Anatomic Feasibility of Next-Generation Stent Grafts for the Management of Type A Aortic Dissection in Japanese Patients

Naoki Fujimura; Shinji Kawaguchi; Hideaki Obara; Akihiro Yoshitake; Masanori Inoue; Satoshi Otsubo; Yuko Kitagawa; Hideyuki Shimizu

doi:10.1253/circj.CJ-17-0100

Abstract

Background: The aims of the present study were to analyze the anatomical characteristics of type A aortic dissections (TAAD) in Japanese patients and evaluate the feasibility of 3 next-generation stent grafts dedicated to ascending/arch aortic lesions.

Methods and Results: We analyzed 172 consecutive patients surgically treated for TAAD at 2 institutions between 2007 and 2015. Computed tomography (CT) images and operative records were used to identify the location of entry tear (ET). The anatomical feasibility of the Zenith Ascend, Zenith A-branch, and TAG Thoracic Branch Endoprosthesis (TBE) was evaluated using the manufacturers’ instructions for use (IFU). In total, 131 patients were included in the final analysis. Dissection was present at the sinotubular junction (STJ) in 107 patients (81.7%), and the mean diameter of the STJ was 39.4±6.0 mm. The ET was at the STJ (n=33), ascending aorta (n=47), aortic arch (n=30), and descending aorta (n=21). The mean lengths from STJ to innominate artery and STJ to ET were 79.5±11.4 mm and 57.8±52.1 mm, respectively. When we applied the IFU to each anatomical measurement, we identified 0 patients as candidates for Zenith Ascend, 9 (6.9%) for Zenith A-branch, and 60 (45.8%) for TAG TBE.

Conclusions: Endovascular treatment for TAAD was not feasible for most of this study population, with risk of stent graft-induced new entry in 81.7% of patients, despite the use of next-generation stent grafts.

Stanford type A aortic dissection (TAAD) remains the most lethal aortic emergency, with a 50% mortality rate within 48 h of onset.¹^,² The only available standard treatment is open surgical repair,³^,⁴ and although recent advances in perioperative management have led to improved outcomes,⁵^,⁶ TAAD is still associated with high rates of morbidity and mortality.⁷^–⁹ Moreover, because of high levels of surgical stress, approximately 20% of patients are still denied treatment.¹

Thoracic endovascular aneurysm repair (TEVAR) was originally developed as a treatment for aneurysms, but when used to close the primary entry tear (ET) of acute complicated type B aortic dissections (TBAD), it had favorable outcomes, including enlargement of the collapsed true lumen, increased flow through the true lumen, thrombus formation leading to occlusion in the false lumen, and ultimately, aortic remodeling to cure the dissection. It has already become the treatment of choice for complicated TBAD.¹⁰^,¹¹ Some studies have demonstrated the benefit of TEVAR even in cases of uncomplicated TBAD,¹² and the application of this surgical technique to manage aortic dissection seems to be expanding.

On the other hand, there have been only a few case series reported in the literature on the use of TEVAR for TAAD.¹³^–¹⁵ The use of this surgical technique for managing TAAD is complicated by multiple factors including the location of the coronary artery, involvement of arch vessels, and proximity of the aortic valve, among others, as all factors could, in theory, contribute to a potentially fatal outcome should operative complications arise.¹⁶ The largest series reported is by Ye et al,¹⁷ who reported the results of 45 TEVARs for Chinese patients with TAAD with excellent results. However, no large case series have been reported since, and it appears that TEVAR for TAAD is still not applicable using current devices.

As a means of teasing out the anatomical problems of TAAD, a few feasibility studies have evaluated TEVAR for TAAD using the manufacturers’ instructions for use (IFU) of currently approved stent grafts. Interestingly, although these reports come from different regions of the world, they all report similar results, with a feasibility rate of approximately 35% in TAAD patient cohorts.¹⁸^–²⁰ In this study, we evaluated the anatomical characteristics of Japanese TAAD patients, and evaluated whether the findings described above were consistent with those obtained in our TAAD cohort. Furthermore, because stent grafts have been developed for ascending/arch aortic lesions, we used the IFUs of these newly developed devices in our feasibility study.

