A systematic review of primary endovascular repair of the ascending aorta

From the Society for Vascular Surgery

A systematic review of primary endovascular repair of the ascending aorta Corbin E. Muetterties, MD,a Rohan Menon, BS,b and Grayson H. Wheatley III, MD,c Philadelphia, Pa; Washington, D.C.; and Nashville, Tenn

ABSTRACT Objective: Endovascular repair of the ascending aorta is currently limited to patients at high surgical risk with aortic diseases originating above the sinotubular junction. A number of different endovascular technologies and approaches have been used, although no consensus exists regarding a standardized technique. To better understand real-world endovascular approaches to the ascending aorta, we performed a comprehensive review of the types of endovascular aortic stents and associated vascular access used in repair of the ascending aorta. Methods: A search of the MEDLINE database was conducted from January 1, 1995, through January 31, 2017, with the search term “ascending aortic stent.” Studies involving endovascular stenting in which the primary therapy was confined exclusively to the ascending aorta were included. Studies involving hybrid arch procedures and surgical replacement of the ascending aorta associated with aortic stenting were excluded. The type of aortic stent, underlying aortic disease, and surgical approach were recorded along with outcomes, need for reinterventions, and follow-up. Results: A total of 46 publications that focused on primary endovascular repair of the ascending aorta were identified. Thirteen different aortic stent grafts of various designs were used in 118 total patients. The most commonly used device types were thoracic stents (n ¼ 84 [71.2%]) along with abdominal cuffs (n ¼ 13 [11%]) and custom-made grafts (n ¼ 12 [10.2%]). The most commonly treated aortic disease was type A aortic dissection (n ¼ 59 [50%]), followed by aortic pseudoaneurysm (n ¼ 35 [29.7%]), aortic aneurysm (n ¼ 6 [5.1%]), penetrating atherosclerotic ulcer (n ¼ 5 [4.2%]), and acute aortic rupture (n ¼ 3 [2.5%]). Femoral arterial access was used in 62.7% of patients (n ¼ 74); transapical (n ¼ 17 [14.4%]), carotid (n ¼ 15 [12.7%]), and axillary (n ¼ 8 [6.8%]) approaches were also used. The overall type I endoleak rate was 18.6% (n ¼ 22), with 11 patients (9.3%) requiring reintervention. Other complications included all-cause mortality (n ¼ 18 [15.2%]), conversions to open surgery (n ¼ 4 [3.4%]), and cerebrovascular complications (n ¼ 4 [3.4%]). Aorta-related mortality was 5% (n ¼ 6), and average follow-up was 17.2 months. Conclusions: Despite the absence of a dedicated aortic stent graft for the ascending aorta, patients with a range of ascending aortic diseases are being successfully treated by endovascular technologies. For optimal outcomes, patient selection is critical to align aortic anatomy with the limited device sizing options, and it should be reserved for patients at high surgical risk. (J Vasc Surg 2018;67:332-42.)

The ascending aorta represents the final frontier of endovascular therapy. Use of endovascular stent grafts in the abdominal aorta is well established and has evolved to become first-line therapy for intact abdominal aortic aneurysms.1 With the immense success of endovascular interventions in the abdominal aorta, From the Lewis Katz School of Medicine at Temple University, Philadelphiaa; the Howard University School of Medicine, Washington, D.C.b; and the Centennial Heart & Vascular Center, Nashville.c Author conflict of interest: G.H.W. is a consultant for TriVascular, Medtronic, Bolton Medical, Lombard Medical, and Abbott Vascular. Presented at the 2016 Vascular Annual Meeting of the Society for Vascular Surgery, National Harbor, Md, June 8-11, 2016. Correspondence: Grayson H. Wheatley III, MD, Centennial Heart & Vascular Center, 2400 Patterson St, Ste 307, Nashville, TN 37203 (e-mail: grayson. [email protected]). The editors and reviewers of this article have no relevant financial relationships to disclose per the JVS policy that requires reviewers to decline review of any manuscript for which they may have a conflict of interest. 0741-5214 Copyright Ó 2017 by the Society for Vascular Surgery. Published by Elsevier Inc. http://dx.doi.org/10.1016/j.jvs.2017.06.099

