Flow Mediated Dilatation and Progression of Abdominal Aortic Aneurysms

Figures

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  Figure 1. Correlation between flow mediated dilatation (FMD) and size of abdominal aortic aneurysm (AAA). There is a significant inverse correlation between the size of AAAs and FMD of forearm brachial artery at the initial assessment. (A) The percentage change in brachial artery diameter after stimuli is presented as FMD(%) (Spearman’s r = −.28, p < .001). (B) There is also a significant reduction of FMD across the different size groups of AAAs (Kruskale–Wallis test p < .001). (C) This significant negative correlation between AAA size and FMD is still present when the large AAAs (> 55 mm) were excluded from the analyses (Spearman’s r = −.27, p = .005). (D) However, such correlation is not observed within the group of moderate sized AAAs (40–55 mm) (Spearman’s r = −.1, p = .4).

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  Figure 2. Correlations between baseline abdominal aortic aneurysm (AAA) diameter, flow mediated dilatation (FMD), and future 12 month AAA growth. Participants with small and moderate sized AAAs (30–55 mm) under surveillance were reassessed at 12 months. The median duration of follow-up for this group was 365 days (interquartile range [IQR] 343–381 days). Annual AAA growth was calculated by [(ΔAP diameter/antero-posterior diameter at baseline)/(number of days lapsed/365days)]. The median progression rate over this period for this group of patients was 2.8% per year (IQR 0–5.7%/year). (A) There is a significant correlation between the baseline diameter of AAAs and the growth rate in the future 12 months (Spearman’s r = .30, p < .005). (B) The correlation between baseline AAA diameter and future growth rate was no longer observed in the moderate sized AAA group (40–55 mm) (Spearman’s r = .12, p = .39). (C) Within the subgroup of small sized AAAs (30–39 mm), there was no correlation between baseline diameter and future growth rate either (Spearman’s r = −.02, p = .9). (D) During the same follow-up period, FMD at baseline correlated significantly with the future growth rate. This significant…

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  Figure 3. Flow mediated dilatation (FMD) deteriorates during abdominal aortic aneurysm (AAA) progression, and is improved by AAA surgery. FMD reduced significantly between assessments during AAA surveillance (from a median of 2.0% at baseline to 1.2% at follow-up, Wilcoxon matched pairs signed rank test [WMPST] p = .004). FMD was measured in 50 patients prior to AAA surgery, and repeated 8–12 weeks afterwards. FMD improved significantly after surgical repair (from 1.1% pre-operatively to 3.8% post-operatively, WMPST p < .001), irrespective of the type of surgery performed (endovascular repair [EVAR] n = 28; open surgical repair [OSR] n = 22).

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  Figure 4. Nitroglycerin mediated dilatation (NMD) and abdominal aortic aneurysm (AAA) progression. (A) There was no correlation between AAA size and NMD. (B) NMD did not deteriorate under AAA surveillance. Ethically, the NMD protocol could not be carried out in most patients with large AAAs scheduled for surgery, as the side effect of hypotension in this setting could potentially have complicated clinical management. As such, no comparison could be made for the pre- and post-operative NMD measurements.

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  Figure 5. Low flow mediated constriction and the progression of abdominal aortic aneurysm (AAA). The low flow mediated constriction (FMC) response of brachial artery at the same time points was investigated, as an extension to the FMD protocol. We hypothesised that the significant changes in FMD observed were driven by the derangement in vasoconstrictive tone in these patients, thereby masking the otherwise normal FMD response. However, there was no correlation between (A) FMC and AAA size or (B) future growth rate of AAA. (C) FMC did not change during the natural history of AAA progression (Wilcoxon matched pairs signed rank test [WMPST] p = .8), and (D) is unaffected by AAA surgery (WMPST p = .8).