Suitability of the Zenith p-Branch Standard Fenestrated Endovascular Graft for Treatment of Ruptured Abdominal Aortic Aneurysms

Abstract

Purpose: To evaluate the anatomic suitability of the Zenith pivot branch (p-branch) fenestrated device in ruptured abdominal aortic aneurysms (rAAA). Methods: Contrast-enhanced computed tomography (CT) images of 206 patients (mean age 75±8 years; 175 men) with rAAA were evaluated in a dedicated 3-dimensional vascular workstation. All aneurysms found unsuitable for standard infrarenal repair were evaluated for Zenith p-branch suitability according to the Investigational Device Exemption protocol for both device configurations (A, pivot fenestrations at the same level; B, right renal fenestration located more cranially). Results: The suitability of the p-branch (A or B configuration) for short neck aneurysms (<15 mm; n=89) was 49%; of the 26 different combinations of exclusion criteria, a mismatch between a renal artery takeoff and the positioning of the corresponding fenestration was the most common. For juxta- and pararenal aneurysms (neck length <10 mm; n=66), suitability was 48%. Suitability assessed by target vessel positioning only (excluding all other limiting factors) was 58% for short neck aneurysms (n=52) and 55% for juxta- and pararenal aneurysms (n=36). Conclusion: Approximately half of patients with short neck rAAAs would be suitable for the Zenith p-branch fenestrated device according to the instructions for use. In almost 60%, the pivot fenestrations can accommodate the corresponding target vessels. More studies are needed to confirm these findings.

Keywords

ruptured abdominal aortic aneurysm endovascular aneurysm repair stent-graft fenestrated stent-graft anatomic suitability

Introduction

Endovascular aneurysm repair (EVAR) has become the main treatment for abdominal aortic aneurysms (AAA) in most specialized centers. However, a large portion of patients are not suitable for infrarenal EVAR due to short proximal necks and/or poor iliac access. To increase EVAR suitability, fenestrated devices are now available where the sealing zone is moved proximally to the level of the visceral vessels, and blood flow to vital organs is secured through fenestrations in the graft fabric. The Zenith fenestrated abdominal aortic aneurysm endovascular graft (Cook Medical, Bloomington, IN, USA) was approved by the US Food and Drug Administration in 2012, and a major shift from open surgery to endovascular repair for juxtarenal aneurysms was expected. Because of morphological variations, each graft is custom made to fit the anatomy of the individual patient based on computed tomography (CT) reconstructions. However, delivery time often exceeds 6 weeks, thereby excluding fenestrated repair as an option in emergency situations.

The Zenith pivot branch (p-branch) device (Cook Medical, Brisbane, Australia) is an investigational off-the-shelf fenestrated graft with the potential to fit the target vessel anatomy in the majority of patients, allowing treatment of ruptures and other emergency situations. Clinical trials are ongoing at a few selected centers, and early reports are promising. The aim of this study was to evaluate the anatomic suitability of the Zenith p-branch device according to its instruction for use (IFU) in an unselected cohort of patients with ruptured AAA (rAAA).

Methods

Data from all 248 patients diagnosed with rAAA at our clinic from January 2006 until June 2013 were retrieved from a prospectively maintained database. Patients with confirmed rupture on thin-slice (0.5–3 mm) contrast-enhanced CT scans of acceptable quality for generating centerline-of-flow (CLF) reconstructions were eligible for the study. Of the 248 patients reviewed, 206 (83%) patients (mean age 75±8 years; 175 men) had CT scans of suitable quality for analysis. Patient demographics and aneurysm morphology are given in Table 1.

Table 1.

Demographics, Comorbidities, and Anatomic Data From 206 Study Patients.^a

Demographics and Comorbidities
Age, y	75±8
Men	175
Diabetes	(9)
Coronary heart disease	(30)
Heart failure	(11)
Hypertension	(42)
COPD	(15)
Cerebrovascular disease	(15)
History of smoking	(88)
Anatomic data
Neck length, mm	15 (5–29)
Neck diameter, mm	25 (22–30)
Diameter at CA, mm	27 (24–29)
Diameter at SMA, mm	25 (23–27)
AAA diameter, mm	74.5 (66–86)
Major suprarenal angle, deg	33.8 (19–44)
Major infrarenal angle, deg	49.3 (35.5–59.5)

Abbreviations: AAA, abdominal aortic aneurysm; CA, celiac artery; COPD, chronic obstructive pulmonary disease; SMA, superior mesenteric artery.

Continuous data are presented as the means ± standard deviation or median (interquartile range); categorical data are given as the counts (percentage).

