New Surgical Device Aims to Stop Strokes
The prototype stroke-busting SHELTER device goes after a mock blood clot -- a Gummi Bear.
CREDIT: Insera Therapeutics
A new surgical instrument aims to trap and entirely remove blood clots that can otherwise cause strokes.
The device's makers hope they have invented the next-generation surgical tool of choice for battling strokes that, although similar to heart attacks, have lagged behind for decades in effective clinical treatments.
Human trials must be done before the device goes to market, which could be years from now.
The instrument carries a hefty acronym: SHELTER (Stroke Help using an Endo-Luminal Transcatheter Embolus Retrieval device). "The acronym is a terrific metaphor for what we’re trying to do here," said Vikram Janardhan, an engineer as well as CEO of Calif.-based Insera Therapeutics. "The device shelters the brain from any debris during the process of clot removal."
"This is the first clot entrapment device wherein the clot is completely entrapped and pulled out . . . and as a consequence we are able to salvage a lot of the brain," Janardhan added.
Current surgical devices do not seal off the far end of a clot, and pieces can break off that cause secondary strokes in smaller blood vessels upstream, said Vallabh Janardhan, an interventional neurologist with Insera Therapeutics and Vikram's brother.
SHELTER goes on the end of a catheter that is threaded into a patient's brain vasculature toward a blood clot. Once there, an ultrathin wire bores through the semi-solid clot and unfurls an umbrella-like filter on the other side.
Tiny holes in this net allow small blood particles to pass through but snare the clot and any fragments. The device essentially bookends the clot, allowing it to be removed and freeing up blood flow in the stricken vessel.
A heart attack in the head
During a stroke, like a heart attack , blood is choked off by a clot in the labyrinth of the brain's blood vessels. (Strokes are sometimes referred to as "brain attacks.")
Victims can experience sudden dizziness, headache, or numbness or paralysis on one side of their body, as well as trouble speaking, seeing and walking.
Time is of the essence in strokes: brain cells deprived of blood-borne oxygen and nutrients start to die off within minutes. According to the World Health Organization, 15 million people suffer strokes worldwide every year, with a third suffering some level of permanent disability and another third dying. In the U.S., though there are more than 780,000 stroke incidents annually, treatment options remain rather limited.
Victims undergoing a stroke who can make it to a hospital in less than three hours are usually given infusions of a drug called a tissue plasminogen activator (tPA) that – rather like Drano for clogged plumbing – breaks up a clot and restores normal blood flow in the brain.
Studies have shown that this therapy, in use since 1996, only works in about a third of patients, Vallabh Janardhan said, and tPA can unleash bleeding elsewhere in the body so some doctors are appropriately "gun shy" about dispensing it.
Overall, 97 percent of brain attack victims never even receive this treatment because of missing its three-hour window of stroke onset. People may not recognize stroke symptoms or be aware of one if it strikes while they are sleeping. Also, many people live too far from one of the 640 specialized stroke care centers in the nation to get there in time.
Accordingly, stroke treatment has been shifting toward so-called interventional, catheter-based therapies that can be effective up to eight hours after a stroke strikes. These treatments have successfully relieved heart attacks for decades by going in and removing clots in blocked arteries.
Currently, about five percent of stroke patients receive catheter-based therapies similar to Insera's, said Vallabh Janardhan, and while the first-generation devices have saved many lives, they have significant room for improvement.
"While these devices work well, there's no perfect mousetrap yet," said Huy Do, an endovascular neurosurgeon at the Stanford Stroke Center in Calif.
The first approved device, in use since 2004, is the Merci Retrieval System made by Concentric Medical. A thin wire that is coiled like a spring pierces the clot and wends through it as a corkscrew would through the cork on a wine bottle.
Vallabh Janardhan, who has used this device in clinical practice, said the wire sometimes does not have the tensile strength necessary to really grip the clot, and the wire straightens out while trying to retrieve the blockage.
"It is a frustrating procedure at 2 a.m. when someone is lying there paralyzed [by a stroke] and the wire just slices through [the clot] and you pull the device back empty-handed," Vallabh Janardhan told TechNewsDaily.
The other catheter-based therapy, made by Penumbra and around since 2008, sucks up a clot like a vacuum. The device's tube becomes very thin to allow it to fit into smaller brain blood vessels, and a result it cannot apply sufficient suction, so the instrument can only reliably get clots in big vessels, said Vallabh Janardhan.
And both devices can leave patients vulnerable to secondary strokes by not capping the far-end of the clot. SHELTER, on the other hand, traps the clot on either end for easy removal without fragmentation, the Janardhans said.
Gumming up the works
While developing SHELTER on an innovative tangle of silicone tubes modeled on blood vessels from human cadavers, Insera actually ended up using Gummi Bears to mimic clots.
The popular candy turned out to be surprisingly good analogs for blood clots, the Janardhans said, that could be sliced into various shapes to represent the sticky, squishy blockages.
To make a facsimile of human vasculature, liquid plastic was injected into the brain of a deceased medical donor. The plastic stiffened in the vessels and created a mold of their tortuous windings. (The technology is similar to that used in "Body Worlds" and "Bodies . . . The Exhibition.")
So SHELTER could be tested in normal as well as damaged vessels, the researchers mimicked disease states, such as aneurysms and blockages, in their silicone model made from these cadaver molds.
Future silicone assemblies based on the one used for testing SHELTER will be more accurate and humane than relying on laboratory animals for medical device development and physician training, the Janardhans said.
Some years off
The brothers plan to submit SHELTER to the Food and Drug Administration in the coming months, after which human trials are expected to begin. Their device is still several years from potentially being available in clinical practice. Fortunately for stroke victims, several other new stroke-busting devices are in the works, such as ev3 Inc's Solitaire brain stent and clot remover.
Stanford's Do said "we interventional neurosurgeons are very excited for new devices and technology," and that devices like Insera's seem poised to revolutionize the stroke treatment field as catheter-based therapies and awareness did for heart attacks in the 1980s.
"From an engineering point of view, [a stroke] is a clog in a pipe," said Vallabh Janardhan. "This is something we should have solved a long time ago."