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aortic stent grafts are now being applied to treat descending, arch, and ascending aortic diseases. The role of endovascular interventions in descending thoracic aortic disease has grown in recent years, and early results have demonstrated reductions in early death, paraplegia, renal insufficiency, cardiac complications, and length of stay compared with open surgery.2 Branched stent grafts are being used in the aortic arch, and various adjunctive techniques, such as endoanchors, in situ laser fenestration, elephant trunk, and chimney graft techniques, continue to expand the applicability of thoracic endovascular aortic repair (TEVAR) in the aortic arch while preserving the patency of the great vessels.3-5 Wedged between the aortic valve, coronary ostia, and great vessels, the ascending aorta presents a formidable challenge in stent graft placement. Nevertheless, during the past 11 years, surgeons have been successfully treating patients endovascularly using various stent grafts and vascular approaches.6 Originally arising out of necessity, stent grafting of the ascending aorta has up to this point been primarily used as a last-ditch effort to treat

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patients who are considered unfit candidates for open surgery.7-9 Open surgery in patients with ascending aortic diseases often has very poor outcomes, and advanced age and medical comorbidities create prohibitive operative risk for many of these patients.10 Despite these risks, early results for stenting of the ascending aorta are promising, and it continues to be applied for a variety of aortic diseases. Because of the early success of these interventions, there has been an evolution toward use of stent grafts to treat focal lesions of the ascending aorta, thus circumventing the need for cardiopulmonary bypass and open surgery. Various approaches have been used, although no consensus exists regarding a standardized technique. To better understand the landscape and outcomes of this rapidly evolving discipline, we performed a comprehensive literature review of the types of endovascular aortic stent grafts and the associated vascular access approaches used in endovascular repair of the ascending aorta. In presenting our findings, we attempt to evaluate the efficacy of the devices and tactics currently used in ascending aortic repair and comment on the importance of continuing to improve on the existing technology and techniques used to manage these patients.

Fig 1. Preferred Reporting Items for Systematic Reviews and Meta-Analyses flow chart.

METHODS A search of the MEDLINE database was conducted from January 1, 1995, through January 31, 2017, with the search term “ascending aortic stent.” Two separate researchers analyzed the data set to ensure accuracy and to capture all available studies. Manuscripts involving endovascular stenting of the ascending aorta in which the primary therapy was confined exclusively to the ascending aorta were included in the analysis. Cases in which stents were deployed in the aortic arch or descending aorta were excluded. Studies involving hybrid arch procedures and surgical replacement of the ascending aorta associated with aortic stenting were also excluded along with papers written in another language and papers for which only the abstract was available. The type of aortic stent, underlying aortic disease, and surgical approach were recorded along with patient outcomes, need for reinterventions, and follow-up.

RESULTS The literature search yielded 779 publications in PubMed. Of these, a total of 46 publications that focused on primary endovascular repair of the ascending aorta were identified from the literature and included in the analysis. In one instance, two papers were published describing the same 15-patient cohort, one providing early outcomes and the other describing midterm follow-up. In this case, only the more recent manuscript was included in the analysis.9,11 Fig 1 shows the results of the literature search according to the Preferred Reporting Items for Systematic Reviews and

Meta-Analyses statement. Table I summarizes the number of patients and diseases managed for each manuscript included in the analysis. Stent graft design. A total of 118 patients were treated with 13 different aortic stent grafts of various designs. The most commonly used device types were thoracic aortic stent grafts (n ¼ 84 [71.2%]), followed by abdominal aortic cuffs (n ¼ 13 [11%]), custom-made stent grafts (n ¼ 12 [10.2%]), stents of unspecified design (n ¼ 8 [6.8%]), and thoracic endovascular cuffs (n ¼ 1 [0.9%]). Custom-made stents included stents industry made to specific patient dimensions as well as off-the-shelf devices physician modified to conform to the ascending aorta. This most frequently involved device shortening to accommodate the short length of the ascending aorta. The most commonly used device was the Zenith TX2 Pro-Form endograft (Cook Medical, Bloomington Ind) with a total of 40 patient implants. An off-the-shelf Zenith ascending dissection device (Cook Medical) designed specifically for the ascending aorta was used in 15 patients. This was followed by the Gore TAG (W. L. Gore & Associates, Flagstaff, Ariz; n ¼ 13) and Gore Excluder abdominal cuff (n ¼ 12; Table II). Aortic disease. Endovascular stenting of the ascending aorta was predominantly used to treat patients with acute type A aortic dissections (n ¼ 59 [50%]) and aortic pseudoaneurysms (n ¼ 35 [29.7%]). Other pathologic processes included ascending aortic aneurysm (n ¼ 6 [5.1%]), penetrating atherosclerotic ulcers (n ¼ 5 [4.2%]), aortic

