Satisfactory Long-term Outcomes of Thoracic Endovascular Aortic Repair With a Bare Stent for Acute Complicated Type B Aortic Dissections

Abstract

Purpose

To compare the clinical outcomes after thoracic endovascular aortic repair (TEVAR) with a bare stent to those after TEVAR alone in patients with complicated acute type B aortic dissection (cATBAD).

Materials and Methods

A prospective, randomized trial was conducted at 2 medical centers in China between 2010 and 2013. Patients with cATBAD were randomly assigned to receive TEVAR with a bare stent (n=42) or TEVAR only (n=42). Patients were scheduled to undergo computed tomography angiography at 3, 6, and 12 months and then annually to 5 years. The primary endpoint was all-cause mortality at 5 years; secondary outcomes were a composite of complications (endoleak, stent-graft–induced new entry, aortic rupture, and secondary intervention) and aortic remodeling at 1 and 5 years.

Results

All-cause death occurred in 1 (2.4%) patient in the TEVAR with bare stent group (lung cancer) and 5 patients (11.9%) in the TEVAR group (4 aorta-related) during the 5-year follow-up (log-rank p=0.025). The 1- and 5-year rates of complications and secondary interventions did not differ between the groups. Patients in the TEVAR with bare stent group had higher increases in the thoracic true lumen diameter (19.7±3.6 vs 17.0±6.2 mm, p=0.018) and abdominal true lumen diameter (13.7±4.8 vs 7.2±6.1 mm, p<0.001) and a higher incidence of complete false lumen thrombosis (80.9% vs 47.6%, p=0.005) at the 1-year follow-up. However, no between-group differences in the changes of aortic remodeling parameters were observed between the 1- and 5-year follow-up periods.

Conclusion

The addition of a distal bare stent to a thoracic stent-graft during TEVAR was associated with significantly improved long-term survival in cATBAD patients vs TEVAR only, likely due to the prevention of true lumen collapse and improvement of complete false lumen thrombosis of the dissected aorta.

Keywords

aortic dissection aortic remodeling bare metal stent complications false lumen thrombosis mortality stent-graft thoracic endovascular aortic repair type B aortic dissection

Introduction

Acute type B aortic dissection (ATBAD), which accounts for 25% to 40% of all aortic dissections, originates from the ostium of the left subclavian artery (LSA) and extends to the abdominal aorta, dividing the aorta into a true lumen (TL) and a false lumen (FL).^1,2 Approximately 50% of ATBAD cases are complicated by aortic rupture, visceral malperfusion or limb ischemia, and refractory pain or hypertension despite adequate medical treatment. Complicated ATBAD (cATBAD) has a mortality of 40% to 100% without prompt medical treatment.³ Thoracic endovascular aortic repair (TEVAR) has emerged as an alternative therapy for ATBAD.^4,5 In early studies, the 30-day mortality after TEVAR was approximately 10%, which was much lower than the nearly 27% for open repair.^6–8 In the prospective, multicenter STABLE study,⁹ a stent-graft combined with a bare stent to treat cATBAD reduced the incidence of 30-day mortality to 5% and 1-year mortality to 10%. Additionally, beneficial aortic remodeling was observed at 2-year¹⁰ and 5-year¹¹ follow-up. In China, a recent study showed that TEVAR with a distal bare stent reduced complications and improved favorable aortic remodeling by increasing FL thrombosis and preventing TL collapse.⁵

However, most previous studies of TEVAR with a bare stent focused on 30-day to 1-year mortality, and few randomized trials have evaluated the long-term outcomes of TEVAR with a bare stent in cATBAD patients. Accordingly, we conducted a study to compare the long-term outcomes of TEVAR with a bare stent to those of TEVAR alone in patients with cATBAD.

