Tracking Down Unhealthy Heart Rhythms: Introducing the Elastrode
By Adrienne Mueller, PhD
September 14, 2020
Atrial fibrillation is a heart condition that affects more than 2.2 million individuals in the U.S. It is caused by the heart's two upper chambers beating out of sync with its two lower chambers. Atrial fibrillation is usually treated by surgically removing the small piece of tissue that is sending the signals causing the heart to beat irregularly. How do clinicians identify which piece of your heart to remove? They feed a small sensor into the heart chambers and use it to detect which specific region is the source of the disorganized signals. Unfortunately, these surgeries have variable outcomes. One reason why surgeries may not be as successful as they could be is that our sensor technology does not give us enough information to fully identify the piece of heart tissue to target.
Current sensor technology is limited in at least two ways. First, conventional sensors have limited spatial resolution—they can only coarsely describe which part of the heart is damaged. Better spatial resolution would help ensure both that all damaged tissue can be removed and that no healthy tissue is targeted. Second, conventional sensors cannot access all regions of the heart. Being able to collect signals from more parts of the heart would provide more information to help ensure all of the correct tissue is targeted for removal. How do you make a sensor that can address these issues? By creating one with more, and smaller, sensing contacts capable of obtaining more accurate readings of heart tissue activity. Ideally this sensor would be able to resolve the activity of even individual cells. The challenge with creating any heart sensor is that the heart is incredibly hard to take readings from—every heartbeat is a dynamic event that can move the tissue away from the sensor's contacts.
A group of Stanford Cardiovascular Institute-affiliated investigators, led by first co-first authors Jia Liu, PhD; Xinyuan Zhang, and Yuxin Liu, as well as co-senior authors Anson Lee, MD, and Zhenan Bao, PhD, have recently developed a new sensor that promises to overcome these technical challenges. How did they do it? They made it intrinsically stretchable so that the sensor could move with the heart. Their newly-developed elastic electrode, or "elastrode," is a wafer-thin array of sensors that can map large tissue surfaces. The elastrode is built so it can adhere to the heart and stretch with its movements. The investigators' recent paper in PNAS describes not only how they developed this new sensor but also how well it works. They tested their technology both in rabbits and in a pig model of atrial fibrillation. Pigs are fantastic models to study human heart disease, because their hearts are similar in size and beat in a similar rhythm to our own. In comparing the performance of the new elastrode to conventional sensors, Liu, Zhang, and Liu, et al, determined that the elastrode was superior in several ways. First, the elastrode is able to capture signals at over 100 times higher spatial resolution. Second, the elastrode can access more regions of the heart, including those normally inaccessible with conventional sensors. And, third, the elastrode has a higher signal to noise ratio, meaning the signals it collects are more accurate.
Additionally, in designing the elastrode, the investigators closely mimicked the properties of organic tissue. Deploying technology that more closely resembles biology lowers the likelihood of foreign-body responses. This more tissue-compatible technology might therefore even be suitable for chronic implantation, allowing data to be collected over a longer period of time.
Creating this innovative sensor and preclinically testing it in a large animal model highlights a unique and extremely successful multidisciplinary collaboration between several Stanford departments: Cardiothoracic Surgery, Chemical Engineering, Cardiology, SLAC, and Biongineering. This new, high-resolution sensor promises to significantly improve current treatment of atrial fibrillation. Further, the elastrode will help scientists access more and clearer data about how disorganized heart signals are generated, which in turn will lead to an improved understanding of the mechanisms underlying heart rhythm disorders and the development of new and better therapies to treat them.
Other Stanford Cardiovascular Institute-affiliated scientists who contributed to this work include Miguel Rodrigo, Patrick D. Loftus, Joy Aparicio-Valenzuela, Jukuan Zheng, Terrence Pong, Kevin J. Cyr, Meghedi Babakhanian, Jasmine Hasi, Jinxing Li, Yuanwen Jiang, Christopher J. Kenney and Paul J. Wang.