Methods

Study Design

We performed a retrospective analysis of 172 consecutive TAAD patients who underwent open surgical repair at 1 of 2 institutions in Japan between 2007 and 2015. All patients had preoperative computed tomography (CT) scans and operative records. We first evaluated the quality of preoperative CT scans and reviewed the patients’ operative records to identify the location of ETs. We excluded 41 patients with unknown locations of ET because of inadequate CT scans (primarily either inadequate timing of contrast enhancement, or slices that were too thick [>5 mm] for analysis). In total, 131 TAAD patients were included in the final anatomical analysis and feasibility study. TAAD patients with ETs located at the descending aorta with retrograde dissection to the proximal aorta were included in the study. We analyzed baseline demographic data for all patients. The study protocol was reviewed and approved by the institutional review boards at both hospitals. Because this study was a retrospective review of charts and CT images, patient consent was not obtained and the opt-out method was used.

Imaging Analysis

All CT scan data were uploaded to a Synapse Vincent workstation (Fujifilm Medical, Tokyo, Japan) and analyzed by a vascular surgeon with assistance from a board-certified radiologist. Briefly, a centerline of flow (CLF) through the true lumen from the sinotubular junction (STJ) to the abdominal aorta was created using the semi-automatic centerline extraction algorithm on Synapse Vincent (Figure 1A–D). When the CLF was off the center point of the true lumen, manual adjustment was applied using three-dimensional and curved multiplanar reconstructions (cMPR). All measurements (diameter, length, and true lumen area) were evaluated using the CLF technique described by O’Neill et al.²¹ ET was defined as an area of intimal disruption, and when there were >2 intimal tears, we defined the most proximal tear as the ET. We identified the location of the ET by reviewing images obtained with both cMPR and CLF techniques. Operative records were reviewed to validate the location of ETs and to identify the location of ETs when this was unclear based on CT imaging alone. The STJ was determined as the point where the sinus of Valsalva becomes the tubular ascending aorta.¹⁹ For the clock position of the arch vessels, the orthogonal plane obtained from CLF (cross-section that is perpendicular to CLF) was used, and the position that was closest to the head was defined as 0° (Figure 2). To evaluate the true lumen area, we calculated the area oversizing ratio (AOR=[total aorta area−true lumen area]/true lumen area) proposed by Pantaleo et al.²² To measure the aortic radius, we used three-dimensional reconstruction images created on the Synapse Vincent workstation.

Figure 1.

Centerline of flow (CLF) image created on a Synapse Vincent workstation. All measurements, including diameter, length, and true lumen area, were evaluated using the CLF technique. (A) CLF created on 3D reconstruction image. (B) Curved multiplanar reconstruction (MPR) image. (C) Stretched MPR image. (D) Corresponding perpendicular view.

Figure 2.

Clock position of arch vessels evaluated on the orthogonal plane obtained with the centerline of flow technique. The position that was closest to the head was defined as 0°. Results are listed as mean±standard deviation (range). CCA, common carotid artery; IA, innominate artery; SCA, subclavian artery.

