The first 150 endovascular AAA repairs at a single institution: how steep is the learning curve?

Lessons learned and learning curve of fenestrated and branched endografts

Fenestrated and branched endovascular repair (F-BEVAR) has been increasingly used to treat patients with complex aortic aneurysms involving the renal-mesenteric arteries. As with any new procedure, there is a learning curve associated with mastering the technique. However, proficiency with deployment is only one aspect of the learning process, and ultimately, this curve is defined not by one quality parameter, but by patient selection, the performance of the entire team, the surgeon's ability to adapt to unexpected events, and the durability of the repair. This article reviews the importance of novel training paradigms, learning curve, and factors affecting outcomes of complex endovascular aneurysm repair.

The Association Between a Surgeon’s Learning Curve With Endovascular Aortic Aneurysm Repair and Previous Institutional Experience

The purpose of the present study was to determine whether an institution’s prior endovascular experience influenced the learning curve of subsequent surgeons. A prospective analysis of the initial 70 endovascular abdominal aortic aneurysm repair (EVAR) cases attempted by an individual surgeon was performed with the primary outcome variable being achievement and 30-day maintenance of initial clinical success. Along with standard statistical analyses, the cumulative sum failure method (CUSUM) was used to analyze the learning curve, with a predetermined acceptable failure rate of 10%. Seventy elective EVAR cases were performed by this surgeon during a 4-year period (2000-2004) (mean age, 73.7 ∓ 5.4 years; mean aneurysm diameter 63.3 ∓ 7.2 mm). Initial clinical success was achieved in 68 of 70 cases (97%), which differed significantly with that of our initial surgeon (88.5%, P = .01). Causes of failure in the present series included 1 early mortality (1.4%) and 1 case of conversion to open repair with no instances of type I endoleak or endograft limb thrombosis. Both surgeons’ cases were plotted sequentially with CUSUM curves revealing a significantly shorter learning curve for the second surgeon. Optimal results were achieved following 10 to 20 EVAR cases, as opposed to 60 cases in the initial series. Such an analysis confirms that as an institution’s experience with EVAR increases, an individual surgeon’s learning curve shortens considerably.

Evaluating the learning curve in the prospective Randomized Clinical Trial of hemodynamic support with Impella 2.5 versus Intra-Aortic Balloon Pump in patients undergoing high-risk percutaneous coronary intervention: a prespecified subanalysis of the PROTECT II study

BACKGROUND

The introduction of new medical devices may be accompanied by a learning curve.

METHODS

To evaluate the impact of the device learning curve on the outcomes of PROTECT II trial, comparing Impella 2.5 versus the intra-aortic balloon pump (IABP) during high-risk percutaneous coronary intervention, we report on a prespecified analysis, excluding the first Impella 2.5 and IABP patients at each site.

RESULTS

A total of 448 patients were enrolled at 74 sites. Among these, 58 patients were the first to receive Impella 2.5 at their site, 62 were the first to receive IABP. A trend toward higher major adverse events (MAEs) at 30 days was observed for the subgroup of first versus remaining Impella 2.5 patients: 44.8% versus 31.7%, P = .072. MAE rates for the first and remaining IABP patients were similar at 30 days. After exclusion of the first patient in each group, MAE rates for Impella 2.5 and IABP were 31.7% versus 40.0% (P = .119) at 30 days and 38.0% versus 50.0% (P = .029) at 90 days.

CONCLUSIONS

Significantly lower 90-day MAE rates were observed with the use of Impella 2.5 compared to the use of IABP after excluding the first patient per group at each site. This prespecified analysis suggests a learning curve associated with initial introduction of the Impella 2.5. Clinical trials should better address the training aspect of new devices, especially when compared with more established devices.

Development of the abdominal aorta and iliac arteries during the fetal period: a morphometric study

PURPOSE

This study aimed to determine the location and morphometric development of the fetal abdominal aorta and the iliac arteries.