Materials and Methods

Study Design

A prospective, randomized trial was conducted at 2 medical centers in China (Shenzhen People’s Hospital and Guangdong General Hospital) between 2010 and 2013. Inclusion criteria included ATBAD complicated by the presence of rapid aortic expansion (diameter ≥60 mm or an expansion rate ≥10 mm while in hospital); aortic rupture and/or hypotension/shock; renal or limb ischemia; paraplegia/paraparesis; periaortic hematoma; recurrent or refractory pain; and/or refractory hypertension despite adequate medical therapy.¹² Patients aged <18 years or >80 years were excluded, as were patients with diagnosed or suspected Marfan syndrome or Stanford type A or B aortic dissection with previous placement of a thoracic stent-graft. Additionally, patients with serious dynamic bowel malperfusion (ie, acute abdomen, intestinal obstruction, and septicemia) who required bowel resection were not eligible for this study and were transferred to open surgery.

Among the 90 consecutive cATBAD patients seen during the observation period, 4 patients refused to participate, and 2 patients with a history of TEVAR were excluded. Using a web-based interactive response system (Figure 1), the remaining 84 patients were randomly assigned to receive TEVAR with a bare stent (n=42; mean age 55.1±10.2 years, 37 men) or conventional TEVAR (n=42; mean age 52.1±10.9 years, 37 men). All participants provided written informed consent. The demographic characteristics, risk factors, clinical symptoms, indications for treatment, and medical treatment are presented in Table 1. Patients were scheduled to undergo computed tomography angiography (CTA) at 3, 6, and 12 months and then annually to 5 years after the operation. Follow-up data, including all-cause death and complications after surgery, were collected by telephone interview. The study protocol was approved by the institutional review board of Shenzhen People’s Hospital.

Table 1.

Baseline Characteristics of the Study Population.^a

Characteristics	TEVAR With Bare Stent (n=42)	TEVAR (n=42)	p
Age, y	55.1±10.2	52.1±10.9	0.195
Men	37 (88.1)	37 (88.1)	—
Admission SBP, mm Hg	198.2±17.9	195.0±16.3	0.400
Admission heart rate, bpm	99.7±10.9	96.7±16.5	0.338
Time from onset to admission, h	4.0±2.1	3.9±2.2	0.919
Hypertension	41 (97.6)	42 (100)	0.986
Diabetes mellitus	6 (14.3)	7 (16.7)	0.967
Current smoking	14 (33.3)	13 (30.9)	0.939
COPD	2 (4.8)	4 (9.5)	0.649
OSAHS	3 (7.1)	3 (7.1)	—
Coronary artery disease	4 (9.5)	2 (4.8)	0.671
eGFR, mL/min/1.73 m²	84.7±35.2	88.8±35.4	0.312
Medical treatment
ACEI/ARB	22 (52.4)	23 (54.8)	0.943
Calcium-channel blockers	42 (100)	42 (100)	—
Antiplatelet	6 (14.3)	5 (11.9)	0.961
Statin	42 (100)	42 (100)	—
Beta-blocker	42 (100)	42 (100)	—
Indications
Branch vessel compromise	16 (38.1)	14 (33.3)	0.770
Renal dynamic malperfusion	10 (23.8)	10 (23.8)	—
Bowel dynamic malperfusion	3 (7.1)	2 (4.8)	0.717
Limb dynamic malperfusion	2 (4.8)	2 (4.8)	—
True lumen collapse	15 (35.7)	14 (33.3)	0.967
Impending rupture	4 (9.5)	3 (7.1)	0.994
Refractory chest pain	41 (97.6)	40 (95.2)	0.996

Abbreviations: ACEI/ARB, angiotensin-converting enzyme inhibitor/angiotensin receptor blocker; bpm, beats per minute; COPD, chronic obstructive pulmonary disease; eGFR, estimated glomerular filtration rate; OSAHS, obstructive sleep apnea–hypopnea syndrome; SBP, systolic blood pressure; TEVAR, thoracic endovascular aortic repair.

Continuous data are presented as the mean ± standard deviation; categorical data are given as the count (percentage).

Endovascular Procedure

The landing zone diameters, regions, and stent-graft dimensions were calculated from preoperative contrast-enhanced CTA scans and 3-dimensional reconstructions. The diameter of the bare stent was selected according to the greatest diameter of the TL, and the length was determined by the distal extension of the dissection and any branch vessel or TL compromise.

