Unplanned stents in thoracic endovascular aortic repair for type B aortic dissection: A 16-year single-center report

Abstract

Background

Unplanned stents in thoracic endovascular aortic repair mean additional stents implantation beyond the preoperative planning to achieve operation success. This study aimed to reveal the prevalence and consequences of unplanned stents in thoracic endovascular aortic repair for type B aortic dissection and explore the reasons, risk factors and solutions for unplanned stents.

Methods

Retrospectively analysis consecutive patients diagnosed as type B aortic dissection with initial tear originating distal from the left subclavian artery and underwent thoracic endovascular aortic repair from September 1998 to June 2014 in our center.

Results

Under the criteria, this study enrolled 322 patients, with 83 (25.8%) patients in unplanned group. The incidence rate of unplanned stents in thoracic endovascular aortic repair for type B aortic dissection in each year demonstrates as a bimodal curve. The curve showed that, 2003 and, 2004 was the first and highest peak and 2007 was the second peak. There was no difference in five-year survival rate between planned and unplanned patients (log-rank test, p = 0.994). The unplanned group had higher hospitalization expenses (142,699.08 ± 78,446.75 yuan vs. 175,238.58 ± 34,838.01 yuan; p = 0.019), longer operation time (104.50 ± 93.24 min vs. 179.08 ± 142.47 min; p < 0.001) and hospitalization time (17.07 ± 16.62 d vs. 24.00 ± 15.34 d; p = 0.001). The reasons for unplanned stents were type Ia endoleak (46 patients, 55.4%), bird beak (25 patients, 30.1%), and inappropriate shaping of stent (9 patients, 10.8%). Asymptomatic aortic dissection patients had higher incidence of unplanned stents. Short proximal neck length (2.66 ± 0.59 mm vs. 2.50 ± 0.51 mm; p = 0.016), short stent coverage length (154.62 ± 41.12 mm vs. 133.60 ± 44.33 mm; p = 0.002), and large distal stent oversize (75.44±10.77% vs. 82.68±15.80%; p <0.001) were risk factors for unplanned stents in thoracic endovascular aortic repair.

Conclusion

There are some special risk factors and reasons for unplanned stents in thoracic endovascular aortic repair for type B aortic dissection. Knowing these can we reduce the utilization of unplanned stents with appropriate methods.

Keywords

Type B aortic dissection thoracic endovascular aortic repair unplanned stents endoleak

Introduction

Thoracic endovascular aortic repair (TEVAR) has been widely used in treating type B aortic dissection (TBAD) and highly selected type A aortic dissection.^1–3 The aims of TEVAR were to exclude the false lumen, to cover the primary entry tear, and to induce thoracic aorta remodeling. Specific planning should be made according to accurate assessment of aorta preoperatively.

Unexpected events beyond planning may happen during the procedure because of anatomic or other reasons. Some could be solved by small fixation such as balloon dilation while others need additional stents. Additional stents beyond preoperative planning may affect in-hospital expense and operating time and few has been reported on these. Whether unplanned stents could influence prognosis and how to reduce them were still unknown. There were few literatures talking about unplanned stents in TEVAR for TBAD. This single-center retrospective study aimed to reveal the prevalence and consequences of unplanned stents in TEVAR for TBAD as well as to explore the reasons and risk factors which might help making better operative plan in the future.

Methods

Study population and protocol

This study was approved by the Clinic Institutional Review Board and Ethics Committee of our institution. A retrospective analysis of patients with Stanford type B aortic dissection who underwent TEVAR in Department of Vascular Surgery, Changhai Hospital, Second Military Medical University from September 1998 to June 2014. All patients were arranged follow-up at 1-, 3-, 6-, and 12-month after TEVAR and annually thereafter, follow-up protocol consisted of computed tomography angiography (CTA) and clinical assessment evaluation. All patients gave their informed consent for TEVAR procedure and agreed with the follow-up protocol.

