Sometimes the human touch just doesn't cut it, literally. Traditional therapy for treating chronic total occlusions (CTOs) in the peripheral vasculature requires the use of stiff wires in the cath lab to manually force through the blockage. It carries a big risk of perforating the artery.
In a more exquisite approach, a 72-year-old active Texas rancher with peripheral artery disease (PAD) will be back in the saddle soon following the first use of the newly FDA-approved Stereotaxis RF PowerAssert Magnetic Guidewire to treat the man's 15-cm total occlusion behind his knee last Wednesday.
"In addition to still actively running his ranch, this man dances with regularity, but for the past two months he has been unable to dance and limited his activity on the ranch. He was walking the day after the procedure; he already went home and he's now doing wonderfully. The procedure was very successful," interventional cardiologist Frank Zidar, MD, told Medical Device Daily.
Stereotaxis (St. Louis) earned FDA clearance last August (MDD, Aug. 28, 2008) for its magnetically tipped, PowerAssert radio frequency (RF) guidewire for CTOs, but the first procedure wasn't performed until last week at the Heart Hospital of Austin (Texas).
That might be because the procedure is more about a symphony of technology, rather than just the delicate new guidewires.
"It's done in a dedicated Stereotaxis lab - it's more than a standard cath lab," Zidar said.
PAD affects up to 12 million people in the U.S. Left untreated, these patients can experience ulcerations and gangrene that significantly increase their risk of losing a limb or death.
The key word to note in the product's name – Stereotaxis RF PowerAssert Magnetic Guidewire – is "magnetic." The fact that the wires are thin is great, but the real innovation is that it's magnetically enabled, capable of intra-lesion steering.
"This new procedure may be even safer than the traditional approach. It can maintain a course because of the steerability," Zidar said. "We don't approach the vessel wall. On top of that, there's less blunt force pushing through the artery. We can literally ablate through the blockage."
The company's Niobe magnetic navigation system directs the guidewire's distal tip very precisely, allowing for accurate navigation with magnetic resonance imaging (MRI) technology guiding the navigation. A Stereotaxis lab include two permanent magnets mounted on articulating and pivoting arms that are enclosed within a stationary housing, with one magnet on either side of the patient table, inside the cath lab.
Magnetic navigation fields are generated that are less than 10% of the strength of fields typically generated by MRI equipment and require significantly less shielding.
There's also a reduction in the amount of contrast dye and imaging radiation to the patient. It's expected to reduce procedure times too, but because this was the first go-around, it actually took a bit longer.
""We took extra time to take extra pictures and study the course of the wires," Zidar said. "I don't think we saved time on this first case. But with more experience, it would allow a more efficient crossing of an occlusion. Total occlusions are typically the longest cases and require more exposure to radiation."
The procedure starts the same way as traditional percutaneous revascularization. A sheath is inserted in the leg. After some baseline images, the complete blockage is mapped out and reconstructed three-dimensionally. A course is plotted, magnetic vectors are planned and the thinner wires are brought down to the blockage.
"When you meet any resistance, you can active the tip," Zidar said. "Once the device crosses the complete blockage and into the true lumen at the end of the leg, we can switch wires out to do a traditional angioplasty with balloons or stents."
Some additional training is required as well as a familiarity with the Stereotaxis lab, but Zidar said that those who are already familiar with vascular intervention would quickly adapt to the new procedure.
The Heart Hospital of Austin was chosen as one of two clinical sites to study the efficacy of the new device.
Stereotaxis reported an agreement two years ago with Baylis Medical (Montreal) to develop a magnetically embedded RF guidewire for CTO applications. That agreement included the development of a range of magnetically enabled RF guidewires for both coronary and peripheral CTO crossing applications (MDD, Oct. 19, 2006).
The core components of the system have received regulatory clearance in the U.S., Europe, Canada, China and Australia.