The surgical procedures were conducted under general anesthesia in the interventional suite. In the test group, a bare aortic Wallstent (Boston Scientific Corporation, Marlborough, MA, USA) of suitable diameter was delivered to the target position; the stent length was chosen to provide a 20- to 40-mm overlap with the main stent-graft. TEVAR was then performed using one of 4 different thoracic stent-grafts: Endurant (Medtronic Cardiovascular, Santa Rosa, CA, USA), Ankura (LifeTech Scientific, Shenzhen, China), Zenith TX2 (William A. Cook Australia, Brisbane, Australia), or Hercules (MicroPort, Shanghai, China). Sizes were selected according to the measurements of the proximal non-dissected aorta, with oversizing of 0 to 15%. Additional procedures, such as the chimney technique (for LSA coverage) or carotid-subclavian bypass, were carried out when necessary. Success of this procedure was defined by complete exclusion of the primary entry without any complications.

Assessment of Aortic Remodeling

The diameters of the TL and FL at the ventricular level (thoracic level) and level of the celiac trunk (abdominal level) were measured (Figure 2). The increases in the thoracic TL and abdominal TL at 1 and 5 years were determined by subtracting the preoperative measurements from the 1-year measurements and subtracting the 1-year measurements from the 5-year measurements, respectively. Complete thrombosis of the FL was evaluated on late (venous) phase CT scans.

Study Endpoints

The primary endpoint was all-cause mortality at 5 years after randomization. The secondary outcomes were a composite of complications [endoleak, stent-graft–induced new entry (SINE), aortic rupture, and secondary intervention] and aortic remodeling at the different postoperative follow-up times.

Statistical Analysis

Continuous data are presented as the mean ± standard deviation; categorical data are given as the count (percentage). Between-group comparisons of continuous data were conducted using the Student t or Kruskal-Wallis test, whereas between-group comparisons of categorical data were performed using the chi-square or Fisher exact test. Five-year survival was analyzed using the Kaplan-Meier method; the curves were compared using the log-rank test. Statistical significance was defined by p<0.05. Statistical analysis was performed using IBM SPSS software (version 22.0; IBM Corporation, Armonk, NY, USA).

Results

No significant differences were observed between the groups in terms of baseline patient characteristics (Table 1), preoperative lumen diameters (Table 2), or main stent-graft models implanted (Table 2); thus, the only difference between the groups was the use of a bare stent in the test group. The LSA was covered in 43 patients; 14 patients had a chimney graft implanted, and 29 patients underwent carotid-subclavian bypass. No differences in procedural characteristics were observed between the groups (Table 2).

Table 2.

Procedural Characteristics.^a

Characteristics	TEVAR With Bare Stent	TEVAR	p
TL diameter, mm
Thoracic level	13.8±2.6	13.4±2.8	0.492
Abdominal level	11.5±4.8	9.9±3.0	0.061
FL diameter, mm
Thoracic level	16.0±3.3	15.9±2.3	0.878
Abdominal level	17.0±4.2	16.7±4.0	0.700
Stent-graft devices
Diameter, mm	33.5±1.9	33.48±2.3	0.917
Length, mm	178.6±25.0	182.1±24.2	0.509
Type
Endurant	22 (52.4)	23 (54.8)	0.827
Zenith TX2	4 (9.5)	5 (11.9)	0.724
Hercules	2 (4.8)	3 (7.1)	0.645
Ankura	14 (33.3)	12 (28.6)	0.812
Bare stent
Diameter, mm	23.2±1.0	—	—
Length, mm	70	—	—
LSA coverage
Total	23 (54.8)	20 (47.6)	0.507
Partial	5 (11.9)	7 (16.8)	0.543
Adjunctive procedures
Chimney graft	8 (19.4)	6 (14.3)	0.770
Carotid-subclavian bypass	15 (35.7)	14 (33.3)	0.878
Length of hospital stay, d	5.6±0.5	5.5±0.5	0.665

Abbreviations: FL, false lumen; LSA, left subclavian artery; TEVAR, thoracic endovascular aortic repair; TL, true lumen.

