Endograft type and anesthesia mode are associated with mortality of endovascular aneurysm repair for ruptured abdominal aortic aneurysms

Abstract

Objective

Endovascular aneurysm repair has become the primary treatment modality for ruptured infrarenal abdominal aortic aneurysm. This study examines the impact of endograft type on perioperative outcomes for ruptured infrarenal abdominal aortic aneurysm.

Method

The targeted endovascular aneurysm repair files of the American College of Surgeons National Surgical Quality Improvement Program database (2012–2017) were used. Only patients treated for ruptured infrarenal abdominal aortic aneurysm were included. All patients requiring concomitant stenting of the visceral arteries or aneurysmal iliac arteries or open abdominal surgery were excluded. The characteristics of patients treated with the different endografts and the corresponding outcomes were compared using Stata software.

Results

There were 479 patients treated with the three most common endografts: Cook Zenith (n = 127), Gore Excluder (n = 239), and Medtronic Endurant (n = 113). The number of other endografts was too small for statistical analysis. Compared to patients treated with Excluder or Endurant, the patients treated with Zenith had significantly lower body mass index (P < .001) and were less likely to be white (P < .001). On the other hand, patients treated with Endurant were less likely to be smoker (P = .016). Patients treated with Zenith had significantly larger ruptured infrarenal abdominal aortic aneurysm diameter (P = .045). The overall mortality was 18% and morbidity 74.3%. There was a statistically significant difference in overall mortality (Zenith = 11.8%, Excluder = 18%, Endurant = 24.8%, P = .033) but not morbidity (P = .808) between the three groups. Post hoc analysis for overall mortality showed only significant difference between Zenith and Endurant. The difference in mortality was not significant in patients presenting with ruptured infrarenal abdominal aortic aneurysm without hypotension (P = .065). On multivariable analysis, treatment with the Endurant endograft was associated with increased mortality compared to Zenith (odds ratio = 3.0 [confidence interval 1.31–6.7]). General anesthesia (odds ratio = 2.67 [confidence interval 1.02–7.02]), rupture with hypotension (odds ratio = 4.49 [confidence interval 2.54–7.95]), and dependent functional status (odds ratio = 5.7 [confidence interval 1.96–16.59]) were independently associated with increased mortality while increasing body mass index (odds ratio = 0.97 [confidence interval 0.95–0.99]) was associated with reduced risk of mortality.

Conclusions

This study highlights contemporary outcomes of endovascular aneurysm repair for ruptured infrarenal abdominal aortic aneurysm with relatively low mortality. Endograft type and anesthesia technique are modifiable factors that can potentially improve outcomes. Significant variation in the outcomes of the different endografts warrants further research.

Keywords

Ruptured infrarenal abdominal aortic aneurysm endovascular aneurysm repair endograft mode of anesthesia mortality

Introduction

Rupture is the most dreaded complication of abdominal aortic aneurysms (AAA) and is associated with high mortality. While the incidence of ruptured AAA (RAAA) has been declining according to multiple reports from the United States and Europe,^1–3 the mortality from this disease continues to be considerably high, despite improvements in screening and perioperative care.^4–7 The increasing use of endovascular aneurysm repair (EVAR) for RAAA has been correlated with some decline in mortality to 20–30% with EVAR compared to 41–46% with open surgical repair.^8–15 The early results of the IMPROVE trial, which is a multicenter randomized control trial, showed early survival benefit in women only treated with EVAR compared to open surgical repair.⁷ However, the midterm outcomes of the trial revealed significant improvement in survival and quality of life in the EVAR group at three years compared to open AAA repair with similar cost and rates of reintervention.^7,16

Based on data from the IMPROVE trial and other studies, the society for vascular surgery practice guidelines on the care of patients with AAA in 2018 recommended EVAR as the preferred treatment modality for RAAA.¹⁷ Several endografts with different characteristics and platforms for delivery are available on the market for EVAR.¹⁸ Even though, multiple industry sponsored trials have studied the various devices for elective AAA repair leading to FDA approval,^19–24 there is paucity of studies comparing the different endografts specially for treatment of RAAA.⁷ The aim of this study is to explore the impact of endograft type on perioperative outcomes for RAAA.

