A Northwest First: Aortic Aneurysm Pressure Sensors Implanted
05/04/06 Portland, Ore.
OHSU patients get wireless sensors permanently implanted in the course of a minimally invasive procedure to relieve pressure in potentially fatal abdominal aortic aneurysms
Abdominal aortic aneurysms, or AAAs, are abnormally enlarged areas in the main artery of the abdomen that are prone to rupture, causing sudden death. Stent grafts are a less invasive alternative to traditional open surgery for treatment of AAAs. These devices are inserted into aortic aneurysms through tiny incisions in the groin area using catheters and X-ray guidance.
The stent graft works by providing a new, reinforced channel for blood flow that takes pressure off the aneurysm. To function properly, the stent graft must have tight seals above and below the aneurysm. If the seals are not tight, or a problem develops in the stent graft, blood can refill the aneurysm and the risk of bursting returns. Until now, the only way to determine whether an aortic stent graft was working was to look at CT (computed tomography) scans or other images. The remote pressure sensors enable doctors to measure in seconds the actual pressure in the aneurysm any time after the stent graft is placed by holding a special antenna over the patient's abdomen. Nothing touches the patient, and the patient feels nothing.
The sensors, approved by the U.S. Food and Drug Administration last fall for use in the United States, had not been utilized anywhere in the Northwest until now. They promise a safer, more effective, less costly and noninvasive way of helping doctors ensure that a stent graft is properly seated at the time of initial placement, and, later, of measuring the pressure in the aneurysm sac outside the stent graft at periodic intervals throughout a patient's life to verify that the stent graft still is working.
Arvid Kulits, a retired 82-year-old civil engineer who is convalescing at home in Vancouver, Wash., was the first OHSU patient with an AAA to have received the device. His was implanted in early February. Kulits was rushed to OHSU when, after showering and going to bed, he suddenly started seeing stars. He remembers little after that until the procedure was completed.
Four other OHSU patients have received the implants since Kulits.
"The device is basically a small passive chip about the size of a piece of Dentyne gum, which we insert through a small catheter and position in the aneurysm outside the new stent graft," said Kaufman, professor of interventional radiology in the OHSU School of Medicine and chief of vascular and interventional radiology in OHSU's Dotter Interventional Institute.
"Although we still have lots to learn, the follow-up after a stent graft may someday be as simple as coming into the doctor's office and having a "magic wand" waved over your abdomen to check the pressure in the aneurysm," said Kaufman. Follow-up examinations after abdominal aortic aneurysm procedures traditionally have relied on expensive CT scans every six months or so, which not only may fail to detect small leaks in the stent graft, but also subject patients to potentially harmful contrast dyes and radiation.
Aortic aneurysms account for about 15,000 deaths in the United States annually, 9,000 of them AAA-related, according to the National Center for Health Statistics. In 2000 they were the 10th leading cause of death in white men aged 65 to 74. Men aged 65 and older who are, or have been, regular smokers are at highest risk. The mortality rate for an aortic rupture occurring outside a hospital setting approaches 90 percent. Aortic weakening is associated with high blood pressure, arteriosclerosis or genetic tissue diseases such as Marfan's Syndrome in addition to smoking.
AAAs typically are asymptomatic and not detectable in routine physical exams. AAA-related deaths are among the most preventable causes of death, health care experts say. The U.S. Preventive Services Task Force (USPSTF) - an independent panel of private-sector experts in prevention and primary care sponsored by the U.S. Department of Health and Human Services' Agency for Healthcare Research and Quality- recommended last year that all men 65 and older who have ever smoked be screened for AAA in one-time ultrasound examinations. And, beginning next January, as a result of the Screening Abdominal Aortic Aneurysms Very Efficiently (SAAAVE) Act signed into law earlier this year Medicare will cover a one-time screening for newly enrolled men with a history of smoking and both men and women aged 65 to 74 with a family history of AAA.
To treat an AAA, an endovascular stent graft is threaded via a catheter through a small incision in the groin and the femoral artery into the aneurysm. By inserting the coiled stent, which expands into a cloth and metal pipe, pressure on the weakened aortic wall is relieved. Blood flows through the stent graft instead of into the aneurysm sac thereby keeping it from rupturing.
The sensors implanted by Kaufman, Landry and Liem in the five AAA patients who have received them so far were put in during the same procedures as when their stent grafts were inserted. The sensors, one component of the Endosure Wireless AAA Pressure Measurement System, were produced by CardioMEMS, Inc., a privately held medical device company in Atlanta.
The system consists of the sensors - composed of microelectromechanical, biocompatible conducting plates that respond to specific radiofrequency wave emissions - and an external lightweight antenna together with an electronics cart, monitor and software. The external tennis-racket shaped antenna is held over the area of the abdomen where the sensor is located to determine the pressure inside the aneurysm sac. The system was approved by the FDA in October 2005 after clinical trials in Brazil, Argentina and Canada and at nine hospitals in the United States.
"What's compelling about this for patients and doctors," said Kaufman, "is that we may no longer have to rely on an image to determine whether the stent-graft procedure has been successful. There's no more guesswork. Although the data linking low pressure in the aneurysm to safety from rupture in the long term doesn't exist yet, this device will certainly make patients and us feel more comfortable about what's happening with their aneurysms."
Landry and Liem are both associate professors in OHSU's division of vascular surgery as well as staff members at the Dotter Interventional Institute.
For more information about the Dotter Interventional Institute and the treatment of abdominal aortic aneurysms: http://www.ohsu.edu/dotter
For more information about the Endosure AAA Wireless Pressure Measurement System, visit www.cardiomems.com