All patients were diagnosed as aortic Stanford type B dissection with CTA. The preoperative measurement and planning for TEVAR were made based on the CTA images.⁴ Only Stanford type B aortic dissection patients that the initial tear originate distal to the left subclavian artery and underwent TEVAR for the first time in our center were included in this study. Emergent procedure indications were acute TBAD complicated by rupture or impending rupture, malperfusion syndrome involving abdominal organs or extremity, uncontrollable hypertension, persistent pain, or any other finding on CT such as rapid expansion of aorta. Elective procedure indications were chronic TBAD with degenerative aneurysmal dilation, compression of abdominal organs and ischemia of organs or extremity. Patients in the following conditions were excluded (a) re-interventions after TEVAR or open surgery; (b) Stanford type A aortic dissection; (c) abdominal aortic dissection which initial tear located below the celiac artery; (d) operation record and/or angiography during procedures were completely different from preoperation plan, that means the operation procedure had been changed for some reasons; (e) patients with unidentified preoperative plan; (f) using special type of stents such as single branch stent or double branch stent; (g) non-coated stent such as multilayer bare stent; (h) surgeon-modified stent such as fenestrated stent; (i) special techniques such as chimney or periscope technique, distal bare stent; and (j) CTA thick cuts more than 1 mm which could not reconstructed by Software.

Definitions

TBAD was defined as aortic dissection which starts at (and involves) the left subclavian artery.¹ TEVAR success was preoperative pathological condition and symptoms (i.e. chest pain, malperfusion syndrome) resolved by TEVAR, and no surgical conversion (open repair of aorta dissection emergently or electively, not including surgical repair of access artery morbidity), mortality, or type I or type III endoleak at the end of the procedure.⁴ The unplanned stents in TEVAR were defined as stents used beyond the preoperation planning for any reasons (i.e. large type I endoleak, stent-graft collapse, and other technical reasons) to achieve TEVAR success. Acute aortic dissection was defined as the aortic dissection within 14 days from symptom onset,⁵ the chronic aortic dissection as longer than 14 days. Typical symptoms included severe sharp and/or stabbing pain in chest and/or back; untypical symptoms included dyspnea, dull chest pain, abdominal and/or waist pain; and asymptomatic aortic dissection was defined as patients without any symptoms and was diagnosed with image examinations for other diseases or in routine health examinations. The indication for aortic CTA included: an X-ray of chest in routine health examinations suggesting abnormal aorta and with hypertension history; CT scan suggesting abnormal aorta in examinations for thoracic and/or abdominal diseases; suspicious visceral ischemia diseases. The onset time of asymptomatic aortic dissection patients cannot be determined and all asymptomatic patients presumed chronic in this study. Malperfusion syndrome was defined as end-organ ischemia in the setting of an aortic dissection,⁶ no matter caused by static or dynamic obstruction of aortic branch artery. Proximal neck length was defined as the distance from the distal origin of the left subclavian artery to the proximal part of proximal entry tear. Proximal and distal aortic diameter was defined as the mean diameter at the cranial and caudal margin of proximal and distal landing zone, respectively. Type I endoleak was defined as a sealing failure at one of the attachment sites of the graft to the vessel wall (proximal leak, type Ia; distal, type Ib).⁷ Bird beak defined as a gap between the aortic wall and the stent, with stent protrusion into the aortic lumen of more than 5 mm.^8,9 Inappropriate shaping of stent was defined as the stentgraft did not fully expanded after released with compromised blood flow and pressure gradient, which can hardly achieve TEVAR success. Aortic-related deaths or aortic-related mortality were defined as deaths directly related to aortic dissection and complications of aortic dissection treatment.

Assessment and grouping

All medical records were reviewed by two independent vascular surgeons (ZR, LJ). Preoperative measurement and planning (Additional Figure 1) were compared with operation record and angiography during the endovascular interventions in each patient, unplanned stents cases were marked if operation record or angiography was not consistent with preoperation planning. All marked unplanned stents cases were reviewed again by authors together. Then, the patients were divided into two groups, planned group and unplanned group. The demography and the preoperation measurement about aortic anatomical features and details of endovascular interventions were recorded and analyzed. Anatomic parameters were obtained by semiautomatic centerline analysis on Aquarius iNtuition 3D workstations Version 4.4 (Terarecon Inc., San Mateo, CA).^10,11 All follow-up records were reviewed.

Figure 1.

(a) Number of TEVAR from 1998 to 2014. (b) Proportion of unplanned stent in TEVAR.