Anatomic Feasibility for Endovascular Repair

For the feasibility study, we utilized newly developed stent grafts designed for ascending/arch aortic lesions. The first stent graft was Zenith^® Ascend^® (Cook, Bloomington, IN, USA), which was developed for the treatment of TAAD (Figure 3A). The IFU proposed by manufacturer were as follows (Table 1): ET at ascending aorta; aortic diameter of 24–40 mm at the landing zone; proximal neck length >10 mm (STJ–ET); distal neck length >10 mm (ET-innominate artery); STJ-innominate artery distance >65 mm; and aortic radius >40 mm. The second stent graft was the Zenith^® A-branch^® (Cook), which is a custom-made stent graft developed mainly for the treatment of arch aneurysms (Figure 3B). The IFU proposed by manufacturer was as follows (Table 1): aortic diameter of 24–38 mm at the landing zone; proximal and distal neck length >20 mm; STJ-innominate artery distance >59 mm; branch vessels diameter of 8–20 mm; branch vessels length >36 mm; without dissection at the branch vessels; and innominate artery-left common carotid artery (CCA) angle <45°. The final stent graft was the GORE^® TAG^® Thoracic Branch Endoprosthesis (TBE) (W.L. Gore and Associates, Flagstaff, AZ, USA). The TAG TBE has an aortic component and a TBE Extender (Figure 3C), which can be used separately or combined, depending on the location of the ET. When the aortic component is used, a debranching procedure is mandatory to revascularize the left CCA and the left subclavian artery (SCA) prior to implantation. Taken together, the IFU proposed by the manufacturers were as follows (Table 1): aortic diameter of 24–48 mm at the proximal landing zone; proximal and distal neck length >20 mm; distal coronary artery (CA)-innominate artery distance >40, 46, or 56 mm (depending on the type of TBE used: TBE aortic component=40 mm; TBE Extender=40 mm for aortic diameter of 24–34 mm, 46 mm for aortic diameter of 34–42 mm, and 56 mm for aortic diameter of 42–48 mm); aortic diameter of 16–48 mm at the distal landing zone; innominate artery diameter of 11–18 mm; and innominate artery length >25 mm. We defined the proximal landing zone as 2 cm distal to the STJ for the Zenith Ascend and Zenith A-branch grafts, and 2 cm distal to the distal CA for the TAG TBE graft. The distal landing zone was defined as the straight portion of the descending aorta adequate for sealing (>2 cm in length). Data obtained from the anatomical analysis were compared for each IFU, and the feasibility of these stent grafts for our TAAD patients was evaluated.

Figure 3.

Photograph and scheme of (A) Zenith Ascend (Cook, Bloomington, IN, USA), (B) Zenith A-branch (Cook), and (C) TAG Thoracic Branch Endoprosthesis (W.L. Gore and Associates, Flagstaff, AZ, USA).

Table 1. Instructions for Use From the Manufacturers of Zenith^® Ascend^®, Zenith^® A-branch^®, and TAG^® TBE^® Graft Devices and Their Feasibility

Stent graft / Criteria	No. of patients (%)
Zenith Ascend
ET at ascending aorta	47 (35.9)
Aortic diameter of 24-40 mm at the landing zone	47 (35.9)
Proximal neck length >10 mm (STJ-ET)	97 (74.0)
Distal neck length >10 mm (ET-IA)	71 (54.2)
STJ-IA distance >65 mm	122 (93.1)
Aortic radius >40 mm	16 (12.2)
Total^a	0 (0)
Zenith A-branch
Aortic diameter of 24–38 mm at the landing zone	31 (23.7)
Proximal neck length >20 mm (STJ-ET)	94 (71.8)
STJ-IA distance >59 mm	129 (98.5)
Branch vessels’ diameter of 8–20 mm^b	91 (69.5)
Branch vessels’ length >36 mm^b	87 (65.9)
Without dissection at the branch vessels^b	73 (55.7)
IA-left CCA angle <45°	125 (95.4)
Total^a	9 (6.9)
TAG TBE
Aortic diameter of 24–48 mm at the proximal landing zone	101 (86.3)
Proximal neck length >20 mm (CA-ET)	94 (71.8)
Distal CA-IA distance >40, 46 or 56 mm^c	131 (100)
Aortic diameter of 16–48 mm at the distal landing zone	131 (100)
IA diameter 11–18 mm	113 (86.3)
IA length >25 mm	122 (93.1)
Total^a	60 (45.8)

^aPatients fulfilled all criteria. ^bInnominate artery and left CCA. ^cDepends on the stent graft used. TBE aortic component: 40 mm; TBE Extender: 40 mm for aortic diameter of 24–34 mm, 46 mm for aortic diameter of 34–42 mm, and 56 mm for aortic diameter of 42–48 mm. CA, coronary artery; CCA, common carotid artery; ET, entry tear; IA, innominate artery; STJ, sinotubular junction; TBE, Thoracic Branch Endoprosthesis.

