Expansion rates of small abdominal aortic aneurysms

Development of pharmacotherapies for abdominal aortic aneurysms

The cardiovascular field is still searching for a treatment for abdominal aortic aneurysms (AAA). This inflammatory disease often goes undiagnosed until a late stage and associated rupture has a high mortality rate. No pharmacological treatment options are available. Three hallmark factors of AAA pathology include inflammation, extracellular matrix remodeling, and vascular smooth muscle dysfunction. Here we discuss drugs for AAA treatment that have been studied in clinical trials by examining the drug targets and data present for each drug's ability to regulate the aforementioned three hallmark pathways in AAA progression. Historically, drugs that were examined in interventional clinical trials for treatment of AAA were repurposed therapeutics. Novel treatments (biologics, small-molecule compounds etc.) have not been able to reach the clinic, stalling out in pre-clinical studies. Here we discuss the backgrounds of previous investigational drugs in hopes of better informing future development of potential therapeutics. Overall, the highlighted themes discussed here stress the importance of both centralized anti-inflammatory drug targets and rigor of translatability. Exceedingly few murine studies have examined an intervention-based drug treatment in halting further growth of an established AAA despite interventional treatment being the therapeutic approach taken to treat AAA in a clinical setting. Additionally, data suggest that a potentially successful drug target may be a central inflammatory biomarker. Specifically, one that can effectively modulate all three hallmark factors of AAA formation, not just inflammation. It is suggested that inhibiting PGE₂ formation with an mPGES-1 inhibitor is a leading drug target for AAA treatment to this end.

Calculating when elective abdominal aortic aneurysm repair improves survival for individual patients: development of the Aneurysm Repair Decision Aid and economic evaluation

BACKGROUND

Abdominal aortic aneurysm (AAA) repair aims to prevent premature death from AAA rupture. Elective repair is currently recommended when AAA diameter reaches 5.5 cm (men) and 5.0 cm (women). Applying population-based indications may not be appropriate for individual patient decisions, as the optimal indication is likely to differ between patients based on age and comorbidities.

OBJECTIVE

To develop an Aneurysm Repair Decision Aid (ARDA) to indicate when elective AAA repair optimises survival for individual patients and to assess the cost-effectiveness and associated uncertainty of elective repair at the aneurysm diameter recommended by the ARDA compared with current practice.

DATA SOURCES

The UK Vascular Governance North West and National Vascular Database provided individual patient data to develop predictive models for perioperative mortality and survival. Data from published literature were used to model AAA growth and risk of rupture. The cost-effectiveness analysis used data from published literature and from local and national databases.

METHODS

A combination of systematic review methods and clinical registries were used to provide data to populate models and inform the structure of the ARDA. Discrete event simulation (DES) was used to model the patient journey from diagnosis to death and synthesised data were used to estimate patient outcomes and costs for elective repair at alternative aneurysm diameters. Eight patient clinical scenarios (vignettes) were used as exemplars. The DES structure was validated by clinical and statistical experts. The economic evaluation estimated costs, quality-adjusted life-years (QALYs) and incremental cost-effectiveness ratios (ICERs) from the NHS, social care provider and patient perspective over a lifetime horizon. Cost-effectiveness acceptability analyses and probabilistic sensitivity analyses explored uncertainty in the data and the value for money of ARDA-based decisions. The ARDA outcome measures include perioperative mortality risk, annual risk of rupture, 1-, 5- and 10-year survival, postoperative long-term survival, median life expectancy and predicted time to current threshold for aneurysm repair. The primary economic measure was the ICER using the QALY as the measure of health benefit.

RESULTS

The analysis demonstrated it is feasible to build and run a complex clinical decision aid using DES. The model results support current guidelines for most vignettes but suggest that earlier repair may be effective in younger, fitter patients and ongoing surveillance may be effective in elderly patients with comorbidities. The model adds information to support decisions for patients with aneurysms outside current indications. The economic evaluation suggests that using the ARDA compared with current guidelines could be cost-effective but there is a high level of uncertainty.

LIMITATIONS

Lack of high-quality long-term data to populate all sections of the model meant that there is high uncertainty about the long-term clinical and economic consequences of repair. Modelling assumptions were necessary and the developed survival models require external validation.