Centerline-of-flow reconstructions were performed on a dedicated vascular 3-dimensional workstation (Aquarius Intuition; TeraRecon, San Francisco, CA, USA) for measurements of AAA neck lengths, diameters, and longitudinal and radial relationships of visceral vessels to the superior mesenteric artery (SMA). Neck angulations were measured with digital calipers and recorded as the higher value on either anteroposterior or lateral view reconstructions. Aneurysms were categorized as infrarenal (neck length ≥15 mm), short neck (neck length <15 mm), or juxta-/pararenal (neck length <10 mm) based on the reporting standards for endovascular aortic aneurysm repair.¹

The p-branch device specifications and implantation technique have been described in detail elsewhere.^2,3 In summary, the device consists of a tubular proximal stent-graft with a scallop for the celiac artery, an 8-mm fenestration for the SMA, and 2 pivot fenestrations for the renal arteries (p-branches). In design A, the pivot fenestrations are at the same level, while in the B configuration, the fenestrations have been offset with the right renal fenestration located more cranially.

Besides visceral vessel morphology compatible with the device, a nonaneurysmal aortic segment of at least 4 mm in length is required between the distal edge of the SMA and the aneurysm, with a diameter between 21 and 31 mm and maximum 45° suprarenal and 60° infrarenal angulations. Both the A and B nominal graft configurations are available with diameters between 26 and 36 mm and with lengths of 144 mm (diameters ≤32 mm) or 151 mm (36-mm diameter). The delivery system is 20-F (inner diameter) for all graft diameters except for the 36-mm graft, which is delivered through a 22-F introducer.

Assessment of Zenith p-branch suitability was done according to the Investigational Device Exemption (IDE) protocol for both the A and B device configurations for each patient using a dedicated grid and overlay sizing sheet for target vessel fit analysis (Figure 1). When 2 or more renal arteries were present on either side, only the main (largest diameter) artery was considered for a fenestration.

For the purpose of this study, suitability was defined as strict or liberal. Strict suitability was assumed when all target vessels fitted within the overlay markings with the SMA takeoff in the center of the corresponding marking. Liberal suitability referred to when the SMA takeoff had to be moved slightly from the center of the marking (still within its outer margins) to accommodate the remaining target vessels.

Results

The p-branch suitability (A or B configuration) for the 89 short neck (<15 mm) aneurysms evaluated was 49% [36 (47%) men and 8 (62%) women]. There were 26 different combinations of exclusion criteria, most commonly due to a mismatch between a renal artery takeoff and the positioning of the corresponding fenestration (38%), severe neck angulation (19%), or a combination of these (29%). Other neck-related exclusion criteria were rare; aortic diameter >31 mm in the sealing zone was the most common (4%). Although no iliac occlusions were present, 7 (9%) patients had narrow iliac arteries (<7.6 mm for the 20-F sheath and <8.5 mm for the 22-F sheath), which could compromise safe introduction of the delivery systems.

For the 66 juxta- and pararenal aneurysms, suitability was 48% [27 (47%) men and 5 (56%) women]. Suitability assessed by target vessel positioning only (excluding all other limiting factors) was 58% for short neck aneurysms [44 (58%) men and 8 (62%) women] and 55% for juxta- and pararenal aneurysms [31 (54%) men and 5 (56%) women]. When suitability was assessed for the entire 206 patient cohort irrespective of aneurysm neck length, suitability was slightly higher at 51% [91 (52%) men and 14 (45%) women] and 62% [109 (62%) men and 19 (61%) women] when based on target vessel positioning only.

Table 2 gives the clock positions of the visceral vessels and their distance from the SMA. Details on strict and liberal suitability in relation to A and B graft configurations and neck length are given in Table 3. Positioning of target vessels in relation to the A and B graft configurations are demonstrated in Figure 2.

Table 2.

Clock Positions of the Visceral Vessels and Distance From the Superior Mesenteric Artery.^a

Artery	Clock Position	Distance From the SMA, mm
CA	12:15 (12:00–12:30)	18 (15–22)
SMA^b	12:00 (12:00–12:00)
RRA	9:37 (9:15–10:00)	14 (8–20)
LRA	2:30 (2:00–3:00)	15 (10–20)

Abbreviations: CA, celiac artery; LRA, left renal artery; RRA, right renal artery; SMA, superior mesenteric artery.

Data are presented as the median (interquartile range).

The position of the SMA was set at 12:00 o’clock in all cases.

Table 3.

Suitability for Configurations A and B in Relation to Aneurysm Neck Length.^a

Neck Length, mm	Configuration A or B (IFU)			Configuration A (TV)			Configuration B (TV)			Configuration A or B (TV)
Neck Length, mm	Overall, %	Strict, %	Liberal, %	Overall, %	Strict, %	Liberal, %	Overall, %	Strict, %	Liberal %	Overall %	Strict %	Liberal, %
All	51.0	36.9	14.1	44.2	23.8	20.4	43.7	28.2	15.5	62.1	45.1	17.0
<15	49.4	32.6	16.9	39.3	19.1	20.2	37.1	21.3	15.7	58.4	39.3	19.1
<10	48.5	31.8	16.7	40.9	21.2	19.7	30.3	16.7	13.6	54.5	37.9	16.7

Abbreviations: IFU, instructions for use; TV, target vessel.