Results

The mean age of the study participants was 63.3±14.5 years, and 62.6% were male (Table S1). The mean height and body weight of the study participants were 162.8±10.2 cm and 63.3±15.2 kg, respectively. The most frequent comorbidity was hypertension (n=95, 72.5%), followed by chronic kidney disease (estimated glomerular filtration rate <60 mL/min/1.73 m²) (n=32, 24.4%); 49.6% patients were smokers.

Anatomical Characteristics

The dissection plane was detectable in all 131 TAAD patients and was at the level of the STJ in 107 patients (81.7%) (Figure 4). The dissection extended into the innominate artery, the left CCA, and the left SCA in 58 patients (44.3%), 18 patients (13.7%), and 20 patients (15.3%), respectively. The most frequent location of the ET was at the ascending aorta (n=47, 35.9%), followed by the STJ (n=33, 25.2%). Among 131 ETs analyzed, 111 (111/172 TAAD patients, 64.5%) were detected using CT scan alone and 20 more were detected from consulting the operative records as well.

Figure 4.

Location of entry tear and dissection. The red diamond shows the entry tear location, and the blue line represents the dissection plane. The frequency of dissection at each location is depicted in a box without an arrow nearest to the location. The frequency of entry tear at each location is depicted in a box with an arrow pointing to the corresponding red diamond. CCA, common carotid artery; IA, innominate artery; SCA, subclavian artery; STJ, sinotubular junction.

The lengths between each location and the lumen diameters at each location are summarized in Table 2 and Table 3, respectively. With regard to the clock position of the arch vessels, the most anterior branch was the innominate artery, with a mean angle of 10.31±13.25°, followed by the left SCA (−3.13±13.36°) and the left CCA (−8.82±12.48°) (Figure 2). This resulted in a mean innominate artery-left CCA angle of 19.12±11.53°.

Table 2. Anatomical Measurements: Length (mm)

	Mean±SD	Median	Range
Distal coronary artery-STJ	6.1±1.8	6	3–11
Distal coronary artery-entry tear	63.9±52.2	60	4–250
Distal coronary artery-IA	85.5±11.6	84	57–118
STJ-entry tear	57.8±52.1	54	0–244
STJ-IA	79.5±11.4	78	52–113
IA-left CCA	12.4±5.5	12	0–40
Left CCA-left SCA	14.2±5.3	13	5–37
Left SCA-distal landing zone^a	88.0±23.0	86	53–224
IA length	40.0±9.5	40	13–68
Aortic radius	31.9±7.0	32	10–55

^aDistal landing zone defined as the straight portion of the descending aorta adequate for sealing (>2 cm in length). SCA, subclavian artery; SD, standard deviation. Other abbreviations as in Table 1.

Table 3. Anatomical Measurements: Diameter (mm)

	Mean±SD	Median	Range
STJ	39.3±6.0	39	28–63
Proximal landing zone^a	43.6±6.3	43	33–70
Maximum diameter at ascending aorta	47.8±7.3	48	34–76
Aortic arch at IA	40.5±5.5	41	27–55
Aortic arch at left CCA	37.4±5.2	37	25–52
Aortic arch at left SCA	34.6±5.4	34	23–56
Distal landing zone^b	30.9±4.1	31	23–42
IA	15.2±2.8	15	7–26
Left CCA	8.5±1.6	8	5–15
Left SCA	10.3±1.6	10	7–15

^aProximal landing zone defined as 2 cm distal to STJ. ^bDistal landing zone defined as the straight portion of the descending aorta adequate for sealing (>2 cm in length). Abbreviations as in Tables 1,2.

