Systematic review and meta-analysis of growth rates of small abdominal aortic aneurysms

Three-dimensional characterization of sex differences in abdominal aortic aneurysm progression via vascular deformation mapping

Although abdominal aortic aneurysms (AAA) are more common in men, women are at greater risk for AAA growth/rupture. Vascular deformation mapping (VDM) utilizes deformable image registration to qualify and quantify 3D-AAA growth using computed tomography angiograms (CTA). In this study we leveraged VDM to investigate sex differences in AAA growth patterns. Patients with infra-renal AAA and ≥ 2 CTA were identified. Males and females were matched for age, hypertension, and smoking history. Patient characteristics, maximum diameter (Dmax), and AAA volume were obtained. CTA images were segmented, and VDM was conducted to quantify 3D AAA growth rate per year (GR, cm/year). Statistical shape modeling was utilized to compute mean aneurysm shapes and 3D GR. Average GR was evaluated at specific regions of the aortic surface for males and females. Seventeen males and 17 females were matched. At the individual level, there were no sex differences in changes in Dmax or AAA volume. However, females had larger GR across the anterior and right lateral AAA (1.33 vs 0.89 and 1.56 vs 0.74 cm/year, respectively), despite no difference in posterior or left lateral AAA GR. Despite comparable changes in Dmax, AAA volume, and GR magnitude, women demonstrated a more eccentric, anterior-predominant, AAA growth pattern.

Radiation therapy for cancer is potentially associated with reduced growth of concomitant abdominal aortic aneurysm

PURPOSE

Co-prevalence of abdominal aortic aneurysm (AAA) and cancer poses a unique challenge in medical care since both diseases and their respective therapies might interact. Recently, reduced AAA growth rates were observed in cancer patients that received radiation therapy (RT). The purpose of this study was to perform a fine-grained analysis of the effects of RT on AAA growth with respect to direct (infield) and out-of-field (outfield) radiation exposure, and radiation dose-dependency.

METHODS

A retrospective single-center analysis identified patients with AAA, cancer, and RT. Clinical data, radiation plans, and aneurysm diameters were analyzed. The total dose of radiation to each aneurysm was computed. AAA growth under infield and outfield exposure was compared to patients with AAA and cancer that did not receive RT (no-RT control) and to an external noncancer AAA reference cohort.

RESULTS

Between 2003 and 2020, a total of 38 AAA patients who had received well-documented RT for their malignancy were identified. AAA growth was considerably reduced for infield patients (n = 18) compared to outfield patients (n = 20), albeit not significantly (0.8 ± 1.0 vs. 1.3 ± 1.6 mm/year, p = 0.28). Overall, annual AAA growth in RT patients was lower compared to no-RT control patients (1.1 ± 1.5 vs. 1.8 ± 2.2 mm/year, p = 0.06) and significantly reduced compared to the reference cohort (1.1 ± 1.5 vs. 2.7 ± 2.1 mm/year, p < 0.001). The pattern of AAA growth reduction due to RT was corroborated in linear regression analyses correcting for initial AAA diameter. A further investigation with respect to dose-dependency of radiation effects on AAA growth, however, revealed no apparent association.

CONCLUSION

In this study, both infield and outfield radiation exposure were associated with reduced AAA growth. This finding warrants further investigation, both in a larger scale clinical cohort and on a molecular level.

Infrarenal Abdominal Aortic Aneurysm

Abdominal aortic aneurysms are found in up to 6% of men and 1.7% of women over the age of 65 years and are usually asymptomatic. The natural history of aortic aneurysms is continued dilation leading to rupture, which is associated with an overall 80% mortality. Of the patients with ruptured aneurysms that undergo intervention, half will not survive their hospitalization. Reduction in aneurysm mortality is therefore achieved by prophylactic repair during the asymptomatic period. On a population-based level, this is supported by abdominal aortic aneurysm screening programs. Approximately 60% of abdominal aortic aneurysms are confined to the infrarenal portion of the aorta and are amenable to repair with off-the-shelf endovascular devices. Endovascular techniques have now replaced open surgery as the primary modality for aneurysm repair.

Characterizing the frequency and indications for repair of abdominal aortic aneurysms with diameters smaller than recommended by societal guidelines

OBJECTIVE

While the Society for Vascular Surgery recommends repair of abdominal aortic aneurysms (AAA) at ≥5.5 cm in men and ≥5.0 cm in women, AAA repair below these thresholds has been well documented. There are clear indications for repair other than these strict size criteria, but the expected proportion of such repairs in one's practice has not been studied. We sought to characterize the indications for repairs of aneurysms below diameter recommendations at a single academic center. Using the assumption that this real-world experience would approximate that of other practices, we then used national data to extrapolate these findings.

METHODS

A single-center retrospective review was conducted of all elective open (oAAA) and endovascular (EVAR) AAA repairs (2010-20) to assess the incidence of and indications for repair of aneurysms below diameter recommendations (defined as <5.5cm in men and <5.0cm in women). Reasons for these repairs were defined as: 1) iliac aneurysm, 2) saccular morphology, 3) rapid expansion, 4) patient anxiety, 5) distal embolization, 6) other, and 7) no documented reason. The Vascular Quality Initiative (VQI) was queried for all asymptomatic oAAA and EVAR (2010-20) and repairs below diameter recommendations were identified. Findings from the single-center analysis were applied to the VQI cohort to extrapolate estimates of reasons for repairs done nationally. In-hospital mortality and major adverse cardiac events (MACE) were compared between those below size recommendations and those meeting size recommendations.

RESULTS

Of 456 elective AAA repairs at our center, 147 (32%) were below size recommendations. This was more common for EVAR (35% vs 28%). Reasons were: not documented (41%), iliac aneurysm (23%), saccular (10%), rapid expansion (10%), patient anxiety (7%), other (6%), and distal embolism (3%). Of 44,820 elective AAA repairs in VQI, 17,057 (38%) were below size recommendations (40% EVAR, 26% oAAA). Patients who were repaired below size recommendations had lower in-hospital death (oAAA: 2.4% vs 4.6% p<0.0001; EVAR: 0.3% vs 0.8% p<0.0001). When single-center findings were applied to the VQI dataset, an estimated 10,064 repairs were performed nationally for acceptable indications other than size criteria. Conversely, there may have been 6993 repairs (with an associated 35 deaths) performed without documented indication.

CONCLUSION

Repairs for AAA below recommended diameter guidelines account for approximately one third of all elective AAA procedures in both VQI and our single-center experience. Assuming our practice is typical, nearly 60% of repairs below size recommendations meet criteria for other clear reasons. The remaining 40% lack a documented reason, meaning 13% of all elective AAA repairs were done for aneurysms below size recommendations without an acceptable indication. As awareness of overuse/underuse is heightened, these data help estimate the expected proportion of repairs for less common pathologies. They also provide a potential baseline data point for efforts at reducing overuse.

Cancer, cancer treatment and aneurysmatic ascending aorta growth within a retrospective single center study

Background: Multi-morbidity poses a substantial challenge for health care in an aging population. Recent studies did not provide evidence for general side effects of anti-cancer therapy regarding the growth rate of coincident abdominal aortic aneurysms, although it was suggested that specific therapeutic substances might accelerate growth. Aneurysm pathology, however, differs with respect to localization. Hence, we present the first ever analysis on the association of cancer and cancer therapy with growth alteration of aneurysms of the ascending aorta (AscAA). Patients and methods: A retrospective single-center identification of AscAA+cancer patients was performed in the institutional picture archiving and communication system (PACS). Included were all patients with ≥2 CT angiograms over ≥6 months and additional malignancy. Clinical data and aneurysm diameters were retrieved and analyzed for an association of cancer (stratified by tumor entity) or cancer therapy (stratified by several classes of chemotherapeutic agents and radiation therapy) with annual growth rate, respectively. Statistics included t-test, Wilcoxon test, and a linear regression model accounting for initial AscAA diameter and type of treatment. Results: From 2003 to 2021, 151 patients (median age 70 years; 85% male) with AscAA and coincident 163 malignancies were identified. Prostate (37%) and hematologic cancer (17%) were most frequent. One-hundred-eleven patients (74%) received chemotherapy and 75 patients (50%) had radiation. After exclusion of six patients with an initial AscAA diameter >55 mm, the average annual AscAA growth rate was 0.18±0.64 mm/year, with only 12 patients experiencing a growth rate >1mm/year. Neither tumor entity nor radiation or chemotherapy - alone or in combination - were significantly associated with an alteration of the annual AscAA growth rate. Likewise, a subanalysis for singular chemotherapeutic agents did not reveal a specific association with AscAA growth alteration. Conclusions: Growth rates of AscAA are low in this cohort with coincident malignancy. Cancer and/or chemotherapy or radiation are not associated with an alteration of the annual growth rate. Additional control examinations seem unnecessary.

