Risk of reintervention after endovascular aortic aneurysm repair

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.

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).

The morphological applicability of a novel endovascular aneurysm sealing (EVAS) system (Nellix) in patients with abdominal aortic aneurysms

OBJECTIVE

Endovascular aneurysm sealing (EVAS) using the Nellix system is a promising alternative to endovascular repair (EVR) and open surgery for abdominal aortic aneurysms (AAA). The aim of this study was to investigate the proportion of patients with AAA who are morphologically suitable for treatment with Nellix.

METHODS

Patients presenting with AAA were investigated at two regionalised vascular units. Separate cohorts were identified, who had undergone infrarenal EVR, open aneurysm repair, fenestrated endovascular repair (FEVR) or non-operative management. Pre-operative morphology was quantified using three-dimensional computed tomography according to a validated protocol. Each aneurysm was assessed for compliance with the instructions for use (IFU) of Nellix

RESULTS

776 patients were identified with mean age 75 ± 9 years. 730/776 (94.1%) had undergone infrarenal EVR, 6/776 (0.8%) open repair, 27/776 (3.5%) FEVR and 13/776 (1.7%) had been managed non-operatively. 544/776 (70.1%) of all AAA were morphologically suitable for Nellix. 533/730 (73.0%) of patients who had undergone infrarenal EVR were compliant with Nellix IFU, compared with 497/730 (68.1%), 379/730 (51.9%) and 214/730 (29.3%) with the IFU for Medtronic Endurant (p = .04) or Cook Zenith (p < .01) and Gore C3 Excluder (p < .01) endografts respectively.

CONCLUSIONS

Nellix technology appears widely applicable to contemporary infrarenal AAA practice, and may provide an option for patients that are outside current EVR device instructions for use. However, formal outcomes study is still required, and will ultimately dictate the clinical relevance of this feasibility study. The major limitation to anatomic suitability for Nellix is currently the maximum patent lumen diameter of large AAA.

Predicting aortic complications after endovascular aneurysm repair

Background

Lifelong surveillance is standard after endovascular repair of abdominal aortic aneurysm (EVAR), but remains costly, heterogeneous and poorly calibrated. This study aimed to develop and validate a scoring system for aortic complications after EVAR, informing rationalized surveillance.

Methods

Patients undergoing EVAR at two centres were studied from 2004 to 2010. Preoperative morphology was quantified using three-dimensional computed tomography according to a validated protocol, by investigators blinded to outcomes. Proportional hazards modelling was used to identify factors predicting aortic complications at the first centre, and thereby derive a risk score. Sidak tests between risk quartiles dichotomized patients to low- or high-risk groups. Aortic complications were reported by Kaplan–Meier analysis and risk groups were compared by log rank test. External validation was by comparison of aortic complications between risk groups at the second centre.

Results

Some 761 patients, with a median age of 75 (interquartile range 70–80) years, underwent EVAR. Median follow-up was 36 (range 11–94) months. Physiological variables were not associated with aortic complications. A morphological risk score incorporating maximum aneurysm diameter (P &lt; 0·001) and largest common iliac diameter (measured 10 mm from the internal iliac origin; P = 0·004) allocated 75 per cent of patients to a low-risk group, with excellent discrimination between 5-year rates of aortic complication in low- and high-risk groups at both centres (centre 1: 12 versus 31 per cent, P &lt; 0·001; centre 2: 12 versus 45 per cent, P = 0·002).

Conclusion

The risk score uses commonly available morphological data to stratify the rate of complications after EVAR. The proposals for rationalized surveillance could provide clinical and economic benefits.