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Table I. Manuscripts in analysis including number of patients and aortic disease treated Article

Author

Year

No. of patients

Aortic disease

1

12

Dorros

2000

1

Aortic dissection

2

Ihnken6

2004

1

Aortic dissection

3

Rayan13

2004

1

Pseudoaneurysm

4

Heye14

2006

1

Pseudoaneurysm

15

5

Zimpfer

2006

1

Aortic dissection

6

Mussa16

2007

1

Pseudoaneurysm

7

Lin17

2007

1

Pseudoaneurysm

8

Guo18

2007

1

Aortic dissection

19

2007

1

Aortic dissection

10

Coscas20

2007

1

Pseudoaneurysm

11

Ailawadi21

2007

1

Traumatic aortopulmonary window

12

Chang22

2007

7

Aortic dissection (7)

13

Palma

23

2008

1

Aortic dissection

14

Uchida24

2010

1

Aortic rupture

15

Yuri25

2010

1

Pseudoaneurysm

16

Vaughan-Huxley26

2011

1

Pseudoaneurysm

9

Senay

27

17

Garg

2011

1

Pseudoaneurysm

18

Saadi28

2011

2

Pseudoaneurysm (2)

19

Veroux29

2011

1

Pseudoaneurysm

20

Metcalfe30

2012

1

Aortic dissection

31

2012

2

Pseudoaneurysm (2)

22

Joyce32

2012

3

Pseudoaneurysm (3)

23

Pontes33

2013

1

Aortic dissection

24

Krankenberg34

2013

1

Aortic rupture

25

Kappert35

2013

1

Intramural hematoma

26

Lee36

2013

1

Penetrating atherosclerotic ulcer

27

Ronchey37

2013

4

Aortic dissection (4)

28

Murakami38

2013

1

Pseudoaneurysm

29

McCallum39

2013

1

Aortic rupture

21

Gray

40

2014

1

Pseudoaneurysm

31

Preventza41

2014

7

Pseudoaneurysm (6), aortic coarctation

32

Zicho42

2014

1

Suture line pseudoaneurysm

33

Atianzar43

2014

1

Aortic dissection

30

Schiro

44

34

Bernardes

2014

7

Aortic dissection (2), pseudoaneurysm (4), aortic aneurysm

35

Tauchi45

2014

1

Aortic dissection

36

Mangialardi46

2015

1

Aortic dissection

37

Vallabhajosyula8

2015

4

Aortic dissection (2), pseudoaneurysm (2)

38

Roselli7

2015

21

Aortic dissection (9), pseudoaneurysm (8), intramural hematoma (2), aortocardiac fistula (2)

39

Wilbring47

2015

1

Aortic dissection

40

48

Oderich

2015

1

Aortic aneurysm

41

Shults49

2015

1

Pseudoaneurysm

42

Rohlffs50

2016

1

43

Tsilimparis51

2016

10

44

Kahlberg52

2016

1

Symptomatic parietal thrombus

11

Aortic dissection Aortic dissection (5), aortic aneurysm (4), dislocated aortic valve

45

Li

2016

15

Aortic dissection (15)

46

Kölbel53

2017

2

Aortic dissection (2)

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Table II. Number of implants for various aortic stent grafts by device category Device Zenith TX2 Pro-Form endograft

(N ¼ 118) 40

Thoracic TAG (Gore)

13

Talent thoracic stent graft (Medtronic)

6

Valiant stent graft (Medtronic)

7

Zenith ascending dissection device (Cook Medical)

15

Seal thoracic stent graft (S&G Biotech)

1

Najuta thoracic stent graft system (Kawasumi)

1

Custom-made graft

12

Excluder abdominal cuff (Gore)

12

patients (60.2%) remained free of complications in the follow-up period, whereas 79 patients (67%) remained free of aorta-related complications. Average follow-up was during a period of 17.2 months (Table V). Complications most frequently occurred in patients with type A aortic dissections. The device most frequently associated with aortic complications was the Cook Zenith TX2, and endoleak was the most frequently encountered complication. Acute aortic mortality was primarily attributable to issues of ventricular arrhythmias, aortic valve insufficiency, and severe endoleak in the immediate postoperative period. Table VI summarizes the various complications encountered on the basis of the aortic disease and stent graft deployed.

