Dr. Kirk Kanter used to correct heart defects in the youngest children the way every other pediatric heart surgeon did. He’d enter the operating room, open the infant’s chest, look at the shape of the heart, and then — based on what he was seeing for the first time — make an on-the-spot judgment about the best surgical option.
Not anymore. While most surgeons still have to make last-minute decisions about rebuilding a heart that didn’t fully develop, Kanter knows what he’s going to do before he walks through the operating room door.
Kanter figures it out ahead of time by using software conceptualized by Ajit Yoganathan, Regents’ Professor in the Wallace H. Coulter Department of Biomedical Engineering. Yoganathan is a leading researcher in cardiovascular fluid mechanics, the study of how blood flows through the heart, and it’s his expertise that clues Kanter in to the best surgical choice.
Where some researchers are satisfied with making contributions to the body of scientific knowledge, Yoganathan is focused on translational research — or as he puts it, “getting things out of the lab from our research to impact healthcare and patients.” He is the department’s associate chair for translational research (a term scientists use for moving findings from the lab into clinical settings), and his dedication to developing real-world applications has made him a hero in the cardiovascular field.
Improving patient care and patients’ lives is what drives Yoganathan. In delivering a 2012 lecture to the Biomedical Engineering Society, which honored him with its Pritzker Award, he said, “I think the main goal should be not the commercialization to make money as a faculty member, but to have the satisfaction of being able to see your research translated in the clinic towards helping human health.”
Examining the tiniest hearts
The pediatric cardiac surgical planning tool that Kanter uses is one such practical application of Yoganathan’s work in fluid mechanics. Kanter uses the tool to help patients whose hearts have only one ventricle. Although such cases are rare – two children per thousand births – the prospects for babies with single ventricle malformations are grim: Their hearts can’t circulate blood through the lungs to be loaded with oxygen and on to the body. The lack of oxygen leads to rapid organ failure and even brain damage.
Today, the outlook for single ventricle patients is better. Prenatal care often reveals the defect before birth, so surgeons are prepared to take immediate action. Doctors reroute the body’s main veins directly into the lungs, bypassing the heart. The blood picks up needed oxygen, then flows from the lungs into the heart’s single ventricle, which pumps it out to the body. To achieve success, surgeons must perform two or three surgeries in the patient’s first three years of life, including the final operation that connects the veins to the lungs.
It’s in preparation for this last operation, known as Fontan surgery, that Kanter uses Yoganathan’s surgical planning tool. On his laptop, Kanter views a three-dimensional image of the patient’s heart. The image has been created using MRI tomography, a series of magnetic scans compiled to show the heart’s exact shape. Interactive features of the surgical planning tool, developed by Professor Jarek Rossignac in Georgia Tech’s College of Computing, allow Kanter to turn the image and examine the heart from different angles. Then, based on his surgical experience, the doctor inputs several possible surgical corrections.
The virtual surgery software has an undeniable coolness factor, but the computation and analysis done in Yoganathan’s lab makes the real difference. It’s there that researchers evaluate each option, using complex formulas to figure out how the blood would flow to each lung after the correction.
Yoganathan never advises the surgeon on which option to choose. Instead, he sends images for each surgical scenario, showing his prediction of blood flow through the lungs and heart. Then the surgeon makes the decision based on priorities for the specific patient.
Kanter says he typically has Yoganathan evaluate four to six options. Once he’s seen the analysis, he can go into the surgery with high certainty he’s choosing the best one.
“Sometimes it's what we think would have worked,” he says, “but I'm surprised at how often the best option is not the one I expected.”
So far, the surgical planning tool, called SURGEM, is used at only a few premier children’s hospitals in the United States, including the Children’s Hospital of Philadelphia and Children’s Hospital of Atlanta at Egleston, where Kanter works as one of the leading pediatric cardiac surgeons in the nation.
“We have people from all over the country contacting us and trying to do simulations for them so we can get the best operations,” says Kanter, who was one of the first surgeons to use the tool. “This is hot stuff.”
From bench to bassinet
Since Yoganathan arrived at Georgia Tech more than 30 years ago, he’s made it his mission to use science as a means to the ultimate end for biomedicine: improving human health. He brought the translational mindset from the California Institute of Technology, where he completed his doctoral work under Professor William Cochran.
“He always said that engineering had a lot to offer towards medicine,” Yoganathan recalls of his mentor. It was Cochran who first exposed Yoganathan to the field of cardiovascular fluid mechanics. Yoganathan, whose parents were a professor of pathology and a general practitioner, was hooked.
Yoganathan uses the common phrase “bench to bedside” when talking about his work, occasionally giving it a twist. “Bench to bassinet,” he says, noting his lab’s impact on treating the heart conditions of infants.
He insists that he doesn’t set out to create new devices or change surgical methods. His goal is to understand the biomechanics of blood flow in the heart. But while he’s doing the research, he sometimes gets a flash of insight about how to improve treatments — an inspiration that can turn into a major advance.