Methods

Database

The targeted EVAR files of the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database were used. ACS-NSQIP is a deidentified database compiled from more than 800 hospitals in the United States. In the participating sites, data are collected by trained nurses using specific data extraction method. The database captures variables related to patient characteristics, operative data, and perioperative outcomes.^19,20 The targeted EVAR files provide additional information on the indication, size, and extent of aneurysm, as well as the endograft type used. As the data were deidentified and no consent was needed, the study was exempted from the institutional review board.

Patient population

All patients in the EVAR targeted file between 2012 and 2017 treated for “rupture with hypotension or use of vasopressors” or “rupture without hypotension” were included. Patients requiring concomitant stenting of the renal or visceral arteries suggestive that the ruptured aneurysm was juxta-renal, suprarenal, or thoracoabdominal were excluded. Patients with concomitant iliac artery aneurysms were excluded. Also, patients who underwent open abdominal surgery or converted to open repair in the initial procedure were excluded.

Patients characteristics

Demographic variables included in the analysis were patient’s gender, age, race, body mass index (BMI) and functional status. Comorbidities included history of diabetes mellitus (DM), smoking status, chronic obstructive pulmonary disease (COPD), congestive heart failure (CHF), hypertension, and dialysis dependency.

Procedural details

The three types of endografts included in the study were Cook Zenith (Cook Medical, Bloomington, Indiana), Gore Excluder (WL Gore, Flagstaff, Arizona), and Medtronic Endurant (Medtronic Minneapolis, Minnesota). The other types of endografts were too low in number for analysis. Other procedural variables accounted for were access type (percutaneous, one groin cut down, bilateral groin cut down, and percutaneous with conversion to open), hemodynamic status at presentation with hypotension or not, aneurysm diameter, principal anesthesia technique classified as general anesthesia (GA) or monitored anesthesia care (MAC), American Society of Anesthesiologists (ASA) class, and total operative time.

Outcomes

The primary outcome was 30-day mortality. Perioperative complications included ischemic colitis, lower extremity ischemia, wound infection, pneumonia, unplanned intubation, failure to wean from the ventilator, cardiac arrest, bleeding, deep vein thrombosis, renal failure, stroke, and sepsis. Wound infection was an aggregate of superficial, deep, and organ space infections. Other outcomes included were any morbidity, reoperation, readmission, and hospital length of stay.

Statistical analysis

Categorical variables were summarized as counts and percentages while continuous variables were summarized as means and standard deviations (SDs). Differences between variables among the three study groups were tested using analysis of variance (ANOVA) for continuous variables and chi-square test for categorical variables, followed by post hoc testing to examine statistically significant differences between individual pairs through t-test and chi-square test, respectively. A multivariable logistic regression was performed to examine independent factors associated with 30-day mortality after EVAR for RAAA. The model included the type of endograft (Zenith vs. Excluder, Zenith vs. Endurant and Endurant vs. Excluder), patient age, male sex, race, BMI, functional status, DM, current smoker, hypertension, history of CHF, access type (percutaneous access vs. cut down), mode of anesthesia (GA vs. MAC), ASA class, hypotension at time of presentation, and aneurysm diameter. The odds ratios (ORs) were reported with 95% confidence intervals (CIs) for all variables included in the model. Stata software version 14.1 was used for the analysis.