Finally, for evaluating true lumen collapse, we used the area for analysis, not diameter, and the obtained mean area of the total aorta and true lumen at the level of the STJ was 1,332.5±380.2 mm² and 632.6±325.1 mm², respectively (Figure 5). The calculated mean AOR in this patient cohort was 2.43±4.79, and it was greater than 3.5 in 16 patients (12.2%).

Figure 5.

Area of total aorta and true lumen. The area oversizing ratio was calculated to evaluate the risk of stent graft-induced new entry. Results are listed as mean±standard deviation (range).

Anatomical Feasibility for TEVAR

Anatomical measurements obtained from imaging analysis were used to evaluate the feasibility of the Zenith Ascend, Zenith A-branch, and TAG TBE by comparing the measurements to those listed in the IFUs. For the Zenith Ascend graft, the biggest limitation was an aortic radius >40 mm, with only 16 patients (12.2%) fulfilling the requirement. Overall, none of the TAAD patients from our database were eligible for the Zenith Ascend graft (Table 1). For the Zenith A-branch, only 9 patients (6.9%) fulfilled the IFU criteria. The main limitation was the aortic diameter of 24–38 mm at the landing zone, with only 31 patients (23.7%) fulfilling the requirement (Table 1). Lastly, for the TAG TBE graft, 60 patients (45.8%) were within the IFU criteria. The main limitation was a neck length >20 mm, with 94 patients (71.8%) fulfilling the requirement (Table 1).

Discussion

Even though open surgical repair is the standard and golden treatment for TAAD, TEVAR for TAAD has potential to become a treatment option for nonsurgical candidates in the future, given its favorable results for managing acute TBAD.¹⁰^–¹² This technique eliminates the need for cardiopulmonary bypass and sternotomy, and thus reduces the risk of perioperative complications, and will be especially beneficial for patients who are not candidates for open surgical repair. However, there are still multiple problems to be solved and TEVAR for TAAD has not been recognized as a standard treatment, with only a few case series reported in the literature thus far.¹⁵^,¹⁶ Furthermore, there have been few studies that have evaluated the feasibility of TEVAR for TAAD.¹⁸^–²⁰ Interestingly, even though these were conducted in different countries, they all report a similar feasibility rate of around 35%. This result is surprising, as it seems disproportionately high given what we have experienced in daily practice. Here, we analyzed the anatomical characteristics of TAAD in Japanese patients, and evaluated the feasibility of next-generation stent grafts dedicated to ascending/arch aortic lesions. We found that these devices were still not suitable to manage the majority of TAAD patients with TEVAR in our Japanese patient population.

It is clear that substantial differences exist between Asian and Caucasian patients, including anatomical variability between the groups.²³^,²⁴ However, even though aortic dissection seems to occur more frequently in Asian countries, most of the literature regarding the anatomy of aortic dissection¹⁹^,²⁰^,²⁵^–²⁸ and the ascending aorta/aortic arch²⁹^–³³ comes from Caucasian countries, with only a few exceptions.¹⁸^,³⁴^,³⁵ In this study, we performed a retrospective analysis of 131 Japanese TAAD patients. Despite the high incidence of smoking in our cohort, the mean age and prevalence of hypertension were similar to those reported by previous studies.¹^,¹⁹^,²¹ Interestingly, our results differed from those of reports published in China, which included a much younger patient population.¹⁸^,³⁶

