Predicting aortic complications after endovascular aneurysm repair

Prediction of endovascular leaks after thoracic endovascular aneurysm repair though machine learning applied to pre-procedural computed tomography angiographs

To predict endoleaks after thoracic endovascular aneurysm repair (TEVAR) we submitted patient characteristics and vessel features observed on pre- operative computed tomography angiography (CTA) to machine-learning. We evaluated 1-year follow-up CT scans (arterial and delayed phases) in patients who underwent TEVAR for the presence or absence of an endoleak. We evaluated the effect of machine learning of the patient age, sex, weight, and height, plus 22 vascular features on the ability to predict post-TEVAR endoleaks. The extreme Gradient Boosting (XGBoost) for ML system was trained on 14 patients with- and 131 without endoleaks. We calculated their importance by applying XGBoost to machine learning and compared our findings between with those of conventional vessel measurement-based methods such as the 22 vascular features by using the Pearson correlation coefficients. Pearson correlation coefficient and 95% confidence interval (CI) were r = 0.86 and 0.75 to 0.92 for the machine learning, r = - 0.44 and - 0.56 to - 0.29 for the vascular angle, and r = - 0.19 and - 0.34 to - 0.02 for the diameter between the subclavian artery and the aneurysm (Fig. 3a-c, all: p < 0.05). With machine-learning, the univariate analysis was significant higher compared with the vascular angle and in the diameter between the subclavian artery and the aneurysm such as the conventional methods (p < 0.05). To predict the risk for post-TEVAR endoleaks, machine learning was superior to the conventional vessel measurement method when factors such as patient characteristics, and vascular features (vessel length, diameter, and angle) were evaluated on pre-TEVAR thoracic CTA images.

Risk factors, risk stratification and risk-specific surveillance strategies after endovascular aneurysm repair: study protocol for a Delphi study by the International RIsk Stratification in EVAR (IRIS-EVAR) working group

INTRODUCTION

Several risk factors for adverse events after endovascular aneurysm repair (EVAR) have been described, but there is no consensus on their comparative prognostic significance, use in risk stratification and application in determining postoperative surveillance.

METHODS AND ANALYSIS

A scoping review of the literature was conducted to identify risk factors for adverse events after EVAR. Main adverse events were considered post-EVAR abdominal aortic aneurysm rupture and reintervention. Risk factors were grouped into four domains: (1) preoperative anatomy, (2) aortic device, (3) procedure performance and (4) postoperative surveillance. The Delphi methodology will be used to steer a group of experts in the field towards consensus organised into three tiers. In tier 1, participants will be asked to independently rate risk factors for adverse events after EVAR. In tier 2, the panel will be asked to independently rate a range of combinations of risk factors across the four domains derived from tier 1. A risk-stratification tool will then be built, which will include algorithms that map responses to signalling questions onto a proposed risk judgement for each domain. Domain-level judgements will in turn provide the basis for an overall risk judgement for the individual patient. In tier 3, risk factor-informed surveillance strategies will be developed. Each tier will typically include three rounds and rating will be conducted using a 4-point Likert scale, with an option for free-text responses.

ETHICS AND DISSEMINATION

Research Ethics Committee and Health Research Authority approval has been waived, since this is a professional staff study and no duty of care lies with the National Health Service to any of the participants. The results will be presented at regional, national and international meetings and will be submitted for publication in peer-reviewed journals. The risk stratification tool and surveillance algorithms will be made publicly available for clinical use and validation.

Predictors of Abdominal Aortic Aneurysm Shrinkage after Endovascular Repair

Recent studies demonstrate that patients with a shrinking abdominal aortic aneurysm (AAA), one-year after endovascular repair (EVAR), have better long-term outcomes than patients with a stable AAA. It is not known what factors determine whether an AAA will shrink or not. In this study, a range of parameters was investigated to identify their use in differentiating patients that will develop a shrinking AAA from those with a stable AAA one-year after EVAR. Hundred-seventy-four patients (67 shrinking AAA, 107 stable AAA) who underwent elective, infrarenal EVAR were enrolled between 2011-2018. Long-term survival was significantly better in patients with a shrinking AAA, compared to those with a stable AAA (p = 0.038). Larger preoperative maximum AAA diameter was associated with an increased likelihood of developing AAA shrinkage one-year after EVAR-whereas older age and larger preoperative infrarenal β angle were associated with a reduced likelihood of AAA shrinkage. However, this multivariate logistic regression model was only able to correctly identify 66.7% of patients with AAA shrinkage from the total cohort. This is not sufficient for implementation in clinical care, and therefore future research is recommended to dive deeper into AAA anatomy, and explore potential predictors using artificial intelligence and radiomics.

Prediction of Abdominal Aortic Aneurysm Growth After Endovascular Aortic Repair by Measuring Brachial-Ankle Pulse Wave Velocity

BACKGROUND

Although endovascular aortic repair (EVAR) has become the dominant therapeutic approach for abdominal aortic aneurysm (AAA), continued sac growth after EVAR remains a major concern and is still unpredictable. Since AAA formation is thought to arise from atherosclerotic vascular damage of the aortic wall, we hypothesize that the severity of atherosclerosis in the AAA wall may influence sac growth. Therefore, we investigated whether brachial-ankle pulse wave velocity (baPWV), a marker of atherosclerosis severity obtained by noninvasive automatic devices, can predict sac growth after EVAR.

METHODS

The data from all patients who underwent elective EVAR for AAA at a single institution from January 2012 to March 2019 were reviewed. We extracted the baPWV before EVAR and divided patients into 2 groups according to the baPWV cut-off value identified by a classification and regression tree (CART). The primary outcome was significant sac growth, defined as an increment of 5 mm or more in aneurysm size after EVAR relative to the aneurysm size before EVAR. Cox regression analysis was performed to assess the potential predictors of sac growth.

RESULTS

During the follow-up period, 222 consecutive patients underwent elective EVAR for AAA. Of these, 175 patients with a median follow-up period of 36 months were included. The baPWV values were classified as <1854 cm/s (Group 0) in 100 patients and ≥1854 cm/s (Group 1) in 75 patients according to the cut-off value identified by CART. During the follow-up period, 10 (10.0%) patients in Group 0 and 18 (24.0%) patients in Group 1 demonstrated significant sac growth (P = 0.021). Risk factors for significant sac growth included baPWV (hazard ratio [HR], 3.059; 95% confidence interval [CI], 1.41-6.64; P = 0.005), age (HR, 1.078; 95% CI, 1.01-1.16; P = 0.036), and persistent type II endoleak (HR, 3.552; 95% CI, 1.69-7.48; P < 0.001). Multivariate analysis revealed that baPWV remained a significant risk factor for sac growth after adjustment for age (HR, 2.602; 95% CI, 1.15-5.82; P = 0.02) and persistent type II endoleak (HR, 2.957; 95% CI, 1.36-6.43; P = 0.006).

CONCLUSIONS

The baPWV before EVAR was associated with significant sac growth after EVAR; thus, measuring the baPWV may be useful for assessing the risk of future sac growth in patients after EVAR.