CONCLUSIONS

The ARDA provides detailed information on the potential consequences of AAA repair or a decision not to repair that may be helpful to vascular surgeons and their patients in reaching informed decisions. Further research is required to reduce uncertainty about key data, including reintervention following AAA repair, and assess the acceptability and feasibility of the ARDA for use in routine clinical practice.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Diagnosis and monitoring of abdominal aortic aneurysm: current status and future prospects

Abdominal aortic aneurysm (AAA) remains an important cause of morbidity and mortality in elderly men, and prevalence is predicted to increase in parallel with a global aging population. AAA is commonly asymptomatic, and in the absence of routine screening, diagnosis is usually incidental when imaging to assess unrelated medical complaints. In the absence of approved diagnostic and prognostic markers, AAAs are monitored conservatively via medical imaging until aortic diameter approaches 50-55 mm and surgical repair is performed. There is currently significant interest in identifying molecular markers of diagnostic and prognostic value for AAA. Here we outline the current guidelines for AAA management and discuss modern scientific techniques currently employed to identify improved diagnostic and prognostic markers.

Thrombus volume is associated with cardiovascular events and aneurysm growth in patients who have abdominal aortic aneurysms

BACKGROUND

Patients with abdominal aortic aneurysms (AAA) are predisposed to cardiovascular events and often experience continual expansion of their aneurysm. Cardiovascular events and expansion rates are positively correlated with aneurysm size. AAA is usually associated with intraluminal thrombus, which has previously been implicated in AAA pathogenesis. This study prospectively assessed the association of infrarenal abdominal aortic thrombus volume with cardiovascular events and AAA growth.

METHODS

Ninety-eight patients with AAAs underwent computed tomography angiography (CTA). The volume of infrarenal aorta thrombus was measured by a previously validated technique. Patients were monitored prospectively for a median of 3 years (interquartile range [IQR], 2.0-3.6 years), and cardiovascular events (nonfatal stroke, nonfatal myocardial infarction, coronary revascularization, amputation, and cardiovascular death) were recorded. Of the original patients, 39 underwent repeat CTA a median of 1.5 years (IQR, 1.1-3.3 years) after entry to the study. Kaplan-Meier and Cox proportional analysis were used to examine the association of aortic thrombus with cardiovascular events and average weighted AAA growth.

RESULTS

There were 28 cardiovascular events during follow-up. The incidence of cardiovascular events was 23.4% and 49.2% for patients with small (smaller than the median) and large (median or larger) volumes of aortic thrombus, respectively, at 4 years (P = .040). AAA thrombus volume of median or larger was associated with increased cardiovascular events (relative risk [RR] 2.8, 95% confidence interval [CI], 1.01-5.24) independent of other risk factors, including initial AAA diameter, but was only of borderline significance when patients were censored at the time of AAA repair (RR, 2.35; 95% CI, 0.98-5.63). In the subset of patients with CTA follow-up, the median annual increase in AAA volume was 5.1 cm³ (IQR, 0.8-10.3 cm³). Annual AAA volume increase was positively correlated with initial AAA diameter (r = 0.44, P = .006) and thrombus volume (r = 0.50, P = .001). Median or larger aortic thrombus volume was associated with rapid AAA volume increase (≥ 5 cm/y), independent of initial aortic diameter (RR, 15.0; 95% CI, 1.9-115.7; P = .009).

CONCLUSION

In this small cohort, infrarenal aortic thrombus volume was associated with the incidence of cardiovascular events and AAA progression. These results need to be confirmed and mechanisms underlying the associations clarified in large further studies.

Growth rates of small abdominal aortic aneurysms correlate with clinical events

Background

This retrospective analysis of prospectively collected abdominal aortic aneurysm (AAA) screening data aimed to identify predictors of AAA-related events (surgery or death) with a view to better targeting of screening.

Methods

For the interval 1984–2007, data for 1649 subjects with an AAA were collected prospectively as part of the Chichester AAA screening programme. This included serial aortic size measurements, blood pressure, risk factors for arterial disease and concurrent medications. AAA growth rates were adjusted for risk factor confounders using flexible hierarchical modelling. AAA growth distribution was analysed using Silverman's test of multimodality.