A systematic review of protocols for the three-dimensional morphologic assessment of abdominal aortic aneurysms using computed tomographic angiography

The morphology of infrarenal abdominal aortic aneurysms (AAAs) directly influences the perioperative outcome and long-term durability of endovascular aneurysm repair. A variety of methods have been proposed for the characterization of AAA morphology using reconstructed three-dimensional (3D) computed tomography (CT) images. At present, there is lack of consensus as to which of these methods is most applicable to clinical practice or research. The purpose of this review was to evaluate existing protocols that used 3D CT images in the assessment of various aspects of AAA morphology. An electronic search was performed, from January 1996 to the end of October 2010, using the Embase and Medline databases. The literature review conformed to PRISMA statement standards. The literature search identified 604 articles, of which 31 studies met inclusion criteria. Only 15 of 31 studies objectively assessed reproducibility. Existing published protocols were insufficient to define a single evidence-based methodology for preoperative assessment of AAA morphology. Further development and expert consensus are required to establish a standardized and validated protocol to determine precisely how morphology relates to outcomes after endovascular aneurysm repair.

Systematic review and meta-analysis of duplex ultrasonography, contrast-enhanced ultrasonography or computed tomography for surveillance after endovascular aneurysm repair

BACKGROUND

Previous analyses suggested that duplex ultrasonography (DUS) detected endoleaks after endovascular aneurysm repair (EVAR) with insufficient sensitivity; they did not specifically examine types 1 and 3 endoleak, which, if untreated, may lead to aneurysm-related death. In light of changes to clinical practice, the diagnostic accuracy of DUS and contrast-enhanced ultrasonography (CEUS) for types 1 and 3 endoleak required focused reappraisal.

METHODS

Studies comparing DUS or CEUS with computed tomography (CT) for endoleak detection were identified. CT was taken as the standard in bivariable meta-analysis.

RESULTS

Twenty-five studies (3975 paired scans) compared DUS with CT for all endoleaks. The pooled sensitivity was 0·74 (95 per cent confidence interval 0·62 to 0·83) and the pooled specificity was 0·94 (0·90 to 0·97). Thirteen studies (2650 paired scans) reported detection of types 1 and 3 endoleak by DUS; the pooled sensitivity of DUS was 0·83 (0·40 to 0·97) and the pooled specificity was 1·00 (0·97 to 1·00). Eleven studies (961 paired scans) compared CEUS with CT for all endoleaks. The pooled sensitivity of CEUS was 0·96 (0·85 to 0·99) and the pooled specificity was 0·85 (0·76 to 0·92). Eight studies (887 paired scans) reported detection of types 1 and 3 endoleak by CEUS. The pooled sensitivity of CEUS was 0·99 (0·25 to 1·00) and the pooled specificity was 1·00 (0·98 to 1·00).

CONCLUSION

Both CEUS and DUS were specific for detection of types 1 and 3 endoleak. Estimates of their sensitivity were uncertain but there was no evidence of a clinically important difference. DUS detects types 1 and 3 endoleak with sufficient accuracy for surveillance after EVAR.

Aortic rupture and sac expansion after endovascular repair of abdominal aortic aneurysm

Background

Long-term concerns about the durability of endovascular aortic aneurysm repair (EVAR) remain after the publication of controlled trials. Increased expertise in endograft technology, case selection and postoperative reintervention has created a need for reappraisal of the longer-term efficacy of EVAR using contemporary data.

Methods

Patients undergoing infrarenal EVAR between 2004 and 2010 were studied prospectively. Morphological compliance with manufacturers' instructions for use (IFU) was established using three-dimensional computed tomography. The primary outcome measures were all-cause and aneurysm-related mortality, postoperative rupture, reintervention and sac expansion. These adverse events were reported using Kaplan–Meier survival analysis, with comparison within, or outside IFU by the log rank test.

Results

Some 478 patients of median age 76 years had a median aneurysm diameter of 62·9 mm. Median follow-up was 44 (range 11–94) months; 198 (41·4 per cent) were compliant with IFU. The 30-day mortality rate was 2·1 per cent (10 of 478 patients): nine (2·0 per cent) of 455 patients who had elective and one (4 per cent) of 23 patients who had non-elective surgery. Aneurysm-related mortality was 0·897 deaths per 100 person-years, and all-cause mortality was 8·558 deaths per 100 person-years, with significantly lower survival outside IFU (P = 0·012). Two patients had a late rupture (0·138 per 100 person-years), of whom one died. There were 6·120 reinterventions per 100 person-years, with no difference for aneurysms treated outside IFU (P = 0·136). Primary sac expansion occurred in 6·721 per 100 person-years and secondary sac expansion in 4·142 per 100 person-years.

