Fly-by-wire intervention promises better reliability and precision

The art of intervention and the science of imaging are at opposite ends of the medical spectrum: each is indispensable, yet they exemplify entirely different approaches. They meet in the cath lab, where interventionalists finesse, coax, wangle, and prod catheters through the vascular maze, while imaging technology delivers moment-to-moment visual feedback.

"There is an awesome array of diagnostic imaging today in the cath labÑx-ray fluoroscopy and rotational angiographyÑproviding almost a surfeit of information," said Bevil J. Hogg, president and CEO of Stereotaxis, a firm pioneering the use of interventional robotics. "All this information is being poured into the brain of one overtaxed interventionalist who is still using manual dexterity to drive instruments that have to be placed precisely in complex areas to deliver new therapies."

It doesn't have to be that way. On Jan. 22, Hogg and his colleagues proved it. On that day at Barnes-Jewish Hospital in St. Louis, a computer-controlled interventional system built by Stereotaxis led a catheter through the vascular system and around the heart of a 40-year-old woman. Flat-panel x-ray fluoroscopy provided visual feedback while physicians used computer controls to exactly adjust magnetic fields that pulled the catheter through the body.

"The ultimate clinical utility of this system lies in its potential to one day address the navigational challenges associated with the treatment of atrial fibrillation and other complex arrhythmias," said Dr. Bruce D. Lindsay, director of clinical cardiac electrophysiology at Barnes-Jewish Hospital, who participated in the case.

The experimental technology, called the Magnetic Navigation System, promises greater precision than the manual guidance of invasive tools, according to Hogg. Manual guidance during cardiac interventions is typically done from outside the body and from as far as a meter away from the tip of the catheter.

"Interventionalists have become artists," he said. "Consequently, outcome is limited by training and by practice."

As therapies grow increasingly complex, results will inevitably vary depending on operator skill. But even if all interventionalists could achieve the same level of excellence, there simply are not enough to go around. The Magnetic Navigation System could solve that problem, allowing technology to handle the minutiae of interventional technique, freeing the physician to ensure quality of care.

"It would turn the physician into a manager of the procedure rather than an acrobat/artist," Hogg said.

Cardiology is a primary application, but it is not the only one. A clinical trial is under way to assess the value of this technology in neurointervention. About two years ago, the system successfully navigated a catheter through the brain of a 31-year-old man diagnosed with a tumor in the frontal lobe of the brain. The procedure has been repeated successfully four times. Stereotaxis, in collaboration with researchers from the Washington University School of Medicine, is planning to expand the use of this system to support neuroradiological interventions.

In these interventions, as in cardiac applications, magnetic fields adjust the path of the catheter to follow curves in the vasculature, increasing efficiency and speed, while reducing the risk that the catheter tip will damage the wall of the blood vessel. The fields interact with a magnetic seed about the size of a grain of rice fitted into the tip of the catheter. The computer alters the fields to change the trajectory as needed.

In cardiac applications, the distal tip of the catheter is maneuvered through the vasculature to various locations within the heart to record electrical signals in search of defects that cause irregular heart beats. This information is then used to identify defective tissue for ablation. In neurointerventional applications, the catheter may be used to biopsy a tumor or repair damaged blood vessels.

X-ray fluoroscopy in the new system is accomplished using a flat-panel detector obtained from Varian and integrated into a C-arm. Flat panels made of amorphous silicon are inherently immune to magnetic fields, Hogg noted, but other components are not. Stereotaxis worked with Varian to come up with a compatible system.

"It is amazing that companies that make MRIs and (those that) make x-ray equipment haven't considered integration issues," Hogg said.

The guidance platform being developed by Stereotaxis could be the leading edge of a shift in technology. Electrophysiologists will soon want more than just x-ray imaging, according to Hogg.

"The ultimate solution will be to use dynamic preoperative MR combined (with) or morphed into an x-ray mapping system that (will) allow intraoperative imaging," he said. "There is an awesome potential here for therapeutic devices, imaging systems, and software systems to become integrated into a seamless cath lab environment."

Hogg and colleagues at Stereotaxis are developing the navigation system as a kind of communications medium between imaging systems and therapeutic devices. It could be among the first in a wave of technologies that will computerize the cardiac catheterization suite, where more than one million procedures are performed annually in the U.S. The Magnetic Navigation System has a long way to go before reaching this point, however.

The FDA has granted the company two investigational device exemptions, one each for cardiovascular and neuroradiological studies. The system will be tested on a total of 40 to 50 patients at clinical sites associated with Washington University and the University of Oklahoma. The trials should be done by the end of 2001, and data will be submitted to the FDA soon after.