Endurant aortic cuff (Medtronic)

1

Unknown

8

Relay NBS thoracic stent graft (Bolton)

1

DISCUSSION

Zenith aortic cuff extender (Cook Medical)

1

Increasing numbers of patients are being treated with endovascular repair of the ascending aorta. A diverse range of devices and vascular access have been used to overcome the lack of approved devices and the technical challenges of the anatomic region. More than 13 different stent grafts were described in the literature. The most commonly used devices were thoracic stents and stent grafts custom made or modified for deployment in the ascending aorta. Custom-made stents included stents industry made to specific patient dimensions as well as physician modifications of off-the-shelf devices. In one case, a Zenith ascending dissection device was modified with a scallop for the innominate artery.50 In another series, authors used a combination of a Zenith Ascend stent (Cook Medical) and an inner Zenith branched arch endovascular graft (Cook Medical) in two patients.53 These modifications reflect the current paucity of off-theshelf devices suitable for deployment in the ascending aorta. The most commonly used combination of device type and vascular access was a thoracic stent deployed through a femoral approach. However, a number of patients were also treated with abdominal aortic cuffs or thoracic cuffs, which have the benefit of smaller profiles and therefore can be used to cover focal defects while avoiding the coronary ostia or innominate artery. In addition, one thoracic stent still in testing, the Zenith ascending dissection device (Cook Medical), represents the first stent graft designed specifically for use in the ascending aorta and has been deployed in 15 reported cases to date. Although technology in the field is developing, endovascular repair of the ascending aorta is presently limited to patients at high surgical risk with complex aortic diseases originating above the sinotubular junction. A number of anatomic characteristics make deployment of stent grafts in the ascending aorta particularly challenging. First, the proximity to the aortic valve and coronary ostia can lead to aortic insufficiency or a myocardial infarction if the stent graft is accidentally deployed in a proximal position. Distally, stent migration

rupture (n ¼ 3 [2.5%]), and intramural hematoma (n ¼ 3 [2.5%]). Thoracic stent grafts were most commonly used to treat type A aortic dissections (42/84 [50%]), whereas abdominal cuffs, when used, were primarily used to treat aortic pseudoaneurysms (10/13 [77%]; Table III). Vascular access. Femoral arterial access was used in 62.7% of patients (n ¼ 74); transapical (n ¼ 17 [14.4%]), carotid (n ¼ 15 [12.7%]), and axillary artery cannulation (n ¼ 8 [6.8%]) were the next most commonly used approaches. One patient was treated with an abdominal cuff deployed through subclavian cannulation, and three patients were treated with stents deployed by accessing the iliac artery. Because of their large size and long delivery sheaths, thoracic stents were primarily deployed through a femoral or a reverse transapical approach. In contrast, abdominal aortic cuffs have much shorter delivery sheaths, and the majority necessitated deployment through a carotid (n ¼ 6 [46%]) or axillary (n ¼ 4 [30.1%]) approach (Table IV). Complications. The overall type I endoleak rate was 18.2% (n ¼ 22). A total of 11 patients (9.1%) required reintervention for various indications, including aortic rupture, stent migration, endoleak, and a new aortic dissection. Other complications included conversions to open surgery (n ¼ 4 [3.3%]), cerebrovascular complications (n ¼ 4 [3.3%]), stent migration (n ¼ 2 [1.7%]), and postoperative myocardial infarction (n ¼ 4 [3.3%]). Allcause mortality was 14.9% (n ¼ 18). Aorta-related mortality was 5% (n ¼ 6), with deaths resulting from aortic valve insufficiency (n ¼ 2), aortic rupture (n ¼ 1), coronary occlusion (n ¼ 1), intraoperative endoleak refractory to repair (n ¼ 1), and in one case an aorta-atrial fistula causing cardiac tamponade. A number of the recorded complications occurred in the same patients. A total of 71

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Table III. Aortic disease treated by device category No. of patients (%)

Aortic dissection

Pseudoaneurysm

Thoracic stent

84 (71.2)

42

20

5

Custom-made stent

12 (10.2)

8

3

0

Abdominal cuff

13 (11)

2

10

0

Unknown stent

8 (6.8)

7

1

0

Device category

Thoracic cuff Total

1 (0.9)

0

N ¼ 118

59 (50%)

PAU

1 35 (29.7%)

Aortic aneurysm

Aortic rupture

3

6

2

6

0

0

1

0

0

0

0

1

0

0

0

0

IMH

Other

0

0

0

0

0

5 (4.2%)

3 (2.5%)

6 (5.1%)

3 (2.5%)

7 (5.9%)

IMH, Intramural hematoma; PAU, penetrating atherosclerotic ulcer.