Neutrophil-to-Lymphocyte Ratio Associated With Adverse Events After Endovascular Aneurysm Repair (EVAR)

BACKGROUND

The blood neutrophil-to-lymphocyte ratio (NLR) is a surrogate biomarker of systemic inflammation with important prognostic significance in multiple disease processes, including cardiovascular diseases. It is inexpensive, widely available, and may be related to the outcomes of patients after surgery. We aimed to investigate the possible association of NLR with the outcomes of patients following endovascular aneurysm repair (EVAR).

METHODS

This single-center, retrospective study of a prospectively maintained database evaluated 777 patients with a diagnosed abdominal aortic aneurysm (AAA) who underwent EVAR and were longitudinally followed between 2001 and 2017. NLR was defined as the ratio of absolute neutrophil count to absolute lymphocyte count. The mortality and reinterventions were used to evaluate outcomes using the appropriate univariate models, and the effect of clinical variables on NLR was further investigated using multivariate modelling.

RESULTS

The median NLR for all patients was 3 IQR [2.2 - 4.6]. A cut-off point of 3.6 was uncovered in a training set of 388 patients using the maximally ranked statistic method. Patients with NLR < 3.6 had significantly improved mortality rates (P< 0.0001) in the training set, and results were internally validated in a testing set of 389 patients (P = 0.042). Multivariate analysis revealed that high NLR (HR 1.4 95% CI [1.0 - 2.0]; P< 0.05) remained an independent predictor of mortality in a multivariate analysis controlling for characteristics such as comorbidities, age, and maximal aortic diameter. 5-year mortality and 30-day, 1-year and 5-year reinterventions were all higher in the high NLR group.

CONCLUSION

High NLR was significantly associated with higher rates of death at 5 years as well as higher rates of reinterventions at 30 days, 1 year and 5 years. We also suggest that an internally validated cut-off point of NLR >3.6 may be clinically important to help segregate patients into high and low NLR categories. It remains unclear whether NLR is directly linked to adverse events post-EVAR or whether it is a surrogate for an inflammatory state that predisposes patients to higher risk of death or reinterventions.

Update of a Model to Predict Outcomes after Endovascular Aneurysm Repair

BACKGROUND

Risk assessment models must be continuously validated and updated to ensure that predictions remain valid. Here, the Endovascular Aneurysm Repair Risk Assessment Model, developed in 2008, is updated and improved.

METHODS

We used prospectively collected data from Australian patients who underwent elective endovascular aneurysm repair between 2009 and 2013 (n = 695). Data were provided by treating surgeons and the National Death Index. Key outcomes were early and midterm survival, early complications (endoleak, operative, and graft-related) and late complications (endoleak and graft-related). Multinomial logistic regression determined which preoperative variables best predicted each outcome. Area under Receiver Operating Characteristic curve (AUROC), model P-value and internal validation statistics were used to select the best model.

RESULTS

Ten preoperative variables were included in the modeling for 10 key outcomes. The most valid outcomes with AUROC>0.7 were 1- and 3-year survival, 30 and 90-day mortality, early and late endoleak (types I, III and IV) and type II endoleak (with an increase in sac size ≥5 mm). The 10 preoperative variables that contributed to outcome models were self-reported fitness, American Society of Anesthesiologists physical status score, history of stroke/transient ischemic attack, age, aneurysm angle, infrarenal neck length, white cell count, respiratory assessment, diabetes and statin therapy. Fitness alone statistically significantly predicted 30 and 90-day deaths better than any other preoperative variable; achieving high AUROCs (0.78 and 0.80), and high odds ratios (12.8 [95% CI: 1.5-110.4] and 18.1 [95% CI: 2.2-149]).

CONCLUSIONS

An updated interactive predictive model of outcomes after endovascular aneurysm repair has been created. Many of the variables used in the 2008 model continued to be significant, however, new variables including fitness and respiratory assessment, improved the model. The new model uses variables routinely collected preoperatively, and hence can better support surgeon-patient discussions prior to operation. Informing patients of potential risks or likely outcomes following elective surgery can assist with preoperative shared decision-making.

Immediate outcome of endovascular treatment of ruptured juxtarenal aneurysm with parallel stents

Rupture of an abdominal aortic aneurysm is an event with a high mortality rate and treatment is a medical emergency. Endovascular treatment of these aneurysms has become established as a minimally invasive alternative to classical open surgery and is now the first-choice option. However, 20 to 50% of patients with abdominal aortic aneurysms do not have anatomy favorable for endovascular treatment because of a short aneurysm neck or because visceral branches are involved by the aneurysm. We report the case of a 70-year-old patient who underwent endovascular repair of a ruptured juxtarenal aneurysm with deployment of parallel stents in the renal arteries (in a chimney technique). Clinical data and details of the procedure are reported. Technical success was achieved and there were no postoperative complications.

Prediction, pattern recognition and modelling of complications post-endovascular infra renal aneurysm repair by artificial intelligence

OBJECTIVES

The study evaluates the plausibility and applicability of prediction, pattern recognition and modelling of complications post-endovascular aneurysm repair (EVAR) by artificial intelligence for more accurate surveillance in practice.

METHODS

A single-centre prospective data collection on (n = 250) EVAR cases with n = 26 preoperative attributes (factors) on endpoint of endoleak (types I-VI), occlusion, migration and mortality over a 13-year period was conducted. In addition to the traditional statistical analysis, data was subjected to machine learning algorithm through artificial neural network. The predictive accuracy (specificity and -1 sensitivity) on each endpoint is presented with percentage and receiver operative curve. The pattern recognition and model classification were conducted using discriminate analysis, decision tree, logistic regression, naive Bayes and support vector machines, and the best fit model was deployed for pattern recognition and modelling.

RESULTS

The accuracy of the training, validation and predictive ability of artificial neural network in detection of endoleak type I was 95, 96 and 94%, type II (94, 83, 90 and 82%) and type III was 96, 94 and 96%, respectively. Endpoints are associated with increase in weights through predictive modeling that were not detected through statistical analytics. The overall accuracy of the model was >86%.

CONCLUSION

The study highlights the applicability, accuracy and reliability of artificial intelligence in the detection of adverse outcomes post-EVAR for an accurate surveillance stratification.

Aortic sac enlargement after endovascular aneurysm repair: volume-related changes and the impact of intraluminal thrombus

PURPOSE

Abdominal aortic aneurysm (AAA) growth after endovascular aneurysm repair (EVAR) is still unpredictable. The issue of optimal frequency of computed tomography angiography for surveillance and its measurement method accuracy remain unclear. We aimed to assess the value of abdominal aneurysm sac volume measurement for detecting expansions and the association of preprocedural intraluminal thrombus (ILT) volume with aneurysm sac growth following EVAR.

MATERIAL AND METHODS

A total of 107 patients underwent elective EVAR. Inclusion criteria provided a cohort of 39 patients. Changes of postoperative maximum aneurysm sac diameter and AAA volume were calculated. Volumetric AAA changes and demographic data of the cases with clinically irrelevant AAA diameter enlargement were evaluated. Preoperative ILT volumes were collected. ILT and AAA sac volume ratio was calculated. Statistical data analysis was performed using standard methods.

