Specialist clinic brings IVC filter innovation into focus

William T Kuo is an interventional radiologist based at Stanford University (Stanford, USA), where he holds a professorship. He spoke to Interventional News about his prize-winning work in the field of advanced inferior vena cava (IVC) filter retrieval— he earned the Cardiovascular and Interventional Radiological Society of Europe’s (CIRSE) Award for Excellence and Innovation in Interventional Radiology (IR) in 2022—and also took the opportunity during the interview to leave aspiring physicianinnovators with some words of wisdom.

What inspired your specialisation in advanced IVC filter retrieval and your invention of excimer laserassisted removal in particular?

I became intrigued by vena cava filters during medical school, and soon began studying everything I could about them including their creative invention, beautiful geometry, crucial function, and evolution. To me, they represented the intersection of art, science, biomedical engineering, and medicine. During my IR training, I enjoyed deploying, and especially removing, these devices which seemed straightforward at first, but I soon realised the retrieval process was not always simple.

In training, I helped develop and publish a wire-loop method to remove tilted filters, and this inventive process was something I really enjoyed. After joining my academic group, I discovered a growing number of patients suffering from problems related to indwelling filters. Although we wanted to offer more help, we soon exhausted all of our retrieval methods, and hardly anyone wanted to see these filter patients in clinic.

Traditional teaching was that filters could be left implanted as permanent devices, and I remember being advised to focus on something else, but I could not turn my back on these patients whose suffering inspired me to do better. I began to wonder if it would be possible to reverse the ‘permanent’ interactions that had formed between the organic vessel and artificial implant, perhaps on a cellular/molecular level.

The vena cava is a thin-walled vessel prone to injury, but through our early histologic analyses, we began to appreciate how a distinct layer of fibrotic tissue consistently formed along the filter attachment sites. I began searching for something that could be precise in this location, and that is when I discovered excimer laser. Rather than burning or cutting, the excimer laser adds just enough energy to disrupt the molecular bonds of surface tissue—a useful property that can remove very fine layers of organic material without impacting underlying tissues. At 308nm wavelength, I hypothesised that excimer laser had the potential to perform 50–100 micron ablation along fibrotic tissue planes surrounding an IVC filter while sparing the native vessel wall.

Interestingly, a group in Japan had attempted excimer laser application within the canine IVC, but they quickly abandoned their experiments after noting significant vessel injury. However, I believed their results were limited due to the shorter-term dwell times (insufficient fibrotic layer) in their animal model versus the histopathology results I had observed in our human data derived from long-term filter implants. This knowledge, along with a sense of urgency in dealing with a rising epidemic of filter-related complications, gave me the confidence to bypass further animal testing and proceed with excimer laser use in humans.

Our inaugural patient travelled 2,000 miles to reach our centre in Stanford; and he became the first human to undergo successful laser-assisted filter retrieval. During the trial, which spanned nearly a decade, we accepted many high-risk cases and encountered some complications, but fortunately these were treatable. We learned from our mistakes while continuously honing our techniques to improve safety; and ultimately, we discovered that a variety of embedded filters previously considered irretrievable could now be safely removed using excimer laser, regardless of dwell time. Many patients could finally be alleviated from their filter-related morbidity or spared the risk of developing such complications.

What have been the highlights of the 10+ years since you first performed this procedure?

Looking back, the requests from our early patients to find solutions that did not yet exist was inspirational, so the main highlight has been developing a patient-inspired procedure to improve the lives of many others. Establishing a first-in-man clinical trial in conjunction with a dedicated IVC Filter Clinic has also been gratifying. It has been an honour to meet and touch the lives of so many patients from around the country and around the world. Sharing this knowledge with our trainees, clinical teams, and early adopters has been rewarding; and seeing our results eventually confirmed across multiple centres was validating. Based on our collective data, the excimer laser sheath was finally cleared by the US Food and Drug Administration (FDA) as the first ever device approved for advanced filter removal.

What led you to set up the Stanford IVC Filter Clinic?

When I began my career, patients with embedded IVC filters came to us because they had no other place to go. In 2010, filter-related complications were acknowledged as an emerging health problem when the US FDA issued a Filter Safety Alert urging all physicians caring for patients with filters to consider removing the filter as soon as protection from pulmonary embolism is no longer needed. Other health agencies and societies soon followed with similar guidelines. However, despite this heightened awareness and improving follow-up, many filters still could not be removed using standard methods, especially after prolonged implantation, subjecting patients to all the risks and anxiety of living with a permanent implant. For all these reasons, I decided to launch the Stanford IVC Filter Clinic dedicated to helping these patients.

What are the challenges and rewards associated with running a clinic of international renown?

Our early challenges were mobilising sufficient clinical resources, integrating new apparatus,training our staff, and creating protocols to safely incorporate cutting-edge techniques. We had to keep up not only with a growing case volume but also increasing case complexity, and we wanted to achieve all of this in a timely fashion. Early on, there was so much learning from each case, and this required meticulous data recording to conduct research and a rigorous process of continuous improvement.

As we began to succeed, we attracted more referrals including more bizarre and unusual cases. From one patient to the next, we had to rapidly adapt by crafting protocols tailored to the patient. In spite of increasing case complexity over many years, the ultimate challenge was maintaining procedural success along with safety. Through these endeavours, we expanded our understanding and capability to help many patients who were previously considered untreatable. Over time, we successfully treated thousands of filter patients referred from all 50 US states and from over 10 countries.

You are currently recruiting for prospective studies evaluating filter removal— what else is on the cards over the next 10 or so years of your career?

We aim to keep studying advanced techniques and outcomes on an ever-growing variety of patients and filter scenarios referred to our centre. There will always be more to learn, and we hope our expanding data in conjunction with other centres will continue to establish new and improved protocols, guidelines, and best practices for advanced filter removal and related venous interventions. We hope to encourage all interventional radiologists to embrace data-driven methods for safer retrieval/management of embedded filters. Furthermore, by taking time to understand not just the disease but the patient with the disease, I hope more interventional radiologists will become inspired to determine further unmet needs that can spark original ideas and innovation.

What advice would you give to aspiring physician-inventors?

Question dogma, cultivate your interests, and open your mind to discover something you are truly passionate about regardless of what others may think. The possibilities are endless but your time is not, so developing intense focus and entering a flow state are essential. Along this journey, find a meaningful purpose and become dedicated to a cause greater