Statistical analysis

Clinical variables across groups were compared using the χ² or a Fisher exact test for categorical variables, and the Student t test or nonparametric Mann-Whitney U test was applied for continuous variables. Overall survival was measured from the date enrolled onto the study until death or date last known alive. Estimated probabilities for overall survival were calculated by the Kaplan-Meier method, and the log-rank test was used to assess differences between survival curves.

P values below 0.05 were considered to be significant. Data analysis and graphing were performed using Microsoft Excel (Microsoft Inc., Redmond, WA, USA) and SPSS (IBM Corp., IBM SPSS Statistics for Windows, Armonk, NY, USA).

Results

Between September 1998 and June 2014, 470 patients underwent TEVAR for aortic dissection. Under the including and excluding criteria, a total of 322 patients were included in this study, the planned group included 239 patients (201 males, 84.1%) and the unplanned group included 83 patients (69 males, 83.1%). In this study, we used five kinds of stent-grafts including TALENT (Medtronic, Santa Rosa, Calif) for 70 cases, Hercules (Microport, Shanghai, Chi) for 83 cases, Zenith TX2 (Cook, Bloomington, IN) for 63 cases, VALENT (Medtronic, Santa Rosa, Calif) for 63cases, Relay(Bolton, Sunrise, FL) for 27 cases, TAG(W. L. Gore and Associates, Flagstaff, Ariz) for 7 cases. A total of 86 (26.7%) complicated TBAD patients in acute phase (within 14 days from symptom onset) were given emergent procedure. Elective procedures were given to 236 (73.3%) patients with TBAD in chronic phase (14 days after from symptom onset). Demographics and clinical characteristics are presented in Table 1. The mean age was 56.1 with majority of male (83.9%), 50 (15.5%) patients were older than age 70 and 86 (26.7%) patients were in the acute phase. Comorbidities included hypertension in 239 (74.2%) patients, coronary heart disease in 22 (6.8%) patients, history of stroke in 11 (3.4%) patients, diabetes mellitus in 21 (6.5%) patients, renal insufficiency in 15 (4.7%) patients, COPD (chronic obstructive pulmonary disease) in 11 (3.4%) patients, gout in 9 (2.8%) patients, and hernia in 11 (3.4%) patients. Malperfusion syndrome occurred in 48 (14.9%) patients. Typical symptoms were found in 240 (74.5%) patients, and untypical symptoms were found in 33 (10.2%) patients, including dyspnea in 8 (2.5%) patients, dull chest pain in 6 (1.9%) patients, abdominal pain in 12 (3.7%) patients, and waist pain in 7 (2.2%) patients. All demographics and clinical characteristics mentioned above had no significant statistical difference between two groups (p > 0.05). Forty-nine (15.2%) patients were asymptomatic aortic dissection and the difference of asymptomatic aortic dissection between the two groups was significant (29, 12.1% vs. 20, 24.1%; p = 0.032).

Table 1.

Demographics and clinical characteristics.a

	Overall	Planned	Unplanned	p value
N	322	239	83	–
Demographics
Male	270 (83.9%)	201 (84.1%)	69 (83.1%)	0.836
Age of operation	56.1±12.9	56.4±13.1	55.4±12.3	0.567
Age over 70	50 (15.5%)	40 (16.7%)	10 (12.0%)	0.380
Acute phase	86 (26.7%)	68 (28.5%)	18 (21.7%)	0.230
Patient history
Hypertension	239 (74.2%)	177 (74.1%)	62 (74.7%)	0.909
Diabetes mellitus	21 (6.5%)	17 (7.1%)	4 (4.8%)	0.466
Coronary heart disease	22 (6.8%)	19 (7.9%)	3 (3.6%)	0.177
Stroke	11 (3.4%)	9 (3.8%)	2 (2.4%)	0.814
COPD	11 (3.4%)	8 (3.3%)	3 (3.6%)	1.000
Renal insufficiency	15 (4.7%)	8 (3.3%)	7 (8.4%)	0.111
Gout	9 (2.8%)	8 (3.3%)	1 (1.2%)	0.526
Hernia	11 (3.4%)	10 (4.2%)	1 (1.2%)	0.349
Symptoms
Typical	240 (74.5%)	184 (77.0%)	56 (67.5%)	0.107
Untypical	33 (10.2%)	26 (10.9%)	7 (8.4%)	0.675
Dyspnea	8 (2.5%)	7 (2.9%)	1 (1.2%)	0.685
Dull chest pain	6 (1.9%)	5 (2.1%)	1 (1.2%)	1.000
Abdominal pain	12 (3.7%)	10 (4.2%)	2 (2.4%)	0.738
Waist pain	7 (2.2%)	4 (1.7%)	3 (3.6%)	0.380
Asymptomatic	49 (15.2%)	29 (12.1%)	20 (24.1%)	0.032
Malperfusion syndrome	48 (14.9%)	34 (14.2%)	14 (16.7%)	0.561
Bowel	14 (4.3%)	11 (4.6%)	3 (3.6%)	1.000
Renal	8 (2.5%)	6 (2.5%)	2 (2.4%)	1.000
Left low extremity	8 (2.5%)	6 (2.5%)	2 (2.4%)	1.000
Right low extremity	8 (2.5%)	4 (1.7%)	4 (4.8%)	0.211
Low extremities	11 (3.4%)	9 (3.8%)	2 (2.4%)	0.735
Paraplegia	2 (0.6%)	1 (0.4%)	1 (1.2%)	0.450

