Catching Artery Stent Failures Before They Happen

Inventors (left to right): Hanseup Kim, Anwar Tandar, and Amit Patel

Catching Artery Stent Failures Before They Happen

Cardiac catheterization procedure

More than half a million Americans are diagnosed with heart disease on an annual basis,[4] adding to the already 27.5 million Americans who currently live with it.[5] Each year, some of the arteries of approximately 600,000 of these individuals become so clogged with plaque (cholesterol, fat, calcium, and other substances), they have to undergo a procedure known as a percutaneous coronary intervention (PCI), or angioplasty with stent, to unblock them.[6] In this procedure, a cardiologist inserts a catheter into the patient’s affected artery. Its movements through the artery are monitored by the use of live x-rays. When the catheter reaches the location of blockage, the cardiologist inflates a tiny balloon on the catheter’s tip. This action widens the artery by compressing the buildup of plaque and restores proper blood flow. As the balloon inflates, a small wire mesh tube known as a stent expands with it. The stent locks into place and is left behind in the artery to help keep blood flowing freely.

The goal of a PCI is to prevent restenosis, or the re-blocking of the stented artery with a new buildup of plaque, as well as clotting, or stent thrombosis. Despite recent advances in stents, restenosis still occurs in up to 40 percent of cases, and often within months.[7] Because of this, patients must be routinely checked. Current methods of monitoring, however, are based entirely on clinical symptoms such as chest pains or shortness of breath.

Kim, Tandar, and Patel’s stent under a microscope

The most commonly used techniques available for restenosis monitoring are difficult on patients. “Cardiac catheterizations are too invasive to be done annually, even though this is the standard of care” explains Amit Patel, professor of surgery at the U. “And coronary CT scans of the heart involve radiation, which can damage DNA and cause cancer with repeated use, and contrast, which can damage the kidneys over time.” Another monitoring method, stress tests, requires patients to either exercise on a treadmill or receive medicine that causes their heart rate to increase. Pictures of the heart are taken before the increase in heart rate begins and when it reaches certain peak levels. This test, explains Anwar Tandar, assistant professor of internal medicine at the U, is “not 100 percent accurate and can be cumbersome.”

Patel goes on to explain that the invasiveness of these monitoring methods is only one problem with the current approach. The other, and perhaps more important issue with current methods, is that they are not proactive. “You don’t know when a stent is going to fail,” Patel explains. “There’s no way to predict re-blockage of an artery beforehand.”

A 3D rendering of a stent

Routinely faced with these problems in their patients, Patel and Tandar, who often work together, decided that a non-invasive method that catches the beginning stages of restenosis and clotting in stented arteries before symptoms develop was needed. In 2012, Tandar came up with a basic idea for a device, that with a great deal of engineering expertise applied to it, would accomplish this goal. As such, Patel and Tandar decided to contact James Thompson, director of the engineering team at TVC at the time, and asked if he knew anyone in the College of Engineering who could work with them on this project. Thompson knew exactly who to contact: Hanseup Kim, an associate professor of electrical and computer engineering at the U. When Thompson approached Kim and explained the project, Kim was intrigued and agreed to meet Patel and Tandar. In this meeting, which Thompson describes as “electric,” Patel and Tandar told Kim what they needed the device to do, what the current clinical hurdles were, and what was needed to make the device acceptable to cardiologists. Kim responded by explaining current engineering limitations but also how he thought he could make this device a reality. “Within three hours,” Kim explains, “we had come up with a plan for how to resolve the issues and meet the requirements.”

Another view of Kim, Tandar, and Patel’s stent under a microscope

After a great deal of effort and time, the novel device that Kim came up with is a stent that non-invasively measures blood pressure along its length. It will be placed in arteries exactly like current stents so that cardiologists won’t have to change the way in which they perform stenting procedures. Embedded on the stent’s wires are pressure-sensing structures on the nanoscale (a scale operating at less than the width of a human hair). To read changes in pressure, an external device containing an electric current is activated and placed near the patient. As the current passes through this device, which the inventors call a “wand,” a magnetic field is produced. This field induces electrical resonance in the stent within the patient’s affected artery. The wand measures changes in resonance frequency. Different resonant frequencies are associated with different levels of pressure buildup within the stent. Slower electrically-resonating stents are associated with higher pressure within the stent, indicating a likely buildup of plaque or a clot, while more rapidly vibrating stents are associated with less pressure, indicating more free-flowing arteries.

Typical stress test

This method of reading pressure requires no batteries or electronics, making it durable and safe for patients. It should also allow for more routine visits that are non-invasive. These frequent visits will likely allow cardiologists to catch the beginning stages of restenosis or a clot developing, possibly saving lives, but almost certainly leading to better outcomes.

The next step for the device is for it to undergo experiments in live pigs. After this, the team will begin raising funds for clinical trials.

Tandar believes that the success of both the first meeting of the group as well as their subsequent interactions comes from the team’s shared desire to solve this problem together regardless of recognition. “The more you work together, the better outcomes you will get,” he explains. “We’re far more interested in achieving better outcomes for our patients than getting credit.” Adding to this, Patel explains, “These multidisciplinary team approaches can work. The key parts are realizing what you don’t know and letting others with expertise in those areas do their part, and realizing that by yourself this can’t be done.”

James Thompson, interim director of TVC, helped connect Kim, Tandar, and Patel together
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[4] Gina Kolata, “Putting Stents to the Test,” New York Times, June 22, 2015, accessed August 5, 2016, http://www.nytimes.com/2015/06/23/health/heart-attack-stent-angiogram-chest-pain-angina.html?_r=0.

[5] “Heart Disease,” Centers for Disease Control and Prevention, accessed August 5, 2016, http://www.cdc.gov/nchs/fastats/heart-disease.htm.

[6] Scott Maier, “Patients With Heart Stents Have Similar Increased Risk of Death from Bleeding and Heart Attacks,” University of California at San Francisco, April 7, 2015, accessed August 5, 2016, https://www.ucsf.edu/news/2015/04/124976/patients-heart-stents-have-similar-increased-risk-death-bleeding-and-heart.

[7] Ehrin J. Armstrong and John R. Laird, “Treatment of Femoropopliteal In-Stent Restenosis for Patients With Diabetes: Do We Have an Answer to the DEBATE?,” Journal of Endovascular Therapy 21, no. 1 (February 2014): 9-11.