Table IV. Vascular access by device type Device category

Femoral

Transapical

61

16

1

4

0

2

7

0

5

0

0

0

Abdominal cuff

1

0

6

4

1

1

Unknown stent

5

1

2

0

0

0

Thoracic stent Custom-made stent

Thoracic cuff Total

Carotid

Axillary

Subclavian

Iliac

0

0

1

0

0

0

74 (62.7%)

17 (14.4%)

15 (12.7%)

8 (6.8%)

1 (0.9%)

3 (2.5%)

Table V. Perioperative and postoperative complications No. (%) Endoleaks

22 (18.6)

Reintervention

11 (9.3)

Nonaortic deaths

12 (10.2)

Aortic deaths

6 (5)

Open conversion

4 (3.4)

Stent migration

2 (1.7)

Postoperative myocardial infarction

4 (3.4)

Stroke

4 (3.4)

Device deployment failure

3 (2.5)

Other

11 (9.3)

Free of complications

71 (60.2)

Free of aorta-related complications

79 (67)

can similarly lead to occlusion of the brachiocephalic artery and a resulting cerebrovascular accident. This necessitates a stent graft with a short length and requires precise stent deployment during TEVAR. Other limiting parameters include the diameter of the ascending aorta, which is often significantly larger than that of the descending thoracic or abdominal aorta. Many stent grafts designed for the descending or abdominal aorta are therefore not large enough to achieve proper stent oversizing. With no devices currently approved for use in the ascending aorta, there is a significant limitation in the available stent grafts. To date, all cases have been done with off-label devices and have been limited to select cases in which the patient’s anatomy could be

aligned with available sizing options. These sizing limitations help illustrate the need for approved devices designed specifically to conform to the anatomic challenges of the ascending aorta. Selection of patients is critical to the success of endovascular interventions in the ascending aorta. Currently, ideal candidates for ascending TEVAR are patients with focal aortic defects including pseudoaneurysms and ascending aortic dissections with focal entry tears in the middle third of the ascending aorta. Because of the complicated anatomic challenges associated with arch involvement, including the need for branched stent grafts, large aortic aneurysms are more difficult to treat endovascularly and may be better candidates for open repair. In addition, patients with lesions involving the coronary ostia or aortic valve should be directed to open surgery. As the current literature demonstrates, endovascular therapies have up until this point primarily been used as a last-ditch effort in patients who did not qualify for or refused open surgery. Only in cases in which patients have small, focal lesions highly amenable to endovascular repair should it be considered over the “gold standard” of open repair. Other prohibitive factors during selection of patients largely involve issues of stent graft design. The first issue is that the majority of stent grafts currently on the market are much too long for deployment in the ascending aorta. The shortest aortic stent graft on the market is 10 cm, and few ascending aortas are long enough to accommodate a graft of this length. Devices should be custom made or modified intraoperatively before

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Table VI. Complications by disease managed Author

Aortic disease

Stent used

Vascular access

Complications description

Dorros

Type A dissection

Custom-made stent

Right femoral

New type B dissection, fatal myocardial infarction at 3 weeks postoperatively

Mussa

Ascending aortic pseudoaneurysm

Gore TAG

Left external iliac

Acute, fatal brainstem cerebrovascular accident at 15 days postoperatively

Chang

Type A dissection

Unknown

Right femoral

Fatal upper gastrointestinal hemorrhage 1 month postoperatively

Palma

Chronic type A dissection

Custom-made stent

Right femoral

Aortic valve insufficiency, cardiac arrest, death

Saadi

Pseudoaneurysm

Gore TAG

Femoral

Endoleak

Krankenberg

Ruptured ascending aortic aneurysm

Medtronic Valiant

Transapical

Cerebrovascular accident and splenic infarction, death

Kappert

Penetrating atherosclerotic ulcer

Medtronic Valiant

Transapical

Persistent endoleak requiring open repair

McCallum

Ruptured ascending aortic aneurysm

Medtronic Talent

Femoral

Endoleak, aneurysm enlargement

Preventza

Ascending aortic pseudoaneurysm

Gore Excluder cuff

Left axillary

Failed deployment, open conversion

Ascending aortic pseudoaneurysm

Gore TAG

Femoral

Postoperative ventricular fibrillation, death

Penetrating atherosclerotic ulcer

Medtronic Valiant

Femoral

Acute aortic insufficiency, intraoperative death

Acute type A dissection

Cook Zenith TX2

Femoral

Repeated aortic dissection requiring reoperation

Acute type A dissection

Gore TAG

Femoral

Repeated aortic dissection requiring reoperation Graft infolding, type IA endoleak