Type I Interferon Receptor Subunit 1 Deletion Attenuates Experimental Abdominal Aortic Aneurysm Formation

Objective: Type I interferon receptor signaling contributes to several autoimmune and vascular diseases such as lupus, atherosclerosis and stroke. The purpose of this study was to assess the influence of type I interferon receptor deficiency on the formation and progression of experimental abdominal aortic aneurysms (AAAs). Methods: AAAs were induced in type I interferon receptor subunit 1 (IFNAR1)-deficient and wild type control male mice via intra-infrarenal aortic infusion of porcine pancreatic elastase. Immunostaining for IFNAR1 was evaluated in experimental and clinical aneurysmal abdominal aortae. The initiation and progression of experimental AAAs were assessed via ultrasound imaging prior to (day 0) and days 3, 7 and 14 following elastase infusion. Aneurysmal histopathology was analyzed at sacrifice. Results: Increased aortic medial and adventitial IFNAR1 expression was present in both clinical AAAs harvested at surgery and experimental AAAs. Following AAA induction, wild type mice experienced progressive, time-dependent infrarenal aortic enlargement. This progression was substantially attenuated in IFNAR1-deficient mice. On histological analyses, medial elastin degradation, smooth muscle cell depletion, leukocyte accumulation and neoangiogenesis were markedly diminished in IFNAR1-deficient mice in comparison to wild type mice. Conclusion: IFNAR1 deficiency limited experimental AAA progression in response to intra-aortic elastase infusion. Combined with clinical observations, these results suggest an important role for IFNAR1 activity in AAA pathogenesis.

Radiation and chemotherapeutics are associated with altered aortic aneurysm growth in cancer patients

INTRODUCTION

Co-prevalence of aorto-iliac aneurysm (i.e. AAA) and cancer confronts patients and physicians with two life-threatening diseases. Modern chemotherapeutics and target therapies might impact the aneurysm wall integrity and subsequently affect growth. The purpose of this study was to assess associations between malignancy, therapeutic regimens and the growth rates of aorto-iliac aneurysms.

PATIENTS AND METHODS

A retrospective single-center analysis identified patients with aneurysm + cancer. Patients with ≥2 CT angiograms over ≥6 months and additional malignancy were included. Clinical data and aneurysm diameters were analyzed. AAA growth under cancer therapy (chemotherapy/radiation) was compared to a non-cancer AAA control cohort and to meta-analysis data. Statistics included t-tests and a linear regression model with correction for initial aortic diameter and type of treatment.

RESULTS

From 2003 - 2020, 217 patients (median age 70 years; 92% male) with 246 aneurysms (58.8% AAA) and 238 malignancies were identified. Prostate (27%) and lung (16%) cancer were most frequently seen, 157 patients (72%) received chemotherapy and 105 patients (48%) radiation, thereof 79 (36.4%) both. Annual AAA growth was not significantly different for cancer and non-cancer patients (2.0±2.3 vs. 2.8±2.1mm/y, p=0.20). However, subgroup analyses revealed that radiation was associated with a significantly reduced aneurysm growth rate compared to cancer patients without radiation (1.1±1.3 vs. 1.6±2.1 mm/y, p=0.046) and to the non-cancer control cohort (1.7±1.9 vs. 2.8±2.1 mm/y, p=0.007). Administration of antimetabolites showed significantly increased AAA growth (+0.9mm/year, p=0.011), while e.g. topoisomerase inhibitors (-0.8mm/year, p=0.17) and anti-androgens (-0.5mm/year, p=0.27) showed a possible trend for reduced growth. Similar was observed for iliac aneurysms (n=85). Additionally, effects were persistent in combinations of chemotherapies (2.6±1.4 substances/patient).

CONCLUSION

Cancer patients with concomitant aortic aneurysms may require intensified monitoring when undergoing specific therapies, such as antimetabolites, since they may experience an increased aneurysm growth rate. Radiation may be associated with reduced aneurysm growth.

Fibrates: A Possible Treatment Option for Patients with Abdominal Aortic Aneurysm?

Abdominal aortic aneurysm (AAA) is a life-threatening disease; however, there is no established treatment for patients with AAA. Fibrates are agonists of peroxisome proliferator-activated receptor alpha (PPARα) that are widely used as therapeutic agents to treat patients with hypertriglyceridemia. They can regulate the pathogenesis of AAA in multiple ways, for example, by exerting anti-inflammatory and anti-oxidative effects and suppressing the expression of matrix metalloproteinases. Previously, basic and clinical studies have evaluated the effects of fenofibrate on AAA. In this paper, we summarize the results of these studies and discuss the problems associated with using fenofibrate as a therapeutic agent for patients with AAA. In addition, we discuss a new perspective on the regulation of AAA by PPARα agonists.

Optimal timing of surveillance ultrasounds in small aortic aneurysms

OBJECTIVE

Small abdominal aortic aneurysms (AAA) surveillance intervals remain controversial and difficult to standardize. Current Society for Vascular Surgery guidelines lack quality evidence. The objective of this study is to examine patients followed in a high volume non-invasive vascular laboratory, determine if the current guidelines are fitting in clinical practice, and attempt to further identify risk factors for accelerated aneurysm growth.

METHODS

A retrospective analysis of patients who underwent at least two ultrasounds for AAA in the vascular laboratory during 2008-2018 with baseline diameter less than 5.0 cm was conducted. Patient demographics were collected. Groups were then created for comparison using the size criteria according to SVS guidelines. In addition, we compared overall growth rates specifically evaluating rapid growth (rate of at least 1.0 cm/year and size change of at least 0.5 cm from previous imaging), expected growth (any growth below 1.0 cm/year and of at least 0.5 cm from baseline) and no growth.

RESULTS

A total of 1581 patients (1232 male and 349 female) were identified with a total of 5945 ultrasound studies. The median age was 73 years and mean follow-up was 27.8 months. Baseline AAA size was 3.0-3.9 cm in 986 patients and 4.0-4.9 cm in 595 patients. The average maximum growth rate was 0.18 cm/year for AAAs 3.0-3.9 cm and 0.36 cm/year for AAAs 4.0-4.9 cm (p<0.001). Patients with AAA 4.0-4.9 cm at baseline were more likely to be white, male, hypertensive and have chronic kidney disease (p <0.05). 1078 patients (68.2%) demonstrated no growth over the observed time period with 342 patients (21.6%) demonstrating expected growth and 161 (10.2%) rapid growth. Male gender and baseline AAA size of 4.0-4.9 cm were more likely to demonstrate rapid growth (p=0.002) and eventual repair (p<0.001). Metformin use was more common in the AAA group with no growth (p <0.05). Freedom from rapid growth and repair indication at two years was significantly lower in those patients with baseline aneurysms 3.0-3.9 cm (p<0.001).

CONCLUSIONS

The overall low rate of events in small AAAs supports continued surveillance every 3 years for AAAs between 3.0 and 3.9 cm and yearly for male patients with AAAs 4.0-4.9 cm as recommended by the SVS Guidelines. Female gender may have less rapid growth than previously reported but likely merit more rigorous surveillance particularly as the AAAs approach 5.0 cm. Metformin use continues to demonstrate it may abrogate aneurysmal growth. Lastly, there is a subset of patients that exhibit more rapid growth of their small AAAs, and further study will be required to further classify these patients.