^aThe data presented are the percentages for categorical variables, the mean ± SD for continuous variables and the median (range) for skewed variables.

The TEVAR in each year and prevalence of unplanned stents in TEVAR are shown in Figure 1. The number of TEVAR for aortic dissection increased year by year as shown in Figure 1(a). The curve of incidence rate of unplanned stents in TEVAR (Figure 1(b)) demonstrates as a bimodal curve that, 2003 and, 2004 was the first and highest peak and, 2007 was the second peak. Then, the incidence rate of unplanned stents decreased gradually, and there was no unplanned case in the first half of 2014.

Within five years follow-up, 50 deaths were documented. The 1-, 3-, and 5-year overall survival rate was 97.5%, 90.1%, and 84.0%, respectively, and 5-year survival rate was 84.0% (95% confidence interval (CI), 79.9–88.1%, Figure 2). The death reasons were aortic related in 25 patients; cancer in 14 patients; heart failure in 5 patients; stroke in 3 patients, and unclear in 3 patients. The 1-, 3-, and 5-year overall survival rate in planned group was 97.9, 88.5, and 84.0%, respectively and in unplanned group was 96.4, 91.5, and 84.3%, respectively. There was no significant difference in five-year survival between planned and unplanned patients (log-rank test, p = 0.994; Figure 3).

Figure 2.

Five-year survival (all-cause mortality) in 322 TEVAR for aortic dissection patients. The Kaplan-Meier estimate is 84.0% (95% confidence interval (CI), 79.9–88.1%).

Figure 3.

Five-year survival (all-cause mortality) in unplanned and planned stent patients who underwent TEVAR for aortic dissection. (log-rank test, p = 0.994).

The unplanned group had higher hospitalization expenses (142,699.08 ± 78,446.75 yuan vs. 175,238.58 ± 34,838.01 yuan; p = 0.019); longer operation time (104.50 ± 93.24 min vs. 179.08 ± 142.47 min; p < 0.001) and longer hospitalization time (17.07 ± 16.62 d vs. 24.00 ± 15.34 d; p = 0.001) than planned group (Figure 4).

Figure 4.

Histogram of mean average hospitalization expenses, average operation time and average hospitalization time between planned group and unplanned group.

The operative characteristics are presented in Table 2. Preoperative measurement showed that mean proximal neck length was 2.62 mm, and difference of proximal neck length between the two groups was significant (2.66 ± 0.59 mm vs. 2.50 ± 0.51 mm; p = 0.016). Mean proximal aortic diameter was 28.23 mm and mean distal aortic diameter was 18.05 mm. General anesthesia was used in 169 (52.5%) patients, spinal anesthesia was used in 140 (43.8%) patients and local anesthesia was used in 13 (4.0%) patients, the difference in anesthesia between two groups was significant (p < 0.001). The mean length of stent coverage was 149.20 mm, the planned group had longer length of stent coverage than unplanned group (154.62 ± 41.12 mm vs. 133.60 ± 44.33 mm; p = 0.002). The mean proximal and distal stent diameter were 32.57 ± 3.60 mm and 31.83 ± 3.75 mm, respectively, and the difference of proximal and distal stent diameter between two groups was not significant. The proximal oversizing of stent was 15.39 ± 1.57% and there was no significant difference between two groups. The distal oversizing of stent was 77.31 ± 12.64%, and the distal oversizing of stent was higher in unplanned group than planned group (75.44±10.77% vs. 82.68±15.80%; p <0.001). There was no difference in in-hospital mortality between two groups (5, 2.1 vs. 3, 3.6%; p = 0.429).