Bernardes

Mangialardi

Type A dissection

Najuta endograft system

Femoral

Vallabhajosyula

Acute type A dissection

Cook Zenith TX2

Transapical

Endoleak

Roselli

Type A dissection

Gore TAG

Femoral

Endoleak, aortic rupture, death

Type A dissection

Cook Zenith TX2

Transapical

Endoleak

Type A dissection

Cook Zenith TX2

Femoral

Left main coronary occlusion, open conversion, multiorgan failure, death

Type A dissection

Cook Zenith TX2

Transapical

Aortoatrial fistula, tamponade, death

Type A dissection

Cook Zenith TX2

Transapical

Endoleak

Pseudoaneurysm

Cook Zenith TX2

Axillary

Stent migration requiring open retrieval

Pseudoaneurysm

Gore TAG

Femoral

Endoleak

Chronic type A dissection

Cook Zenith TX2

Axillary

Retained delivery system, open conversion

Wilbring

Acute type A dissection

Relay NBS

Femoral

Endoleak

Tsilimparis

Type A dissection

Zenith Ascend graft

Unidentifiable

Endoleak, death

Li

Type A dissection

Zenith TX2 Pro-Form

Femoral

New dissection

Type A dissection

Zenith TX2 Pro-Form

Femoral

Cardiovascular ischemia

Type A dissection

Zenith TX2 Pro-Form

Femoral

Supraventricular tachycardia, retrograde type A aortic dissection, and ventricular pseudoaneurysm

Type A dissection

Zenith TX2 Pro-Form

Femoral

Pericardial effusion

Type A dissection

Zenith TX2 Pro-Form

Femoral

Left kidney atrophy

Type A dissection

Zenith TX2 Pro-Form

Femoral

Perigraft endoleak

Type A dissection

Zenith TX2 Pro-Form

Femoral

Bird beak sign

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Fig 2. Computed tomography scans showing ascending aortic aneurysm before treatment (A) and after treatment (B) with an ascending aortic stent.

deployment to achieve the proper length of stent graft coverage based on preoperative scans of the patient. A second issue is the challenge of achieving adequate landing zone. A landing zone of at least 2 cm is ideal in TEVAR, which can be difficult to obtain in a short, angulated ascending aorta. A third issue lies in the difficulty with achieving precise device deployment while preserving the function of the aortic valve and patency of the coronary ostia. Close to the aortic valve, high-pressure aortic pulses can cause displacement of the stent graft during deployment. Techniques to overcome this challenge include temporary cardiac pacing and pharmacologic interventions to decrease blood pressure during deployment and to prevent windsock effect. Finally, the nose cone of many existing devices is long and can interfere with the native aortic valve during device deployment. Devices with short nose cones should be used if possible and may have to be prolapsed into the aortic valve during deployment. Techniques for procedural case planning, device sizing, and intraprocedural deployment of ascending aortic stent grafts have yet to be standardized or perfected. The lack of an approved aortic stent graft device for the ascending aorta, along with a general paucity of published clinical cases as highlighted by this review, means that few experts have worked through the learning curve for treating patients with complex ascending aortic diseases using an endovascular approach. Nevertheless, our center has performed a number of ascending aortic stent grafts for a diverse array of aortic diseases and believes that a number of crossover principles from standard TEVAR procedures exist (Fig 2). For selection of patients, we prefer patients who are at extremely high risk for open surgical repair because of either existing comorbidities or numerous previous sternotomy incisions. As we do for all TEVAR procedures, we use a three-dimensional centerline computed tomography angiography reconstruction

