TOTAL SERENDIPITY
Dr. Julio PalmazWhile angioplasty is a standard treatment option for clogged coronary arteries today, use of balloonmounted catheters to open narrowed or blocked blood vessels of the heart was met with widespread skepticism in 1974 when first performed in humans. Even though the primary treatment to open clogged arteries at the time was bypass surgery — a lengthy and invasive procedure that resulted in long and painful recoveries for patients — many physicians believed that angioplasty would never become a viable treatment alternative. Many viewed it as a problematic procedure that sometimes caused the blocked blood vessel to return to its original narrow size or, in some cases, actually become narrower.
However, some, including Julio Palmaz, MD, were inspired by the potential of angioplasty and sought to develop better ways of treating cardiovascular disease without invasive surgery. Dr. Palmaz was generally interested in medical engineering, electronics and physics, but it was not until he turned his attention to angioplasty that he became inspired to become a medical technology innovator.
Evaluating the limitations of balloon angioplasty, Dr. Palmaz thought he could find a way to keep the artery open while the balloon was fully expanded. His goal was to slow down or halt the rate of restenosis — the re-narrowing of the blood vessel — to improve patient outcomes. What he envisioned was a stainless tube with slots that would be mounted on a balloon catheter. When the balloon was inflated, the slotted tube around the balloon would expand and embed itself against the inner wall of the coronary artery, holding the artery open after the balloon was deflated and removed. Working on his idea, Dr. Palmaz began researching different types of materials that could be implanted in the body and continued to experiment with metal wires in his garage at home.
A COINCIDENCE? OR A STROKE OF GENIUS?
Although Dr. Palmaz made significant initial progress through the work he conducted on his own, he hit a stumbling block when trying to figure out how to create an advanced prototype, a working model of a device. The required open slotted design that would allow tissue to grow into the implant was difficult to make in the very small sizes he needed. He also determined that if the metal device was to be implanted into the body, then it would have to be all one piece, so there would not be a concern about undesirable tissue reaction to dissimilar metals.
The answer came unexpectedly one day while Dr. Palmaz was working in his garage: he found a piece of metal on the floor bearing the solution. The piece of flexible metal lath, used by masons to build walls, looked exactly like what he was trying to create. It was this serendipitous discovery that led to the creation of what he called a balloon-expandable stent, a small medical implant device that would in time help millions of patients around the world.
After this discovery, Dr. Palmaz began to realize that the sophisticated tools and equipment to make his ideas a reality were beyond his reach. Dr. Palmaz started working with physicians at The University of Texas Health Science Center in San Antonio to perform the necessary cadaver and animal testing of his device. As he was working with these physicians, he followed the path taken by many other medical technology innovators and secured venture capitalist funding to continue his research and testing.
The stents developed in the Texas hospital showed some impressive results. The investigators found during their early research that when a stent was implanted in a diseased artery, a framework of healthy tissue formed, isolating the diseased tissue from contact with the blood stream. Like traditional angioplasty, the use of stents helped increase blood flow and relieve chest pain when implanted in humans, thus increasing their quality of life. In addition, since the procedure would be performed through a small hole in the groin or sometimes the arm, the researchers gleaned the benefits of its less invasive nature compared to bypass surgery.1
Researchers knew from previous experience with angioplasty that in some cases the artery would collapse after the balloon was deflated, but with the help of the balloon-expandable stents, the blockage in the arteries was reduced and the blocked or collapsed arteries in the heart and other major organs were held open.2 Armed with this knowledge, the researchers strove to perfect the technology, performing tests to find the right combination of strength and flexibility for the stent. They determined that for the artery to remain open, the stent would need to be flexible enough to adjust to the shape of the artery once implanted, but strong enough to remain securely in place. After finding this balance, the researchers determined that when compared with traditional angioplasties, where the chance of restenosis was 40 percent, the balloon-stent they created reduced the chance of restenosis to 25 percent.3
SUCCESS AND ENHANCEMENT
After years of work, the first human balloon-expandable stent procedure was performed by Dr. Palmaz in October 1987 at the University of Freiburg in West Germany, almost a decade after he first started thinking about the device. This first stent was placed in an occluded iliac artery, a large vessel that carries blood to the lower extremity. Placement of stents in other critical arteries soon followed. Later the following year, Dr. Palmaz performed the first coronary stent placement in Sao Paolo, Brazil.
Shortly before these procedures took place, Dr. Palmaz joined forces with a leading device manufacturer to further develop his invention and produce sufficient supply to ensure widespread availability for patients. Working with the company’s engineers and other resources, Dr. Palmaz was able to refine the device by making it more flexible, which helped in the ease of insertion of the device and ensure that it could adjust to the artery shape once it was implanted. The FDA approved Palmaz’s stent in 1991 for use in peripheral blood vessels and for use in coronary arteries three years later. Approximately one million stents are implanted every year worldwide.
Dr. Palmaz has remained active in continuously enhancing his invention. After Dr. Palmaz developed the initial concept of the open mesh balloon-expandable stent, a flurry of new designs appeared. Dr. Palmaz compares his invention to the discovery of the radial tire, “once the concept of a radial tire was invented, thousands of different treads were created for it.” He has continued to work with the device manufacturer on new stent designs and provides insight into new technology opportunities. Dr. Palmaz sees cardiovascular medical technology as about to enter into an exciting new era of innovation. “The era of cardiovascular medicine that started in the early ‘80s gave us the state-of-the art designs and concepts that we use today,” said Palmaz. “The next step is to introduce new technology into these medical devices, particularly nanotechnology.”
- Heartsite.com. Coronary Stents. http://www.heartsite.com/html/stent.html (17 November 2006).
- Johnson&Johnson Web site. Dr. Julio Palmaz, Inventor of Stent Widely Used in Coronary and Peripheral Disease, Inducted Into National Inventors Hall of Fame. Posted June, 2004. Oct. 23, 2006. www.jnj.com/news/jnj_news/20060508.
- Dangas, George, Kuepper, Frank. Restenosis: Repeat Narrowing of a Coronary Stent. http://circ.ahajournals.org/cgi/content/full/105/22/2586 (17 November 2006).