That’s what led to the development of a surgical technique called a Y graft, which Kanter has used in two dozen Fontan surgeries. Yoganathan dreamed up the technique while he was studying single ventricle cases, analyzing post-surgical blood flows. He saw that when blood from the upper body and lower body entered the lungs, it was colliding and mixing. That effect slowed its movement, making it harder for the blood to be pumped through the lungs.
He wondered if grafting the veins in a Y-shape, instead of a straight graft, would help. Computer models gave credence to his idea. They showed the Y graft would make circulation more balanced and efficient. That would reduce the stress on the heart, which ideally would allow patients to live longer with less risk of heart failure — a common outcome that forces many single ventricle patients to undergo a heart transplant in their teens or early 20s, when their surgically repaired hearts give out.
Finding the answers
Yoganathan has seen his work translated to health care settings many times over. During decades of research on heart valves, he’s worked with every manufacturer that has a replacement valve on the American market. He’s also assisted the Food and Drug Administration in its regulation of cardiac devices.
This exploration of valves is both vast and painstaking. Much of his lab’s work is done with porcine or ovine heart valves, which closely match human physiology. Researchers modify the valves to mimic different types and stages of valve failure. Then, they use engineering tools and techniques to monitor the resulting changes in blood flow and mechanical stress. Finally, they make a surgical correction and see what effect it has.
Yoganathan explains that his research aims to see how the valve’s performance changes when its shape is changed by disease in the surrounding tissues or breakdowns of the valve itself. Then, investigators want to know how well various surgical corrections work to restore the valve’s function. Finally, they try to figure out why some surgical repairs have a limited lifespan.
“It’s really trying to understand why some of the surgical repairs eventually fail,” he says.
The research done in the lab is invaluable, because only in the lab can a scientist control all the variables. In clinical practice, the differences among patients’ overall health makes it nearly impossible to isolate the problems with a particular surgery or device. In Yoganathan’s lab, though, the conditions are consistent, so scientists can isolate the sources of breakdowns – as they did when they studied bileaflet valves, the most common type of mechanical prosthetic heart valve.
In as many as 5 percent of patients, prosthetic valves lead to life-threatening blood clots. To reduce this risk, patients are prescribed anticoagulant drugs for the remainder of their lives; however, these medications can have serious long-term side effects. Yoganathan wanted to figure out what caused the clots in the first place.
His research showed how some of the blood traveling through the artificial valve tended to stagnate around the valve hinges. Stagnant blood leads to clots. If the valve could be redesigned to get that blood flowing, it could minimize or alleviate the clots.
Device manufacturers and surgeons pay careful attention to Yoganathan’s work and adjust their practices accordingly. Likewise, Yoganathan listens to manufacturers and doctors and allows their practical needs to guide his research.
Don Giddens, Ph.D., the former dean of the College of Engineering who helped recruit Yoganathan, says Yoganathan has always taken a collaborative approach to working with clinicians, even when such approaches were rare. He believes Yoganathan always knew that working hand-in-hand with practicing doctors would lead to the greatest impact on health.
“His focus on translational research – that is, getting things to patients, and direct interaction with the clinical environment – was path-breaking,” Giddens says.
Yoganathan’s influence has also shaped teaching at Georgia Tech, Giddens notes. Yoganathan spurred the creation of the master’s and Ph.D. degrees in bioengineering, and he was a leader in the effort to establish the Coulter Department of Biomedical Engineering.
Beyond that is Yoganathan’s impact on the future of biomechanical engineering by mentoring the engineers of the future. Over the years, more than 100 graduate students and post-doctoral fellows have trained and worked in Yoganathan’s lab. One former student, research engineer Jorge Jimenez, Ph.D., says Yoganathan passes on to them his passion for improving lives through biomedical engineering.
“The scientist is a very serious person, really driven,” Jimenez says in describing Yoganathan, “but if you talk to him personally, you see that he also cares a lot” about the patients he’s helping.
Jimenez became a full-time member of Yoganathan’s research faculty in 2007 and now divides his time between working in the lab and leading Apica Cardiovascular, a commercial venture launched in 2009 based on research done in the lab. Apica is testing a device that would change heart valve replacement from an open-heart surgery to a minimally invasive procedure. The device can be inserted into the left ventricle of the heart without opening the whole chest. It can implant a replacement heart valve, then close the incision in the heart with minimal blood loss, alleviating the need to use a heart bypass machine.
That kind of radical shift in cardiovascular repair would only add to Yoganathan’s already stellar reputation. Yet as much as he has accomplished during his career, and as proud as he is of how his research has set new standards for cardiovascular care, Yoganathan’s pride in his own work is tempered by his reverence for the inherent design of the heart.
“No matter what, the human body and the heart are very well designed — from an engineering point of view,” he says. “It has built-in safety factors. Even when there are small problems, the [heart] valve works fine. It takes a lot before that valve begins to fail and create significant medical problems... It’s a marvel.”