RESULTS

The mean changes of maximum AAA diameter and volume in percentage after EVAR were -5.08 ± 8.20 mm and -13.39 ± 23.32%, respectively. A moderate positive linear correlation between those changes was found (R 2 = 0.731; p < 0.0001). The mean relative AAA volume increase in cases without clinically relevant diameter enlargement was 11.50 ± 8.27%. The means of ILT and AAA sac ratios were 0.59 ± 0.17 and 0.52 ± 1.8 in growing AAA sac and in stable or shrinking AAA sac groups, respectively (p = 0.308).

CONCLUSIONS

Volumetric AAA measurement may be useful as an additional method to diameter measurement after EVAR to identify clinically relevant sac growth. Preoperative volume of ILT may not significantly affect the growth rate of AAA after EVAR.

Is Abdominal Aortic Aneurysm Behavior after Endovascular Repair Associated with Aneurysm Wall Density on Computed Tomography Angiography?

Background and objectives: Abdominal aortic aneurysm (AAA) growth is unpredictable after the endovascular aneurysm repair (EVAR). Continuing aortic wall degradation and weakening due to hypoxia may have a role in post-EVAR aneurysm sac growth. We aimed to assess the association of aortic wall density on computed tomography angiography (CTA) with aneurysm growth following EVAR. Materials and Methods: A total of 78 patients were included in the study. The control group consisted of 39 randomly assigned patients without aortic pathology. Post-EVAR aneurysm sac volumes on CTA were measured twice during the follow-up period to estimate aneurysm sac behavior. A maximum AAA sac diameter, aortic wall and lumen densities in Hounsfield units (HU) on CTA were measured. A relative aortic wall density (the ratio of aortic wall to lumen densities) was calculated. A statistical data analysis was performed using standard methods. Results: An increase in the AAA sac volume was observed in 12 (30.8%) cases. Median relative aortic wall density on CTA scores in both the patient and the control group at the level of the diaphragm were similar: 0.15 (interquartile range (IQR), 0.11–0.18) and 0.16 (IQR 0.11–0.18), p = 0.5378, respectively. The median (IQR) relative aortic wall density score at the level of the maximum AAA diameter in the patient group was lower than at the level below renal arteries in the control group: 0.10 (0.07–0.12) and 0.17 (0.12–0.23), p < 0.0001, respectively. The median (IQR) relative growing AAA sac wall density score was lower than a relative stable/shrinking AAA sac wall density score: 0.09 (0.06–0.10) and 0.11 (0.09–0.13), p = 0.0096, respectively. Conclusions: A lower aortic aneurysm wall density on CTA may be associated with AAA growth after EVAR.

Endovascular treatment of bilateral isolated aneurysm of the internal iliac artery

Isolated aneurysms of the iliac arteries comprise less than 2% of abdominal aneurysms. The internal iliac artery is involved in 10-30% of cases. In most cases patients are asymptomatic, unless rupture occurs. They can be diagnosed by Doppler ultrasonography, magnetic resonance imaging or, preferably, angiotomography. Significant expansion, diameter of 3 cm or greater, and symptomatic cases are indications for surgery. We present the case of a patient with an incidental ultrasonographic finding of bilateral aneurysm of the internal iliac arteries, both with indications for surgery. The patient was successfully treated with endovascular techniques, first repairing the right internal iliac with a branched iliac stent graft, preserving patency, then embolizing the left internal iliac artery. Knowledge of the various different techniques and devices and their limitations is fundamental to adequate planning of endovascular treatment, even in rare cases.

Stent-graft surface movement after endovascular aneurysm repair: baseline parameters for prediction, and association with migration and stent-graft-related endoleaks

OBJECTIVES

To evaluate the influence of baseline parameters on the occurrence of stent-graft surface movement after endovascular aneurysm repair (EVAR) and to investigate its association with migration and stent-graft-related endoleaks (srEL).

METHODS

In this retrospective, cross-sectional study, three-dimensional surface models of the stent-graft, delimited by landmarks using custom-built software, were derived from the pre-discharge and last follow-up computed tomography angiography (CTA). Stent-graft surface movement in the proximal anchoring zone between these examinations was considered significant at a threshold of 9 mm. The Cox proportional hazards model was used to determine baseline variables associated with the occurrence of stent-graft surface movement. The association between migration and srEL with stent-graft surface movement was tested with the chi-square and the Fisher exact test, respectively.

RESULTS

Stent-graft surface movement was observed in 54 (28.9%) of 187 patients. Multivariate analysis revealed that age ([HR] 1.05; p = 0.017), proximal neck diameter ([HR] 5.07; p < 0.001), infrarenal aortic neck angulation ([HR] 1.02, p = 0.002), and proximal neck length ([HR] 0.62, p < 0.001) were significantly associated with the occurrence of stent-graft surface movement. Migration and srEL occurred in 17 (31.5%) and 5 (9.3%) patients, with and 11 (8.3%) and 2 (1.5%) without stent-graft surface movement (p < 0.001, p = 0.022).

CONCLUSIONS

Age, neck diameter, infrarenal neck angulation, and proximal neck length were significantly associated with the occurrence of stent-graft surface movement. Apart from possible use of adjunctive sealing systems, concerned patients may benefit from regular CTA surveillance, enabling timely diagnosis of subtle changes of stent-graft position.

KEY POINTS

• Stent-graft surface movement, demonstrating subtle, three-dimensional changes in stent-graft position in the proximal anchoring zone, can be derived from CTA examinations. • Age, proximal neck diameter, and infrarenal neck angulation were significantly associated with an increased incidence of stent-graft surface movement. Stent-graft surface movement is significantly more frequent in patients with stent-graft migration and stent-graft-related endoleaks. • Consideration of risk factors for stent-graft surface movement may help to identify patients who might benefit from regular CTA surveillance and timely diagnosis of subtle changes of stent-graft position, enabling re-interventions to prevent migration and srEL.

Application of Baseline Clinical and Morphological Parameters for Prediction of Late Stent Graft Related Endoleaks after Endovascular Repair of Abdominal Aortic Aneurysm

OBJECTIVES

To evaluate the influence of baseline clinical and morphological parameters on the occurrence of a late stent graft related endoleak (srEL; types 1 and 3) after endovascular aneurysm repair (EVAR).

METHODS

This is a retrospective case control study of patients who were routinely followed up after EVAR of abdominal aortic aneurysms. Pre-interventional, pre-discharge, and last available multislice computed tomography angiogram (MSCTA) of 279 patients were analysed. Stent graft related endoleaks detected by follow up MSCTA at least six months after EVAR were specified as late srEL. Baseline demographic characteristics and morphological variables were derived from the pre-interventional and pre-discharge MSCTA. Univariable and multivariable analysis with a Cox proportional hazards model were used to determine baseline factors associated with the occurrence of a late srEL.

RESULTS

Twenty-four (8.6%) of 279 patients suffered a late srEL, during a mean MSCTA follow up of 30.9 ± 25.8 (23.5, IQR 10.6-42.8) months. In the univariable analysis, age (hazard ratio [HR] 1.09; p = .001), female sex (HR 3.25; p = .014), right iliac sealing diameter (HR 10.04; p = .03), left iliac sealing diameter (HR 8.65; p = .001), infrarenal aortic neck angulation (HR 1.02; p = .011), and suprarenal fixation level (HR 3.47; p = .014) were significantly associated with an increased incidence of late srEL. Age (HR 1.08; p = .012), female sex (HR 2.72; p = .049), and left iliac sealing diameter (HR 4.48; p = .033) proved to be risk factors significantly associated with a higher incidence of late srEL in multivariable analysis.

