Professor Paul Breedveld is head of Bio-Inspired Technology at TU Delft. Together with Professor Ton van der Steen of Erasmus MC, he is developing an all-in-one instrument that allows cardiologists to reach, inspect and treat clogged coronary arteries in a single procedure. This is important because, says Breedveld, “the available treatment methods often cause complications.”
Atherosclerosis is a condition in which cholesterol, calcium and connective tissue form plaques inside the arteries. As the deposit grows, the artery slowly clogs up and the blood flow becomes restricted. If this occurs in the blood vessels that supply the heart with oxygen-rich blood (the coronary arteries), the heart does not receive enough oxygen. These patients often suffer from chest pain. A severe form of atherosclerosis is the chronic total occlusion (CTO), where a coronary artery is completely obstructed for a period of more than three months. These patients have survived a myocardial infarction, but are seriously hampered in their physical condition.
Balloons and stents
CTOs are often treated with angioplasty. During this procedure, a cardiologist inflates a balloon within the coronary artery to open the vessel and restore blood flow. A stent may then be placed to support the artery. Van der Steen explains: “The cardiologist first inserts a catheter in a blood vessel in the wrist or groin. This flexible plastic tube is gently manoeuvred through the vessel towards the heart. Next, an extremely thin guidewire is inserted into the catheter. The cardiologist directs the guidewire to the coronary artery with the aid of contrast dyes and X-ray imaging, and then pushes the wire through the blockage. If this is successful, a hollow catheter with a deflated balloon and a stent on top is inserted over the guidewire and transported to the site of the blockage. The cardiologist then inflates the balloon and the stent is implanted.”
“Unfortunately, it’s often difficult for the guidewire to get past the blockage, which may consist of very hard material. As a result, the procedure is only successful in 55-80% of cases, compared to 90% in non-occluded arteries,” says Breedveld. The cardiologist can use an additional catheter to support the guidewire, but this may cause complications, such as vessel dissection and false lumen creation. What’s more, this procedure may take hours, leading to high irradiation and toxic contrast dye exposure of the patient. “This is less than optimal. So we have set out to improve the treatment of CTOs together with Ton van der Steen’s group and Philips,” says Breedveld.
The team is developing an all-in-one support catheter that will allow cardiologists to reach, inspect and treat CTOs with one single instrument. “Ton’s group is developing an ultrasound transducer that does not only look sideways, but also in front,” says Breedveld. “This will allow the cardiologist to identify areas of the CTO that can be crossed more easily. The research team at Philips is designing an optical fibre that will allow for 3D visualisation of the catheter position without the use of X-ray. My own research group is addressing the fine mechanical functionalities of the instrument, such as a steerable catheter tip and a miniature hammer that can force a way through the blockage. In the end, we will incorporate all these elements into one catheter, so everything should be as small as possible.”
Aimée Sakes is a PhD student in Breedveld’s lab. She has developed a prototype of the miniature hammer. “It’s been quite a challenge to make the instrument small yet strong enough to be able to puncture through the CTO,” says Sakes, “but I think we succeeded. The hammer prototype is only two millimetres thick and is covered by a shaft. It can be loaded and fired by the cardiologist using a small handle. We’re currently working on a second prototype with a long flexible shaft.”
The researchers have evaluated the hammer prototype in an artificial model consisting of calcium and gelatine. “It’s been extremely difficult to find a good model system to test our miniature hammer,” she says. “Ideally, we would use CTOs that have been surgically removed from patients. However, CTOs immediately start disintegrating once outside the body. And there are no adequate animal models either.” So the team has generated an artificial system with calcium and gelatine. “We’ve adapted the concentrations of these components to mimic CTOs. The first results are very promising. We feel that with some minor tweaking and some redesigning of the shaft portion, the prototype has real potential of improving the success rate of the angioplasty procedure for CTO in the future.”
Jovana Janjic is a PhD student in Van der Steen’s lab. Her task is to develop a forward-looking intravascular ultrasound transducer and to test the final integrated device. “A forward-looking ultrasound transducer is of great importance during CTO intervention,” she says, “since images ahead of the catheter tip will enable us to localise the best entry point into CTOs, facilitating the crossing with the guidewire. The major challenge is to integrate all the components in a small catheter suitable for intravascular application. The knowledge of Philips and the Delft group are key components in the realisation of this novel imaging device. This project is an example of good collaboration between groups with different fields of expertise.”
Medical Delta makes it easier for medical and technical research groups to meet and find opportunities to collaborate. That is wonderful.
Prof. Paul Breedveld
This project is part of series of studies that aim to develop instruments for minimally invasive interventions, the ‘interactive Multi-Interventional Tools programme (iMIT) ’, funded by the Dutch Technology Foundation STW. “The iMIT studies are intertwined,” says Breedveld, “and Erasmus MC and TU Delft collaborate in many of them. Ton and I have had a fruitful collaboration for a long time already. Medical Delta makes it easier for medical and technical research groups such as ours to meet and collaborate. That is wonderful.”
Interview by: Linda van den Berg