Continuous data are presented as the mean ± standard deviation; categorical data are given as the count (percentage).

During the 5-year follow-up, 1 patient in the TEVAR with bare stent group died (lung cancer) vs 5 patients in the TEVAR group (aortic rupture in 3, retrograde dissection at the distal end of the stent-graft, and stroke; Table 3). Kaplan-Meier analysis revealed a significant between-group difference in 5-year survival (log-rank p=0.025; Figure 3).

Table 3.

Primary Outcomes During the 5-Year Follow-up.

Patient	Group	Time to Death, mo	Cause of Death	Relationship to Dissection Repair
1	TEVAR with bare stent	55	Non-small-cell lung cancer	Not related
2	TEVAR	0.5	Aortic rupture	Related
3	TEVAR	12	Hypotensive shock after aortic rupture	Related
4	TEVAR	31	Retrograde dissection, distal end of endoprosthesis	Related
5	TEVAR	27	Suspicion of aortic rupture and acute abdomen	Related
6	TEVAR	60	Stroke	Not related

Abbreviation: TEVAR, thoracic endovascular aortic repair.

At the 1-year follow-up, no significant differences were observed between the TEVAR with bare stent and TEVAR only groups with regard to complications: endoleak (2.3% vs 7.1%), SINE (0% vs 7.1%), aortic rupture (0% vs 4.8%), and secondary intervention (0 vs 2.4%), respectively. However, the percentage of patients with complete thrombosis of the FL was higher in the TEVAR with bare stent group than in the TEVAR group (80.9% vs 47.6%, p=0.005; Figure 4A). Over 5 years of follow-up, no additional complications occurred in the TEVAR with bare stent group (Figure 4B).

At 1 year, the maximum TL diameters at the thoracic and abdominal levels in the TEVAR with bare stent vs the TEVAR groups were 33.4±2.5 vs 29.7±7.7 mm, respectively (p=0.004) and 20.3±3.2 vs 14.6±6.7 mm, respectively (p<0.001), while the FL maximum diameters at the thoracic and abdominal levels were 4.4±1.9 vs 6.5±3.5 mm, respectively (p=0.001) and 5.5±3.0 vs 9.4±6.3 mm, respectively (p<0.001). Accordingly, the TEVAR with bare stent group had a greater increase in the thoracic TL diameter (19.7±3.7 vs 17.1±6.2 mm, p=0.018). The same trend was observed for the increase in the abdominal TL diameters (13.7±4.8 vs 7.2±6.1 mm, p<0.001); together, these results indicated better TL recovery and FL shrinkage in the TEVAR with bare stent group (Figure 5A). However, no between-group differences in the changes of aortic remodeling parameters were observed from the 1-year to 5-year follow-up (Figure 5B). The mean C-reactive protein (CRP) levels at 1 year (Table 4) were lower but did not reach statistical significance in the TEVAR with bare stent group (p=0.059).

Table 4.

CRP Levels Before Surgery and at Follow-up.^a

CRP Levels, mg/L	TEVAR With Bare Stent	TEVAR	p
Before surgery	100.9±23.7	99.2±31.7	0.774
At 1 year	1.4±0.7	1.8±1.0	0.059
At 5 years	0.9±0.4	1.10±0.7	0.100

Abbreviations: CRP, C-reactive protein; TEVAR, thoracic endovascular aortic repair.

Data are presented as the mean ± standard deviation.

Discussion

The main findings of the present study are that TEVAR with a bare stent was associated with a significant reduction of all-cause death within the 5-year follow-up. Importantly, the composite device was not associated with additional adverse events over the course of follow-up.