CONCLUSIONS

Older patients, those with female gender, and those with larger left iliac sealing diameters seem to experience higher rates of late srEL. Independent confirmation of these must be addressed in larger studies.

Predicting risk of rupture and rupture-preventing reinterventions following endovascular abdominal aortic aneurysm repair

Background

Clinical and imaging surveillance practices following endovascular aneurysm repair (EVAR) for intact abdominal aortic aneurysm (AAA) vary considerably and compliance with recommended lifelong surveillance is poor. The aim of this study was to develop a dynamic prognostic model to enable stratification of patients at risk of future secondary aortic rupture or the need for intervention to prevent rupture (rupture‐preventing reintervention) to enable the development of personalized surveillance intervals.

Methods

Baseline data and repeat measurements of postoperative aneurysm sac diameter from the EVAR‐1 and EVAR‐2 trials were used to develop the model, with external validation in a cohort from a single‐centre vascular database. Longitudinal mixed‐effects models were fitted to trajectories of sac diameter, and model‐predicted sac diameter and rate of growth were used in prognostic Cox proportional hazards models.

Results

Some 785 patients from the EVAR trials were included, of whom 155 (19·7 per cent) experienced at least one rupture or required a rupture‐preventing reintervention during follow‐up. An increased risk was associated with preoperative AAA size, rate of sac growth and the number of previously detected complications. A prognostic model using predicted sac growth alone had good discrimination at 2 years (C‐index 0·68), 3 years (C‐index 0·72) and 5 years (C‐index 0·75) after operation and had excellent external validation (C‐index 0·76–0·79). More than 5 years after operation, growth rates above 1 mm/year had a sensitivity of over 80 per cent and specificity over 50 per cent in identifying events occurring within 2 years.

Conclusion

Secondary sac growth is an important predictor of rupture or rupture‐preventing reintervention to enable the development of personalized surveillance intervals. A dynamic prognostic model has the potential to tailor surveillance by identifying a large proportion of patients who may require less intensive follow‐up.

Potential to tailor surveillance

Identifying and addressing the limitations of EVAR technology

INTRODUCTION

Endovascular aortic repair (EVAR) has improved over the last two decades. Approximately 80% of the patients presenting with an abdominal aortic aneurysm (AAA) is nowadays primarily treated with EVAR.

AREAS COVERED

In this review, the differences between endovascular and open repair, the clinical characteristics needed for EVAR, the role of clinical imaging and the developments in EVAR technology will be discussed. Early mortality is lower in EVAR as compared to open repair, whereas this benefit is lost after 3 years postoperatively. EVAR comes with a high reintervention rate, with endoleak being the most important predictive factor for reintervention. Expanding technical possibilities have allowed surgeons to choose from a palate of endovascular approaches in aneurysm patients with challenging anatomies.

EXPERT COMMENTARY

Although EVAR has taken a giant leap forward in development, the new developments have seemed to surpass the long-term limitations with older devices. It is important to start focusing on the current limitations of EVAR, in particular the durability of devices in the human variable anatomic and dynamic environment.

Short- and long-term survival after open versus endovascular repair of abdominal aortic aneurysm-Polish population analysis

OBJECTIVES

The aim of the study was to compare short and long-term mortality and readmissions in patients with non-ruptured abdominal aortic aneurysm (AAA) treated with endovascular aortic repair (EVAR) or open aneurysm repair (OAR).

DESIGN

Retrospective survival analysis based on prospectively collected medical records of the national Polish public health insurer.

MATERIALS

In the National Health Fund database we identified all patients who underwent elective open or endovascular treatment of AAA between January 1st 2011 and March 22nd 2016. The data on mortality, selected concomitant diseases and readmissions were collected. A total of 7805 patients (mean age 70.9±8.1 yrs, 85.8% males) underwent OAR (n = 2336) or EVAR (n = 5469). A median follow up was 27.5 months (IQR range 10.0-38.4 months).

METHODS

The primary outcome variable was all-cause mortality, secondary outcomes included 30-day mortality and readmissions. Kaplan-Meier (K-M), Cox proportional-hazards and propensity score analyses were performed for primary and secondary outcomes adjusting for repair type of AAA (OAR vs. EVAR), age, sex and concomitant diseases.

RESULTS

EVAR patients had higher all-cause mortality (6.4% vs. 4.6% P = 0.002, adjHR 1.34, 95%CI 1.07-1.67, P = 0.010) compared with OAR. The mortality risks for OAR patients decreased below those for EVAR patients after 9.9 months. Of all the tested confounding factors only age independently and significantly influenced long-term mortality. Readmissions occurred more often in EVAR than in OAR (16.5% vs. 8.4% P<0.001, adjHR 2.15, 95%CI 1.84-2.52, P<0.001) independently from other covariants. Survival and readmissions Kaplan-Meier curves remained statistically different between OAR and EVAR patients after propensity score matching.

CONCLUSIONS

Survival benefit of EVAR over OAR disappeared early during the first year after procedure, particularly in patients below 70 years of age, accompanied by an increased frequency of readmissions of EVAR patients. Our data suggest re-evaluation of the strategy for AAA management in vascular units in the country.

Midterm results of endovascular aneurysm sealing to treat abdominal aortic aneurysm

BACKGROUND

Endovascular aneurysm sealing (EVAS) represents a novel approach to the treatment of abdominal aortic aneurysms. It uses polymer technology to achieve an anatomic seal within the sac of the aneurysm. This cohort study reports the early clinical outcomes, technical refinements, and learning curve during the initial EVAS experience at a single institution.

METHODS

Results from 150 consecutive EVAS cases for intact, infrarenal abdominal aortic aneurysms are reported here. These cases were undertaken between March 2013 and July 2015. Preoperative, perioperative, and postoperative data were collected for each patient prospectively.

RESULTS

The median age of the cohort was 76.6 years (interquartile range, 70.2-80.9 years), and 87.3% were male. Median aneurysm diameter was 62.0 mm (IQR, 58.0-69.0 mm). Adverse neck morphology was seen in 69 (46.0%) patients, including aneurysm neck length <10 mm (17.3%), neck diameter >32 mm or <18 mm (8.7%), and neck angulation >60 degrees (15.3%). Median follow-up was 687 days (IQR, 463-897 days); 37 patients (24.7%) underwent reintervention. The rates of unresolved endoleak are 1.3% type IA, 0.7% type IB, and 2.7% type I. There were no type III endoleaks. There have been seven secondary ruptures in this cohort; all but one of these patients survived after reintervention. Only one rupture occurred in an aneurysm that had been treated within the manufacturer's instructions for use (IFU).

CONCLUSIONS

The rate of unresolved endoleaks is satisfactorily low. The incidence of secondary rupture is of concern; however, when the IFU are adhered to, the rate is very low. The results of this study suggest that working within the IFU yields better clinical results.

