Abdominal aortic aneurysm sac shrinkage after endovascular aneurysm repair: Correlation with chronic sac pressure measurement

Objectives. Abdominal aortic aneurysm (AAA) sac shrinkage after endovascular aneurysm repair (EVAR) is considered to be evidence of clinical success. Exclusion of the sac from systemic pressure is the likely cause of shrinkage. We report our continuing clinical experience with the use of a permanently implantable, ultrasound-activated remote pressure transducer to measure intrasac pressure and its correlation with changes in sac diameter over time. Methods. Over a 22-month period, 21 patients underwent EVAR of an infrarenal AAA with implantation of an ultrasound-activated remote pressure transducer fixed to the outside of the stent-graft and exposed to the excluded aortic sac. Intrasac pressures were measured directly with an intravascular catheter and by the remote sensor at the time of stent-graft deployment. Follow-up sac pressures were measured by remote sensor and compared with systemic arterial pressure at every follow-up visit. Mean follow-up was 11.4 +/- 5.0 months (range, 1 to 26 months). Twenty patients had follow-up of :6 months. Mean pressure index (MPI) was calculated as the ratio of mean sac pressure to mean systemic pressure. Results. Pressures could be obtained at all visits in 15 of the 21 patients. Fourteen of these 15 patients had follow-up of at least 6 months. Aneurysm sac shrinkage of >5 turn was seen in seven (50%) of these 14 patients. No aneurysm enlargement was observed in any patient. The MPI was significantly lower in patients with sac shrinkage at 6 months and at final follow-up. Conclusions: Endovascular aneurysm repair results in marked reduction of sac pressure in most patients. Patients with aneurysm shrinkage after EVAR have significantly lower MPI; however, the absence of sac shrinkage does not imply persistent pressurization of the sac. Further clinical follow-up will delineate the role of long-term sac pressure monitoring in surveillance after EVAR.