METHODS

The study was carried out between 1996 and 2008 on 172 spontaneously aborted human fetuses (76 males and 96 females) aged between 9 and 40 weeks. None of the fetuses had any external pathology or anomaly. The location of the abdominal aorta was determined in reference to the vertebral column. This was followed by measurements of the lengths, external diameters of the origin of the aorta, and bifurcation of aorta as well as the bifurcation angles of the abdominal aorta. The vertebral levels at which the abdominal aorta started and bifurcated were determined. The lengths and external diameters of the common iliac arteries, diameters of the internal and external iliac arteries, and lengths of the external iliac arteries were measured. The vertebral levels of bifurcation of the common iliac arteries were determined.

RESULTS

The fetal abdominal aorta lay in the midline, in front of the vertebral column. The mean bifurcation angle of the abdominal aorta was greater than adults in the third trimester and at full term. The lengths and diameters of the abdominal aorta and the iliac arteries increased with gestational age, and significant positive correlations were found. There were no sex or laterality differences in either parameter. External diameter of the internal iliac artery was larger than that of the external iliac artery. Bifurcation of the abdominal aorta to the common iliac arteries was more inferior compared to the adults, and these levels rose with gestational age.

CONCLUSION

The morphometric parameters and location of the fetal abdominal aorta and the iliac arteries were determined by the present study. We conclude that the abdominal aorta lay in the midsagittal plane. The bifurcation level of the abdominal aorta arose with gestational age and at full term, and reaches to the same level as adults. In the early fetal period, the bifurcation level of the common iliac artery was more inferior compared to the adults, and they reach the adult positions around full term. The diameter of the internal iliac artery was nearly one and a half times larger than the external iliac artery. The findings of this study would be present, detailed information about the development of the abdominal aorta and the iliac arteries; this will also contribute to radiological (ultrasound and MR) studies in the intrauterine period.

Propensity scored analysis of outcomes after ruptured abdominal aortic aneurysm

Background

This study examined the population outcome of ruptured abdominal aortic aneurysm (rAAA) in England, the role of endovascular repair (EVAR), and the relationship between outcome and hospital workload.

Methods

Data were retrieved from Hospital Episode Statistics between 1 April 2003 and 31 March 2008. Propensity scoring was used to compare the outcomes of stratified patients undergoing EVAR and open repair. The relationship between workload and outcome was determined.

Results

Some 3725 urgent and 4414 rAAA repairs were included. Mortality rates were 21·3 per cent for urgent repair and 46·3 per cent for rAAA repair. EVAR was employed for 16·3 and 7·6 per cent of urgent and rAAA repairs respectively. EVAR was associated with significantly reduced mortality for urgent repair (odds ratio (OR) 0·531, 95 per cent confidence interval 0·415 to 0·680; P < 0·001) and rAAA repair (OR 0·527, 0·416 to 0·668; P < 0·001). A propensity scored analysis confirmed the benefit of EVAR for rAAA repair (P < 0·001). Repair of rAAA at hospitals with a higher elective aneurysm workload was associated with lower mortality rates irrespective of the mode of treatment (P < 0·001). Higher-volume hospitals were more likely to operate on rAAA (P = 0·033).

Conclusion

EVAR offered a survival advantage over open repair for non-elective aneurysm procedures. Services for the treatment of rAAA should incorporate access to EVAR and would benefit from being based in units with a high elective caseload.

Outcomes of care of abdominal aortic aneurysm in Veterans Health Administration facilities: results from the National Surgical Quality Improvement Program

This report describes outcomes of care for abdominal aortic aneurysms (AAAs), along with methods used by the Veterans Affairs (VA) National Surgical Quality Improvement Program (NSQIP) in tracking, monitoring, and improving surgical results in VA facilities. Since the inception of NSQIP in 1994, a continual drop in overall surgical mortality, along with decreased morbidity, has occurred. A parallel improvement in results of vascular surgery and AAA repair was also observed. Soon after introduction of endovascular aneurysm repair (EVAR), with Food and Drug Administration device approval in 1999, robust electronic NSQIP records immediately began to capture individual facility performances and outcomes for both types of AAA repair. The NSQIP data center provided actual and risk-adjusted analyses for both procedures semiannually. These analyses have been used by its executive board to provide recommendations, often based on site visits, to improve outcomes. Requirements for reporting of facility-specific data and feedback, paper audits, and site visits appear to relate directly to improved AAA care. Veterans Health Administration (VHA) outcomes of AAA repair are comparable to those reported nationally and internationally and have continued to improve in recent years. National VHA initiatives, based on data feedback and active oversight, relate to some of the lowest AAA mortality rates available. This review describes past, present, and possible future NSQIP strategies to improve outcomes for AAA repair with general comments about recent alternative proposals.