Results

Some 1231 subjects met the inclusion criteria of having more than one scan and a surveillance interval of over 3 months. AAA growth showed a bimodal pattern with nearly 50 per cent of all aneurysms never progressing to surgery or rupture. Adjusted annual AAA growth rates of at least 2 mm significantly predicted AAA-related events.

Conclusion

This analysis identified a bimodal growth pattern for AAA, with a significant association between annual AAA growth rate of at least 2 mm and AAA-related events.

The efficacy of pharmacotherapy for decreasing the expansion rate of abdominal aortic aneurysms: a systematic review and meta-analysis

Background

Pharmacotherapy may represent a potential means to limit the expansion rate of abdominal aortic aneurysms (AAAs). Studies evaluating the efficacy of different pharmacological agents to slow down human AAA-expansion rates have been performed, but they have never been systematically reviewed or summarized.

Methods and Findings

Two independent reviewers identified studies and selected randomized trials and prospective cohort studies comparing the growth rate of AAA in patients with pharmacotherapy vs. no pharmacotherapy. We extracted information on study interventions, baseline characteristics, methodological quality, and AAA growth rate differences (in mm/year). Fourteen prospective studies met eligibility criteria. Five cohort studies raised the possibility of benefit of beta-blockers [pooled growth rate difference: −0.62 mm/year, (95%CI, −1.00 to −0.24)], but this was not confirmed in three beta-blocker RCTs [pooled RCT growth rate difference: −0.05 mm/year (−0.16 to 0.05)]. Statins have been evaluated in two cohort studies that yield a pooled growth rate difference of −2.97 (−5.83 to −0.11). Doxycycline and roxithromycin have been evaluated in two RCTs that suggest possible benefit [pooled RCT growth rate difference: −1.32 mm/year (−2.89 to 0.25)]. Studies assessing NSAIDs, diuretics, calcium channel blockers and ACE inhibitors, meanwhile, did not find statistically significant differences.

Conclusions

Beta-blockers do not appear to significantly reduce the growth rate of AAAs. Statins and other anti-inflammatory agents appear to hold promise for decreasing the expansion rate of AAA, but need further evaluation before definitive recommendations can be made.

Assessment of pre-operative delays in the management of elective abdominal aortic aneurysms

INTRODUCTION

Successful endovascular aneurysm repair (EVAR) requires detailed pre-operative imaging to allow device planning. This process may delay surgery and some aneurysms may rupture prior to intervention. The aim of this study was to quantify these delays.

PATIENTS AND METHODS

Data were collected prospectively on all patients presenting with non-ruptured abdominal aortic aneurysms (AAAs) between January 2003 and October 2005. The delay between referral, the first out-patient visit, CT-scan, follow-up appointment and surgery were quantified in all patients and compared between two groups undergoing open repair and EVAR.

RESULTS

A total of 146 patients underwent AAA repair during the study (48 EVAR versus 98 open repair). There was no significant differences in the wait for CT scans between the groups (median 42 days for EVAR versus 47 days for open repairs [P = 0.48]) or the median interval between decision to operate and surgery (56 days versus 42 days [P = 0.075]). However, the median delay between referral and surgery was significantly longer in those patients undergoing EVAR at 129 days versus 77 days for open repair (P = 0.02).

CONCLUSIONS

Patients presenting electively with AAAs experienced significant delay from referral to surgery. This delay was significantly greater in those patients undergoing endovascular repair. Inevitably, some patients will rupture whilst waiting and strategies aimed at reducing delay should be pursued.

Growth Rate and Associated Factors in Small Abdominal Aortic Aneurysms

OBJECTIVE

To study the growth rate and factors influencing progression of small infrarenal abdominal aortic aneurysms (AAA).

DESIGN

Observational, longitudinal, prospective study.

PATIENTS AND METHODS

We followed patients with AAA <5 cm in diameter in two groups. Group I (AAA 3-3.9 cm, n = 246) underwent annual ultrasound scans. Group II (AAA 4-4.9 cm, n = 106) underwent 6-monthly CT scans.