Results

Patients characteristics

There were 479 patients treated with the three most common endografts: Zenith n = 127 (26.5%), Excluder n = 239 (49.9%), and Endurant n = 113 (23.6%). Across the treatment groups, there was no difference in distribution of age, sex, or functional status. Compared to patients treated with Excluder or Endurant, the patients treated with Zenith had significantly lower BMI (Zenith = 19 ± 16.1, Excluder = 25.3 ± 11.5, and Endurant = 24.6 ± 12.9, P < .0001) and were less likely to be white (Zenith = 54.3%, Excluder = 83.3%, and Endurant = 79.6%, P < .0001). On the other hand, patients treated with Endurant were less likely to be smoker compared to patients treated with Zenith or Excluder (Zenith = 40.1%, Excluder = 41.8%, and Endurant = 26.5%, P = .016). Other comorbidities were not different between the groups (Table 1).

Table 1.

Characteristics of patients treated with endovascular aneurysm repair (EVAR) for ruptured abdominal aortic aneurysm (RAAA) with the different endografts.

Patients characteristics			Cook Zenith n = 127 (25.6%)	Gore Excluder n = 239 (49.9%)	Medtronic Endurant n = 113 (23.6%)	P
Demographics
Male gender			102 (80.3)	185 (77.4)	94 (83.2)	.441
Age groups		18–64	25 (19.7)	54 (22.6)	24 (21.2)	.525
		65–80	63 (49.6)	117 (48.9)	54 (47.8)
		>80	39 (30.7)	68 (28.4)	35 (31)
Race		White	69 (54.3)^2,3	199 (83.3 )^1,3	90 (79.6 )^1,2	<.001*
Race		Others	58 (45.7)	40 (16.7)	23 (20.3)	<.001*
BMI, M ± SD			19^2,3	25.3¹	24.6¹	<.001*
Dependent functional status			6 (4.7)	9 (3.8)	5 (4.4)	.899
Comorbidities
Diabetes mellitus			21 (16.5)	26 (10.9)	17 (15)	.245
Current smoker			52 (40.1)³	100 (41.8)³	30 (26.5)^1,2	.016*
COPD			17 (13.4)	46 (19.2)	19 (16.9)	.365
Congestive heart failure			1 (0.8)	14 (5.9)	4 (3.5)	.15
Hypertension			90 (70.9)	163 (68.2)	90 (79.6)	.082
Dialysis dependency			2 (1.6)	4 (1.7)	3 (2.6)	.515
ASA class	≤3		16 (12.6)	16.7 (40)	15 (13.3)	.317
	4		74 (58.3)	130 (54.4)	74 (65.5)
	5		37 (29.1)	69 (28.9)	24 (21.2)
Aneurysm diameter, M ± SEM (cm)			7.6 ± .2^2,3	7.2 ± .1¹	7.4 ± .2¹	.045*

*Post hoc analysis was statistically different between Zenith,¹ Excluder,² and Endurant.³

ASA: American Society of Anesthesiologists; BMI: body mass index, COPD: chronic obstructive pulmonary disease.

Procedural details

Patients treated with Zenith had significantly larger RAAA diameter (Zenith = 7.6 ± 0.2 cm, Excluder = 7.2 ± 0.1 cm, and Endurant = 7.4 ± 0.2 cm, P = .045). Access type, emergent nature of the case, hypotension at the time of presentation, principal anesthesia technique, the ASA classification, and the mean total operative time were not different between the three groups (Table 2).

Table 2.

Procedural details of patients treated with endovascular aneurysm repair (EVAR) for ruptured abdominal aortic aneurysm (RAAA) with the different endografts.

Procedural details	Cook Zenith n = 127 (25.6%)	Gore Excluder n = 239 (49.9%)	Medtronic Endurant n = 113 (23.6%)	P
Access type
Bilateral cutdown	76 (59.8)	111 (46.4)	66 (58.4)	0.078
Percutaneous	42 (33.1)	100 (41.8)	40 (35.4)
One groin cutdown	8 (6.3)	23 (9.6)	6 (5.3)
Percutaneous converted to open	1 (0.8)	5 (2.1)	0 (0)
Emergency case	111 (87.4)	213 (89.1)	100 (88.5)	.886
Hypotension	48 (37.8)	110 (46)	47 (41.6)	.516
Principal anesthesia technique				.062
General anesthesia	102 (80.3)	202 (84.5)	103 (91.1)
Monitored anesthesia care	25 (19.7)	37 (15.5)	10 (8.8)
Total operation time, M ± SEM (min)	142.7 ± 6.1	138.8 ± 4.8	160.8 ± 7.7	.074