National outcomes for the treatment of ruptured abdominal aortic aneurysm: comparison of open versus endovascular repairs

OBJECTIVES

Endovascular repair (EVAR) of ruptured abdominal aortic aneurysms (rAAA) has been shown to acutely decrease procedural mortality compared to open aortic repair (OAR). However, little is known about the effect of choice of procedure; EVAR vs OAR, or the impact of physician and institution volume on long-term survival and outcome.

METHODS

Patients hospitalized with rAAA who underwent either OAR or EVAR, were derived from the Medicare inpatient dataset (1995-2004) using ICD9 codes. We evaluated long-term survival after OAR and EVAR in the entire fee-for-service Medicare population, and then in patients matched by propensity score to create two similar cohorts for comparison with Kaplan-Meier analysis. Annual surgeon and hospital volumes of EVAR (elective and ruptured), OAR (elective and ruptured), and rAAA (EVAR and OAR) were divided into quintiles to determine if increasing volumes correlate with decreasing mortality. Predictors of survival were determined by Cox modeling.

RESULTS

A total of 43,033 Medicare beneficiaries had rAAA repair: 41,969 had OAR and 1,064 had EVAR. The proportions of patients with diabetes, hypertension, cardiovascular, cerebrovascular, renal disease, hyperlipidemia, and cancer were statistically higher in the EVAR than in the OAR group, whereas lower extremity vascular disease was higher in the OAR group. The initial evaluation of EVAR vs OAR, prior to propensity matching, showed no statistical advantage in EVAR-survival after 90 days. The survival analysis of patients matched by propensity score showed a benefit of EVAR over OAR that persisted throughout the 4 years of follow-up (P = .0042). Perioperative and long-term survival after rAAA repair correlated with increasing annual surgeon and hospital volume in OAR and EVAR and also with rAAA experience. EVAR repair had a protective effect (HR = 0.857, P = .0061) on long-term survival controlling for comorbidities, demographics, and hospital and surgeon volume.

CONCLUSION

When EVAR and OAR patients are compared using a reliable statistical technique such as propensity analysis, the perioperative survival advantage of rAAA repaired endovascularly is maintained over the long term. Institutional experience with rAAA is critical for survival after either OAR or EVAR.

Endovascular Abdominal Aortic Aneurysm Repair: A Community Hospital's Experience

Endovascular abdominal aortic aneurysm repair (EVAR) has become the first-line approach for the treatment of abdominal aortic aneurysms. Outcomes outside of tertiary care settings remain unknown. The purpose of this study is to report the midterm outcomes of EVAR in a community hospital. A retrospective review of 75 elective, consecutive EVARs performed at a single nonacademic community hospital was performed. There were no conversions to open repair during or after endovascular repair. The mean follow-up was 18 months. There were no postoperative ruptures or aneurysm-related deaths. At 24 months, freedom from aneurysm-related death was 100%, freedom from secondary interventions was 91%, and freedom from endoleak was 69%. EVAR in the community setting is a safe and durable procedure, even in a medically high-risk population. Comparable outcomes can be achieved to tertiary care centers, in carefully selected patients with favorable anatomy.

Methods for Three-Dimensional Geometric Characterization of the Arterial Vasculature