Endovascular Aortic Repair in Patients of Advanced Age

PURPOSE

Treatment decisions for the elderly with abdominal aortic aneurysms (AAAs) are challenging. With advancing age, the risk of endovascular aneurysm repair (EVAR) increases while life expectancy decreases, which may nullify the benefit of EVAR. The purpose of this study was to quantify the impact of EVAR on 1-year mortality in patients of advanced age.

MATERIALS AND METHODS

The 2003-2020 Vascular Quality Initiative Database was utilized to identify patients who underwent EVAR for AAAs. Patients were included if they were 80 years of age or older. Exclusions included non-elective surgery or missing aortic diameter data. Predicted 1-year mortality of untreated AAAs was calculated based on a validated comorbidity score that predicts 1-year mortality (Gagne Index, excluding the component associated with AAAs) plus the 1-year aneurysm-related mortality without repair. The primary outcome for the study was 1-year mortality.

RESULTS

A total of 11 829 patients met study criteria. The median age was 84 years [81, 86] with 9014 (76.2%) being male. Maximal AAA diameters were apportioned as follows: 39.6% were <5.5 cm, 28.6% were 5.5-5.9 cm, 21.3% were 6.0-6.9 cm, and 10.6% were ≥7.0 cm. The predicted 1-year mortality rate without EVAR was 11.9%, which was significantly higher than the actual 1-year mortality rate with EVAR (8.2%; p<0.001). The overall rate of perioperative MACE was 4.4% (n = 516). Patients with an aneurysm diameter <5.5cm had worse actual 1-year mortality rates with EVAR compared to predicted 1-year mortality rates without EVAR. In contrast, those with larger aneurysms (≥5.5cm) had better actual 1-year mortality rates with EVAR. The benefit from EVAR for those with Gagne Indices 2-5 was largely restricted to those with AAAs ≥ 7.0cm; whereas those with Gagne Indices 0-1 experience a survival benefit for AAAs larger than 5.5 cm.

CONCLUSION

The current data suggest that EVAR decreases 1-year mortality rates for patients of advanced age compared to non-operative management in the elderly. However, the survival benefit is largely limited to those with Gagne Indices 0-1 with AAAs ≥ 5.5 cm and Gagne Indices 2-5 with AAAs ≥ 7.0 cm. Those of advanced age may benefit from EVAR, but realizing this benefit requires careful patient selection.

Defining a master curve of abdominal aortic aneurysm growth and its potential utility of clinical management

OBJECTIVE

The maximum diameter measurement of an abdominal aortic aneurysm (AAA), which depends on orthogonal and axial cross-sections or maximally inscribed spheres within the AAA, plays a significant role in the clinical decision making process. This study aims to build a total of 21 morphological parameters from longitudinal CT scans and analyze their correlations. Furthermore, this work explores the existence of a "master curve" of AAA growth, and tests which parameters serve to enhance its predictability for clinical use.

METHODS

106 CT scan images from 25 Korean AAA patients were retrospectively obtained. We subsequently computed morphological parameters, growth rates, and pair-wise correlations, and attempted to enhance the predictability of the growth for high-risk aneurysms using non-linear curve fitting and least-square minimization.

RESULTS

An exponential AAA growth model was fitted to the maximum spherical diameter, as the best representative of the growth among all parameters (r-square: 0.94) and correctly predicted to 15 of 16 validation scans based on a 95% confidence interval. AAA volume expansion rates were highly correlated (r=0.75) with thrombus accumulation rates.

CONCLUSIONS

The exponential growth model using spherical diameter provides useful information about progression of aneurysm size and enables AAA growth rate extrapolation during a given surveillance period.

Vascular Deformation Mapping of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a complex disease that requires regular imaging surveillance to monitor for aneurysm stability. Current imaging surveillance techniques use maximum diameter, often assessed by computed tomography angiography (CTA), to assess risk of rupture and determine candidacy for operative repair. However, maximum diameter measurements can be variable, do not reliably predict rupture risk and future AAA growth, and may be an oversimplification of complex AAA anatomy. Vascular deformation mapping (VDM) is a recently described technique that uses deformable image registration to quantify three-dimensional changes in aortic wall geometry, which has been previously used to quantify three-dimensional (3D) growth in thoracic aortic aneurysms, but the feasibility of the VDM technique for measuring 3D growth in AAA has not yet been studied. Seven patients with infra-renal AAAs were identified and VDM was used to identify three-dimensional maps of AAA growth. In the present study, we demonstrate that VDM is able to successfully identify and quantify 3D growth (and the lack thereof) in AAAs that is not apparent from maximum diameter. Furthermore, VDM can be used to quantify growth of the excluded aneurysm sac after endovascular aneurysm repair (EVAR). VDM may be a useful adjunct for surgical planning and appears to be a sensitive modality for detecting regional growth of AAAs.

Hemodynamic Changes in an Actively Rupturing Abdominal Aortic Aneurysm

Computational fluid dynamics were used to assess hemodynamic changes in an actively rupturing abdominal aortic aneurysm (AAA) over a 9-day period. Active migration of contrast from the lumen into the thickest region of intraluminal thrombus (ILT) was demonstrated until it ultimately breached the adventitial layer. Four days after symptom onset, there was a discrete disruption of adventitial calcium with bleb formation at the site of future rupture. Rupture occurred in a region of low wall shear stress and was associated with a marked increase in AAA diameter from 6.6 to 8.4 cm. The cross-sectional area of the flow lumen increased across all time points from 6.28 to 12.08 cm2. The increase in luminal area preceded the increase in AAA diameter and was characterized by an overall deceleration in recirculation flow velocity with a coinciding increase in flow velocity penetrating the ILT. We show that there are significant hemodynamic and structural changes in the AAA flow lumen in advance of any appreciable increase in aortic diameter or rupture. The significant increase in AAA diameter with rupture suggests that AAA may actually rupture at smaller sizes than those measured on day of rupture. These findings have implications for algorithms the predict AAA rupture risk.

Validation of natural language processing to determine the presence and size of abdominal aortic aneurysms in a large integrated health system

OBJECTIVE

Previous studies of the natural history of abdominal aortic aneurysms (AAAs) have been limited by small cohort sizes or heterogeneous analyses of pooled data. By quickly and efficiently extracting imaging data from the health records, natural language processing (NLP) has the potential to substantially improve how we study and care for patients with AAAs. The aim of the present study was to test the ability of an NLP tool to accurately identify the presence or absence of AAAs and detect the maximal abdominal aortic diameter in a large dataset of imaging study reports.

METHODS

Relevant imaging study reports (n = 230,660) from 2003 to 2017 were obtained for 32,778 patients followed up in a prospective aneurysm surveillance registry within a large, diverse, integrated healthcare system. A commercially available NLP algorithm was used to assess the presence of AAAs, confirm the absence of AAAs, and extract the maximal diameter of the abdominal aorta, if stated. A blinded expert manual review of 18,000 randomly selected imaging reports was used as the reference standard. The positive predictive value (PPV or precision), sensitivity (recall), and the kappa statistics were calculated.

RESULTS

Of the randomly selected 18,000 studies that underwent expert manual review, 48.7% were positive for AAAs. In confirming the presence of an AAA, the interrater reliability of the NLP compared with the expert review showed a kappa value of 0.84 (95% confidence interval [CI], 0.83-0.85), with a PPV of 95% and sensitivity of 88.5%. The NLP algorithm showed similar results for confirming the absence of an AAA, with a kappa of 0.79 (95% CI, 0.799-0.80), PPV of 77.7%, and sensitivity of 91.9%. The kappa, PPV, and sensitivity of the NLP for correctly identifying the maximal aortic diameter was 0.88 (95% CI, 0.87-0.89), 88.8%, and 88.2% respectively.

CONCLUSIONS

The use of NLP software can accurately analyze large volumes of radiology report data to detect AAA disease and assemble a contemporary aortic diameter-based cohort of patients for longitudinal analysis to guide surveillance, medical management, and operative decision making. It can also potentially be used to identify from the electronic medical records pre- and postoperative AAA patients "lost to follow-up," leverage human resources engaged in the ongoing surveillance of patients with AAAs, and facilitate the construction and implementation of AAA screening programs.

