MRI-compatible pacemaker takes first step to clinical use

Fiber optics provide crucial link

Biophan Technologies is carving out a niche in the MRI market. The key ingredient of Biophan's technology is fiber optics, augumented by minilasers that together replace the metal wires commonly found in medical electronics.

The Rochester, NY, company has been burrowing in with MRI-compatible technologies that might be used in a variety of devices, including cardiac pacemakers, pumps, intraluminal MRI coils, and even cardiac defibrillators. As of late March, the company had filed applications for 38 patents containing more than 1000 claims and covering a dozen would-be products. The patents address issues of catheter design, electrode materials, and hermetic sealing of components.

"We started out just wanting to solve the problem of pacemaker contraindication (for MR exams)," said Michael Weiner, Biophan CEO. "That led us to explore implantable cardiodefibrillators. We then turned our attention to implantable insulin pumps."

None has yet made the jump to commercial sales, but some promising signs are emerging. The most prominent involves the company's flagship technology, the MRI-compatible pacemaker.

A working prototype of the fiber-optic lead designed for use in the pacemaker held up well in laboratory tests. The lead withstood 20 minutes of MRI-related in vitro heating in an independent test conducted by Frank G. Shellock, Ph.D., an adjunct clinical professor of radiology at the University of Southern California and founder of the Institute for Magnetic Resonance Safety, Education, and Research.

The technology was tested for its resistance to effects created by the magnetic field and radio-frequency heating, which present the biggest problems for implanted pacemakers. Shellock used a deflection angle test in association with a 1.5T MR system to evaluate magnetic field interaction. He then pounded the lead with high-power RF while it was immersed in saline. The lead passed on both counts, exhibiting a deflection angle within the range prescribed by the American Society for Testing and Materials and heating about equivalent to what occurred in the surrounding saline.

Whether the integrated pacemaker can perform properly under the adverse conditions created during an MR exam, however, has yet to be demonstrated. Future tests of the fiber-optic lead, embedded in a pacemaker, will examine the ability of the device to interpret the R wave despite RF interference. Another question still to be answered is whether the pacemaker will shut down as a consequence of interference from the strong magnetic field.

Human tests aimed at addressing these and other questions could begin within a year, Weiner said. They would likely be done with the fiber-optic lead attached to a wearable temporary external pacemaker. Initially an MRI-compatible device might be widely used as a safety net, rather than as an implantable device.

"Our goal is to assure to pacing-dependent patients that their hearts will be safely paced, even if their implantable pacemaker fails," Weiner said. "We are working with cardiologists and radiologists on developing the protocol for use of the temporary device during an MRI procedure."

Wilson Greatbatch, who created the first successful implantable pacemaker with a lithium battery, developed much of the MRI-compatible technology now patented by Biophan. The effort to patent the various technologies involved in the MRI-compatible pacemaker and other such devices, however, has come from Stuart MacDonald and Jeffrey Helfer, two former Johnson & Johnson executives recruited to head up Biophan's further development of Greatbatch's technology.

How far fiber optics can go may be a matter of voltage. These leads can deliver enough of a jolt to pace the heart but not necessarily enough to shock it back to a normal rhythm, as is done by implantable defibrillators. Greatbatch reportedly has a solution in mind, but that solution has yet to be tested.