The length and diameter of the ascending aorta are the most studied anatomical factors that are believed to be related to the initiation of TAAD.²⁶^,²⁸^,³¹^,³²^,³⁵ In our study, the mean distal CA-innominate artery length was 85.5±11.6 mm, which was almost identical to that reported by Sobocinski et al.²⁰^,²⁸ Other aortic lengths, as well as the innominate artery length, were also similar, and this finding was surprising given the fact that our patient population had considerably smaller body size compared with the Caucasian population studied by Sobocinski et al. On the other hand, the distal CA-innominate artery length was longer than that reported by Huang et al from China,¹⁸ and this was not expected because we would anticipate the body size of these two Asian populations to be similar. The discrepancy between our data and those obtained from Chinese patients, along with the similarity between our data and those from Caucasian patients, may be because, compared with the Chinese population, the majority of the Japanese population receives a level of advanced medical care that is similar to that available to Western populations.³⁶

The diameter of the aorta at each location seemed to be smaller than those in previously published reports, but the mean maximum diameter of the ascending aorta was similar to that described in the literature.¹⁸^–²⁰ As for the location of the ET, our results were similar to those of previous studies.¹⁹^,²⁷ The most frequent location was at the ascending aorta (n=47, 35.9%), followed by the STJ (n=33, 25.2%). However, the mean distance between the distal CA and the ET was 63.9±52.2 mm in our study, which was considerably longer than what has been reported previously.¹⁸^–²⁰ Because the mean length of each part of the aorta and the distribution of ETs was similar to that cited in previous reports, this suggested that our patients with an ET located in the descending aorta had more distal ETs compared with those examined in previous studies. The mean distance between the distal CA and the ET in patients with the ET at ascending aorta was 33.3±28.9 mm, which was similar to what has been reported.

For the feasibility study, we evaluated 3 newly developed stent grafts dedicated to lesions of the ascending aorta/aortic arch. Surprisingly, both the Zenith Ascend and Zenith A-branch grafts had extremely low feasibility rates of 0% and 6.9%, respectively, in our TAAD patients. The biggest limitation for the Zenith Ascend graft was an aortic radius >40 mm, as the mean aortic radius in our TAAD patients was only 31.9±7.0 mm. This probably reflects the steep aortic arch angle caused by a relatively long ascending aorta, which is similar to what has been reported in Caucasian patients.²⁰^,²⁸ The problem with the Zenith Ascend graft is that even when we discounted an aortic radius >40 mm from the IFU and evaluated only patients with ETs located at the ascending aorta (n=47), only 12 patients (25.5%) were suitable for TEVAR using this stent graft. These results indicate that the Zenith Ascend graft is effective only in certain Japanese TAAD patients under special circumstances.

The Zenith A-branch graft seemed to be a good solution for Japanese TAAD patients, because it is capable of covering ETs located in the arch and descending aorta, which was applicable to approximately 40% of the present TAAD patients. Indeed, other than an aortic diameter of 24–38 mm at the landing zone, which was the biggest limitation, the Zenith A-branch adapted quite well to our cohort, with >60% eligibility for most of the IFU criteria. If we were to perform an aortic debranching procedure, this would eliminate all of the problems with the branch vessels, and raise the eligibility rate up to 20.1% (27 patients), which would be a significant improvement.

The TAG TBE could theoretically treat up to 60 of the present TAAD patients (45.8%). Even though it must be noted that a debranching procedure to revascularize the left CCA and left SCA is included in the IFU for the TAG TBE aortic component, this device is still considerably better than the Zenith Ascend and Zenith A-branch grafts. The main advantage of the TAG TBE is the ability to treat an aortic diameter up to 48 mm at the landing zone. If there were a Zenith A-branch capable of treating an aortic diameter of 46 mm at the landing zone while also facilitating a simultaneous debranching procedure, then 59 patients (45.0%) would be eligible for TEVAR using that device. This rate would then be similar to that described for TAG TBE.

