Getting to the ‘heart’ of the matter
Student uses series of complex equations to pinpoint the exact location of a heart attack
A. Sue Weisler
Five years ago, as an undergraduate optical engineering student in Zhejiang, China, Jingjia Xu tragically lost a young friend due to a heart attack. Today, this is all too common, as 30 percent of all deaths worldwide are the result of cardiovascular disease, according to the World Health Organization.
“As I sat with some college friends from varying degree programs, we thought that there must be something we could do to prevent heart disease like this,” Xu says. “For a physician there are many ways to help, but as a computer scientist and engineer what could I do?”
Today, Xu, a second-year computing and information sciences Ph.D. student at RIT, is using a combination of mathematics, computational methods and 3-D computer simulations to find ways to help. Together with Pengcheng Shi, director of the Ph.D. program, and Linwei Wang, her adviser in the Ph.D. program, Xu is finding accurate ways to pinpoint and map electrical propagations in the heart, along with exact locations of excitation stimuli.
The heart functions because electrical currents that couple with mechanical forces cause the cardiac muscles to move. The mechanical functions of the heart are widely understood and can be mapped using techniques such as MRIs that visualize internal structures of the body. Electrical currents, however, can only be mapped one-dimensionally using an electrocardiogram, which shows electrical activity of the heart over a finite period of time. Physicians know ECGs have limitations in creating full representations of the heart and are in need of a better tool.
“We are working to create electrophysiological models that show exactly how electrical waves propagate throughout heart muscles triggering contractions,” says Wang. “It’s similar to how waves radiate through a pond when you throw a stone in the water.”
Current medical techniques can only show waves on the surface of the heart, but Wang’s research strives to show how waves propagate deep beneath the surface. Seeing how waves propagate is crucial to finding dead tissue or incorrect stimulus points that can cause circulation of electrical waves. Circulating waves will make the heart quiver and can cause irregular heartbeats and sudden death.
“Linwei asked me where I wanted to begin my work on the electrical functions of the heart,” says Xu. “I suggested, why not start at the very start, with electrical stimulus?”
By using ECG data along with expert opinions and best practices, physicians can estimate where an individual’s electrical stimulus starts, but they cannot easily pinpoint the exact location. CARTO mapping, an expensive and invasive procedure that involves using a catheter to actually touch inside the heart, does detect voltage changes on the heart surface but cannot provide accurate stimulation locations.
“It’s important to know the exact location because it affects everything throughout the propagation,” says Shi. “For example, a car ride from RIT to Wegmans can take a significantly different amount of time, depending on where at RIT you start.”
To find the exact point of stimulus, Xu uses a seemingly simple formula——that turns out not to be so simple. The formula uses ECG and MRI data, Maxwell’s equation—the foundation of classical electrodynamics—and error to find the exact locations.
The problem is mathematical—ECG data is based off of only 120 electrodes on the body surface, while the exact starting point could be any of more than 1,000 tiny points within the heart. Xu created methods she calls the neighborhood-smoothness estimation and sparse-based iteration re-weight. It’s with these formulas and calculations that Xu is able to solve this ill-posed, or seemingly immeasurable, problem.
“To complete these calculations I create all of the code and programs, which result in bulky sets of numbers,” says Xu.
The numbers are used to create 3-D computer simulations that display exact starting points along with the activation time as electricity propagates throughout the heart. She has completed multiple stages of computer-based experiments and clinical testing using a porcine heart that confirm her work.
“Jingjia’s methods are groundbreaking because they produce some of the most consistent results with each test,” says Shi.
Moving forward, Xu plans to reduce errors in her methods, working to include individual freeze-frames of ECG data in order to capture a more accurate propagation path. Students and faculty working with the heart projects envision their maps as cyber-enabled tools, used to assist physicians in practicing personalized noninvasive medicine. As they begin clinical work with University of Rochester Medical Center cardiologists, Xu looks forward to seeing her tools help save lives.
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