AAA Endografts Show Sac-Pressure Differences

BY MITCHEL L. ZOLER

BALTIMORE -- Monitoring sac pressures within abdominal aortic aneurysms following endograft repair hinted at a possible efficacy difference between two repair devices in a nonrandomized study with 50 patients.

Aneurysm repair with the Gore Excluder device led to a significantly lower sac pressure, compared with repair by the Cook Zenith device, in a study that was primarily designed to assess the ability of an implanted sensor to detect endoleaks, Dr. David H. Stone said at the Vascular Annual Meeting. The differences in sac pressure seen in patients treated with one of the two devices "requires further investigation. It may reflect the physical constructs of the devices," said Dr. Stone, a vascular surgeon at Duke University in Durham, N.C. The clinical significance of the differences in pressure measurements between the two devices is uncertain, he added.

THE CLINICAL SIGNIFICANCE OF THE DIFFERENCES IN PRESSURE MEASUREMENTS BETWEEN THE TWO DEVICES IS UNCERTAIN.

Dr. Stone and his associates evaluated the Endosure wireless aneurysm monitor that is marketed by CardioMEMs and is approved by the Food and Drug Administration for measuring pressure within an aneurysm sac during endovascvular repair of an abdominal aortic aneurysm. The goal was to see if making serial pressure measurements within the aneurysm sac was a useful way to monitor the durability of endovascular repair and was a useful alternative to the conventional method of serial CT imaging. The study included 50 patients who underwent endovascular repair of an abdominal aortic aneurysm during April 2006 to November 2006 at Duke. By chance, 24 of the patients in the study were treated with the Gore device and 24 were treated with the Zenith device. The remaining two patients were repaired with an Endologix Powerlink System.

Before repair, the average ratio of the pulse pressure (as measured by the Endosure device) within the aneurysm sac to the systemic pulse pressure was 1.02. Immediately after the repair device was deployed, this ratio fell to an average of 0.63. After a balloon was inflated within the repair device to mold and seal it, the average pressure ratio further fell to 0.36. One month after repair, the average ratio of pressure within the sac to systemic pressure had dropped even further, to 0.21.

The results have so far failed to prove valuable for pressure monitoring for the study's primary end point. Follow-up CT scans made 30 days after aneurysm repair found eight patients who had type II endoleaks. But there was no significant difference in the sac pressures of these patients, compared with the 42 patients who did not have endoleaks, Dr. Stone said. One possible explanation is that, although the eight patients had endoleaks based on anatomic criteria using CT imaging, the leaks may not have been physiologically significant and hence did not cause a significant change in sac pressure.

An unexpected finding was that at 30 days after repair, the average pressure ratio was 0.13 in the patients treated with the Gore Excluder device, and 0.26 in those treated with the Cook Zenith device--a statistically significant difference. However, the patients were not prospectively randomized into the two repair groups, and the report did not include an analysis of baseline differences between the patients groups. These limitations and the small number of patients make it hard to draw firm conclusions, Dr. Stone said.

When asked to comment on this story, Dr. James McKinsey, chief, division of vascular surgery, Columbia University, New York, stated: "This presentation shows that there is a detectable pressure drop in AAA sac after endograft repair as detected by the Cardiomems Endosure pressure sensor. Although there was a modest difference between the Zenith and Excluder device both had significant pressure decreases.

"The most concerning issue is that there was no pressure difference between those grafts with an endoleak (all type 2) and those without. This raises the question of the utility of this device. Further follow-up and additional cases may reveal greater utility in detecting type 1 endoleaks and type 2 endoleaks that are associated with sac expansion." Dr. McKinsey is an associate medical editor for VASCULAR SPECIALIST.