As a fellow in cardiology in the early 1980s, Paul Yock, MD, had developed a keen interest in a nascent field—the use of balloon catheters to treat blocked coronary arteries. It was a revolutionary moment in the treatment of heart disease; however, this new procedure, called balloon angioplasty, was not without problems. Approximately 40 percent of balloon-dilated patients experienced restenosis, a condition in which arterial blockage recurs after dilation of the artery.

Dr. Yock found this statistic troubling as it meant that these patients would need to undergo additional procedures that would be painful and time consuming. At the time there was not a good understanding of what was causing the restenosis processes. Part of the problem was poor visualization: angiography, the X-ray procedure used to guide angioplasty, showed only a limited, two-dimensional profile of the blood vessel's interior.

In 1985, during his training in coronary angioplasty under the guidance of his mentor Dr. John Simpson, a renowned interventional cardiologist, Dr. Yock found a solution to the visualization problem. “At the time, John Simpson was experimenting with the concept of directional atherectomy, a technique performed to cut plaque out of the walls of the coronary artery,” said Dr. Yock. Dr. Yock was concerned that the X-ray guidance technique they were using would not be accurate enough to show the surgeon where to cut into the artery to remove the plaque. He thought that if the cardiologists could get a detailed picture of the interior of the coronary arteries during the procedure, then he or she could better find where the plaque was located to remove it and avoid cutting the normal vessel wall.

The solution Yock proposed consisted of a tiny ultrasound transmitter on the tip of the catheter, which could provide a complete view of the inside of the blood vessel through the surrounding blood column. The imaging catheter would be attached to computerized ultrasound equipment to provide real-time, high-resolution images of a coronary segment. The technique and system came to be called Intravascular Ultrasound or IVUS for short. 1 The IVUS system is used while the patient is awake and does not cause him or her any pain.

SEEKING SOLUTIONS

To patent and distribute his device, Dr. Yock and colleagues decided to start a company. “At the time we founded our company, none of the existing companies were willing to take on this project – it was too early and too risky,” said Dr. Yock.

In 1988, Dr. Yock's fledgling company began a long and interactive process with the Food and Drug Administration (FDA), testing the prototype on animal and cadaver subjects. “The initial clinical trial was a registry in collaboration with the FDA, in which we demonstrated the safety of the device and the ability to obtain high-resolution images from inside the artery,” said Dr. Yock. Together with the FDA, the team made small alterations to the system – particularly to the size of the catheter, the ultrasound frequencies and the imaging components. The team also worked with an existing noninvasive ultrasound company in Norway to develop some of the finely turned electronics of the system.

After nearly three years of testing, Dr. Yock's device was approved by the FDA. Perhaps the most important application of the technology was in optimizing the placement of intracoronary stents – tiny metal mesh tubes that are used to prop open arteries after angioplasty. Physicians soon found that by using the IVUS system to more accurately position stents, the rate of restenosis developing in stented patients was reduced. 2

Today, the IVUS system is used to guide angioplasty, stenting and atherectomy. The IVUS system allows the physician to see the precise location and extent of plaque buildup within the arterial wall, a marked improvement over  the X-ray based system previously used. By using the IVUS system, physicians are better equipped to determine how the procedure must be performed and which tools are required. In the future, the IVUS system may help physicians prevent restenosis completely by providing them with a better understanding into plaque formation. 3

In addition to the IVUS system Dr. Yock is also responsible for many other medical technology advances. His inventions, known in the medical field as “The Yock Patents,” are a series of 44 issued patents with numerous applications pending. Among the most widely recognized are the “Smart Needle” Doppler Ultrasound System and the Rapid Exchange Catheter System™. The “Smart Needle” Doppler Ultrasound System includes a sonar transmitter that allows doctors and nurses to "hear" the veins or arteries and thus limit the number of times a patient needs to be stuck with a hypodermic needle. The Rapid Exchange balloon angioplasty system is the primary angioplasty and stenting system used worldwide.

Today, Dr. Yock has shifted his focus from inventor to mentor and teacher. Because of the important role that mentors have played in his own career, Dr. Yock believes it is of the utmost importance to guide and support young inventors of medical technology to keep the field evolving and to find future solutions to health problems. Currently serving as the co-chair of Stanford University's new Department of Bioengineering and director of the Stanford Program in Biodesign, Dr. Yock mentors young people interested in the field to support his belief and experience that “blockbuster inventions seem to come from young minds.”

Although Dr. Yock is proud of his many accomplishments, he is adamant about not losing sight of what still needs to be accomplished to continue to improve health care and patient outcomes. Dr. Yock views collaboration between doctors and medical technology companies as extremely important to the development of the next generation of medical innovations. He also emphasizes that there are two unbreakable rules for developing new medical technologies: “the first, and by far the most important, is to keep the patient in the center of any innovation. The second – keep the technology as simple as possible,” said Dr. Yock. “There are still important technology solutions out there that are simple, elegant and undiscovered.”

1. Health Cares.net. http://heart-disease.health-cares.net/intravascular-ultrasound.php . (10 October 2006).
2. de Jaegere P, Mudra H, Figulla H et al. “Intravascular ultrasound-guided optimized stent deployment. Immediate and 6 months clinical and angiographic results from the Multicenter Ultrasound Stenting in Coronaries Study.” European Heart Journal (1998) 19: 1214-23.
3. Angioplasty.com. Intravascular Ultrasound. http://www.ptca.org/devices8.html (26 September 2006).