workstation to analyze the aortic anatomy and to obtain aortic diameters at the sinotubular junction and proximal aortic arch along with inner and outer curve lengths. For aortic dissections, we choose a graft diameter equal to the wall-to-wall diameter without oversizing. For aortic aneurysms, we choose a graft oversized 20% to 30% based on the larger of the two measurements at either the sinotubular junction or distal ascending aorta. Stent deployment presents another challenge, in particular when devices designed for deployment in the abdominal aorta are used. The most common approach was femoral cannulation, which was used most commonly for thoracic stent grafts. In the case of abdominal cuffs, the majority of these devices are designed with short delivery sheaths that cannot reach the ascending aorta from a femoral approach. To overcome this obstacle, inventive surgeons have turned to alternative vascular approaches including axillary, subclavian, carotid artery, and reverse transapical approaches. The most commonly used alternative access sites were either transapical or carotid approaches, both of which are easily accessed and give a relatively straight deployment into the ascending aorta. The axillary artery is also easily accessed through an axillary cutdown approach and has the added benefit of serving as a pre-established bailout site for cardiopulmonary bypass should the need to convert to an open procedure arise.54 Whereas femoral artery access is preferred, some delivery devices are not long enough to reach the ascending aorta. The axillary and carotid arteries are less likely to be affected by peripheral vascular disease and therefore can often provide viable access in patients with severely diseased femoral or iliac vessels.55 Review of the literature showed no difference in outcomes with use of a femoral vs alternative access approach, and these techniques can be safely performed in the hands of a skilled endovascular specialist.

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Fig 3. Intraoperative fluoroscopy with endograft before deployment in the ascending aorta.

For device access delivery, we prefer a right axillary approach through a conduit. This approach has a number of benefits in that it facilitates accuracy of deployment and avoids the extra deployment forces associated with navigating the multiple curvatures of the iliac arteries and thoracic aorta and aortic arch (Fig 3). Most important, the right axillary approach allows the stent graft to open on the inner curve and to be placed accurately at the left main coronary artery. From a transfemoral or transapical approach, the outer curve would lead the device to deploy on the noncoronary cusp and have less accuracy for the left main coronary artery. Essentially, the inner curve of the aortadwhere the left main coronary artery originatesdbecomes the outer curve of the stent graft delivery system when delivery is from the right axillary approach, thus facilitating accurate landing at the left main coronary artery (Fig 4). The right axillary approach also can serve as a bailout cannulation site for converting to cardiopulmonary bypass if there were intraprocedural complications. To decrease cardiac output at the time of graft deployment, we prefer placing a temporary transvenous pacing wire into the right ventricle and rapidly pace the heart at 180 beats/min. This is the same technique used by the heart team in transcatheter aortic valve deployments. Even patients with very poor ejection fractions can tolerate 15 to 20 seconds of rapid ventricular pacing. Intraoperative transesophageal echocardiography is also used to assess the proximal aortic root and to assist with accuracy of deployment. If intraoperative

Fig 4. Intraoperative fluoroscopy showing right axillary deployment of endograft in the ascending aorta.

transesophageal echocardiography demonstrates a pericardial effusion related to the aortic dissection or leaking aortic aneurysm, we place a subxiphoid pericardial drain using fluoroscopic guidance at the beginning of the case. Despite the population of high-risk patients, early outcomes appear to be good in patients treated endovascularly for ascending aortic diseases. Many of the patients treated with ascending aortic stents were considered unfit candidates for open surgery on the basis of their medical comorbidities. Aorta-related mortality was 5% and all-cause mortality was 14.9%, which is significantly lower than that observed for patients with type A dissections treated with open surgery, which ranges from 17% to 26%.56 One population of patients that is poised to benefit from endovascular therapies in the ascending aorta is patients with acute type A aortic dissections. The International Registry of Acute Aortic Dissection reports that patients undergoing open surgical repair for acute type A dissections have an in-hospital mortality of 26.9%, and up to 30% of patients are considered unfit candidates for open surgery on the basis of advanced age, medical comorbidities, and preference of the patient.10 Endovascular approaches are an appealing prospect for these patients because they are minimally invasive, circumvent the need for cardiopulmonary bypass, and involve a much less extensive