Table 2.

Operative characteristics.a

	Overall	Planned	Unplanned	p value
Preoperation measurement
Proximal neck length (mm)	2.62 ± 0.58	2.66 ± 0.59	2.50 ± 0.51	0.016b
Proximal aortic diameter (mm)	8.23 ± 3.14	28.14 ± 3.24	28.47 ± 2.84	0.437
Distal aortic diameter (mm)	18.05 ± 2.52	18.12 ± 2.62	17.84 ± 2.18	0.319
Anesthesia
General anesthesia	169 (52.5%)	109 (44.4%)	60 (72.3%)	<0.001b
Spinal anesthesia	140 (43.8%)	118 (49.8%)	22 (26.5%)	<0.001b
Local anesthesia	13 (4.0%)	12 (5.0%)	1 (1.2%)	<0.001b
Stent characteristics
Stent proximal diameter (mm)	32.57 ± 3.60	32.47 ± 3.71	32.84 ± 3.29	0.516
Proximal oversizing (%)	15.39 ± 1.57	15.40 ± 1.66	15.34 ± 1.24	0.975
Stent distal diameter (mm)	31.83 ± 3.75	31.64 ± 3.93	32.39 ± 3.13	0.147
Distal oversizing (%)	77.31 ± 12.64	75.44 ± 10.77	82.68 ± 15.80	<0.001b
Length of stent coverage (mm)	149.20 ± 42.90	154.62 ± 41.12	133.60 ± 44.33	0.002b
Operation time (min)	123.72 ± 112.68	104.50 ± 93.24	179.08 ± 142.47	<0.001b
Post-operation
In-hospital mortality	8 (2.5%)	5 (2.1%)	3 (3.6%)	0.429
Hospitalization time (days)	18.85 ± 16.56	17.07 ± 16.62	24.00 ± 15.34	0.001b

^aThe data presented are the percentages for categorical variables, the mean ± SD for continuous variables, and the median (range) for skewed variables.

^bMeans p value < 0.05.

The reasons of unplanned stents in TEVAR are presented in Table 3. Type Ia endoleak was the most common reason for unplanned stents in TEVAR which happened in 46 (55.4%) patients; bird beak was the second common reason which happened in 25 (30.1%) patients. The incidence of bird beak for each kind of stent-graft is Medtronic TALENT 7.14% (5/70), Microport Hercules 3.61% (3/83), Cook Zenith TX2 17.46% (11/63), Medtronic VALENT3.17% (2/63), Bolton Relay 14.8%(4/27), Gore TAG 0, respectively; inappropriate shaping of stent was the third common reason which happened in 9 (10.8%) patients and type Ib endoleak and proximal tear uncovered in 3 (3.6%) and 1 (1.2%) patients, respectively.

Table 3.

Reasons of unplanned stents in TEVAR.

Reason	N (%)
Type Ia endoleak	46 (55.4)
Bird beak	25 (30.1)
Inappropriate shaping of stent	9 (10.8)
Type Ib endoleak	3 (3.6)
Proximal tear uncovered	1 (1.2)
Total	83 (100)

TEVAR: thoracic endovascular aortic repair.

Discussion

Aortic dissection is the most catastrophic event in aorta, Dake et al. first successfully treated aortic dissection with stent-grafts in 1994.¹² Nienaber et al. first systematically summary the technology of endovascular stent-graft in 1999, named TEVAR, hence it gradually become an attractive alternative treatment for Stanford type B aortic dissection.¹³

For the first time in China, our center used endovascular stent-graft to treat Stanford type B aortic dissection in 1998. The first and the highest peak of incidence rate of unplanned stents in TEVAR was 75% (both 6 in 8) occurred in 2003 and 2004. We analyzed the cases in these two years and found that the patients suffered from more complicated anatomic morphology than before. Based on the TEVAR experiences from 1998 to 2002, it was a trying to treat more complicated anatomic morphology aortic dissection with endovascular technics in 2003 and 2004, experience for complicated anatomic morphology began to accumulate. The second peak occurred in 2007, the second generation stent-graft was gradually used since then, and it was a learning curve for new endovascular instrument.