Risk Factors and Mouse Models of Abdominal Aortic Aneurysm Rupture

Abdominal aortic aneurysm (AAA) rupture is an important cause of death in older adults. In clinical practice, the most established predictor of AAA rupture is maximum AAA diameter. Aortic diameter is commonly used to assess AAA severity in mouse models studies. AAA rupture occurs when the stress (force per unit area) on the aneurysm wall exceeds wall strength. Previous research suggests that aortic wall structure and strength, biomechanical forces on the aorta and cellular and proteolytic composition of the AAA wall influence the risk of AAA rupture. Mouse models offer an opportunity to study the association of these factors with AAA rupture in a way not currently possible in patients. Such studies could provide data to support the use of novel surrogate markers of AAA rupture in patients. In this review, the currently available mouse models of AAA and their relevance to the study of AAA rupture are discussed. The review highlights the limitations of mouse models and suggests novel approaches that could be incorporated in future experimental AAA studies to generate clinically relevant results.

Variation in Surgical Treatment of Abdominal Aortic Aneurysms With Small Aortic Diameters in the Netherlands

OBJECTIVE

To evaluate reasons to deviate from aneurysm diameter thresholds, and focus on the difference in how Dutch vascular surgical units (VSUs) perceive their deviation and their actual deviation.

BACKGROUND

Guidelines recommend surgical treatment for asymptomatic abdominal aortic aneurysms (AAAs) with a diameter of at least 55 mm for men and 50 mm for women. We evaluate reasons to deviate from these guidelines, and focus on the difference in how Dutch vascular surgical units (VSUs) perceive their deviation and their actual deviation.

METHODS

All patients undergoing elective AAA repair between 2013 and 2016 registered in the Dutch Surgical Aneurysm Audit (DSAA) were included. Surgery at diameters of <55 mm for men and <50 mm for women were considered guideline deviations. National deviation and hospital variation in deviation were evaluated over time. Questionnaires were distributed among all Dutch VSUs, inquiring for acceptable reasons for guideline deviation. VSUs were asked to estimate the guideline deviation percentage in their hospital which was then compared with their DSAA percentage.

RESULTS

In all, 9039 patients were included. In 15%, we found guideline deviation, varying from 2% to 40% between VSUs. Over time, 21 VSUs were identified with a lower percentage of deviation than the national mean each year and 8 VSUs with a higher percentage. 44/60 VSUs completed the questionnaire. Most commonly reported reasons to deviate were concomitant large iliac diameter (91%) and saccular aneurysm (82%). The majority of the VSUs (77%) estimated their guideline deviation to be <5%. Eleven VSUs (25%) estimated their deviation concordant with their DSAA percentage, but 75% of VSUs underestimated their deviation.

CONCLUSIONS

Dutch VSUs regularly deviate from the guidelines regarding aneurysm diameter, with variation between VSUs. Consensus exists amongst VSUs on acceptable reasons for guideline deviations; however, the majority underestimates their actual deviation percentage.

Combining Volumetric and Wall Shear Stress Analysis from CT to Assess Risk of Abdominal Aortic Aneurysm Progression

Background Despite known limitations, the decision to operate on abdominal aortic aneurysm (AAA) is primarily on the basis of measurement of maximal aneurysm diameter. Purpose To identify volumetric and computational fluid dynamics parameters to predict AAAs that are likely to progress in size. Materials and Methods This study, part of a multicenter prospective registry (NCT01599533), included 126 patients with AAA. Patients were sorted into stable (≤10-mL increase in aneurysm volume) and progression (>10-mL increase in aneurysm volume) groups. Initial AAA characteristics of the derivation cohort were analyzed (maximal diameter and surface, thrombus and lumen volumes, maximal wall pressure, and wall shear stress [WSS]) to identify relevant parameters for a logistic regression model. Model and maximal diameter diagnostic performances were assessed in both cohorts and for AAAs smaller than 50 mm by using area under the receiver operating characteristic curve (AUC). Results Eighty-one patients were included (mean age, 73 years ± 7 years [standard deviation]; 78 men). The derivation and validation cohorts included, respectively, 50 and 31 participants. In the derivation cohort, there was higher mean lumen volume and lower mean WSS in the progression group compared with the stable group (60 mL ± 14 vs 46 mL ± 18 [P = .005] and 66% ± 6 vs 53% ± 9 [P = .02], respectively). Mean lumen volume and mean WSS at baseline were correlated to total volume growth (r = 0.47 [P = .002] and -0.42 [P = .006], respectively). In the derivation cohort, a regression model including lumen volume and WSS to predict aneurysm enlargement was superior to maximal diameter alone (AUC, 0.78 vs 0.52, respectively; P = .003); although no difference was found in the validation cohort (AUC, 0.79 vs 0.71, respectively; P = .51). For AAAs smaller than 50 mm, a regression model that included both baseline WSS and lumen volume performed better than maximal diameter (AUC, 0.79 vs 0.53, respectively; P = .01). Conclusion Combined analysis of lumen volume and wall shear stress was associated with enlargement of abdominal aortic aneurysms at 1 year, particularly in aneurysms smaller than 50 mm in diameter. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Mitsouras and Leach in this issue.

Predicting abdominal aortic aneurysm growth using patient-oriented growth models with two-step Bayesian inference

OBJECTIVE

For small abdominal aortic aneurysms (AAAs), a regular follow-up examination is recommended every 12 months for AAAs of 30-39 mm and every six months for AAAs of 40-55 mm. Follow-up diameters can determine if a patient follows the common growth model of the population. However, the rapid expansion of an AAA, often associated with higher rupture risk, may be overlooked even though it requires surgical intervention. Therefore, the prognosis of abdominal aortic aneurysm growth is clinically important for planning treatment. This study aims to build enhanced Bayesian inference methods to predict maximum aneurysm diameter.

METHODS

106 CT scans from 25 Korean AAA patients were retrospectively obtained. A two-step approach based on Bayesian calibration was used, and an exponential abdominal aortic aneurysm growth model (population-based) was specified according to each individual patient's growth (patient-specific) and morphologic characteristics of the aneurysm sac (enhanced). The distribution estimates were obtained using a Markov Chain Monte Carlo (MCMC) sampler.

RESULTS

The follow-up diameters were predicted satisfactorily (i.e. the true follow-up diameter was in the 95% prediction interval) for 79% of the scans using the population-based growth model, and 83% of the scans using the patient-specific growth model. Among the evaluated geometric measurements, centerline tortuosity was a significant (p = 0.0002) predictor of growth for AAAs with accelerated and stable expansion rates. Using the enhanced prediction model, 86% of follow-up scans were predicted satisfactorily. The average prediction errors of population-based, patient-specific, and enhanced models were ±2.67, ±2.61 and ± 2.79 mm, respectively.

CONCLUSION

A computational framework using patient-oriented growth models provides useful tools for per-patient basis treatment and enables better prediction of AAA growth.

Statins Reduce Abdominal Aortic Aneurysm Growth, Rupture, and Perioperative Mortality: A Systematic Review and Meta-Analysis

Background

There are no recognized pharmacological treatments for abdominal aortic aneurysms (AAA), although statins are suggested to be beneficial. We sought to summarize the literature regarding the effects of statins on human AAA growth, rupture, and 30‐day mortality.

Methods and Results

We conducted a systematic review and meta‐analysis of randomized and observational studies using the Cochrane CENTRAL database, MEDLINE, and EMBASE up to June 15, 2018. Review, abstraction, and quality assessment were conducted by 2 independent reviewers, and a third author resolved discrepancies. Pooled mean differences and odds ratios with 95% confidence intervals were calculated using random effects models. Heterogeneity was quantified using the I² statistic, and publication bias was assessed using funnel plots. Our search yielded 911 articles. One case‐control and 21 cohort studies involving 80 428 patients were included. The risk of bias was low to moderate. Statin use was associated with a mean AAA growth rate reduction of 0.82 mm/y (95% confidence interval 0.33, 1.32, P=0.001, I²=86%). Statins were also associated with a lower rupture risk (odds ratio 0.63, 95% confidence interval 0.51, 0.78, P<0.0001, I²=27%), and preoperative statin use was associated with a lower 30‐day mortality following elective AAA repair (odds ratio 0.55, 95% confidence interval 0.36, 0.83, P=0.005, I²=57%).

