Intra-aneurysm Sac Pressure in Patients with Unchanged AAA Diameter after EVAR.

OBJECTIVE: To study intra-aneurysm sac pressure and subsequent abdominal aortic aneurysm (AAA) diameter changes in patients without endoleaks that remain unchanged in AAA diameter more than 1 year after endovascular aneurysm repair (EVAR). METHODS: A total of 23 patients underwent direct intra-aneurysm sac pressure (DISP) measurements 16 months (IQR: 14-35 months) after EVAR. Tip-pressure sensors were used through translumbar AAA puncture. Mean pressure index (MPI) was calculated as the percentage of mean intra-aneurysm pressure relative to the simultaneous mean intra-aortic pressure. Aneurysm expansion or shrinkage was assumed whenever the diameter change was >/=5mm. Values are presented as median and interquartile range. RESULTS: In 18 patients, no fluid was obtained upon AAA puncture (group A). In five patients, fluid was obtained (group B). In group A, follow-up continued for 29 months (IQR: 15-35 months) after DISP; five AAAs shrank, 10 remained unchanged and three expanded (MPIs of 26% (IQR: 18-42%), 28% (IQR: 20-48%) and 63% (IQR: 47-83%) and intra-sac pulse pressures of 3mmHg (IQR: 0-5mmHg), 4mmHg (IQR: 2-8mm Hg) and 12mmHg (IQR: 6-20mmHg), respectively, for the three subgroups). MPI and intra-sac pulse pressures were higher in AAAs that subsequently expanded (P=0.073 and 0.017, respectively). MPI and pulse pressure correlated with total diameter change (r=0.49, P=0.039 and r =0.39, P=0.109, respectively). Pulse pressure had a greater influence than MPI on diameter change (R(2)=0.346, P=0.041, beta standardised coefficient of 0.121 for MPI and 0.502 for pulse pressure). Similar results with stronger, and significant correlation to pulse pressure were obtained when relative diameter changes were used (r=0.55, P=0.017). In group B, MPI and AAA pulse pressure were 32% (IQR: 18-37%) and 1mmHg (IQR: 0-6mmHg), respectively. After 36 months (IQR: 21-38 months), one AAA shrank, three continued unchanged while one expanded. CONCLUSIONS: AAAs without endoleak and unchanged diameter more than 1 year after EVAR will often continue unchanged. Expansion can eventually occur in the absence of intra-sac fluid accumulation and is associated with higher and more pulsatile intra-sac pressure. However, in patients with intra-sac fluid, expansion can occur with low intra-sac pressures.