Battling Aneurysms

Wireless microchip and stapling technology may help reduce AAA deaths

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Two new technologies aim to keep life-threatening aneurysms at bay – one by wirelessly monitoring the pressure inside an aortic aneurysm, and the other by locking into place a graft often inserted into a weakened aorta to create a new path for blood flow. Information on these technologies, as well as a call for routine screening for abdominal aortic aneurysms, was presented recently at the 16th Annual International Symposium on Endovascular Therapy.

Abdominal aortic aneurysm (AAA) is the 17th leading cause of death in the United States, accounting for more than 15,000 deaths each year. It is caused by a weakened area in the main artery that supplies blood from the heart to the rest of the body. When blood flows through the aorta, the weakened area bulges like a balloon. If the balloon grows large enough, there is a danger that it will burst, resulting in death 80 percent to 90 percent of the time.

The most common treatment for a large (nearly two inches or larger), unruptured aneurysm is open surgical repair, however, a less-invasive option called endovascular repair has become widespread in recent years. For this technique, a device called an endograft is threaded through a blood vessel in the groin and into the aorta. The flow of blood is redirected through the graft so that the pressure on the aneurysm is relieved.

Endovascular repair is a highly successful procedure, but not everyone is a good candidate. Endografts cannot accommodate all anatomical differences, and serious problems have occurred in some patients, including improper device placement, leakage and slippage.

Monitoring with MEMS

In as many as one in five patients who have had an AAA repaired with an endograft, the threat of rupture persists because blood continues to leak around the graft and into the bulging aneurysm sac. For this reason, all patients undergoing an endograft repair need to be monitored for life with CT, the best tool currently available but one with limitations, including an inability to detect reduction in aneurysm pressure, the main goal of treatment.

Application of a wireless microchip technology developed for use in jet engines, called micro-electro mechanical systems (MEMS), may soon allow physicians to detect so-called endoleaks by remotely monitoring pressure inside a repaired AAA. The technology also will allow monitoring to be conducted on a continual basis; whereas, CT cannot be repeated as often as might be needed to detect potential problems.

The device, created by Atlanta-based CardioMEMS Inc., is a small, oval-shaped pressure sensor that would be implanted non-surgically into the aneurysm during endograft placement. Blood pressure readings inside the aneurysm could be taken at any time, in physicians' offices and even by patients in their own homes.

A separate electronic instrument with an antenna is used to take readings after the sensor has been implanted within the aneurysm sac. The patient can be fully clothed and the process is painless, similar to the manner in which a secondary screening using a handheld wand is conducted at airport security stations. An increase in pulse pressure within the aneurysm sac may indicate that blood is still flowing to the aneurysm and signal that additional tests or treatment may be necessary to prevent rupture.

"The wireless pressure sensor has the potential to revolutionize how we treat patients with abdominal aneurysms," says Takao Ohki, MD, chief of the division of vascular and endovascular surgery at Montefiore Medical Center in New York. "Because of the lack of a good method to monitor patients, and because of the persistent risk of aneurysm rupture, the use of endografts has been limited to select patients who are otherwise poor candidates for standard surgery. The CardioMEMS implantable sensor will hopefully improve the outcome of endografting by better detecting failures before they cause a problem and, ultimately, increase the number of people who may be eligible for endovascular repair."

The application of MEMS technology in the treatment of AAA has been studied for more than two years in the laboratory and in animals by Ohki. The first CardioMEMS implant in a human with AAA is expected to occur early this year. A clinical trial at eight centers also is expected to start this year.

"Previous studies have shown that the sensor can be safely and successfully delivered into a simulated aneurysm sac, measurements can be made within the sac, and that the sensor is reliable and accurate," Ohki says.

Treating Endoleaks

Many endoleaks are caused when an endograft slips out of position or is insufficiently sealed to block blood flow, which fuels the growth of aneurysms. The U.S. Food and Drug Administration recently approved human testing of a new technology to treat endoleaks by securely fastening endografts to the wall of the aorta. Developers expect the device to increase the number of people who are candidates for the less-invasive endovascular procedure.

The Endostaple device is a miniaturized ring of metal coils that resembles a tiny version of a Slinky™ toy. Each coil is about the thickness of a dime. The device is designed to rivet an endograft securely to the entire thickness of the aortic wall, most importantly the strongest portion, the outer layer of the aorta. It is implanted non-surgically through a catheter during endovascular repair.

"We believe that this technology will reduce complications resulting in reintervention from 3 percent to 1 percent annually, which represents a substantial percent reduction in risk over a 10-year period," says Hugh H. Trout III, MD, FACS, chairman of the EVA Corporation, makers of the Endostaple, and clinical professor of surgery at George Washington University and the Uniform Services University of Health Sciences, Bethesda, Md. "In addition to treating endoleaks, the staple is designed to prevent endograft migration. Endografts don't fit or hold in place well in aortas that are too wide, too short or angulated; this device is designed to securely lock the graft into place and compensate for these types of anatomical differences." Testing of the Endostaple technology in 15 patients is scheduled to begin this spring at Washington University; St. Louis; Stanford University, Stanford, Calif.; and Massachusetts General Hospital, Boston.

Screening Is Still Rare

AAA is relatively easy to detect using ultrasound and CT, however, screening for the disease is rarely done in the United States. In addition, often there are no obvious symptoms prior to rupture that would prompt someone with AAA to seek medical attention.

"Although more than 15,000 people in this country die from ruptured AAAs each year – more than many other diseases for which routine screening is offered – the vast majority of people who have an aneurysm don't even know they have it," says Hugh G. Beebe, MD, director emeritus of the Jobst Vascular Center, Toledo, Ohio.

Cervical cancer, which is detected by a Pap smear test, claims about 4,000 lives each year.

"The bottom line is that studies have shown that about half of AAA ruptures could be prevented through screening," Beebe says. "A Medicare reimbursement code is needed to cover the test, and patients and doctors alike need to know that screening is easy, safe, noninvasive and effective, and lives can be saved."

Those at highest risk for AAA are males over the age of 60 who smoke, have high blood pressure and/or who have a history of clogged blood vessels (atherosclerosis or "hardening of the arteries"). Also at elevated risk are males and females with a family history of AAA.

For more information, call 888-334-7495 or visit www.iset.org.

— International Symposium on Endovascular Therapy