RESULTS

We included 352 patients (333 men and 19 women) followed for a mean of 55.2+/-37.4 months (6.3-199.8). The mean growth rate was significantly greater in group II (4.72+/-5.93 vs. 2.07+/-3.23 mm/year; p<0.0001). Group II had a greater percentage of patients with rapid aneurysm expansion (>4 mm/year) (36.8 vs. 13.8%; p<0.0001). The classical cardiovascular risk factors did not influence the AAA growth rate in group I. Chronic limb ischemia was associated with slower expansion (< or = 4 mm/year) (OR 0.47; CI 95% 0.22-0.99; p = 0.045). Diabetic patients in group II had a significantly smaller mean AAA growth rate than non-diabetics (1.69+/-3.51 vs. 5.22+/-6.11 mm/year; p = 0.032).

CONCLUSIONS

The expansion rate of small AAA increases with the AAA size. AAA with a diameter of 3-3.9 cm expand slowly, and they are very unlikely to require surgical repair in 5 years. Many 4-4.9 cm AAA can be expected to reach a surgical size in the first 2 years of follow-up. Chronic limb ischemia and diabetes are associated with reduced aneurysm growth rates.

Increased Growth Rate of Abdominal Aortic Aneurysms in Women. The Tromsø Study

OBJECTIVES

The present study was undertaken in order to assess the effect of gender on the growth rate of abdominal aortic aneurysms (AAAs).

METHODS

One hundred and eighty-five men and 49 women with AAAs were studied, mean follow-up 62 months, giving 14,544 patient-months of follow-up. A mean of 16 ultrasound examinations was performed on each patient.

RESULTS

The mean growth rate was 1.82; 1.65 and 2.43 mm per year in men and women, respectively. In a weighted linear regression analysis, high initial diameter and female gender were independent and significant (p < 0.001 and p = 0.003, respectively) predictors for increased growth rate of AAAs. None of the other considered risk factors predicted the growth rate.

CONCLUSIONS

This is the first study to report a significantly different growth rate of AAAs in females compared to males. It, thus, adds evidence to the view that AAA is a more malignant condition in females than in males and could have implications for the frequency of follow-up in women.

Indications for operative management of abdominal aortic aneurysms

The increasing incidence of abdominal aortic aneurysms, along with the more frequent use of screening techniques, has resulted in greater numbers of patients with small abdominal aortic aneurysms. The questions of frequency of surveillance and timing of intervention are the two most controversial issues faced by surgeons dealing with this condition. Most management decisions are based on the size of the aneurysm but other factors must also be considered. This review makes recommendations on the management of small abdominal aortic aneurysms according to the current available evidence.

Comparison of abdominal aortic aneurysm diameter measurements obtained with ultrasound and computed tomography: Is there a difference?

OBJECTIVES

Accurate diameter measurements of abdominal aortic aneurysm (AAA) with both computed tomography (CT) and ultrasound (US) are essential for screening, planning surgical intervention, and follow-up after endovascular repair. Often there is a discrepancy between measurements obtained with CT and US, and neither limit of agreement (LOA) nor correlation between the two imaging methods has been clearly established. The purpose of this study was to assess the paired differences in AAA diameter measurements obtained with CT and US in a large national endograft trial.

METHODS

CT and US measurements were obtained from an independent core laboratory established to assess imaging data in a national endograft trial (Ancure; Guidant, Menlo Park, Calif). The study included only baseline examinations in which both CT and US measurements were available. Axial CT images and transverse US images were assessed for maximal AAA diameter and recorded as CT(max) and US(max), respectively. Correlations and LOA were performed between all image diameters, and differences in their means were assessed with paired t test.

RESULTS

A total of 334 concurrent measurements were available at baseline after endovascular repair. CT(max) was greater than US(max) in 95% (n = 312), and mean CT(max) (5.69 +/- 0.89 cm) was significantly larger (P <.001) than mean US(max) (4.74 +/- 0.91 cm). The correlation coefficient between CT(max) and US(max) was 0.705, but the difference between the two was less than 1.0 cm in only 51%. There was less discrepancy between CT(max) and US(max) for small AAA (0.7 cm, 15.3%) compared with medium (0.9 cm, 17.9%) and large (1.46 cm, 20.3%) AAA; however, the difference was not statistically significant. LOA between CT(max) and US(max) (-0.45-2.36 cm) exceeded the limits of clinical acceptability (-0.5-0.5 cm). Poor LOA was also found in each subgroup based on AAA size.