The effectiveness of endovascular repair for aortic dissection depends on closure of the primary tear, re-expansion of the TL, or depressurization of the FL, which leads to FL thrombosis and aortic wall stabilization.^13–15 However, a prospective, multicenter European clinical trial reported a 30-day mortality of 12% after TEVAR in 50 ATBAD patients.¹⁶ Another trial showed that 17.9% of patients experienced complications (including endoleak, dissection extension, additional stent-graft procedure, and type A dissection) within a median 306 days after surgical treatment for cATBAD.¹⁷ These complications have been attributed to persistent FL perfusion and partial thrombosis after TEVAR.¹⁸

Accordingly, TEVAR with a bare stent has emerged as an approach to improve restoration of distal perfusion and to enhance aortic remodeling in patients with cATBAD. The use of a bare stent with TEVAR to promote TL expansion was first described in a case report by Mossop et al.¹⁹ In China, He et al⁵ conducted a study comparing TEVAR with preplacement of a distal bare stent and TEVAR alone in patients with cATBAD; they reported 30-day mortality rates of 2.8% (1/34) vs 4.1% (5/108) for the procedures. The STABLE trial demonstrated favorable outcomes over 2 years of follow-up after TEVAR with a composite device (covered stent-graft and bare metal stent) in cATBAD patients.¹⁰ The 30-day mortality rate was 5%; survival rates at 1 and 2 years were 88.3% and 84.7%, respectively. A long-term survival analysis in 136 patients with cATBAD showed a lower 5-year survival rate of 74.8%, ascribed to the fact that half of the patients (71, 52%) received conventional medical treatment.²⁰ However, in our study, the 92% 5-year survival rate was due to the younger age of the patients and a higher rate of complete FL thrombosis.

In our clinical trial, no patients died of complications in the TEVAR with bare stent group in the 5 years of observation, whereas 4 patients in the TEVAR group suffered aorta-related complications including aortic rupture and distal retrograde dissection. The underlying pathophysiological mechanism by which TEVAR with a bare stent improved the survival outcome of patients with cATBAD is in part the control of SINE, a serious complication specific to TEVAR. Previous studies have demonstrated that the combined use of a restrictive stent could be effective for preventing SINE and significantly reducing mortality.²¹ In our cohort, there was no SINE in the TEVAR with bare stent group vs 9.5% in the TEVAR only group. We suggest that the preplacement of the bare stent can shield the fragile dissected aortic wall from the spring-back force.

Secondly, placement of a bare stent maintains the restored distal blood flow and improves visceral perfusion by reducing FL pressure. Thirdly, dissection-related mortality after TEVAR is significantly associated with FL thrombosis.²² Techniques or devices to enhance complete thrombosis of the FL along with improved TL recovery and FL shrinkage are critical to achieving positive long-term outcomes after TEVAR.²³ In our study, TEVAR with a bare stent led to greater increases in the thoracic and abdominal TL diameters and a higher incidence of complete FL thrombosis at the 1-year follow-up. Finally, patients who underwent TEVAR with a bare stent had a lower CRP level at the 1-year follow-up, potentially indicating less inflammation in these patients. A lack of false lumen thrombosis is often associated with prolonged presence of inflammatory markers at increased levels.²⁴

Limitations

First, the measurements to assess aortic remodeling included the lumen diameters only at the thoracic and abdominal levels. Measurements of aortic remodeling at other levels (LSA ostium, tracheal carina, and diaphragm) were not included in this study. Second, due to the small number of patients in the groups, the differences in the incidences of complications between the TEVAR with bare stent and TEVAR groups were not statistically significant. Third, patients with severe visceral malperfusion were not enrolled in the study, similar to the STABLE 2 study. Finally, the between-group difference in the CRP level at the 1-year follow-up might have been statistically significant with larger group sizes.

Conclusion

The addition of a distal bare stent to a thoracic stent-graft during TEVAR was associated with significantly improved long-term survival in cATBAD patients vs TEVAR only, likely due to the prevention of TL collapse and improvement of complete FL thrombosis of the dissected aorta. These findings will hopefully increase awareness of the potential efficacy of TEVAR with a bare stent for the treatment of cATBAD.

Footnotes

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) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by a grant from the Foundation of Health and Family Planning Commission of Shenzhen Municipality, Shenzhen, China (SZFZ2017029 and SZLY2017025) and Shenzhen Foundation (JCYJ20170307100512856).

ORCID iD

Yaowang Lin

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