A stent graft capable of treating a dilated ascending aorta in Japanese TAAD patients seems to be one of the key solutions to improving the feasibility of TEVAR for TAAD. However, a bigger stent graft would introduce the risk of stent graft-induced new entry, which is already a major issue in TEVAR for TBAD.²² Having a new entry tear at the STJ would obviously be critical in TAAD, and given that 81.7% of our patients had dissection at the level of the STJ, it appears that most of our TAAD patients already had a risk of stent graft-induced new entry. Pantaleo et al reported that AOR >3.5 is a significant risk factor for stent graft-induced new entry in TEVAR for TBAD.²² Because some of our TAAD patients had a totally collapsed true lumen at the STJ, when we calculated the AOR the mean value was 2.43, but this ranged widely from 0 to 36.4. In total, there were 16 patients (12.2%) with AOR >3.5 and 25 patients (19.1%) with AOR >3.0, indicating a high risk for stent graft-induced new entry in our TAAD patients. We therefore propose that the development of new stent grafts for TAAD should focus on proper sizing methods that can avoid stent graft-induced new entry, as this is critical to a good outcome.

From the imaging standpoint, we believe there are at least 2 problems that need to be solved. First, identifying the exact location of ETs for the use of TEVAR for TAAD requires special attention. Recent advances in both image processing and acquiring technology, such as multidetector CT scans and high-resolution ECG-gated CT scans, have location of the dissection plane in almost all patients; however, when identifying the exact location of the ET, the reported incidence varies from 38% to 84%.¹⁸^–²⁰^,³⁷ With additional information from the patients’ operative records, we were able to identify the ET in 131 patients (76.2%). However, when we re-reviewed the CT scans without the help of these records, we could only locate the ET in 111 patients (64.5%). This incidence is still better than that previously reported in the literature, but given the risk of fatal complications in TEVAR for TAAD, we believe that there is no room for error. Improvement in the accuracy of locating the exact location of the ET is imperative, and if there is any doubt in its location, as in 20 of our TAAD patients for whom we used the operative record to detect the exact location of the tear, TEVAR for TAAD should not be considered.

Second, both the distal CA and the STJ have been used as the landmark for the proximal landing zone,¹⁸^–²⁰ but it has not yet been established which of these is superior for TEVAR. Because TAAD frequently involves the STJ and results in dilation, the applicability of the STJ is sometimes unclear.¹⁹ Some studies utilized the CA as a landmark for measurement to overcome this problem.¹⁸^,²⁰ However, we still believe that measurement at the STJ is better, because when the STJ exists, the sinus of Valsalva is always more dilated than the STJ, thus making the sinus of Valsalva inadequate for sizing of stent grafts and an inappropriate landing zone. Also, having some space to the distal CA seems safer when considering the possibility of device migration during the deployment.

Study Limitations

First, this was a retrospective review of only those patients fit for open surgery who had identifiable ETs on CT images. We excluded more than 40 patients from the analysis, which may have influenced our final results. Also, because our study included patients from over a long period of time, and CT scans for TAAD are usually performed in an emergency setting, not all of CT scans were ECG-gated, which may have significantly influenced the measurements, especially in some cases with extreme true lumen collapse. However, we still believe that because this anatomical analysis reviewed the largest number of patients to date with new information such as aortic branch angle and dissection, it will help to advance the development of stent grafts for managing TAAD in the future.¹⁸^–²⁰

Conclusion

Dilation of the proximal ascending aorta, a small aortic radius, and an ET at the level of the STJ precluded the use of TEVAR for managing TAAD in most of Japanese patients studied in our review, even when utilizing next-generation stent grafts dedicated to ascending/arch aortic lesions. In order for TEVAR to be feasible for TAAD, there must be improvements in stent graft design, as well as development of proper sizing methods that will eliminate the risks of endoleaks at the ET, while still avoiding stent graft-induced new entry. Moreover, new imaging technology capable of precisely identifying the exact location of the ET is needed to expand the application of TEVAR to other patient populations.

Funding

No financial support was provided by any entity for the conduct of this study.

All authors declare no association with any individual, company, or organization having a vested interest in the subject mentioned in this article.

Supplementary Files

Supplementary File 1

Table S1. Patients’ baseline and demographic characteristics

Please find supplementary file(s);

http://dx.doi.org/10.1253/circj.CJ-17-0100

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