Conclusions

Statin therapy may be associated with reduction in AAA progression, rupture, and lower rates of perioperative mortality following elective AAA repair. These data argue for widespread statin use in AAA patients.

Clinical Trial Registration

URL: http://www.crd.york.ac.uk. Unique identifier: CRD42017056480.

Estimation of Abdominal Aortic Aneurysm Rupture Risk with Biomechanical Imaging Markers

PURPOSE

To evaluate whether the biomechanical marker known as rupture risk equivalent diameter (RRED) was superior to the actual abdominal aortic aneurysm (AAA) diameter in estimating future rupture risk in patients who had undergone pre-rupture computed tomography (CT) angiography.

MATERIALS AND METHODS

A retrospective study was conducted in 13 patients with ruptured AAAs who had undergone CT angiography before and after rupture between 2001 and 2015. The median time between the 2 scans was 731 days. Biomechanical and geometrical markers such as maximal AAA diameter, peak wall stress (PWS), and RRED were calculated with AAA-dedicated software. The main analyses determined whether RRED was higher than the actual diameter and the threshold diameter for elective surgery (55 mm for men, 50 mm for women) in AAAs before and after rupture. Differences between diameter and biomechanical markers before and after rupture were tested with appropriate statistical tests.

RESULTS

RRED before and after rupture was smaller than the actual diameter in 7 of 13 cases. Post-rupture RRED was estimated to be smaller than the threshold diameter for elective repair in 4 cases, again suggesting a low rupture risk. The median PWS before and after rupture was 181.7 kPa (interquartile range [IQR], 152.1-244.2 kPa) and 274.1 kPa (IQR, 172.2-377.2 kPa), respectively.

CONCLUSIONS

RRED was smaller than the actual diameter in more than half of pre-rupture AAAs, suggesting a lower rupture risk than estimated with the actual diameter. The results suggest that the currently available biomechanical imaging markers might not be ready for use in clinical practice.

An evaluation of the effect of an angiotensin-converting enzyme inhibitor on the growth rate of small abdominal aortic aneurysms: a randomised placebo-controlled trial (AARDVARK)

BACKGROUND

Although data are inconsistent, angiotensin-converting enzyme inhibitors (ACE-Is) have been associated with a reduced incidence of abdominal aortic aneurysm (AAA) rupture in analysis of administrative databases.

OBJECTIVES

(1) To investigate whether or not the ACE-I perindopril (Coversyl arginine, Servier) reduces small AAA growth rate and (2) to evaluate blood pressure (BP)-independent effects of perindopril on small AAA growth and to compare the repeatability of measurement of internal and external aneurysm diameters.

DESIGN

A three-arm, multicentre, single-blind, randomised placebo-controlled trial.

SETTING

Fourteen hospitals in England.

PARTICIPANTS

Men or women aged ≥ 55 years with an AAA of 3.0-5.4 cm in diameter by internal or external measurement according to ultrasonography and who met the trial eligibility criteria.

INTERVENTIONS

Patients were randomised to receive 10 mg of perindopril arginine daily, 5 mg of the calcium channel blocker amlodipine daily or placebo daily.

MAIN OUTCOME MEASURES

The primary outcome was AAA diameter growth using external measurements in the longitudinal plane, which in-trial studies suggested was the preferred measure. Secondary outcome measures included AAA rupture, AAA repair, modelling of the time taken for the AAA to reach the threshold for intervention (5.5 cm) or referral for surgery, tolerance of study medication (measured by compliance, adverse events and quality of life) and a comparison of the repeatability of measures of internal and external AAA diameter. Patients were followed up every 3-6 months over 2 years.

RESULTS

In total, 227 patients were recruited and randomised into the three groups, which were generally well matched at baseline. Multilevel modelling was used to determine the maximum likelihood estimates for AAA diameter growth. No significant differences in the estimates of annual growth were apparent [1.68 (standard error 0.02) mm, 1.77 (0.02) mm and 1.81 (0.02) mm in the placebo, perindopril and amlodipine groups, respectively]. Similarly, no significant differences in the slopes of modelled growth over time were apparent between perindopril and placebo (p = 0.78) or between perindopril and amlodipine (p = 0.89). The results were essentially unaffected by adjustment for potential confounders. Compliance, measured by pill counts, was good throughout (> 80% at all visit time points). There were no significant in-trial safety concerns. Six patients withdrew because of adverse events attributed to the study medications (n = 2 perindopril, n = 4 amlodipine). No patients ruptured their AAA and 27 underwent elective surgery during the trial (n = 9 placebo, n = 10 perindopril, n = 8 amlodipine).

CONCLUSIONS

We were unable to demonstrate a significant impact of perindopril compared with placebo or amlodipine on small AAA growth over a 2-year period. Furthermore, there were no differences in the times to reach a diameter of 5.5 cm or undergo surgery among the three groups. Perindopril and amlodipine were well tolerated by this population. External AAA measurements were found to be more repeatable than internal measurements. The observed AAA growth measurement variability was greater than that expected pre trial. This, combined with slower than expected mean growth rates, resulted in our having limited power to detect small differences between growth rates and hence this adds uncertainty to the interpretation of the results. Several further analyses are planned including a multivariate analysis of determinants of AAA growth, an evaluation of the possible differential effect of perindopril on fast AAA growth and an investigation into the roles of central BP and BP variability on AAA growth.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN51383267.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 20, No. 59. See the NIHR Journals Library website for further project information. The NIHR Biomedical Research Centre based at Imperial College NHS Trust supported the trial. Servier provided perindopril at no charge.

Correlation between transversal and orthogonal maximal diameters of abdominal aortic aneurysms and alternative rupture risk predictors

PURPOSE

There is no standard for measuring maximal diameter (Dmax) of abdominal aortic aneurysm (AAA) from computer tomography (CT) images although differences between Dmax evaluated from transversal (axialDmax) or orthogonal (orthoDmax) planes can be large especially for angulated AAAs. Therefore we investigated their correlations with alternative rupture risk indicators as peak wall stress (PWS) and peak wall rupture risk (PWRR) to decide which Dmax is more relevant in AAA rupture risk assessment.

MATERIAL AND METHODS

The Dmax values were measured by a trained radiologist from 70 collected CT scans, and the corresponding PWS and PWRR were evaluated using Finite Element Analysis (FEA). The cohort was ordered according to the difference between axialDmax and orthoDmax (D_a-o) quantifying the aneurysm angulation, and Spearman's correlation coefficients between PWS/PWRR - orthoDmax/axialDmax were calculated.

RESULTS

The calculated correlations PWS/PWRR vs. orthoDmax were substantially higher for angulated AAAs (with D_a-o≥3mm). Under this limit, the correlations were almost the same for both Dmax values. Analysis of AAAs divided into two groups of angulated (n=38) and straight (n=32) cases revealed that both groups are similar in all parameters (orthoDmax, PWS, PWRR) with the exception of axialDmax (p=0.024).

CONCLUSIONS

It was confirmed that orthoDmax is better correlated with the alternative rupture risk predictors PWS and PWRR for angulated AAAs (D_A-O≥3mm) while there is no difference between orthoDmax and axialDmax for straight AAAs (D_A-O<3mm). As angulated AAAs represent a significant portion of cases it can be recommended to use orthoDmax as the only Dmax parameter for AAA rupture risk assessment.