Complex vascular anatomy often affects endovascular procedural outcome. Accurate quantitative assessment of three-dimensional (3D) in-vivo arterial morphology is therefore vital for endovascular device design, and preoperative planning of percutaneous interventions. The aim of this work was to establish geometric parameters describing arterial branch origin, trajectory, and vessel curvature in 3D space that eliminate the errors implicit in planar measurements. 3D branching parameters at visceral and aortic bifurcation sites, as well as arterial tortuosity were determined from vessel centerlines derived from magnetic resonance angiography data for three subjects. Errors in coronal measurements of 3D branching angles for the right and left renal arteries were 3.1 +/- 3.4 degrees and 7.5 +/- 3.7 degrees , respectively. Distortion of the anterior visceral branching angles from sagittal measurements was less pronounced. Asymmetry in branching and planarity of the common iliac arteries was observed at aortic bifurcations. The renal arteries possessed considerably greater 3D curvature than the abdominal aorta and common iliac vessels with mean average values of 0.114 +/- 0.015 and 0.070 +/- 0.019 mm(-1) for the left and right, respectively. In conclusion, planar projections misrepresented branch trajectory, vessel length, and tortuosity proving the importance of 3D geometric characterization for possible applications in planning of endovascular interventional procedures and providing parameters for endovascular device design.

Systematic Review and Meta-analysis of 12 Years of Endovascular Abdominal Aortic Aneurysm Repair

BACKGROUND

Endovascular repair (ER) of abdominal aortic aneurysm (AAA) is a new technique, and reported rates of endoleak, conversion to open repair, rupture and mortality vary widely. The aim of this study was to estimate these rates from the published data, and examine how this has changed as more patients have undergone ER.

METHODS

A systematic review and meta-analysis of publications identified through searches of the electronic databases EMBASE and Medline. All publications quoting endoleak, conversion to open repair, rupture and mortality rates for a series of patients undergoing ER were included.

RESULTS

163 studies pertaining to 28,862 patients undergoing ER were identified as relevant for the review and meta-analysis. The pooled estimate for operative mortality was 3.3% (95% confidence interval 2.9 to 3.6%). The pooled estimate for type 1 endoleaks was 10.5% (95% confidence interval 9.0 to 12.1%), with an annual rate of 8.4% (95% confidence interval 5.7% to 12.2%). The pooled estimate of type 2,3 and 4 endoleaks was 13.7% (95% confidence interval 12.3 to 15.3%), with an annual rate of 10.2% (95% confidence interval 7.4% to 14.1%). The pooled estimate for primary conversion to open repair was 3.8% (95% confidence interval 3.2 to 4.4%), and for secondary conversion to open repair 3.4% (95% confidence interval 2.8 to 4.2%). The pooled estimate for post-operative rupture was 1.3% (95% confidence interval 1.1 to 1.7%), with an annual rupture rate of 0.6% (95% confidence interval 0.5% to 0.8%). Multivariate meta-regression analysis showed that rates of operative mortality, post-operative rupture and total number of endoleaks all fell significantly (p<0.05) over time.

CONCLUSIONS

This study demonstrates a low mortality and a gradual reduction in vascular morbidity and mortality associated with endovascular repair since it was first introduced.

Systematic review of recent evidence for the safety and efficacy of elective endovascular repair in the management of infrarenal abdominal aortic aneurysm

Background

Conventional management of abdominal aortic aneurysm (AAA) is by open repair and is associated with a mortality rate of 2–6 per cent. Endovascular aneurysm repair (EVAR) is an alternative technique first introduced in 1991. A systematic review was undertaken of the evidence for the safety and efficacy of elective EVAR in the management of asymptomatic infrarenal AAA.

Methods

Thirteen electronic bibliographical databases were searched, covering biomedical, health-related, science and social science literature. Outcomes were assessed with respect to efficacy (successful deployment, technical success, conversion rates and secondary intervention rates) and safety (30-day mortality rate, procedure morbidity rates and technical issues—endoleaks, graft thrombosis, stenosis and migration).

Results

Of 606 reports identified, 61 met the inclusion criteria (three randomized and 15 non-randomized controlled trials, and 43 uncontrolled studies). There were 29 059 participants in total; 19 804 underwent EVAR. Deployment was successful in 97·6 per cent of cases. Technical success (complete aneurysm exclusion) was 81·9 per cent at discharge and 88·8 per cent at 30 days. Secondary intervention to treat endoleak or maintain graft patency was required in 16·2 per cent of patients. Mean stay in the intensive care unit and mean hospital stay were significantly shorter following EVAR. The 30-day mortality rate for EVAR was 1·6 per cent (randomized controlled trials) and 2·0 per cent in nonrandomized trials and case series. Technical complications comprised stent migration (4·0 per cent), graft limb thrombosis (3·9 per cent), endoleak (type I, 6·8 per cent; type II, 10·3 per cent; type III, 4·2 per cent) and access artery injury (4·8 per cent).