Outcomes

The mortality was 18% and morbidity 74.3%. There was a statistically significant difference in overall mortality (Zenith = 11.8%, Excluder = 18%, Endurant = 24.8%, P = .033) but not morbidity (P = .808) between the patients being treated with the three different endografts. Post hoc analysis for mortality showed only significant difference between Zenith and Endurant. The difference in mortality was not significant in patients presenting with RAAA without hypotension (P = .065). There was no other significant difference in complications, reoperation, or readmission (Table 3).

Table 3.

Perioperative outcomes of patients treated with endovascular aneurysm repair (EVAR) for ruptured abdominal aortic aneurysm (RAAA) with the different endografts.

	Cook ZenithN = 127 (25.6%)	Gore ExcluderN = 239 (49.9%)	Medtronic EndurantN = 113 (23.6%)	P
Complications
Ischemic colitis	5 (3.9)	15 (6.3)	5 (4.4)	0.575
Lower extremity ischemia	3 (2.4)	3 (1.3)	5 (4.4)	0.179
Superficial Wound infection	6 (4.7)	3 (1.3)	2 (1.8)	0.099
Pneumonia	6 (4.7)	21 (8.8)	13 (11.5)	0.156
Unplanned intubation	10 (7.9)	28 (11.7)	12 (10.6)	0.809
Failed weaning ventilator	14 (11)	39 (16.3)	19 (16.9)	0.335
Cardiac arrest	6 (4.7)	16 (6.7)	14 (12.4)	0.171
Acute Renal Failure	7 (5.5)	17 (7.7)	8 (7.1)	0.82
Pulmonary Embolism	1 (0.8)	3 (1.3)	2 (1.8)	0.79
Stroke	3 (2.4)	4 (1.7)	2 (1.8)	0.72
Bleeding	71 (55.9)	146 (61.1)	70 (62)	0.338
DVT/thrombophlebitis	6 (4.7)	10 (4.2)	2 (1.8)	0.431
Outcomes
Any morbidity	92 (72.4)	178 (74.5)	86 (76.1)	0.808
Overall Mortality	15 (11.8)³	43 (18)	28 (24.8)¹	0.033*
Mortality of RAAA without hypotension	5 (6.3)	13 (10)	6 (9.1)	0.646
Mortality of RAAA with hypotension	10 (20.8)³	30 (27.3)	22 (46.8)¹	0.014*
Reoperation	17 (13.4)	35 (14.6)	14 (12.4)	0.808
Readmission	13 (10.2)	27 (11.3)	8 (7.1)	0.393
Hospital length of stay Mean ± SEM (days)	7 ± 1	8.6 ± 0.8	8.3 ± 0.9	0.425

*Post hoc analysis was statistically different between Zenith,¹ Excluder,² and Endurant.³

DVT: deep vein thrombosis; RAAA: ruptured abdominal aortic aneurysm; SEM: standard error of the mean.

Factors associated with mortality on multivariable regression

The type of endograft was an independent risk factor for mortality in the model as treatment with the Endurant endograft was associated with increased mortality compared to Zenith (OR = 2.97 [1.31–6.7]), while treatment with Zenith versus Excluder (OR = 0.6 [0.28–1.29]), and treatment with Excluder versus Endurant (OR = 1.78 [0.96–3.31]) were not associated with mortality. RAAA with hypotension (OR = 4.49 [2.54–7.95]), using GA vs MAC (OR = 2.67 [1.02–7.02]), and dependent functional status (OR = 5.7 [1.96–16.59]) were independently associated with increased mortality. Increasing BMI (OR = 0.97 [0.95–0.99]) was associated with a slight but statistically significant reduced risk of mortality (Table 4).

Table 4.

Factors associated with mortality on multivariable regression analysis.