Local Diameter, Wall Stress, and Thrombus Thickness Influence the Local Growth of Abdominal Aortic Aneurysms

Purpose: To investigate the influence of the local diameter, the intraluminal thrombus (ILT) thickness, and wall stress on the local growth rate of abdominal aortic aneurysms. Methods: The infrarenal aortas of 90 asymptomatic abdominal aortic aneurysm (AAA) patients (mean age 70 years; 77 men) were retrospectively reconstructed from at least 2 computed tomography angiography scans (median follow-up of 1 year) and biomechanically analyzed with the finite element method. Each individual AAA model was automatically sliced orthogonally to the lumen centerline and represented by 100 cross sections with corresponding diameters, ILT thicknesses, and wall stresses. The data were grouped according to these parameters for comparison of differences among the variables. Results: Diameter growth was continuously distributed over the entire aneurysm sac, reaching absolute and relative median peaks of 3.06 mm/y and 7.3%/y, respectively. The local growth rate was dependent on the local baseline diameter, the local ILT thickness, and for wall segments not covered by ILT, also on the local wall stress level (all p<0.001). For wall segments that were covered by a thick ILT layer, wall stress did not affect the growth rate (p=0.08). Conclusion: Diameter is not only a strong global predictor but also a local predictor of aneurysm growth. In addition, and independent of the diameter, the ILT thickness and wall stress (for the ILT-free wall) also influence the local growth rate. The high stress sensitivity of nondilated aortic walls suggests that wall stress peaks could initiate AAA formation. In contrast, local diameters and ILT thicknesses determine AAA growth for dilated and ILT-covered aortic walls.

Biomechanical Rupture Risk Assessment: A Consistent and Objective Decision-Making Tool for Abdominal Aortic Aneurysm Patients

Abdominal aortic aneurysm (AAA) rupture is a local event in the aneurysm wall that naturally demands tools to assess the risk for local wall rupture. Consequently, global parameters like the maximum diameter and its expansion over time can only give very rough risk indications; therefore, they frequently fail to predict individual risk for AAA rupture. In contrast, the Biomechanical Rupture Risk Assessment (BRRA) method investigates the wall's risk for local rupture by quantitatively integrating many known AAA rupture risk factors like female sex, large relative expansion, intraluminal thrombus-related wall weakening, and high blood pressure. The BRRA method is almost 20 years old and has progressed considerably in recent years, it can now potentially enrich the diameter indication for AAA repair. The present paper reviews the current state of the BRRA method by summarizing its key underlying concepts (i.e., geometry modeling, biomechanical simulation, and result interpretation). Specifically, the validity of the underlying model assumptions is critically disused in relation to the intended simulation objective (i.e., a clinical AAA rupture risk assessment). Next, reported clinical BRRA validation studies are summarized, and their clinical relevance is reviewed. The BRRA method is a generic, biomechanics-based approach that provides several interfaces to incorporate information from different research disciplines. As an example, the final section of this review suggests integrating growth aspects to (potentially) further improve BRRA sensitivity and specificity. Despite the fact that no prospective validation studies are reported, a significant and still growing body of validation evidence suggests integrating the BRRA method into the clinical decision-making process (i.e., enriching diameter-based decision-making in AAA patient treatment).

Abdominal aortic aneurysms and diabetes mellitus

There is accumulating evidence that risk profiles differ between coronary artery disease and abdominal aortic aneurysms (AAAs). However, diabetes mellitus (DM) appears to be negatively associated with AAA formation. The underlying mechanisms for this negative relationship are far from defined, but may include: increased arterial wall matrix formation via advanced glycation end products; suppression of plasmin and reduction of levels and activity of matrix metalloproteinases (MMP)-2 and 9; diminished aortic wall macrophage infiltration, elastolysis and neovascularization. In addition, the effect of pharmacological agents used for the treatment of patients with DM on AAA formation has been studied with rather controversial results. Statins, angiotensin converting enzyme inhibitors, angiotensin receptor blockers, fenofibrate, antibiotics and some hypoglycemic agents are beginning to be appreciated for a potential modest protection from AAAs, but further studies are needed.

TElmisartan in the management of abDominal aortic aneurYsm (TEDY): The study protocol for a randomized controlled trial

BACKGROUND

Experimental studies suggest that angiotensin II plays a central role in the pathogenesis of abdominal aortic aneurysm. This trial aims to evaluate the efficacy of the angiotensin receptor blocker telmisartan in limiting the progression of abdominal aortic aneurysm.

METHODS/DESIGN

Telmisartan in the management of abdominal aortic aneurysm (TEDY) is a multicentre, parallel-design, randomised, double-blind, placebo-controlled trial with an intention-to-treat analysis. We aim to randomly assign 300 participants with small abdominal aortic aneurysm to either 40 mg of telmisartan or identical placebo and follow patients over 2 years. The primary endpoint will be abdominal aortic aneurysm growth as measured by 1) maximum infra-renal aortic volume on computed tomographic angiography, 2) maximum orthogonal diameter on computed tomographic angiography, and 3) maximum diameter on ultrasound. Secondary endpoints include change in resting brachial blood pressure, abdominal aortic aneurysm biomarker profile and health-related quality of life. TEDY is an international collaboration conducted from major vascular centres in Australia, the United States and the Netherlands.

DISCUSSION

Currently, no medication has been convincingly demonstrated to limit abdominal aortic aneurysm progression. TEDY will examine the potential of a promising treatment strategy for patients with small abdominal aortic aneurysms.

TRIAL REGISTRATION

Australian and Leiden study centres: Australian New Zealand Clinical Trials Registry ACTRN12611000931976 , registered on 30 August 2011; Stanford study centre: clinicaltrials.gov NCT01683084 , registered on 5 September 2012.

Morphologic predictors of aortic expansion in chronic type B aortic dissection

Aim

To identify morphologic factors affecting aortic expansion in patients with uncomplicated type B aortic dissections.

Methods

Computed tomography data of 24 patients (18 male; median age: 61 years), diagnosed with acute uncomplicated type B aortic dissections between 2002 and 2013, were retrospectively reviewed. All patients had at least two computed tomography angiography scans and six months of uneventful follow-up. Computed tomography scans were assessed by two independent readers with regard to presence and number of entry tears. Thoracic and abdominal aortic diameters were derived using image processing software.

Results

Twenty-two of 24 patients showed aortic expansion over a median computed tomography angiographic follow-up of 33.2 months. Annual rates showed an increase of 1.7 mm for total aortic diameter, 2.1 mm for the false and a decrease of −0.4 mm for the true lumen. In three patients (12.5%), aortic diameter exceeded 60 mm during follow-up, and all three patients underwent thoracic endovascular aortic repair. Patients with a maximum aortic diameter <4 cm at baseline showed a significantly higher expansion rate compared to cases with an initial maximum aortic diameter of ≥4 cm ( p=0.0471). A median of two entries (range: 1–5) was recognized per patient. Presence of more than two entry tears ( n = 13) was associated with faster overall diameter expansion (mean annual rates: 2.18 mm vs. 1.16 mm; p = 0.4556), and decrease of the cross-sectional surface of the true lumen over time (annual rate for > 2 entries vs. ≤2 entries: −7.8 mm2 vs. +37.5 mm2; p = 0.0369). Median size of entry tears was 12 mm (range: 2–53 mm).

Conclusions

The results presented herein suggest that uncomplicated type B aortic dissection patients with more than two entry tears and/or an initial maximum aortic diameter of<4 cm are at risk for aortic dilatation and, therefore, may require stricter follow-up including the possible need for early intervention.

The similarities and differences among patients with abdominal aortic aneurysms referred to a tertiary hospital and found at necropsy

OBJECTIVE

To analyze the characteristics of patients with abdominal aortic aneurysms referred to a tertiary center and to compare with individuals with abdominal aortic aneurysm found at necropsy.

METHODS

We have retrospectively analyzed the medical records of 556 patients with abdominal aortic aneurysm and 102 cases abdominal aortic aneurysm found at necropsy.

RESULTS

At univariated analysis, hypertension, tobacco use and maximum diameter were significant risk factors for symptomatic aneurysm, while diabetes tended to be a protective factor for rupture. By logistic regression analysis, the largest transverse diameter was the only one significantly associated with abdominal aortic aneurysm rupture (p < .0001, odds ratio 1.7, 95% confidence interval 1.481-1.951). Intact abdominal aortic aneurysm found at necropsy showed similarities with outpatients in relation to abdominal aortic aneurysm diameter and risk factors.

