Dr. Palmaz shares with us how he came to develop one of the most revolutionary devices in modern medicine.
How did you come up with the idea of a stent? It was serendipitous. I attended the SCVIR meeting in 1978 and heard Dr. Andreas Gruentzig speak about balloon angioplasty’s limitations. After his didactic presentation, I thought to myself: why not put a scaffold in there? I discussed this idea with Dr. Stewart Reuter, who encouraged me to conduct research. I didn’t find any literature on this concept at that time, so I missed the fact that Dotter had explored the idea in 1969. I wrote a monograph on balloon-expandable stents and became more heavily involved in the subject. Once I finished my residency, I was ready to work on it seriously and came to San Antonio in 1983, where I was offered the time and facilities to develop the project.
What were some of the early competing ideas about stenting? The early Dotter stent was nonexpandable. It was a fixed-diameter tube designed to be placed in arteries using a device similar to a coaxial dilator. He placed this device in dogs and published his work in 1969, so he is recognized as the first one thinking of a stent. While I was working on my idea, two papers came out on different principles: one about thermal-memory stents, and the other about self-expanding stents. I had the original idea of the balloon-expandable stent. I presented my first paper on the subject at the 1984 RSNA meeting. At the same time, Gianturco’s group presented the Z-stent self-expanding stent idea.
How does one first attempt to create a stent? When I started experimenting, I used soft materials that could be soldered. I went to RadioShack and bought copper wire and solder material and started to play with kits and tubes in bench experimentation. At night, I would go home and tinker with rubber tubes and balloons and test jigs. My first iteration was a woven stent, and then I moved to a slotted stent, which I tested as large cardboard models.
How did you get the stent from these initial ideas to market? Several companies turned me down, but one gave me the address of a bioengineering technologist who could help me with manufacturing prototypes. He proposed several different ways of making stents using various manufacturing techniques. I made my early prototypes by hand, using biocompatible materials such as stainless-steel wire and silver solder. The first lot of stents was made using Electro Mechanical Discharge machining, or EDM. I immediately moved into animal experimentation and was able to make much smaller stents. I began working with Dr. Richard Shatz, who brought in a capital investor so we could hire technicians and devote more resources to the research. We pursued an industrial sponsor, but had trouble generating interest until we met with Johnson & Johnson. We started collaborating on the development of the product and eventually J&J took the stent through the peripheral and coronary regulatory phases.
Had your team ever thought of using a drug to prevent restenosis? No, initially we hadn’t thought of using a drug to combat restenosis. Of course, we knew that antithrombotic and anticoagulation medications were essential. We were not surprised when the restenosis rates dropped after the use of appropriate antithrombotic medication. In the mid-1990s, I never thought that we would end up using drug-eluting stents for the prevention of hyperplasia. I thought that the real limitation was going to be the relative difficulty of placement of the stent. I believed stent placement would be limited to a few skilled operators. I was amazed to see how the technology evolved. The catheter and guidewire technology progressed along with the stent, making placement safe and simple. To me, the major breakthrough was making the stent easily deliverable. Today, I am mostly interested in materials and biocompatibility. The materials we use are so imperfect, and yet, we haven’t really tried to improve them. The level of impurities and contamination in stents is high, which perhaps may relate to the present restenosis rate with bare metal stents.