CONCLUSIONS

Maximal AAA diameter measured with CT is significantly and consistently larger than maximal AAA diameter measured with US. The clinical significance of this difference and its cause remains a subject for further investigation.

Abdominal aortic aneurysm

Abdominal aortic aneurysm is a chronic dilation of the aorta with a natural history toward enlargement and rupture. Its pathogenesis is believed to be multifactorial and complex. Clinical presentation may be asymptomatic, symptomatic, or as rupture. Elective surgery by open transperitoneal or retroperitoneal approach is the most common repair intervention. However, placing an endoluminal stent graft within the aneurysm is currently being evaluated as an alternative to open repair. Nursing care of the patient with abdominal aortic aneurysm involves intensive care skills as well as a foundation in chronic illness management. This article presents information on pathogenesis, natural history, clinical presentation, surgical interventions, and postoperative complications.

Peripheral vascular disease and hypertension: a forgotten association?

Peripheral vascular disease (PVD) is associated with a high cardiovascular morbidity and mortality. Intermittent claudication is the most common symptomatic manifestation of PVD, but is also an important predictor of cardiovascular death, increasing it by three-fold, and increasing all-cause mortality by two to five-fold. Hypertension is a common and important risk factor for vascular disorders, including PVD. Of hypertensives at presentation, about 2-5% have intermittent claudication, with this prevalence increasing with age. Similarly, 35-55% of patients with PVD at presentation also have hypertension. Patients who suffer from hypertension with PVD have a greatly increased risk of myocardial infarction and stroke. Apart from the epidemiological associations, hypertension contributes to the pathogenesis of atherosclerosis, the basic underlying pathological process underlying PVD. Hypertension, in common with PVD, is associated with abnormalities of haemostasis and lipids, leading to an increased atherothrombotic state. Nevertheless, none of the large antihypertensive treatment trials have adequately addressed whether a reduction in blood pressure causes a decrease in PVD incidence. There is therefore an obvious need for such outcome studies, especially since the two conditions are commonly encountered together.

Follow-up evaluation of endoluminally treated abdominal aortic aneurysms with duplex ultrasonography: validation with computed tomography

OBJECTIVE

A growing number of patients with abdominal aortic aneurysms are currently being offered endoluminal treatment. However, the incidence of endoleaks, stenosis, and thrombosis is around 25% to 30%. As a result, a strict post procedure imaging surveillance protocol is necessary. The purpose of this study was to compare duplex ultrasonography (DU) and computed tomography (CT) for the follow-up of endoluminally treated aortic aneurysms.

METHODS

A total of 89 patients were followed up with serial CT and DU at 1, 3, 6, 12, and 24 months after endoluminal treatment. Special attention was directed toward the presence of endoleaks and aneurysm diameter evolution. Preoperative CT and DU were also reviewed to assess aneurysm diameter correlation.

RESULTS

With DU, 14 type I and 21 type II endoleaks were identified. In one case the DU did not visualize a type II endoleak present on CT, and CT did not confirm three type II leaks identified with DU. There was only one false positive for type I endoleak with DU. The sensitivity of DU was 96% with a specificity of 94%, when compared with CT. A linear regression analysis of the diameters obtained with DU and CT revealed a good correlation. However, variability was high, indicating poor agreement. Regarding diameter evolution, the range was identical in 45%, and the trend was similar in 73%. However, in 9% of the cases, DU showed a decrease in diameter, whereas CT showed a significant increase.

CONCLUSION

DU is an accurate tool for the diagnosis of endoleaks, but is less valuable for diameter measurements, when compared with CT. Currently, DU is a useful tool, but CT remains a key part of the postoperative evaluation after endoluminal treatment of abdominal aortic aneurysms. At institutions where DU is used for follow-up, researchers should perform quality control studies to avoid potentially significant errors.