Measurement of aortic compliance in abdominal aortic aneurysms before and after open and endoluminal repair: preliminary results.
PURPOSE
To assess aortic wall compliance as a portent of rupture risk in patients with abdominal aortic aneurysms.


METHODS
In this pilot study, 38 patients (32 men; median age 78 years, range 63-95) underwent an ultrasound scan: 20 pre-repair and 24 post-repair (18 endovascular [EVR] and 6 open). Six patients from the pre-repair group were included in a post repair study after EVR. Cine loop images were analyzed offsite using wall tracking software, which measured aortic diameter changes during cardiac cycles. Brachial blood pressure was measured, and elastic modulus (Ep) and stiffness (beta) were calculated. Preop Ep and beta were determined at the neck, inflection points (IP), and mid sac levels. Postop Ep and beta were calculated in mid sac only for technical reasons.


RESULTS
Preoperative Ep and beta were significantly higher at IP compared with neck (median Ep 24.22 versus 12.95 N/cm(2), p<0.003; median beta 16.27 versus 8.65, p<0.003). At the mid sac, Ep and beta were also significantly higher compared with neck: Ep 26.41 versus 12.95 N/cm(2), p=0.001; beta 17.94 versus 8.65, p=0.001. The values for IP and mid sac were Ep 24.22 versus 26.41 N/cm(2), p=0.64; beta 16.27 versus 17.94, p=0.64. In the postop cases (n=24), Ep and beta in successful endovascular repair (n=12) were significantly higher than in open repair, respectively: median Ep 34.31 versus 12.33 N/cm(2), p<0.001; median beta 23.18 versus 8.24, p<0.001. Patients with endoleaks or endotension (n=6) had significantly elevated Ep and beta compared with those without endoleaks (n=12): median Ep 79.79 versus 34.31 N/ cm(2), p=0.002; median beta 51.52 versus 23.18, p<0.002. Six patients scanned before and after EVR showed a decrease of Ep and beta in 3, no change in 1, and an increase in 2. An increase greater than 2 fold was noted in a patient with a gross type II endoleak.


CONCLUSIONS
This pilot study shows that estimates of aortic wall compliance agree well with known values for wall stress distribution. EVR leaves patients with greater wall stiffness than those undergoing open repair, a situation accentuated by endoleaks. Wall compliance and stiffness measurement promises to be useful for the evaluation of success of endovascular repair.