CONCLUSION

Intact abdominal aortic aneurysm at necropsy and at outpatients setting showed similarities that confirmed that abdominal aortic aneurysm repair is less offered to women, and they died more frequently with intact abdominal aortic aneurysm from other causes.

Diabetes and abdominal aortic aneurysms

Epidemiologic evidence suggests that patients with diabetes may have a lower incidence of abdominal aortic aneurysm (AAA); however, the link between diabetes and AAA development and expansion is unclear. The aim of this review is to analyze updated evidence to better understand the impact of diabetes on prevalence, incidence, clinical outcome, and expansion rate of AAA. A systematic review of literature published in the last 20 years using the PubMed and Cochrane databases was undertaken. Studies reporting appropriate data were identified and a meta-analysis performed using the generic inverse variance method. Sixty-four studies were identified. Methodological quality was "fair" in 16 and "good" in 44 studies according to a formal assessment checklist (Newcastle-Ottawa). In 17 large population prevalence studies there was a significant inverse association between diabetes and AAA: pooled odds ratio (OR) 0.80; 95% confidence intervals (CI) 0.70-0.90 (p = .0009). An inverse association was also confirmed by pooled analysis of data from smaller prevalence studies on selected populations (OR 0.59; 95% CI 0.35-0.99; p = .05), while no significant results were provided by case-control studies. A significant lower pooled incidence of new AAA in diabetics was found over six prospective studies: OR 0.54; 95% CI 0.31-0.91; p = .03. Diabetic patients showed increased operative (30-day/in-hospital) mortality after AAA repair: pooled OR 1.26; 95% CI 1.10-1.44; p = .0008. The increased operative risk was more evident in studies with 30-day assessment. In the long-term, diabetics showed lower survival rates at 2-5 years, while there was general evidence of lower growth rates of small AAA in patients with diabetes compared to non-diabetics. There is currently evidence to support an inverse relationship between diabetes and AAA development and enlargement, even though fair methodological quality or unclear risk of bias in many available studies decreases the strength of the finding. At the same time, operative and long-term survival is lower in diabetic patients, suggesting increased cardiovascular burden. The higher mortality in diabetics raises the question as to whether AAA repair should be individualized in selected diabetic populations at higher AAA rupture risk.

Modeling the Growth of Infrarenal Abdominal Aortic Aneurysms

BACKGROUND

Abdominal aortic aneurysm (AAA) growth is a complex process that is incompletely understood. Significant heterogeneity in growth trajectories between patients has led to difficulties in accurately modeling aneurysm growth across cohorts of patients. We set out to compare four models of aneurysm growth commonly used in the literature and confirm which best fits the patient data of our AAA cohort.

METHODS

Patients with AAA were included in the study if they had two or more abdominal ultrasound scans greater than 3 months apart. Patients were censored from analysis once their AAA exceeded 5.5 cm. Four models were applied using the R environment for statistical computing. Growth estimates and goodness of fit (using the Akaike Information Criterion, AIC) were compared, with p-values based on likelihood ratio testing.

RESULTS

Of 510 enrolled patients, 264 met the inclusion criteria, yielding a total of 1861 imaging studies during 932 cumulative years of surveillance. Overall, growth rates were: (1) 0.35 (0.31,0.39) cm/yr in the growth/time calculation, (2) 0.056 (0.042,0.068) cm/yr in the linear regression model, (3) 0.19 (0.17,0.21) cm/yr in the linear multilevel model, and (4) 0.21 (0.18,0.24) cm/yr in the quadratic multilevel model at time 0, slowing to 0.15 (0.12,0.17) cm/yr at 10 years. AIC was lowest in the quadratic multilevel model (1508) compared to other models (P < 0.0001).

CONCLUSION

AAA growth was heterogeneous between patients; the nested nature of the data is most appropriately modeled by multilevel modeling techniques.

Local wall thickness in finite element models improves prediction of abdominal aortic aneurysm growth

OBJECTIVE

Growing evidence suggests that peak wall stress (PWS) derived from finite element analysis (FEA) of abdominal aortic aneurysms (AAAs) predicts clinical outcomes better than diameter alone. Prior models assume uniform wall thickness (UWT). We hypothesize that the inclusion of locally variable wall thickness (VWT) into FEA of AAAs will improve its ability to predict clinical outcomes.

METHODS

Patients with AAAs (n = 26) undergoing radiologic surveillance were identified. Custom MATLAB algorithms generated UWT and VWT aortic geometries from computed tomography angiography images, which were subsequently loaded with systolic blood pressure using FEA. PWS and aneurysm expansion (as a proxy for rupture risk and the need for repair) were examined.

RESULTS

The average radiologic follow-up time was 22.0 ± 13.6 months and the average aneurysm expansion rate was 2.8 ± 1.7 mm/y. PWS in VWT models significantly differed from PWS in UWT models (238 ± 68 vs 212 ± 73 kPa; P = .025). In our sample, initial aortic diameter was not found to be correlated with aneurysm expansion (r = 0.26; P = .19). A stronger correlation was found between aneurysm expansion and PWS derived from VWT models compared with PWS from UWT models (r = 0.86 vs r = 0.58; P = .032 by Fisher r to Z transformation).

CONCLUSIONS

The inclusion of locally VWT significantly improved the correlation between PWS and aneurysm expansion. Aortic wall thickness should be incorporated into future FEA models to accurately predict clinical outcomes.

Abdominal aortic aneurysm imaging with 3-D ultrasound: 3-D-based maximum diameter measurement and volume quantification

The clinical reliability of 3-D ultrasound imaging (3-DUS) in quantification of abdominal aortic aneurysm (AAA) was evaluated. B-mode and 3-DUS images of AAAs were acquired for 42 patients. AAAs were segmented. A 3-D-based maximum diameter (Max3-D) and partial volume (Vol30) were defined and quantified. Comparisons between 2-D (Max2-D) and 3-D diameters and between orthogonal acquisitions were performed. Intra- and inter-observer reproducibility was evaluated. Intra- and inter-observer coefficients of repeatability (CRs) were less than 5.18 mm for Max3-D. Intra-observer and inter-observer CRs were respectively less than 6.16 and 8.71 mL for Vol30. The mean of normalized errors of Vol30 was around 7%. Correlation between Max2-D and Max3-D was 0.988 (p < 0.0001). Max3-D and Vol30 were not influenced by a probe rotation of 90°. Use of 3-DUS to quantify AAA is a new approach in clinical practice. The present study proposed and evaluated dedicated parameters. Their reproducibility makes the technique clinically reliable.

Intravenous administration of mesenchymal stem cells prevents angiotensin II-induced aortic aneurysm formation in apolipoprotein E-deficient mouse

Background

Mesenchymal stem cells (MSCs) are known to be capable of suppressing inflammatory responses. We previously reported that intra-abdominal implantation of bone marrow-derived MSCs (BM-MSCs) sheet by laparotomy attenuated angiotensin II (AngII)-induced aortic aneurysm (AA) growth in apolipoprotein E-deficient (apoE^−/−) mice through anti-inflammation effects. However, cell delivery by laparotomy is invasive; we here demonstrated the effects of multiple intravenous administrations of BM-MSCs on AngII-induced AA formation.

Methods

BM-MSCs were isolated from femurs and tibiae of male apoE^−/− mice. Experimental AA was induced by AngII infusion for 28 days in apoE^−/− mice. Mice received weekly intravenous administration of BM-MSCs (n=12) or saline (n=10). After 4 weeks, AA formation incidence, aortic diameter, macrophage accumulation, matrix metalloproteinase (MMP)’ activity, elastin content, and cytokines were evaluated.

Results

AngII induced AA formation in 100% of the mice in the saline group and 50% in the BM-MSCs treatment group (P < 0.05). A significant decrease of aortic diameter was observed in the BM-MSCs treatment group at ascending and infrarenal levels, which was associated with decreased macrophage infiltration and suppressed activities of MMP-2 and MMP-9 in aortic tissues, as well as a preservation of elastin content of aortic tissues. In addition, interleukin (IL)-1β, IL-6, and monocyte chemotactic protein-1 significantly decreased while insulin-like growth factor-1 and tissue inhibitor of metalloproteinases-2 increased in the aortic tissues of BM-MSCs treatment group.