Accurate measurement of anatomic parameters in images of aortic dissection patients was an important step in preoperative planning. With the advances of image technique and image software,^10,11 semiautomatic centerline analysis could provide the least variable and fast diameter measurements in preoperative planning with the same accuracy as manual double-oblique multiplanar reformations.^14,15 It was an important reason that our center using semiautomatic centerline analysis as preoperative measurement decreased the unplanned stents cases since 2008. Controlling the homogeneity of anatomic parameters, we used the semiautomatic centerline analysis for all enrolled patients.

Although there was no statistical difference in survival rate between planned and unplanned groups in the five-year follow-up, unplanned stents in TEVAR for TBAD increased the hospitalization expenses, not only for the stent cost but also the prolonged operation time and hospitalization time. Retrospectively analysis the reasons and risk factors of unplanned stents could help understanding TEVAR better, and help making more accurate preoperative plan for the patients with risk factors of unplanned stents.

The most common reason for unplanned stents in TEVAR was type Ia endoleak (55.4%, 46 in 83). There were another three cases of type Ib endoleak (3.6%) in unplanned stents group. Boufi et al. found that short proximal landing zone was a unique independent predictor of type I endoleak.¹⁶ Sze et al. followed up patient who underwent TEVAR for aortic dissection and found that 59% of them had endoleak, and they found coverage of the left subclavian artery, small radius of aortic arch curvature and greatest length of unapposed proximal stent-graft were associated with endoleak.¹⁷ And as we previous reported¹⁸ and as Mestres et al. reviewed,¹⁹ re-interventions after TEVAR are mostly related to endoleaks. In our experience, it should be deal with aggressively if type I endoleak visualized early and fast after aorta visualized in aortography after stent-grafts deployment. Proximal neck length was shorter in unplanned stents group and this may result in high incidence of type Ia endoleak which need unplanned stents to bail out.

The second reason for unplanned stents in TEVAR was bird beak (30.1%, 25 in 83). Boufi et al. found the bird beak in 46 (57%) patients who underwent TEVAR,⁹ the lower incidence of bird beak in our study was because some of them accompanied with endoleak were counted as endoleak. The occurrence of bird beak which was a risk factor for type Ia endoleak, depending on anatomy of the aortic arch and stiffness of the stents.²⁰ Boufi et al. suggested that aortic angle of stent deployment zone more than 50° could be predictive of bird beak occurrence.⁹ Many older generations of grafts were stiff and with big “z” rings and prone to lead to “bird beaking,” newer modifications helped significantly with the problem. Further study is needed to explore the risk factors, solutions, and prognosis about bird beak in TEVAR.

Oversizing of stent is a very important factor that could influence the outcome of TEVAR. Adventitia-to-adventitia (outer wall diameters) was recommended in guidelines from American College of Cardiology/American Heart Association and Canadian Cardiovascular Society.^21,22 The aorta diameter could be measured from intima-to-intima (inner wall diameters) or from adventitia-to-adventitia (outer wall diameters).²³ Outer wall diameters could avoid confounding with thrombus or atheroma, and inner wall diameter can reflect the size of the true lumen.²⁴ We calculated that the thickness of aortic wall about 2.5 mm could mislead the oversizing as high as 20%. Iezzi et al. suggested that stent sizing should follow the manufacturer's recommendations.²³ In this study, we follow the stent manufacturer's recommendations (15–20%) because they were more consistent with stent characteristics. With as many as 73% of the patients (n = 136) in chronic phase, it may be reasonable to choose large oversizing for them to achieve better aortic remodeling. A mean 15% oversizing may be aggressive for TBAD in acute phase and retrograde aortic dissection was observed.²⁵

We were very careful in deciding oversize of stent, and there was no difference in proximal oversize of stent between two groups. Because the aorta is a tapered lumen and the tapered ratio was different in different patients especially in aortic dissection patients,²⁵ it was difficult to control the distal oversize, and that is why the mean distal oversize was as high as 77.31%.