Suitability is demonstrated according to the IFU and for TV positioning only. Liberal suitability was assumed when a slight movement of the superior mesenteric artery takeoff from the center of the overlay marking was necessary to accommodate the remaining target vessels.

Discussion

Endovascular repair has become a valid treatment option for rAAA in most vascular units. Large systematic reviews and meta-analyses on published data have shown early survival benefits for EVAR compared to open repair, although overall mortality still remains high.⁴ The same differences were not seen in recent randomized trials,⁵ but this has been widely debated and is beyond the scope of this study.

A major drawback of EVAR of rAAA is the limited suitability of these devices due to anatomical restrictions for both intact and ruptured aneurysms.^6,7 Chimney grafts have been shown to slightly increase the applicability of EVAR,⁸ but this may require the sacrifice of a renal artery, and the sealing quality of this type of solution is still debatable due to the risk of gutters alongside the chimney in the proximal part of the stent-graft.

To further increase the applicability for endovascular repair, fenestrated devices that allow treatment of short neck aneurysms in the elective setting are now commercially available. However, due to the complexity and customized nature of the fenestrated EVAR devices, planning and delivery often exceeds 6 weeks, making those grafts unavailable in emergency situations. An off-the-shelf option suitable for the majority of rAAA patients is therefore desirable, and 2 such devices are under development. The Zenith p-branch is based on the Zenith platform and altered from the original design by creating dome-like fenestrations, which theoretically allow catheterization of target vessels that fall within a diameter of 15 mm.² Early IDE experience in 23 cases has shown a high level of technical success during deployment, with minimal complications during short-term follow-up.^2,3 Additionally, anatomic suitability of the device in patients with intact juxta- and pararenal aneurysms has been estimated to be >70%.⁹ However, this estimate was based on a cohort of patients previously treated with custom-made fenestrated stent-grafts, which may have introduced a selection bias.

The Ventana fenestrated graft (Endologix Inc, Irvine, CA, USA) is based on a different platform with expandable fenestrations for varying target vessel diameters that can be moved by up to 35 mm from their nominal positions.¹⁰ The early reports from investigational studies were promising (31 patients), with a high level of technical success and few stent-graft–related complications.¹¹ Later, there were reports of a high incidence of visceral adverse events leading to the call back of the device.

Farber et al¹² reported 21% of patients with type IV thoracoabdominal aneurysms (including paravisceral and juxtarenal aneurysm) were suitable for the Ventana device compared with 40% for the p-branch. A recent study comparing the suitability for both stent-graft models in 390 juxtarenal and pararenal aneurysms according to strict IFU criteria showed 33% suitability for the p-branch and 27% suitability for the Ventana, which could be increased to 49% and 42%, respectively, by accepting more liberal IFU criteria, that is, difficult access and more severe neck angulation (deemed feasible by an experienced endovascular surgeon).¹³

Because of the different design platforms, unsuitability is based on different factors for each of the stent-graft models. The most common exclusion factor for the p-branch is the inability to incorporate both renal arteries in a large number of patients due to the fixed position of the SMA fenestration, which is always stented. For the Ventana device, the major limitation is the inability to achieve a proximal seal below the SMA scallop.^12,13 However, all of the studies have been based on mainly elective cases, where ruptured AAAs are known to have more challenging anatomies.

In the current study, we exclusively assessed the anatomic suitability for the p-branch in an unselected cohort of patients with rAAA, thus excluding all patients where a custom-made device was an option. This patient cohort should therefore more accurately reflect the patient subgroup in whom only an off-the-shelf device can allow successful endovascular repair. Interestingly, the 49% suitability for p-branch in short neck rAAAs (not suitable for standard infrarenal EVAR) was in line with the above-mentioned reports on the suitability in elective juxta- or pararenal aneurysms. However, this was achieved only by taking advantage of both configurations of the p-branch (A or B) and by accepting liberal suitability in one-third of patients, which potentially could negatively affect the technical success. Additionally, as both configurations in varying lengths and diameters are needed to fulfill the anatomical requirements, a great demand will be put on the hospital to stock the device.

One other interesting finding of this study was the higher anatomical applicability of the p-branch in women. This is of potential importance since recent reports have suggested that the benefits of EVAR in rAAA could be higher in women than in men.⁵

Limitations

Not all patients with rAAA had a CT scan of sufficient quality to allow image postprocessing. However, this reflects everyday practice and more importantly underlines the feasibility of capturing high-quality CT scans in the majority of patients with rAAA. Another issue is the technical feasibility of implanting a triple fenestrated EVAR in the acute setting. This is usually time consuming, which places specific demands on the unstable patient in whom balloon occlusion of the suprarenal aorta may be required.

Conclusion

Almost half of patients with rAAA and hostile aneurysm neck morphology are suitable for the Zenith p-branch fenestrated device. The most common reason for unsuitability is a mismatch between a renal artery takeoff and the positioning of the corresponding pivot fenestration.

Footnotes

Declaration of Conflicting Interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: Nuno Dias is a consultant for Cook Medical.

Funding

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

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