Risk factors	OR [95% CI]
Zenith vs. Excluder	0.6 [0.28–1.29]
Endurant vs. Excluder	1.78 [0.96–3.31]
Endurant vs. Zenith	2.97 [1.31–6.70] *
Age	1.67 [1.09–2.56]*
Male sex	0.96 [0.50–1.84]
White race	1.31 [0.65–2.60]
BMI	0.97 [0.95–0.99]*
Dependent functional status	5.70 [1.96–16.59]*
Diabetes	0.58 [0.22–1.50]
Smoking	0.80 [0.43–1.47]
Hypertension	0.63 [0.35–1.14]
History of CHF	1.29 [0.67–2.50]
Percutaneous access	1.1 [0.91–1.33]
General anesthesia vs. MAC	2.67 [1.02–7.02]*
ASA	0.91 [0.58–1.44]
Rupture WITH hypotension	4.49 [2.54–7.95]*
Aneurysm diameter	0.99 [0.99–1.00]

*Statistically significant.

OR: odds ratio, P: p value; CI: 95% confidence interval; BMI: body mass index; CHF: congestive heart failure; MAC: monitored anesthesia care; ASA: American society of anesthesia.

Discussion

This study describes the contemporary outcomes of EVAR for ruptured AAA with relatively low mortality (18%) compared to historical reports of endovascular (15–35%) and open repair of ruptured infrarenal aortic aneurysms (33–45%).^7,21–23 It demonstrates independent relations of mortality with age, functional status, hypotension, and type of anesthesia consistent with the published literature. Most notably, the results suggest that the type of endograft used for EVAR is independently associated with mortality. Patients treated with Endurant seemed to have three times higher OD of mortality compared to patients treated with Zenith. Interestingly, the mortality of patients treated with the Zenith endograft was only 11% and is probably among the lowest reported in the literature. Even though this association does not imply causality or prove that a certain endograft has superior outcomes for ruptured AAA, a discussion of this finding and explanation of probable causes are warranted.

The observed difference in mortality between the endografts is likely multifactorial related to clinical, anatomical, and operator variables but there are endograft differences that are worthy of highlighting. The three devices included in the analysis have different configurations, delivery systems, and material. The Zenith and Endurant endografts have suprarenal fixation while the Endurant and the Excluder are bimodular. In theory, the Zenith endograft would require more time for completion of deployment since it is tri-modular compared to the other endografts. The Excluder should be the fastest to deploy since it lacks suprarenal fixation and hence require one less step for deployment. The operative time was lowest in Excluder and highest in Endurant but that did not reach statistical significance and did not seem to be associated with mortality. Zenith stents are made of stainless steel while Endurant and Excluder stents are nitinol based and may have different radial strengths with different ability to immediately obtain a seal within the infrarenal aorta. Zenith has rigid hooks and barbs at the proximal position in addition to a 26-mm suprarenal fixation mechanism that is longer than other devices and may confirm some advantage in immediate sealing and control of hemorrhage.²⁴ An experimental study comparing proximal and distal fixation of commercially available endografts showed that the Zenith had the highest displacement force needed to move the device >20 mm from its fixation site.²⁵ On the other hand, Endurant is the only endograft indicated for shorter aortic necks of 1 cm length and it is possible that patients with unfavorable anatomy and shorter necks were preferentially treated with Endurant endograft associated with increased use outside the instructions for use (IFU) leading to higher rates of type 1 endoleak. Van Keulen et al. showed that 19–31% of the patients undergoing elective EVAR with the Endurant had anatomy outside the IFU.²⁶ However, Faizer et al. showed that the increased use of Endurant outside the IFU resulted in greater risk of type 1 endoleak but was not associated with higher reintervention rates in that study.²⁷ In another study comparing the outcomes of EVAR for RAAA based on the type of endograft, the rate of type 1 endoleak in the Zenith group was 0% compared to 18% in the Endurant group.²⁸ Even though a small type 1 endoleak after elective EVAR can thrombose or be treated with delayed reintervention, the presence of a type 1 endoleak after EVAR for RAAA can be devastating as the hemorrhage is likely not totally controlled. Lastly, the experience and skills of the operators in this study are unknown. Vascular surgeons tend to choose a primary device for most EVARs based on personal experience and institutional resources. It is possible that the surgeons using Zenith were more experienced than surgeons using Endurant, since the Zenith endograft has been on the market for longer period (2003 vs. 2010). On the other hand, Cook offers the only currently available device for fenestrated endografts based on the Zenith platform. Therefore, surgeons using Cook Zenith for RAAA might have had more experience treating complex aneurysms and potentially had superior skills and outcomes compared to surgeons using other endografts.^29,30

