By Khalida Sarwari
To most, it’s Silicon Valley: the region that produced silicon chip innovators and manufacturers, globally influential high-tech corporations and thousands upon thousands of startup companies.
One local surgeon, however, likes to refer to the area as “Vascular Valley,” acknowledging the prolific development of minimally invasive medical device technology. And who would know better than a man who created a new and innovative way to treat patients at risk for stroke?
For Dr. David Chang, a vascular surgeon from Cupertino whose office is in Los Gatos, innovation is a way of life. With more than 10 patents to his name over the course of 16 years of professional practice experience, Chang’s biggest achievement to date is the development of a minimally invasive technique to treat blockages in the carotid artery at risk of causing a stroke. The procedure, called “transcarotid artery revascularization,” or TCAR, has the potential to be used as an alternative to the traditional open surgical technique of carotid endarterectomy (CEA). CEA is a more invasive surgical technique requiring a larger incision and can be at a higher risk for nerve injury and typical complications from open surgery like infection and bleeding.
In TCAR, a small incision is made just above the collar bone to expose the carotid artery and then a soft, flexible sheath is placed directly into the artery. The sheath is connected to a system that reverses the flow of blood away from the brain to protect against plaque that may come loose during the procedure. Next, the blood is filtered and returned through a second sheath placed in the femoral vein in the patient’s thigh. While blood flow is reversed, the system allows balloon angioplasty and stenting to be performed to stabilize the plaque in the artery. Once that objective is completed, the blood flow resumes in its normal direction.
TCAR will come to replace another less-invasive procedure devised by a cardiologist called “transfemoral carotid stenting,” said Chang, where surgeons tried to access the carotid artery by entering the body through an artery in the groin. The transfemoral approach puts the patient at higher risk of having a stroke during the procedure as the devices had to pass through arteries in the chest which often are diseased with plaque. Studies show that procedural stroke rates for transfemoral access to treat the artery in the neck carried a stroke rate twice that of traditional surgery.
The benefits of the new procedure for people at risk for transient ischemic attacks–the technical term for mini-strokes–over the previous technique are manifold, said Chang. It’s faster, safer and less painful.
“Before TCAR, carotid artery disease was really the last arterial frontier to be without a minimally invasive solution,” he said. “We definitely have shown that TCAR is comparable to the CEA, the traditional approach (and) has the potential to be better.”
Whereas the traditional CEA procedure takes about two hours, and more often than not requires patients to stay overnight for supervision, TCAR can be performed in 30 to 45 minutes, and at least in Chang’s case, half of his patients were able to go home post-surgery. The current recommendation, Chang said, is to keep patients overnight just to be safe.
Patients who’ve had the TCAR procedure also report less discomfort, he said. In fact, local anesthetics prevent patients from feeling anything during or after the surgery. “We don’t completely put them to sleep, but they don’t feel anything afterward,” Chang said.
What’s more, patients aren’t sent home with a grim reminder of their surgery in the form of a big scar, as was the case with the CEA procedure.
Chang said he came up with the idea for the TCAR technique in 2001 while he was involved in unrelated clinical trials. At the time, he was helping a San Jose startup named VNUS pioneer a minimally invasive treatment of varicose veins and perforator veins. He was serving on VNUS’s medical advisory board. The company was later bought by the Medtronic corporation.
“We were one of the early groups to do trials on these devices that are used in the groin,” he said. “It got me thinking, is there a better way to fix the carotid that doesn’t have the disadvantages of the transfemoral and open surgical techniques?”
When he did stumble upon the idea, Chang said, it was less of an “aha!” moment and more of a, “Uh, huh? You want to do what?” moment.
His initial trial was at O’Connor Hospital and expanded later to Good Samaritan Hospital. Chang continues to practice at both hospitals today. Further trials were done in Europe and at more than 15 major medical centers, including UCLA and Massachusetts General Hospital in Boston. Chang published his findings in medical journals, catching the attention of a cardiologist and venture capitalist by the name of Tony Chou. The two went on to found Silk Road Medical in 2007, a Sunnyvale-based company that develops and manufactures less invasive medical devices for the treatment of carotid artery disease. The company was a triumph over the naysayers in the vascular surgeon community who questioned his methods, said Chang.
“Our company was able to do what these giant medical companies could not do, because the results were good,” he said, while noting, “It required some perseverance because not everyone had the vision.”
The TCAR procedure has caught on at other hospitals across the country. Chang said he anticipates it will eventually replace carotid endarterectomy.
“To conquer this means we can save lives and we can save people from potentially a lifetime of disability,” he said.
Recently, Medicare expanded its coverage of the TCAR procedure to people who haven’t had a stroke but are found to have significant plaque. Medicare will pay for the procedure for symptomatic as well as asymptomatic patients at risk for traditional CEA, said Chang.
Chang considers TCAR a personal “major milestone,” but acknowledges that public recognition “comes significantly later once a procedure is established as a new gold standard.”
“I guess I’ll be featured in textbooks one day,” he said.
Still, the medical pioneer likes to think of himself as a product of his environment, one that is “a major medical device hub of innovation,” he said.
“Most new techniques to treat blood vessels are developed here,” Chang said. “It’s the most successful region for developing new blood vessel devices.”
To learn more about the TCAR method, visit silkroadmed.com.