Abdominal aortic aneurysm endovascular repair: profiling post-implantation morphometry and hemodynamics with image-based computational fluid dynamics

Endovascular aneurysm repair (EVAR) has disseminated rapidly as an alternative to open surgical repair for the treatment of abdominal aortic aneurysms (AAAs), because of its reduced invasiveness, low mortality and morbidity rate. The effectiveness of the endovascular devices used in EVAR is always at question as postoperative adverse events can lead to re-intervention or to a possible fatal scenario for the circulatory system. Motivated by the assessment of the risks related to thrombus formation, here the impact of two different commercial endovascular grafts on local hemodynamics is explored through 20 image-based computational hemodynamic models of EVAR-treated patients (N=10 per each endograft model). Hemodynamic features, susceptible to promote thrombus formation, such as flow separation and recirculation, are quantitatively assessed and compared with the local hemodynamics established in image-based infrarenal abdominal aortic models of healthy subjects (N=10). The hemodynamic analysis is complemented by a geometrical characterization of the EVAR-induced reshaping of the infrarenal abdominal aortic vascular region. The findings of this study indicate that: (1) the clinically observed propensity to thrombus formation in devices used in EVAR strategies can be explained in terms of local hemodynamics by means of image-based computational hemodynamics approach; (2) reportedly pro-thrombotic hemodynamic structures are strongly correlated with the geometry of the aortoiliac tract postoperatively. In perspective, our study suggests that future clinical follow up studies could include a geometric analysis of the region of the implant, monitoring shape variations that can lead to hemodynamic disturbances of clinical significance.

Analysis of Iliac Artery Geometric Properties in Fenestrated Aortic Stent Graft Rotation

Introduction:

A complication of fenestrated endovascular aneurysm repair is the potential for stent graft rotation during deployment causing fenestration misalignment and branch artery occlusion. The objective of this study is to demonstrate that this rotation is caused by a buildup of rotational energy as the device is delivered through the iliac arteries and to quantify iliac artery geometric properties associated with device rotation.

Methods:

A retrospective clinical study was undertaken in which iliac artery geometric properties were assessed from preoperative imaging for 42 cases divided into 2 groups: 27 in the nonrotation group and 15 in the rotation group. Preoperative computed tomography scans were segmented, and the iliac artery centerlines were determined. Iliac artery tortuosity, curvature, torsion, and diameter were calculated from the centerline and the segmented vessel geometry.

Results:

The total iliac artery net torsion was found to be higher in the rotation group compared to the nonrotation group (23.5 ± 14.7 vs 14.6 ± 12.8 mm−1; P = .05). No statistically significant differences were found for the mean values of tortuosity, curvature, torsion, or diameter between the 2 groups.

Conclusion:

Stent graft rotation occurred in 36% of the cases considered in this study. Cases with high iliac artery total net torsion were found to be more likely to have stent graft rotation upon deployment. This retrospective study provides a framework for prospectively studying the influence of iliac artery geometric properties on fenestrated stent graft rotation.

Editor's Choice - The Implications of Non-compliance to Endovascular Aneurysm Repair Surveillance: A Systematic Review and Meta-analysis

OBJECTIVE/BACKGROUND

Increasingly, reports show that compliance rates with endovascular aneurysm repair (EVAR) surveillance are often suboptimal. The aim of this study was to determine the safety implications of non-compliance with surveillance.

METHODS

The study was carried out according to the Preferred Items for Reporting of Systematic Reviews and Meta-Analyses (PRISMA) guidelines. An electronic search was undertaken by two independent authors using Embase, MEDLINE, Cochrane, and Web of Science databases from 1990 to July 2017. Only studies that analysed infrarenal EVAR and had a definition of non-compliance described as weeks or months without imaging surveillance were analysed. Meta-analysis was carried out using the random-effects model and restricted maximum likelihood estimation.

RESULTS

Thirteen articles (40,730 patients) were eligible for systematic review; of these, seven studies (14,311 patients) were appropriate for comparative meta-analyses of mortality rates. Three studies (8316 patients) were eligible for the comparative meta-analyses of re-intervention rates after EVAR and four studies (12,995 patients) eligible for meta-analysis for abdominal aortic aneurysm related mortality (ARM). The estimated average non-compliance rate was 42.0% (95% confidence interval [CI] 28-56%). Although there is some evidence that non-compliant patients have better survival rates, there was no statistically significant difference in all cause mortality rates (year 1: odds ratio [OR] 5.77, 95% CI 0.74-45.14; year 3: OR 2.28, 95% CI 0.92-5.66; year 5: OR 1.81, 95% CI 0.88-3.74) and ARM (OR 1.47, 95% CI 0.99-2.19) between compliant and non-compliant patients in the first 5 years after EVAR. The re-intervention rate was statistically significantly higher in compliant patients from 3 to 5 years after EVAR (year 1: OR 6.36, 95% CI 0.23-172.73; year 3: OR 3.94, 85% CI 1.46-10.69; year 5: OR 5.34, 95% CI 1.87-15.29).

CONCLUSION

This systematic review and meta-analysis suggests that patients compliant with EVAR surveillance programmes may have an increased re-intervention rate but do not appear to have better survival rates than non-compliant patients.

Endovascular aneurysm repair in the elderly: First do no harm

Endovascular aneurysm repair (EVAR) has become the intervention of choice for supra-threshold aortic aneurysms due to the lower 30-day mortality of EVAR as compared with open surgery, despite no long-term longevity gains. Trials such as EVAR-1 that established the current status of endovascular aortic intervention often excluded participants over the age of 80, and specific studies of EVAR in the elderly reveal higher mortality than accepted averages. Analyses of the cost-effectiveness of EVAR have not demonstrated superiority of endovascular intervention over open repair, in particular when considering complications such as endoleak. Post-intervention surveillance and the frequent need for re-intervention following EVAR has a detrimental impact on quality of life. Taking these factors into consideration, combined with an ageing population and the likely increase in octogenarian endovascular intervention, there is a clear clinical need for appropriate risk-stratification of elderly patients with supra-threshold aneurysms to determine who will benefit from endovascular repair.

Feature selection through validation and un-censoring of endovascular repair survival data for predicting the risk of re-intervention

Background

Feature selection (FS) process is essential in the medical area as it reduces the effort and time needed for physicians to measure unnecessary features. Choosing useful variables is a difficult task with the presence of censoring which is the unique characteristic in survival analysis. Most survival FS methods depend on Cox’s proportional hazard model; however, machine learning techniques (MLT) are preferred but not commonly used due to censoring. Techniques that have been proposed to adopt MLT to perform FS with survival data cannot be used with the high level of censoring. The researcher’s previous publications proposed a technique to deal with the high level of censoring. It also used existing FS techniques to reduce dataset dimension. However, in this paper a new FS technique was proposed and combined with feature transformation and the proposed uncensoring approaches to select a reduced set of features and produce a stable predictive model.

Methods

In this paper, a FS technique based on artificial neural network (ANN) MLT is proposed to deal with highly censored Endovascular Aortic Repair (EVAR). Survival data EVAR datasets were collected during 2004 to 2010 from two vascular centers in order to produce a final stable model. They contain almost 91% of censored patients. The proposed approach used a wrapper FS method with ANN to select a reduced subset of features that predict the risk of EVAR re-intervention after 5 years to patients from two different centers located in the United Kingdom, to allow it to be potentially applied to cross-centers predictions. The proposed model is compared with the two popular FS techniques; Akaike and Bayesian information criteria (AIC, BIC) that are used with Cox’s model.