Discussion

EVAR is technically effective and safe, with lower short-term morbidity and mortality rates than open surgery. However, there is a need for extended follow-up as the long-term success of EVAR in preventing aneurysm-related deaths is not yet known.

Biocompatibility Studies of the Anaconda Stent-Graft and Observations of Nitinol Corrosion Resistance

PURPOSE

To validate the deployment, in vivo performance, biostability, and healing capacity of the Anaconda self-expanding endoprosthesis in a canine aortic aneurysm model.

METHODS

Aneurysms were surgically created in 12 dogs by sewing a woven polyester patch onto the anterior side of the thoracic or abdominal aorta. Anaconda prostheses were implanted transfemorally for prescheduled periods (1 or 3 months). Aneurysm exclusion and stent-graft patency were monitored angiographically. Healing was assessed with histological analysis and scanning electron microscopy (SEM). Textile analysis determined the physical and chemical stability of the woven polyester material, while the biostability of the nitinol wires was evaluated with SEM and spectroscopy.

RESULTS

All prostheses were intact at explantation. After 1 month, endothelial-like cells were migrating in a discontinuous manner both proximally and distally over the internal collagenous pannus at the device-host boundary. After 3 months, endothelialization had reached the midsections of the devices, with a thicker collagenous internal capsule. Patches of endothelial-like cells were sharing the luminal surface with thrombotic deposits. However, the wall of the device at the level of the aneurysm was generally poorly healed, with multiple thrombi scattered irregularly over the luminal surface. The polyester fabric was intact except for some filaments that were ruptured adjacent to the sutures and some abrasion caused by the nitinol wires. No evidence of corrosion was found on the nitinol stents.

CONCLUSIONS

This Anaconda stent-graft has demonstrated its ability to exclude arterial aneurysms. The device used in this study was an experimental prototype, and the manufacturer has incorporated new immobilization features into the model for clinical use. The constituent materials appear to be suitable in terms of biocompatibility, biofunctionality, and short-term durability.

Cumulative sum failure analysis of the learning curve with endovascular abdominal aortic aneurysm repair

PURPOSE

The purpose of this study was to evaluate the importance of experience and the learning curve with endovascular abdominal aortic aneurysm (AAA) repair.

METHODS

A retrospective analysis was performed of all elective endovascular AAA repairs attempted by an individual surgeon and radiologist over a 4-year period. The primary outcome variable was achievement and 30-day maintenance of initial clinical success as defined by the Society for Vascular Surgery/American Association of Vascular Surgery reporting standards. Following standard statistical analysis, the cumulative sum (CUSUM) method was used to analyze the learning curve, with a predetermined acceptable failure rate of 10% and calculated 80% alert and 95% alarm lines.

RESULTS

Ninety-six elective endovascular AAA repairs were attempted by this team between 1998 and 2002 (mean age 74 +/- 0.8 years; mean aneurysm diameter 5.98 +/- 0.8 cm). Initial clinical success was achieved and maintained in 85 of 96 patients (88.5%). Although results were acceptable throughout the study period, improved results with respect to the target failure rate (10%) were not achieved until 60 patients were treated. The learning or CUSUM curves did not differ for different device manufacturers, with improved results being achieved following 20 implantations of each device. The results did differ when comparing aortouniiliac grafts (n = 27) and bifurcated grafts (n = 64). Results with bifurcated grafts remained consistent throughout the study period, whereas with aortouniiliac grafts, results improved after only a few procedures in comparison with the target failure rate.

CONCLUSION

Success rates with endovascular aneurysm repair will improve with an individual's experience. The CUSUM method is a valuable tool in the evaluation of this learning curve, which has credentialing and training implications. Although acceptable results were obtained throughout the study period, this analysis indicates that 60 endovascular aneurysm repairs, or 20 with an individual device, are necessary before optimal rates of initial clinical success can be achieved. These results can be achieved more readily with aortouniiliac grafts than with bifurcated grafts.