Written By: Danny Ge, University of Illinois at Peoria, 2019
Editor: Giovanni C. Santoro, DO, PGY-1

Introduction

An aortic aneurysm is an enlargement of a portion of the aorta that involves all three layers (i.e. intima, media, adventitia) of the vessel. A dilation ≥1.5 times the normal lumen diameter is considered to be an aneurysm. Aortic aneurysms are most commonly located in the abdominal aorta, though they also occur in the thoracic aorta. While they are typically asymptomatic, aortic aneurysms can rupture, especially as the aneurysm increases in size. It has long been recommended that prophylactic repair be performed to reduce the risk of rupture. Current guidelines recommend abdominal aortic aneurysm (AAA) repair for aneurysms ≥5.5 cm, or between 5.0-5.4 cm in women1. While open repair has been performed since 1951, endovascular repair emerged as an alternative in 19913. Endovascular repair involves obtaining access via a small incision at the groin, which allows catheter access to distal branches of the aorta, where a stent can be deployed at the aneurysm site. This study aims to compare the long-term efficacy of open versus endovascular repair.

Study Design and Patient Population

This study is a randomized controlled trial involving 1252 patients, 626 of whom were assigned to endovascular repair and 626 assigned to open repair. Groups were matched according to various characteristics and there were no differences between groups. Patients were recruited from 1999 through 2004 and were followed until 2009. All patients were at least 60 years old with aneurysms ≥5.5 cm on CT scan. Patients also had to be candidates for both open repair and endovascular repair. Follow up CT scans were performed at one and three months post-procedure in the endovascular repair group, and annually in both treatment groups. Primary endpoints for the study were all-cause mortality and mortality related to the aneurysm. Secondary endpoints included graft-related complications (e.g. leaks, ruptures, anastomotic aneurysm, kinking, thrombosis, stenosis, infection) and graft-related reinterventions.

Statistical Analysis

All statistical analysis was performed based on the intention-to-treat principle, which means that all patients that were randomized in the trial were included in the analysis as part of the initial group they were randomized to, regardless of any deviations from the protocol after randomization. Logistic regression was performed to compare in-hospital mortality. Logistic regression is a predictive analysis used to compare a binary dependent variable with an independent variable. Cox regression was used to compare total mortality, aneurysm-related mortality, and rates of graft-related complications/reinterventions. Cox regression is a statistical method used to compare survival time of patients with one or more predictor variables. Hazard ratios were calculated for total follow up and at three time periods:

randomization to 6 months, >6 months to 4 years, and after 4 years. The hazard ratio measures the effect of an intervention on an outcome in two groups over a time period. A per-protocol analysis was performed on the patients that underwent their randomly assigned treatment. This analysis excluded patients that did not undergo repair, patients whose repair was abandoned during surgery, or those who did not undergo their randomly assigned treatment.

Results

The mean age was 74.1 +/– 6.1 and the mean aneurysm diameter was 6.4 +/– 0.9 cm. After 30-days from the time of surgery, 1.8% of endovascular repair patients died, compared to 4.3% of open repair patients (adjusted odds ratio 0.39; 95% confidence interval 0.18 – 0.87; p=0.02). The total number of patients that died during hospitalization for aneurysm repair included 2.3% of the endovascular repair group and 6.0% of the open repair group (adjusted odds ratio 0.39; 95% CI 0.20 – 0.76; p=0.006). The study consisted of 6904 total person-years of follow up. Person-years refer to the total number of years that all participants contributed to the study. After follow-up was completed, total mortality rate was 7.5 deaths per 100 person-years in the endovascular repair group and 7.7 deaths per 100 person-years in the open-repair group (adjusted hazard ratio 1.03; 95% CI 0.86 – 1.23; p=0.72). Total aneurysm related mortality was 1 death per 100 person-years in the endovascular repair group and 1.2 deaths per 100 person-years in the open repair group (adjusted hazard ratio 0.92; 95% CI 0.57 – 1.49; p=0.73). For the Kaplan-Meier curves depicting survival rate vs. time, total mortality for both groups converges at 2 years, while aneurysm-related mortality converges at 6 years. The endovascular repair group had a higher rate of graft-related complications by a factor of three to four compared to the open repair group. Endovascular repair was also associated with a significantly higher overall cost (mean cost $4,568 more).

Conclusion

Endovascular aneurysm repair was associated with significantly lower perioperative mortality when compared to open repair. However, this benefit was lost in the long term as there is no significant difference in total mortality between the two groups. The increase in long-term aneurysm related mortality may be attributed to secondary rupture after repair, which was only seen in the endovascular repair group. The increase in complications also contributes to the higher overall cost of endovascular repair. Limitations of this study include the usage of older versions of endografts, as the long-term efficacy of the newer technology has yet to be evaluated. Additionally, the study began 3 years before the reporting of graft-related complications was standardized. Therefore, graft-related complications were evaluated by radiologists at each participating institution, rather than a common core. Finally, outpatient and other minor procedures were not recorded, which may have resulted in underreporting of post-operative complications. This study demonstrates the benefits of endovascular aneurysm repair in terms of short-term mortality, thereby establishing EVAR as a viable option compared to open repair.

Sources

1. Chaikof EL et al. The Society for Vascular Surgery practice guidelines on the care of patients with an abdominal aortic aneurysm. Journal of Vascular Surgery. January 2018. Volume 6, issue 1, pg. 2-77.

2. Greenhalgh RM et al. Endovascular versus open repair of abdominal aortic aneurysm. New England Journal of Medicine. May 20, 2010. 362:1863-1871

3. Parodi JC, Palmaz JC, Barone HD. Transfemoral intraluminal graft implantation for abdominal aortic aneurysms. Annals of Vascular Surgery. November 1991. Volume 5, issue 6, pg 491-499