Results

The final model outperforms other methods in distinguishing the high and low risk groups; as they both have concordance index and estimated AUC better than the Cox’s model based on AIC, BIC, Lasso, and SCAD approaches. These models have p-values lower than 0.05, meaning that patients with different risk groups can be separated significantly and those who would need re-intervention can be correctly predicted.

Conclusion

The proposed approach will save time and effort made by physicians to collect unnecessary variables. The final reduced model was able to predict the long-term risk of aortic complications after EVAR. This predictive model can help clinicians decide patients’ future observation plan.

Electronic supplementary material

The online version of this article (doi:10.1186/s12911-017-0508-3) contains supplementary material, which is available to authorized users.

A Systematic Review of Predictors of Reintervention After EVAR: Guidance for Risk-Stratified Surveillance

BACKGROUND

Current surveillance protocols after endovascular aneurysm repair (EVAR) are ineffective and costly. Stratifying surveillance by individual risk of reintervention requires an understanding of the factors involved in developing post-EVAR complications. This systematic review assessed risk factors for reintervention after EVAR and proposals for stratified surveillance.

METHODS

A systematic search according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines was performed using EMBASE and MEDLINE databases to identify studies reporting on risk factors predicting reintervention after EVAR and proposals for stratified surveillance.

RESULTS

Twenty-nine studies reporting on 39 898 patients met the primary inclusion criteria for reporting predictors of reintervention or aortic complications with or without suggestions for stratified surveillance. Five secondary studies described external validation of risk scores for reintervention or aortic complications. There was great heterogeneity in reporting risk factors identified at the pre-EVAR, intraoperative, and post-EVAR stages of treatment, although large preoperative abdominal aortic aneurysm diameter was the most commonly observed risk factor for reintervention after EVAR.

CONCLUSION

Existing data on predictors of post-EVAR complications are generally of poor quality and largely derived from retrospective studies. Few studies describing suggestions for stratified surveillance have been subjected to external validation. There is a need to refine risk prediction for EVAR failure and to conduct prospective comparative studies of personalized surveillance with standard practice.

Improving the results of transarterial embolization of type 2 endoleaks with the embolic polymer Onyx

Introduction

Type 2 endoleaks (T2E) occur in 10 to 20% of patients after endovascular abdominal aortic aneurysm repair (EVAR) and remain a significant clinical issue.

Aim

To evaluate the efficacy and clinical outcomes of transarterial treatment of persistent type II endoleaks after EVAR using the liquid embolic Onyx.

Material and methods

From February 2012 to August 2015 transarterial T2E embolization was attempted in 22 patients (21 men, median age: 73, range: 62–88 years). Indications for treatment included an increase in the diameter of the aneurysm sac above 5 mm and a persistent endoleak observed for more than 6 months. Mean time from EVAR to endoleak treatment was 43 months (range: 2–125 months).

Results

Primary technical success was achieved in 17 (77.3%) patients and secondary technical success in 81.8%, with 0% in-hospital mortality. The mean procedure time was 95 ±48 min, with an average fluoroscopy time of 54 ±25 min. The mean amount of Onyx used was 7.5 ±6.6 ml. Clinical success was seen in 17/21 patients with follow-up imaging (80.9%). Mean follow-up time was 17 months (range: 3–38 months).

Conclusions

Onyx has been shown to effectively stabilize previous aneurysm growth as a result of the T2E in the majority of our patients. Transarterial embolization of T2E can be significantly improved as compared to previously reported results by using liquid embolic polymers such as Onyx.

Predictive Models of Complications after Endovascular Aortic Aneurysm Repair

BACKGROUND

The risk of long-term complications after endovascular aneurysm repair (EVAR) is still higher than open surgery and is a critical issue. This study aims to make available reliable statistical predictive models of complications after EVAR.

METHODS

Two hundred and thirteen patients who underwent EVAR between 2002 and 2012 were included in this study. The preoperative computed tomography scans were analyzed with a dedicated workstation to provide spatially correct 3-dimensional data. Age, gender, operation-related factors, and 21 morphologic variables were measured and included in the analyses. Five postoperative outcomes were studied. After an initial selection of predictors based on univariate analysis, binomial logistic regression models were proposed for each outcome. The ability to predict each outcome was assessed with receiver operating characteristic curves considering that an area under the curve (AUC) > 0.70 is generally considered sufficiently accurate.

RESULTS

The mean age was 74.8 ± 8.6 years with a mean follow-up of 43.8 ± 22.1 months. Respectively, rates and risk factors of each outcome were 25.3% (n = 51) for abdominal aortic aneurysm (AAA) enlargement (age, number of patent sac branches, iliac calcifications and tortuosity, aneurysmal thrombus), 7% (n = 15) for type IA endoleak (neck calcification and AAA diameter), 3.7% (n = 8) for type IB endoleak (iliac tortuosity, AAA diameter, neck thrombus), 19.8% (n = 40) for type II endoleak (female, number of patent sac branches), and 25.9% (n = 55) for reintervention from any cause (neck calcification). The risk associated to each outcome can be calculated with a combination of these different preoperative variables. AUC for each outcome were 79.6% for AAA enlargement, 70.4% for reintervention, 81.3% for type IA endoleak, 92.3% for type IB endoleak, 70.6% for type II endoleak.

CONCLUSIONS

This study shows that an exhaustive description of the preoperative anatomy before EVAR is a powerful and reliable tool to predict the risk of developing the most common complications after EVAR.

Extended use of endovascular aneurysm sealing: Chimneys for juxtarenal aneurysms

Hostile infrarenal aortic neck anatomy presents a challenge for the endovascular treatment of abdominal aortic aneurysm. Open surgical repair has been seen as the gold standard treatment for juxtarenal abdominal aortic aneurysm; however, endovascular techniques are now becoming more prevalent, particularly in patients deemed high risk for morbidity and mortality with open repair. The morphology of an aneurysm is a determinant of long-term outcomes, and short aneurysm necks are associated with poorer outcomes and a higher rate of secondary reinterventions. Parallel grafts have been used in combination with endovascular aneurysm repair to elongate the sealing zone into the paravisceral segment of the aorta. This technique is associated with a risk of proximal Type I endoleak due to "guttering." This risk may be decreased when parallel grafts are used in combination with endovascular aneurysm sealing and, as such, this technique may represent an alternative to current techniques for the treatment of juxtarenal abdominal aortic aneurysm, such as the use of conventional bifurcated grafts (with or without parallel grafts) and fenestrated endovascular stent grafts.