Conclusion

In this series EVAR had a lower aneurysm-related mortality rate than demonstrated in early controlled trials, and with lower sac expansion rates than reported from image repositories. Data from earlier studies should be applied to current practice with caution.

Comparison of survival rates for abdominal aortic aneurysm treatment methods

BACKGROUND

We compared relative survival rates of patients after various operative treatments for abdominal aortic aneurysm (AAA) to those for the general population. We calculated a point of "recovery," defined as the survival rate equal to that of the general population.

METHODS

Survival data were collected from patients who underwent open repair for a ruptured AAA (rAAA), elective open repair of an AAA (OPEN), and endovascular repair (EVAR) in our hospital between 1995 and 2005. The cumulative relative survival rate and time-specific relative survival rate were calculated for these patients compared to those for the general population. The point of "recovery" was defined as the cumulative relative survival rate equaling the survival rate for the population, and the time-specific relative survival rate reaching 1.0.

RESULTS

The cumulative relative survival rate of the patients immediately after OPEN was lower than for the comparison group at the time the cumulative relative survival rate was regained. The time-specific relative survival rate of the rAAA reached 1.0 at 16 months following emergency surgery, and for OPEN after 10 months. The cumulative relative survival rate in the EVAR group had no impairment following intervention. The relative long-term survival rate in all three surgical groups was the same as that for the general German population.

CONCLUSIONS

Patients treated successfully for AAA have the same relative long-term survival as the general population. The time required to reach the same survival, however, differs between the treatment groups and is longest in the group with a rAAA. The variable survival rates should be taken into consideration when treating patients with an AAA.

Transverse minilaparotomy for open abdominal aortic aneurysm repair

INTRODUCTION

Traditional open surgical repair for abdominal aortic aneurysm (AAA) is a major procedure with a relatively high risk of perioperative morbidity. This article describes the results of minimally invasive open AAA repair through a transverse left upper quadrant minilaparotomy.

METHODS

Between January 2007 and June 2010, 83 consecutive patients (77 men) underwent elective or urgent repair of a nonruptured AAA through a horizontal transperitoneal left upper quadrant minilaparotomy. Postoperatively, patients were fast-tracked through a multidisciplinary recovery program.

RESULTS

Repairs were urgent in 15 patients (18%), and 10 (12%) had aortoiliac aneurysms. American Society of Anesthesiologists (ASA) scores 1 to 4 were 3.6%, 44.6%, 42%, and 11%, respectively. Median (range) age was 73 (61-87) years, AAA size was 5.9 (5.1-10) cm, body mass index was 27 (19-39) kg/m(2), operation time was 150 (85-280) minutes, blood loss was 625 (200-4150) mL, critical care bed days was 1 (0-19), and hospital stay was 4 (2-88) days. Four (4.8%) patients returned to the operating theater within the same admission. No patients required conversion to full laparotomy and none had reintervention postdischarge. Two patients (2.4%) died in the hospital, and 18 (21.7%) had postoperative adverse events, ranging from urinary retention to myocardial infarction. New-onset atrial fibrillation was the commonest of these events (11, 13.3%). Respiratory tract infection incidence was low (4.8%). Incisional herniation developed in two patients (2.4%) at a median (range) follow-up of 10 (6-25) months. Correcting for age, cardiac complications were associated with increased odds of hospital stay >4 days (odds ratio [OR], 7.59; 95% confidence interval [CI], 1.12-52.42; P = .014). Correcting for ASA score, advancing age was associated with increased risk of cardiac complications (OR, 1.18; 95% CI, 1.08-1.28; P = .001), whereas AAA screening (patient identified through screening) and maintaining higher intraoperative systolic pressure were both protective (OR, 0.24; 95% CI, 0.07-0.87; P = .018) and (OR, 0.93; 95% CI, 0.89-0.98; P = .009), respectively.

CONCLUSION

Left upper quadrant minilaparotomy is a feasible minimally invasive approach to open AAA repair. This technique is associated with low morbidity and mortality and short hospital stay, particularly in patients identified through AAA screening.