Thanks to advances in cardiology and in magnetic technology, it’s now possible to use magnetic fields to guide tools used to treat certain heart rhythm problems. A team at Washington University School of Medicine in St. Louis has published the first prospective trial of a magnetic guidance system for mapping and treating heart rhythm abnormalities in the Journal of the American College of Cardiology.
“I think the most exciting thing about this procedure is that, in theory, it could be applied to many areas of medicine, enabling us to get anywhere in the body to take biopsies or deliver treatments,” says principal investigator Mitchell N. Faddis, M.D., Ph.D., assistant professor of medicine, who treats heart patients at Barnes-Jewish Hospital.
Currently, invasive surgery to treat heart rhythm abnormalities is not usually necessary thanks to minimally invasive treatment options using a catheter. Catheters are long, narrow tubes that are inserted from the groin to the heart via blood vessels using X-ray images for guidance.
But there are important limitations to this approach. In particular, physicians manually rotate, push and pull one end of the catheter outside the body. Not only are these manual adjustments somewhat crude, they also are inefficient. Twists initiated outside the body yield much smaller movements at the wire’s tip several feet away.
For more than six years, Faddis and his colleagues have been testing and improving the Magnetic Navigation System (MNS) developed by Stereotaxis Inc. Instead of a standard design, MNS catheters contain a magnetic tip. In the same way the needle on a compass aligns itself with the direction of the Earth’s magnetic field, the catheter’s magnetic tip aligns itself with a magnetic field surrounding the patient.
“The development of electromagnets have made it possible to use very powerful magnets that don’t have to be physically manipulated to get the field to change,” Faddis explains. “Instead, we can guide the catheter by adjusting the amount of current sent to different coils in the magnets.”
Using this system, a heart rhythm expert draws commands for each desired direction or movement on a specially designed pen-tablet or by using a three-dimensional computer software interface, with the commands overlaid onto the patient’s constantly updated X-rays.
The new Washington University study confirms preliminary evidence that the device is safe and effective for mapping electrical abnormalities. The team successfully reached 200 out of 202 target points on the right side of the heart and 13 out of 13 on the left side. Moreover, the magnetically guided catheters produced recordings of the heart’s electrical activity comparable to those produced by traditional, manually guided catheters.
Another significant benefit of this approach is that physicians can control the catheter remotely, limiting their exposure to X-rays and the need to wear uncomfortably heavy lead smocks.
Based in part on these findings, the Food and Drug Administration (FDA) already has cleared this device for mapping electrical activity in the right side of the heart.
The study also presents the first evidence in humans that the device is safe and effective in treating simple heart rhythm conditions.
Traditionally, catheters are used to apply radiofrequency energy to heat — and thereby destroy — areas of diseased heart tissue. This ablation procedure diverts abnormal electrical activity, thereby treating simple heart rhythm abnormalities. In seven out of seven patients tested in this study, the magnetic guidance system succeeded in navigating a catheter within heart, mapping the origin of an irregular heart rhythm and ablating that area of tissue.
According to Faddis, the most exciting aspect of this finding for cardiology is that it brings the field closer to an easier, minimally invasive treatment of atrial fibrillation, the most common type of irregular heart rhythm. In addition to often causing severe symptoms, atrial fibrillation accounts for roughly 15 percent of all strokes in the United States.
A surgical cure for this condition called the Cox-Maze procedure was developed by James L. Cox, M.D., and coworkers at Washington University School of Medicine in St. Louis and Barnes-Jewish Hospital. However, the procedure is difficult to perform and requires patients to be on the heart-lung machine for several hours, decreasing the percentage of patients who qualify for surgery.
A minimally invasive, catheter-based treatment for atrial fibrillation has been developed, but it is not as effective as the Cox-Maze procedure and takes longer to perform. According to Faddis, magnetically guided catheter ablation may address both of these issues.
“This line of research brings us significantly closer to being able to achieve the same results as the Cox-Maze procedure with a much less invasive technique,” he says. “By making the procedure easier to perform, it also levels the playing field and enables more people to do procedures that otherwise require years of specialized training and experience.”
As the team continues to test the use of magnetically guided catheters to treat simple heart rhythm abnormalities, they also are testing the device on patients with atrial fibrillation.
In addition, the team is working with Stereotaxis Inc. to combine magnetically guided catheters with three-dimensional imaging techniques.
“Right now we have a Ferrari with Volkswagon wheels,” Faddis explains. “We really need that three-dimensional imaging component to realize the full benefit of this procedure.”
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Faddis MN, Chen J, Osborn J, Talcott M, Cain ME, Lindsay BD. Magnetic guidance system for cardiac electrophysiology. Journal of the American College of Cardiology, vol. 42(11), pp. 1952-8, Dec. 3, 2003
Funding from Stereotaxis, Inc. supported this research.
The full-time and volunteer faculty of Washington University School of Medicine are the physicians and surgeons of Barnes-Jewish and St. Louis Children’s hospitals. The School of Medicine is one of the leading medical research, teaching and patient-care institutions in the nation. Through its affiliations with Barnes-Jewish and St. Louis Children’s hospitals, the School of Medicine is linked to BJC HealthCare.