Abdominal Aortic Aneurysm Repair: Results from a Series of Young Patients

Objectives. To compare durability and survival after endovascular aneurysm repair (EVAR) and open repair (OR) of abdominal aortic aneurysms (AAAs) in young patients. Material and Methods. A retrospective study was conducted between 2005 and 2014 on all consecutive patients of 60 years of age or younger. Measures considered for analysis were reintervention related to AAA, laparotomy and access vessel injury during EVAR, and all-cause mortality during hospitalization and follow-up. Results. Seventy out of 119 patients were treated by OR (58.8%) and 49 (41.2%) by EVAR, 9 in off-label fashion (18.3%). Technical success was achieved in all cases. No AAA-related death was recorded. Overall in-hospital mortality was zero and the reintervention rate was 2.5% (3/119: 1/70 OR, 2/49 EVAR, p = 0.36). There is no death at 30-day or 1-year follow-up. Thirty-day reintervention rate was 1.6% (2/119; 0/70 OR, 2/49 EVAR, p = 0.16), while the 1-year rate was 2.5% (3/119; 1/70 OR, 2/49 EVAR, p = 0.36). At the mean follow-up of 56.8 ± 42.7 months, mortality and reintervention rates were 5.8% (7/119; 3/70 OR, 4/49 EVAR, p = 0.38) and 10% (12/119; 8/70 OR, 4/49 EVAR, p = 0.39), respectively. The overall reintervention rate, mortality, and freedom from adverse events did not differ between the two groups. No differences in outcome were recorded between patients treated by EVAR in on-label versus off-label fashion. Conclusion. Our (albeit limited) experience suggests that, in an unselected young patient population undergoing elective AAA repair, OR or EVAR can be performed safely with similar immediate and long term outcomes.

Extended use of endovascular aneurysm sealing for ruptured abdominal aortic aneurysms

Endovascular repair of abdominal aortic aneurysms (EVAR) is now an established treatment modality for suitable patients presenting with aneurysm rupture. EVAR for ruptured aneurysms reduces transfusion, mechanical ventilation, intensive care. and hospital stay when compared with open surgery. In the emergency setting, however, EVAR is limited by low applicability due to adverse clinical or anatomical characteristics and increased need for reintervention. In addition, ongoing bleeding from aortic side branches post-EVAR can cause hemodynamic instability, larger hematomas, and abdominal compartment syndrome. Endovascular aneurysm sealing, based on polymer filling of the aneurysm, has the potential to overcome some of the limitations of EVAR for ruptured aneurysms and to improve outcomes. Recent literature suggests that endovascular aneurysm sealing can be performed with early mortality similar to that of EVAR for ruptured aortic aneurysms, but experience is limited to a few centers and a small number of patients. The addition of chimney grafts can increase the applicability of endovascular aneurysm sealing in order to treat short-neck and juxtarenal aneurysms as an alternative to fenestrated endografts. Further evaluation of the technique, with larger longitudinal studies, is necessary before advocating wider implementation of endovascular aneurysm sealing in the emergency setting.

Appearance of the Nellix endovascular aneurysm sealing system on computed tomography: implications for postoperative imaging surveillance

PURPOSE

To describe the imaging characteristics of the Nellix Endovascular Aneurysm Sealing (EVAS) System on serial computed tomography (CT) surveillance.

METHODS

Sixty-eight patients undergoing EVAS were enrolled in a surveillance protocol that included CT scans prior to hospital discharge and at 3, 6, and 9 months postoperatively. Images were analyzed for the presence of gas within the endobag, endoleak, and for maximum radiodensity measured in Hounsfield units (HU) within the uppermost, middle, and lowermost regions of each endobag.

RESULTS

Gas was seen within the endobags of all 68 EVAS repairs at the first postoperative CT compared with 2 (5.6%) of 36 undergoing the 3-month scan. The endobags appeared radiodense during initial imaging, and the median (interquartile range) radiodensity of the Nellix polymer decreased from 158.3 HU (149.5; 169.5) at the postoperative CT to 81.0 HU (74.0; 88.0) at 3 months, excluding 3 cases in which contrast pre-fill was utilized. Type I endoleak was seen at the periphery of the aneurysm sac or in the cleft between the endobags, with a substantially different appearance to endoleak after endovascular aneurysm repair.

CONCLUSION

The evolution of CT appearances after EVAS was characteristic and predictable. The device endobags were initially radiodense, which may impact the detection of endoleak within 3 months of EVAS. Endoleaks after EVAS were seen in a different anatomical area to endoleaks after conventional stent-graft repair.

Late single-center outcome of the Talent Abdominal Stent Graft after a decade of follow-up

OBJECTIVE

Lifelong yearly surveillance is advised after endovascular aneurysm repair (EVAR) for abdominal aortic aneurysms. This follow-up requires a substantial amount of health care resources. The aim of this paper was to assess the occurrence of stent graft-related complications and secondary interventions during a minimum 10-year follow-up after elective EVAR.

METHODS

Patients who were treated in a high-volume endovascular center in The Netherlands with the Talent infrarenal stent graft (Medtronic Vascular, Santa Rosa, Calif) between June 1999 and February 2005 were included. Patients with previous aortic surgery or emergency interventions were excluded. Our primary outcome was clinical success up to 10 years. Secondary end points were technical success and survival.

RESULTS

A total of 149 patients were included; 91.9% were male. The mean age was 70.2 ± 7.8 years. A stent graft was implanted in 98% of patients; technical success was achieved in 89.9%. Clinical success after 30 days, 1 year, 5 years, and 10 years was 81.1%, 74.3%, 70.3%, and 65.5%, respectively. In 30 patients (20.7%), a secondary intervention was required; 80.0% of first secondary interventions occurred within the first 5 years. Six late conversions were necessary because of stent graft infection (2), migration (2), or persisting endoleak (2). The 5- and 10-year overall survival rates were 55.2% and 38.6%, respectively.

CONCLUSIONS

The risk of EVAR-related complication is highest in the first 5 years. Consequently, the main focus should be on that period; further follow-up must not be neglected, as complications occur up to 10 years after treatment.

Evaluation of the Zenith low-profile abdominal aortic aneurysm stent graft

BACKGROUND

Low-profile (LP) stent grafts are now commercially available in Europe for endovascular aortic aneurysm repair (EVAR). In this study the midterm outcomes and characteristics of patients treated with this last generation of stent grafts were compared with a cohort of patients treated with "standard-profile" (SP) stent grafts.

METHODS

The current study enrolled all patients treated for elective EVAR by the SP Zenith Flex stent graft (Cook Medical, Bloomington, Ind) between March 2010 and November 2011 and patients treated for elective EVAR by the Zenith LP stent graft (Cook Medical) between November 2011 and March 2013. All patients had a follow-up >18 months. Preoperative computed tomography angiograms were analyzed on a dedicated three-dimensional workstation. All data were prospectively collected in an electronic database and retrospectively analyzed. A comparative study was conducted.

RESULTS

The present study included 208 patients (107 SP and 101 LP). Patients' physiologic characteristics were similar in both groups. The iliac anatomy was considered "more challenging" in LP patients: respectively, 7% and 22% (P = .002) of SP and LP patients had bilateral external iliac diameter <7 mm; and 16% and 34% (P = .005) had a combination of an external iliac diameter <7 mm and an iliac tortuosity ratio index >1.5. No 30-day deaths were documented. The 24-month freedom from reintervention and overall survival rates after SP and LP were, respectively, 88% and 91% (P = .450) and 92% and 96% (P = .153). The 24-month rates for freedom from sac expansion and from limb occlusion were 96.4% and 98.7% (P = .320) and 92% and 95% (P = .293), respectively. One patient in each group presented with a type I endoleak during follow-up, and two LP patients presented with a type III endoleak (P = .235).

CONCLUSIONS

This study demonstrates that the last-generation LP stent grafts have favorable midterm outcomes similar to SP stent grafts despite being used to treat more patients with unfavorable iliac anatomy.

