This medtech developer is throwing everything at clots

Retriever Medical is developing a thrombectomy system with a four-front approach for treating blood clots.

The Las Vegas-based startup calls its technology VORS AMD, for vascular occlusion removal system with aspiration, mechanical and drug delivery. The approach combines nitinol baskets for mechanical thrombectomy with aspiration, clot-busting drugs and blood filtration for reinfusion.

“This is a seminal approach — a seminal design,” Retriever Medical co-founder, President and CEO Ben Bobo said in an interview. “… There’s nobody quite doing it the way we’re doing it. And I think this design will prove itself to probably be the most effective on the market.”

Retriever Medical’s devices in development include the ClotHound ACE Blue and Gold mechanical thrombectomy catheters for deep vein thrombosis (ACE Blue) and pulmonary embolism (ACE Gold).

These catheters each have two spherical baskets for physically grabbing, breaking up and removing clots — and they could someday elute clot-busters and other drugs.

Retriever Medical is also developing aspiration catheters to work with the ClotHounds. The DogTail catheter is a 16-French aspiration catheter for use with ClotHound ACE Blue, while the large-bore DogLeg (24-French) and DogCurve (20-French) aspiration catheters are designed to work with ClotHound ACE Gold.

On top of that, Retriever Medical designed the BloodHound BOSS (blood saver system) to collect, filter and reinfuse blood removed from a patient during aspiration.

Designing Retriever Medical’s system

The ClotHound Ace Blue and Gold catheters each have two independent, adjustable nitinol spheres with fixed-diameter controllers, allowing a physician to move one of the spheres back and forth for curettage to dislodge stubborn clots, with the aspiration catheter removing the remaining bits, said Retriever Medical R&D VP Hieu Le.

“In developing thrombectomy technology for over 20 years, I do believe that Retriever has a chance to work on sub-acute and chronic clot — basically scrubbing it and removing it so that we can aspirate it out with the aspiration catheter,” he said. “…  You need to remove it from the wall and break it down into small particles so that the aspiration can suck it out.”

The distal sphere blocks bits of clot from escaping, acting as an “anchoring mechanism that provides embolic protection while you work on this tenacious clot” with the proximal sphere, Bobo said.

ClotHound ACE Blue for deep vein thrombosis has a slightly larger distal sphere to accommodate the increasing size of the vein as you approach the heart, Le said, while the ClotHound ACE Gold’s sphere’s are identical in size. The two catheters also differ in length, inner diameter and outer diameter, but are otherwise essentially the same.

“In my mind, I’m developing one system,” Le said.

Rather than relying on nitinol’s superelastic properties to passively self-expand the baskets when they exit the catheter, ClotHound lets a physician control the expansion to force its way through particularly thick, impacted clots. Those braided nitinol spheres can be expanded in 0.1 mm increments to fit blood vessels of various diameters and maintain their shape.

The spheres have a rounded wire design rather than a flat wire to minimize trauma to the endothelial lining of the blood vessel.

“The other thing it does is distribute the load as you start to expand it,” Bobo said. “Let’s say you have an 8 mm vessel. The sphere will go oblong-shaped like a football so it spreads the force along the whole section of the vessel as we curettage it. What we found is it really has minimal to no impact on the vessel wall, but it’s really great at engaging the clot.”

The design of the two ClotHound devices is identical for muscle memory proficiency to accelerate use by physicians, Bobo said.

“When you go to use a device and you start to drive adoption, it’s much easier if they understand the functionality is the same whether it be removing a clot from the lungs or the legs,” he said.

The aspiration catheters use laser-cut stainless steel hypotube to avoid kinking or ovalization to maximize aspiration flow. The catheters have an inner layer of polytetrafluoroethylene (PTFE) and an outer layer of a polyurethane hybrid similar to polyvinyl acetate (PVA).

Laser-cut hypotube is more expensive than braided or coil approaches, but “we thought it was worth the trade off in performance,” Bobo said.

Retriever Medical used off-the-shelf components to accelerate prototyping, and then modified them — grinding hypotube down by a few thousandths of an inch to reduce the wall thickness, for example.

“The overall goal is that we try to utilize what is out there and try to minimize invention because we want to go fast, which we are,” Le said. “We utilize what’s out there — off-the-shelf or readily available technology — and put it together into the patent recipe that we have to make it unique.”

Pairing the clot-catching ClotHound baskets with aspiration allows a physician to leave the mechanical thrombectomy catheter inside the patient between passes, with the aspiration catheter clearing the clot that the ClotHound caught.

That gravity-fed BloodHound system passes clot blood through an initial ThromboGuard filter with 2 mm inlet holes, then through a 250-micron ThromboScreen filter and a 40-micron MicroGuard filter and into a reservoir for reinfusion back into the patient.

“If you want me to use your catheter you need to give me a blood reinfusion device, because if I’m pulling out blood, I want to give it back,” Bobo recalls one physician telling him about the system, leading to the BloodHound project.

Retriever Medical wants to use injection ports on the spheres to break up clots with anticoagulant ethylenediaminetetraacetic acid (EDTA).

Adding clot-busting drugs to the system “takes it to a whole other level,” Bobo said.

Retriever Medical also wants to incorporate a drug-eluting coating on the spheres for polyglycerol sebacate (PGS), anti-inflammatory agents, stem cells, modulators, lytics or other drugs.

What’s next for Retriever Medical

Retriever Medical is on track for a design freeze and the start of verification and validation in 2024 and to submit for FDA 510(k) clearance in 2026, Bobo and Le said.

That doesn’t include the drug elution approach due to the different regulatory path for drug-device combinations, but Retriever is keeping that vision during product development.

“That’s going to be really where the future is,” Bobo said. “People are just thinking in terms of mechanical, aspiration — pharmacological will be an important addition to the procedure.”

Read more from this interview at MassDevice: Retriever Medical launches Series A funding round to advance thrombectomy system