GA was associated with significantly higher mortality compared to MAC. This is likely related to the adverse effects of GA on the cardiovascular system as suggested by the IMPROVE trial³¹ and also reported by Torsello et al.³² GA has negative effects on thermoregulation, inflammatory state, and hemodynamic autoregulation, augmenting the second hit of stress and predisposing to multisystem organ failure.³³ In a recent report based on data from the vascular quality initiative database, patients with RAAA treated with EVAR under MAC had shorter operative time, decreased number of intraoperative transfusions, ICU length of stay, pulmonary complications, and lower mortality both at 30 days and one year compared to patients treated with EVAR under GA.³³ The presence of hypotension on presentation was independently associated with a fivefold increase in mortality. In the IMPROVE trial, systolic blood pressure was directly related to survival in linear fashion.³¹ In another study, systolic blood pressure less than 70 was associated with 2.7-fold increased risk of mortality.³⁴

The association of mortality with age and dependent functional status is consistent with the literature.^35–39 The combination of old age, frailty, and poor functional status puts patients with RAAA at a very high risk of perioperative morbidity and mortality.³⁸ The study also shows slight but significant reduction in mortality with increased BMI. Whether obesity is associated with improved survival after RAAA is controversial in the literature.^40–47 However, multiple studies suggest that obese patients with RAAA have improved outcomes with EVAR compared to open repair.^40,43 Studies suggest that increased frailty and decreased BMI often go hand in hand, and while in a chronic setting, obesity is hazardous, in an acute event such as rAAA, high albumin, and good nutritional in obese patients compared to frail patients could provide survival benifit.⁴⁹

There are several important limitations to this research project. Despite using the EVAR targeted ACS-NSQIP files that minimize errors related to diagnostic and procedural codes, trained abstractors gathering data may still have inaccurate entries. The database also lacks important details such as the response to resuscitation in patients who are hypotensive. The anatomy of the neck of the aneurysm including length, angulation, and configuration, as well as iliac tortuosity, calcification, and size (which can impact the short-term as well as the long-term outcomes of EVAR) are not available. The three endografts have different IFU and the proportions of patients treated outside the IFU in each group cannot be determined. Unknown confounders may affect outcomes—although we accounted for possible confounders clinically and statistically through multivariable regression analysis. A limitation of the database is that while data come from a representative selection of hospitals in relation to all hospitals nationally, no data are given about individual center or surgeon volumes. The impact of operator experience and center volume in relation to graft type is an area that merits future investigation.

Conclusion

This study highlights contemporary outcomes of EVAR for RAAA with relatively low mortality. Endograft type and anesthesia technique are modifiable factors that can potentially improve mortality further. Significant variation in the outcomes of the different endografts warrants further research.

Footnotes

Acknowledgment

This paper was presented as a poster at the 33rd annual meeting of the Eastern Vascular Society.

Authors' contribution

Conception and design: KB, SY, COC; Analysis and interpretation: KB, YZ, SY, COC, AG, AD; Writing the article: SY, KB, COC; Critical revision of the article: KB, YZ, SY, COC, AG, AD; Final approval of the article: KB, SY, YZ, COC, AG, AD; Overall responsibility: COC.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Sameh Yousef

Alan Dardik

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