OCE method to assess physical tissue responses of the left ventricle, including the propagation of elastic waves in the tissues and the localized displacement damping characteristics.

"Because of the small size and delicate nature of the mouse heart, we had to make special equipment to generate very small perturbations on the tissue," said Larin. "The pressure, timing and location of this applied force had to be very precise. The waves also had to have very small amplitudes, which was important for preserving the tissue."

Therapy and recovery
At six weeks after an induced MI, researchers saw that the damaged tissue showed reduced elastic wave velocity, decreased natural frequency, and less mechanical anisotropy compared to healthy tissue, indicating that the muscle fibers in the damaged area were now more disorganized.

In the published paper, the team notes that OCE has advantages over some existing elastography approaches, such as those employing ultrasound stimulation with MRI or atomic force microscopy. OCE methods focus on a larger scale, characterizing the mechanical properties of tissue structures rather than their individual components, and can better represent how cardiac muscle functions.

The next steps for the Houston team include development of small probes able to carry out similar OCE analysis inside living mice, along with assessment of the mechanical properties of a heart valve as an insight into the ways in which valves can stop working properly.

There may also be applications in other medical fields, including ophthalmology. Larin's group is using OCE to study degenerative eye diseases, with the goal of developing better therapies for patients.

"This is the first application of OCE for high-resolution mapping of muscle mechanical properties of the heart," he said. "We were able to see differences in the mechanical properties of normal heart tissue and areas with myocardial infarction. In the future, we want to use the technique to examine regenerated heart tissue, to help us find a therapy that can benefit the millions of people worldwide who have experienced a heart attack."