An Artificial Neural Network Stratifies the Risks of Reintervention and Mortality after Endovascular Aneurysm Repair; a Retrospective Observational study

Background

Lifelong surveillance after endovascular repair (EVAR) of abdominal aortic aneurysms (AAA) is considered mandatory to detect potentially life-threatening endograft complications. A minority of patients require reintervention but cannot be predictively identified by existing methods. This study aimed to improve the prediction of endograft complications and mortality, through the application of machine-learning techniques.

Methods

Patients undergoing EVAR at 2 centres were studied from 2004-2010. Pre-operative aneurysm morphology was quantified and endograft complications were recorded up to 5 years following surgery. An artificial neural networks (ANN) approach was used to predict whether patients would be at low- or high-risk of endograft complications (aortic/limb) or mortality. Centre 1 data were used for training and centre 2 data for validation. ANN performance was assessed by Kaplan-Meier analysis to compare the incidence of aortic complications, limb complications, and mortality; in patients predicted to be low-risk, versus those predicted to be high-risk.

Results

761 patients aged 75 +/- 7 years underwent EVAR. Mean follow-up was 36+/- 20 months. An ANN was created from morphological features including angulation/length/areas/diameters/volume/tortuosity of the aneurysm neck/sac/iliac segments. ANN models predicted endograft complications and mortality with excellent discrimination between a low-risk and high-risk group. In external validation, the 5-year rates of freedom from aortic complications, limb complications and mortality were 95.9% vs 67.9%; 99.3% vs 92.0%; and 87.9% vs 79.3% respectively (p<0.001)

Conclusion

This study presents ANN models that stratify the 5-year risk of endograft complications or mortality using routinely available pre-operative data.

International validation of a risk score for complications and reinterventions after endovascular aneurysm repair

Background

Lifelong surveillance is considered mandatory after endovascular repair (EVAR) of abdominal aortic aneurysms to detect endograft complications and prevent aneurysm rupture. Current protocols are not cost-effective or clinically effective. The international validity of the St George's Vascular Institute (SGVI) score for EVAR complications was examined.

Methods

The ENGAGE registry recruited patients undergoing EVAR at 79 centres in 30 countries. Reinterventions and endograft complications were recorded for up to 3 years after surgery. Preoperative aneurysm morphology was extracted from the registry database, and used to predict whether patients would be at low or high risk of complications after EVAR based on the SGVI score. Kaplan–Meier analysis was used to compare the incidence of endograft complications and reinterventions in patients predicted to be at low risk compared with those predicted to be at high risk.

Results

Some 1207 patients underwent EVAR, with follow-up of up to 3 years. The SGVI score accurately discriminated freedom from reinterventions (90·5 versus 79·3 per cent in low- versus high-risk patients; P &lt; 0·001), freedom from endograft complications (77·9 versus 69·6 per cent in low- versus high-risk patients; P = 0·012), and freedom from a composite outcome measure of reinterventions or endograft complications (75·0 versus 66·1 per cent in low- versus high-risk patients; P = 0·006) during mid-term follow-up.

Conclusion

This study has provided international validation of a morphological risk score that predicts mid-term reinterventions and endograft complications. The results may enable risk-stratified surveillance after EVAR.

A systematic review and meta-analysis indicates underreporting of renal dysfunction following endovascular aneurysm repair

Deterioration in renal function has been described after endovascular repair of abdominal aortic aneurysms (EVRs). The etiology is multifactorial and represents an important therapeutic target. A need exists to quantitatively summarize incidence and severity of renal dysfunction after EVR to allow better-informed attempts to preserve renal function and improve life expectancy. Here a systematic search was performed using Medline and Embase for renal function after EVR applying PRISMA statements. Univariate and multivariate random-effects meta-analyses were performed to estimate pooled postoperative changes in serum creatinine and creatinine clearance at four time points after EVR. Clinically relevant deterioration in renal function was also estimated at 1 year or more after EVR. Pooled probability of clinically relevant deterioration in renal function at 1 year or more was 18% (95% confidence interval of 14-23%, I2 of 82.5%). Serum creatinine increased after EVR by 0.05 mg/dl at 30 days/1 month, 0.09 mg/dl at 1 month to 1 year, and 0.11 mg/dl at 1 year or more (all significant). Creatinine clearance decreased after EVR by 5.65 ml/min at 1 month-1 year and by 6.58 ml/min at 1 year or more (both significant). Thus, renal dysfunction after EVR is common and merits attention.

The effect of aortic morphology on peri-operative mortality of ruptured abdominal aortic aneurysm

AIMS

To investigate whether aneurysm shape and extent, which indicate whether a patient with ruptured abdominal aortic aneurysm (rAAA) is eligible for endovascular repair (EVAR), influence the outcome of both EVAR and open surgical repair.

METHODS AND RESULTS

The influence of six morphological parameters (maximum aortic diameter, aneurysm neck diameter, length and conicality, proximal neck angle, and maximum common iliac diameter) on mortality and reinterventions within 30 days was investigated in rAAA patients randomized before morphological assessment in the Immediate Management of the Patient with Rupture: Open Versus Endovascular strategies (IMPROVE) trial. Patients with a proven diagnosis of rAAA, who underwent repair and had their admission computerized tomography scan submitted to the core laboratory, were included. Among 458 patients (364 men, mean age 76 years), who had either EVAR (n = 177) or open repair (n = 281) started, there were 155 deaths and 88 re-interventions within 30 days of randomization analysed according to a pre-specified plan. The mean maximum aortic diameter was 8.6 cm. There were no substantial correlations between the six morphological variables. Aneurysm neck length was shorter in those undergoing open repair (vs. EVAR). Aneurysm neck length (mean 23.3, SD 16.1 mm) was inversely associated with mortality for open repair and overall: adjusted OR 0.72 (95% CI 0.57, 0.92) for each 16 mm (SD) increase in length. There were no convincing associations of morphological parameters with reinterventions.

CONCLUSION

Short aneurysm necks adversely influence mortality after open repair of rAAA and preclude conventional EVAR. This may help explain why observational studies, but not randomized trials, have shown an early survival benefit for EVAR.

CLINICAL TRIAL REGISTRATION

ISRCTN 48334791.

Bayesian neural network approach for determining the risk of re-intervention after endovascular aortic aneurysm repair

This article proposes a Bayesian neural network approach to determine the risk of re-intervention after endovascular aortic aneurysm repair surgery. The target of proposed technique is to determine which patients have high chance to re-intervention (high-risk patients) and which are not (low-risk patients) after 5 years of the surgery. Two censored datasets relating to the clinical conditions of aortic aneurysms have been collected from two different vascular centers in the United Kingdom. A Bayesian network was first employed to solve the censoring issue in the datasets. Then, a back propagation neural network model was built using the uncensored data of the first center to predict re-intervention on the second center and classify the patients into high-risk and low-risk groups. Kaplan-Meier curves were plotted for each group of patients separately to show whether there is a significant difference between the two risk groups. Finally, the logrank test was applied to determine whether the neural network model was capable of predicting and distinguishing between the two risk groups. The results show that the Bayesian network used for uncensoring the data has improved the performance of the neural networks that were built for the two centers separately. More importantly, the neural network that was trained with uncensored data of the first center was able to predict and discriminate between groups of low risk and high risk of re-intervention after 5 years of endovascular aortic aneurysm surgery at center 2 (p = 0.0037 in the logrank test).