Conclusions

Multiple intravenous administrations of BM-MSCs attenuated the development of AngII-induced AA in apoE^−/− mice and may become a promising alternative therapeutic strategy for AA progression.

Outcomes of an abdominal aortic aneurysm screening program

OBJECTIVE

In 2007, Medicare guidelines were established to identify persons at risk for the presence of an abdominal aortic aneurysm (AAA). The purpose of this study is to evaluate the 5-year outcomes of an AAA screening program in a regional Veterans Affairs (VA) health care system.

METHODS

Data were extracted from a regional VA health care network identifying all veteran males 65 to 75 years of age who smoked at least 100 cigarettes during their lifetime. In 2007, an AAA screening mandate was implemented allowing patients meeting screening criteria to be evaluated for AAA as part of the patient's health maintenance. AAA is identified as an aortic diameter size of 3.0 cm or greater. Clinician adherence to screening protocols and referral to a vascular surgeon for aneurysms >5.5 cm were also evaluated.

RESULTS

A total of 9751 patients (71.5 ± 5.6 standard deviation years of age) were screened for an AAA over a 5-year period from January 1, 2007 to December 31, 2011. A total of 698 aneurysms (7.1%) were found. Referrals to a vascular surgeon were made on 45 patients with aneurysms >5.5 cm. Over a 5-year period, a total of 2754 patients (28.2%) were inappropriately screened: 416 patients were under 65 years old, 2243 patients were over 75 years old, 36 patients were women, and 123 patients without aneurysms had multiple screenings. In 2007, during the first year of implementation, 39.2% of patients were inappropriately screened. Over the next 4 years, inappropriate screenings decreased with 33.7% in 2008, 28.6% in 2009, 17.7% in 2010, and 14.3% in 2011.

CONCLUSIONS

A large AAA screening program at the VA detects more aneurysms, but at smaller diameters than that published in clinical trials. Over time, the number of inappropriate AAA screenings has continued to decrease, demonstrating greater awareness and application of the AAA screening guidelines by primary care providers. Developing surveillance guidelines for small and medium aneurysms is a potential area for future research.

A modern experience with saccular aortic aneurysms

OBJECTIVE

Repair of saccular aortic aneurysms (SAAs) is frequently recommended based on a perceived predisposition to rupture, despite little evidence that these aneurysms have a more malignant natural history than fusiform aortic aneurysms.

METHODS

The radiology database at a single university hospital was searched for the computed tomographic (CT) diagnosis of SAA between 2003 and 2011. Patient characteristics and clinical course, including the need for surgical intervention, were recorded. SAA evolution was assessed by follow-up CT, where available. Multivariate analysis was used to examine potential predictors of aneurysm growth rate.

RESULTS

Three hundred twenty-two saccular aortic aneurysms were identified in 284 patients. There were 153 (53.7%) men and 131 women with a mean age of 73.5±10.0 years. SAAs were located in the ascending aorta in two (0.6%) cases, the aortic arch in 23 (7.1%), the descending thoracic aorta in 219 (68.1%), and the abdominal aorta in 78 (24.2%). One hundred thirteen (39.8%) patients underwent surgical repair of SAA. Sixty-two patients (54.9%) underwent thoracic endovascular aortic repair, 22 underwent endovascular aneurysm repair (19.5%), and 29 (25.6%) required open surgery. The average maximum diameter of SAA was 5.0±1.6 cm. In repaired aneurysms, the mean diameter was 5.4±1.4 cm; in unrepaired aneurysms, it was 4.4±1.1 cm (P<.001). Eleven patients (3.9%) had ruptured SAAs on initial scan. Of the initial 284 patients, 50 patients (with 54 SAA) had CT follow-up after at least 3 months (23.2±19.0 months). Fifteen patients (30.0%) ultimately underwent surgical intervention. Aneurysm growth rate was 2.8±2.9 mm/yr, and was only weakly related to initial aortic diameter (R2=.19 by linear regression, P=.09 by multivariate regression). Decreased calcium burden (P=.03) and increased patient age (P=.05) predicted increased aneurysm growth by multivariate analysis.

CONCLUSIONS

While SAA were not found to have a higher growth rate than their fusiform counterparts, both clinical and radiologic follow-up is necessary, as a significant number ultimately require surgical intervention. Further clinical research is necessary to determine the optimal management of SAA.

Standardization of outcome measures in clinical trials of pharmacological treatment for abdominal aortic aneurysm

An abdominal aortic aneurysm (AAA) is a common aortic wall disease with an increased prevalence in the elderly population (4-8% for those aged >65 years). Many AAAs are slow growing and remain insidious. Current standard of care for patients with small AAAs (<49 mm) is surveillance, with interventional therapy (open surgical repair or endovascular aneurysm repair) recommended for large (>50-55 mm), rapidly growing (>10 mm/year) or symptomatic AAAs. Although open surgical repair or endovascular aneurysm repair are effective, significant short- and long-term postoperative morbidity and mortality occurs. Currently, there is no pharmacological treatment specific for AAA; the need for the development of targeted pharmacological therapies based on clinically relevant and feasible outcomes acceptable to the medical community, regulatory agencies and third-party payers is high. A consensus on such end points will be critical to accelerating the development of pharmacological agents to prevent formation, arrest the expansion and reduce the rupture risk of AAA.

Growth of screen-detected abdominal aortic aneurysms in men: a bayesian analysis

There is considerable interindividual variability in the growth of abdominal aortic aneurysms (AAAs), but an individual's growth observations, risk factors, and biomarkers could potentially be used to tailor surveillance. To assess the potential for tailoring surveillance, this study determined the accuracy of individualized predictions of AAA size at the next surveillance observation. A hierarchical Bayesian model was fitted to a total of 1,732 serial ultrasound measurements from 299 men in whom ultrasound screening identified an AAA. The data were best described by a nonlinear model with a constant first derivative of the AAA growth rate with size. The area under the receiver operating characteristic (ROC) curves for predicting whether an AAA was ≥40 or ≥50 mm at the next observation were 0.922 and 0.979, respectively, and the median root mean squared error was 2.52 mm. These values were nearly identical for models with or without plasma D-dimer effects.CPT: Pharmacometrics & Systems Pharmacology (2012) 1, e12; doi:10.1038/psp.2012.13; advance online publication 24 October 2012.

Final follow-up of the Multicentre Aneurysm Screening Study (MASS) randomized trial of abdominal aortic aneurysm screening

BACKGROUND

The long-term effects of abdominal aortic aneurysm (AAA) screening were investigated in extended follow-up from the UK Multicentre Aneurysm Screening Study (MASS) randomized trial.

METHODS

A population-based sample of men aged 65-74 years were randomized individually to invitation to ultrasound screening (invited group) or to a control group not offered screening. Patients with an AAA (3·0 cm or larger) detected at screening underwent surveillance and were offered surgery after predefined criteria had been met. Cause-specific mortality data were analysed using Cox regression.

RESULTS

Some 67 770 men were enrolled in the study. Over 13 years, there were 224 AAA-related deaths in the invited group and 381 in the control group, a 42 (95 per cent confidence interval 31 to 51) per cent reduction. There was no evidence of effect on other causes of death, but there was an overall reduction in all-cause mortality of 3 (1 to 5) per cent. The degree of benefit seen in earlier years of follow-up was slightly diminished by the occurrence of AAA ruptures in those with an aorta originally screened normal. About half of these ruptures had a baseline aortic diameter in the range 2·5-2·9 cm. It was estimated that 216 men need to be invited to screening to save one death over the next 13 years.

CONCLUSION

Screening resulted in a reduction in all-cause mortality, and the benefit in AAA-related mortality continued to accumulate throughout follow-up.

REGISTRATION NUMBER

ISRCTN37381646 (http://www.controlled-trials.com).