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surgery. Whereas it remains to be seen whether these interventions will provide a long-term solution for these patients, one application of the technology is stabilization of acutely sick patients who can later go on to have a definitive open repair. The complication most commonly encountered in patients treated with ascending aortic stents was endoleak, with an overall rate of 18.2%. The overall endoleak rate encountered in TEVAR ranges from 3.6% to 8.7% and represents a significant limitation of this technology.57 Endoleak can contribute to false lumen expansion in dissections and increase risk for aortic rupture. In response to this issue, a number of promising technologies including endoanchors, branched stent grafts, and in situ fenestration are currently being used both to prevent and to treat endoleak in the abdominal aorta and aortic arch.58-60 As adjunctive technologies continue to develop, they may in the future help overcome the issue of endoleak due to poor stent deployment or inadequate landing zones in the ascending aorta. With the majority of manuscripts consisting of case reports and small series, there remains a strong selection bias in the literature with regard to endovascular management of the ascending aorta. However, within the past 2 years, a few larger studies have been published that help provide greater insight into emerging ascending aortic interventions. Li et al presented one of the largest cohorts to date, with a total of 15 patients with type A aortic dissections treated endovascularly with stenting of the ascending aorta. In this cohort, long-term follow-up revealed eight complications, including new dissection, cardiovascular ischemia, supraventricular tachycardia, retrograde type A aortic dissection and ventricular pseudoaneurysm, pericardial effusion, kidney atrophy, perigraft endoleak, and stent graft bird beaking. No deaths were reported in the follow-up period. A total of four reinterventions occurred, including branched stent graft deployment for a new dissection, radiofrequency ablation, coronary stenting, and one open surgical repair. Although the overall complication rate was high in these patients, close monitoring allowed early detection and successful treatment of these complications, avoiding long-term mortality. In addition, these patients were originally selected to receive endovascular interventions after being deemed ineligible for open surgical repair.11 These results suggest that endovascular interventions can serve as a valuable intervention for patients who are considered unfit candidates for open surgery; however, close follow-up is needed to prevent and to treat complications as these arise. There are very few cases of failed ascending aortic stenting published in the literature, which adds to the publication bias in this study. Nevertheless, based on our extensive surgical experience with proximal aortic

diseases and our endovascular experience with ascending aortic stenting, there are a few types of aortic dissection anatomy that are not suitable for endovascular repair. First, if there is severe associated aortic valve insufficiency due to prolapse of the dissection septum into the aortic valve apparatus, we do not recommend an endovascular approach. Furthermore, if the dissection tear originates in the aortic root at or below the sinotubular junction, this is not amenable to endovascular repair. Finally, if the sinotubular junction is effaced and severally dilated, it becomes impossible to obtain seal with the largest diameter stent grafts. Most important, the short length of the ascending aorta is the most frequent reason that patients fail to be endovascular candidates. Thus far, published results are positive, but the data are based almost exclusively on single-center experiences in case reports or case series. To truly understand the outcomes associated with endovascular interventions in the ascending aorta, a prospective, randomized controlled trial must be completed. Ideally, this would be completed across multiple, high-volume aortic centers and use a stent graft designed specifically for use in the ascending aorta. With the current device limitations and limited clinical experience, this technology should be reserved for high-risk surgical candidates, particularly those denied open interventions. Interventions should be performed in select patients whose focal ascending aortic lesions can be aligned with currently available device sizing options. In addition, these procedures should be performed by experienced endovascular surgeons, and steps should be taken to prepare for open interventions should complications arise.

CONCLUSIONS Despite the absence of a dedicated stent graft for the ascending aorta, at present, patients with a range of ascending aortic diseases are being successfully treated by endovascular technologies. Surgeons are currently limited to high-risk surgical patients considered unfit for open surgery. For optimal outcomes, selection of the patient is critical to align aortic anatomy with the limited device sizing options, and many cases necessitate alternative vascular access or device modifications to overcome the anatomic limitations of the region. These interventions require a high degree of technical skill and at this time should be attempted only at dedicated aortic centers with surgeons who have a large amount of experience in performing endovascular interventions in the thoracic aorta. In addition, follow-up for these patients is limited, and the durability of endovascular therapies in the ascending aorta remains to be seen. As devices are developed specifically for the ascending aorta, patients with a variety of aortic diseases may begin to be treated with endovascular stenting of the ascending aorta; however, further study is needed.

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AUTHOR CONTRIBUTIONS Conception and design: CM, GW Analysis and interpretation: CM, GW Data collection: CM, RM, GW Writing the article: CM, RM, GW Critical revision of the article: CM, RM, GW Final approval of the article: CM, RM, GW Statistical analysis: CM, GW Obtained funding: Not applicable Overall responsibility: GW

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Submitted Nov 15, 2016; accepted Jun 19, 2017.