November 17, 2006

(SACRAMENTO, Calif.) — Specialists from the UC Davis Vascular Center are the first team in Sacramento, and one of the first in Northern California, to implant a new, wireless sensing device for patients receiving stent grafts to repair abdominal aortic aneurysms. The device enables physicians to monitor patients postoperatively and detect possible problems with stent performance without the need for surgery or radiological imaging procedures.

The pressure-sensing device is inserted during a procedure to repair an aortic aneurysm with a stent graft. The sensor allows physicians to verify the success of the implanted stent by simply waving a tennis-racket-sized antenna over the patient's chest.

“This new technology represents a tremendous benefit for patients,” said David Dawson, a professor of vascular and endovascular surgery at the UC Davis Vascular Center, who last week implanted the device during the repair of an abdominal aortic aneurysm in a 52-year-old man. “When we implant a stent graft, this new sensor allows us to immediately see the results, on a real-time basis, as well as conduct follow-up monitoring in a safer and less-expensive way than the other methods available to us.”

An abdominal aortic aneurysm is a ballooning of a portion of the aorta, the large artery that begins at the heart and runs across the abdomen. An aneurysm results from the weakening and thinning of the aortic wall and, if left untreated, will continue to expand and may eventually rupture or tear. A ruptured aneurysm is a life-threatening condition requiring immediate medical care.

An increasingly popular method for treating an abdominal aortic aneurysm is endovascular surgery, consisting of the placement of a stent graft inside the aneurysm sac. A stent graft is a tube-like device that allows blood to flow through it instead of through the aneurysm, reducing the pressure there and keeping it from bursting. The stent graft is inserted into the artery through an incision in the groin.

The new pressure monitor, which the Food and Drug Administration approved for use in 2005, is implanted during the insertion of a stent graft. Equipped with a microchip, the peanut-sized monitor measures the pressure in the aneurysm sac, enabling physicians to verify the success of the stent by using an antenna to pick up signals from the sensor, which gauges the local fluid pressure.

Dawson said that the monitor produced immediate benefits during last week's surgery.

“When we put the graft in, we could see from the pressure monitor that the pressure within the aneurysm was not relieved, that the graft did not do what we had intended it to do,” Dawson said. Equipped with the readings from the monitor, Dawson and his surgical team adjusted the graft for a better fit.

As long as their grafts remain in place, patients who undergo an endovascular aneurysm repair have a low but increased risk of complications from their aneurysm, including leakage, migration and rupture. Consequently, stent grafts need to be monitored annually or biannually to ensure that they are preventing the buildup of pressure within the aneurysm sac. Changes in pressure may indicate that the stent has not fully repaired the aneurysm and may be leaking.

Until now, the usual method for monitoring aneurysm repairs consisted of performing computed tomography scans once or twice a year. While still useful CT scans are costly and expose the patient to radiation. In addition, the intravenous dye used during the procedure can be toxic to the kidneys of some patients.

The wireless sensor has the added benefit of being able to detect problems more accurately than CT scans, said Dawson. Known as the Endosure Wireless AAA Pressure Measurement System, the sensor is manufactured by CardioMEMS, Inc. It is the first wireless, permanently implanted pressure monitor based on microelectromechanical systems technology to become commercially available in the United States.

The UC Davis Vascular Center provides state-of-the-art comprehensive care to patients with atherosclerosis and other vascular problems, such as aneurysms, vein disorders and less common conditions. The center brings together specialties from a variety of disciplines, including vascular surgery, cardiology, radiology, endocrinology and nephrology.