New magnetic percutaneous system navigates vessels

A new magnetic navigation system shows promise for use during percutaneous coronary interventions (PCI), researchers reported at the American Heart Association’s Scientific Sessions 2004.

“The computer-controlled magnetic system is useful to steer guide wires and navigate turns in tortuous coronary arteries that would otherwise be impossible to negotiate,” said study co-author Neal S. Kleiman, M.D., director of cardiac catheterization laboratories at the Methodist DeBakey Heart Center and associate professor of medicine at Baylor College of Medicine in Houston, Texas.

The magnetic-assisted intervention is being introduced in the United States and Europe, with fewer than 15 systems installed at institutions worldwide. Developed by Stereotaxis, Inc., a St. Louis firm, the system was approved by the U.S. Food and Drug Administration in 2003.

The researchers presented a study of the first 26 patients who underwent 31 magnetic-assisted interventions (MAI) at the Methodist DeBakey Heart Center, leading to a high success rate. The three-dimensional system is installed in the center’s catherization laboratory.

The system consists of two permanent magnets that generate a magnetic field over the heart and a magnet-tipped coronary guide wire. The magnetic navigation involves interaction between the magnetic field of specified direction and magnitude, positioned externally to the patient, and a tiny magnet in the tip of the interventional device. An automatic advancement system controls the catheter advancement and retraction.

Kleiman said the magnetic system is useful in patients with difficult lesions who are undergoing a coronary intervention, such as balloon angioplasty. He said the more tortuous the vessel, the more difficult it is to place the wire manually.

“About 20 percent of patients treated with the magnetic system were poor candidates for standard angioplasty or had already failed the standard procedure,” Kleiman said. “These are the patients who can benefit from the magnetic navigation system.” However, he noted that the magnetic system is not for use in every case.

Cardiology fellow Satya Reddy Atmakuri, M.D., lead author of the study, reported that 26 male and female patients, with an average age of 64, were selected because of their potentially difficult to cross lesions during angioplasty.

Fifty-four percent of the patients had diabetes mellitus, a patient population especially vulnerable to cardiovascular disease that often has tortuous vessels.

The study found that most stenoses (48 percent) were in the circumflex coronary artery (which supplies the back wall of the heart and usually poses a challenge to the interventionalist because of its many bends and sharp angles) and its branches, 22.5 percent were in the left anterior descending artery (which supplies the front wall of the heart) and 20 percent were in the right coronary artery. Saphenous vein grafts represented 10 percent.

The target lesion was successfully crossed using MAI in 28 of 31 lesions, a 90 percent success rate, Atmakuri said. Two lesions were successfully crossed with the wire, but the balloon could not cross the lesion, leading to a success rate of 84 percent.

Kleiman said the magnetic navigation system has the potential to allow coronary interventions to be done more quickly than conventional guide wire techniques. Its major advantage is the ability to treat tortuous vessels.

“Just how broad a niche this technique will occupy is not yet clear,” Kleiman said. He said there is a steep learning curve, but the intervention will become easier to use with experience and upgraded software.

Co-authors are cardiology fellow Eli I. Lev, M.D., and Albert E. Raizner, M.D., director of The Methodist DeBakey Heart Center.