The length of stent-graft coverage was another important preoperative planning for TEVAR. Qing et al. found that progressive distal migration of stent-grafts was more prominent in shorter stent-grafts (<162 mm), and they also found longer stent-grafts (>162 mm) placed in the aorta resulted in significantly higher percentage of thrombosis in the false lumen,²⁶ and they suggested that longer stent-grafts may provide more fixation force because the inherent higher contact surface of the stents with the aortic wall. In our study, there was significant difference between the two groups on length of stent coverage and it demonstrated that short length of stent coverage was a risk factor for unplanned stents. Long enough stent-grafts were not available in early years as it was an important reason for unplanned stents. A longer stent-graft could stable longer vulnerable aortic wall, avoiding endoleak or other adverse event to obtain a better therapeutic effect of TEVAR for TBAD.

Our study showed that the asymptomatic patients had high incidence of unplanned stents in TEVAR (20 in 83, 24.1% vs. 29 in 239, 12.1%; p = 0.032). As previous study showed that there were 5–17% of aortic dissection patients without symptoms of pain.^27,28 Mechanisms of painless aortic dissection was not clear, slower dissection with less wall stretching and the sparing of the adventitial layer where aortic innervation sited were speculated the reasons for painless aortic dissections.^29,30 Park et al. reported that painless aortic dissection patients had a higher mortality than painful aortic dissection patients, especially in type B aortic dissection.³¹ In our study, asymptomatic aortic dissection patients were diagnosed with image examinations for other diseases or in routine health examinations. The onset time of these patients cannot be determined and presumed chronicity. Successful endovascular treatment may be challenging in chronic patients because of thickening of the intimal flap.³² And we found that in TEVAR procedure aorta of asymptomatic patient was more inflexible, the stents could hardly conform to the anatomic features and could not fully expand the true lumen. These characteristics may be the reason that the unplanned stents were more in asymptomatic patients.

TEVAR as well as endovascular stent-grafts was fast developed since it was introduced. Nowadays, more and more different types of stent-grafts were available for patients with special anatomical features, such as stent-grafts with proximal bare stent and knobs for the patients with short proximal neck length, more flexible stent-grafts or greater radial force stent-grafts for patients with different characteristics. On the other hand, during the 16-year clinical practice of TEVAR for not only type B but also type A aortic dissection,³ the cases gradually increased, so was our understanding of unplanned stents. Special preoperative planning which included customized stent-graft (single or double branch stent, fenestrated stent, etc.), special techniques (chimney or periscope technique, distal restrictive bare stent, etc.) were made when patients with potential risk factor for unplanned stents in TEVAR. These measures decreased the risk of unplanned stent in TEVAR but these cases were excluded from this study for controlling the homogeneity of patients. With these efforts, the incidence of unplanned stents decreased gradually since 2007, and there was no unplanned case in the first half of 2014. Knowing unplanned stents in TEVAR for TBAD, as well as the reasons and risk factors for unplanned stent may do some help with future TEVAR preoperative planning and the development of endovascular instruments or techniques.

Limitations

Although this was the first report of unplanned stents in TEVAR for TBAD, this single-center experience still had some limitations. First, the vascular surgeons from one center may have common view in dealing with some problems, and that means it may have some bias in single-center experience. Second, the follow-up time was short and longer follow-up was needed. Third, the sample is small; many cases were excluded from this study because we want control the homogeneity of patients.

Conclusions

Unplanned stents were not rare in TEVAR especially in early years, although it did not impact the five-year survival rate, these patients had higher hospitalization expenses, longer operation time, and longer hospitalization time. Asymptomatic aortic dissection, short proximal neck length, too large distal oversizing of stent-graft, and short stent coverage were risk factors for unplanned stents in TEVAR, and type Ia endoleak, bird beak, inappropriate shaping of stent and type Ib endoleak were the reasons for unplanned stents in TEVAR. More accurate preoperative planning was made and incidence rate of unplanned stents decreased gradually after recognizing the reasons and risk factors of unplanned stents in TEVAR for TBAD.

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 study was supported by the National Natural Science Foundations of China (No. 81330034, 81270386, 81500369), scientific research project of Shanghai Science and Technology Committee (No.14411963900, 16411966400) and the Shanghai Medical Talents Training Plan (No. XYQ2013087).

References

Nienaber

Clough

RE.

Management of acute aortic dissection. Lancet 2015; 385: 800–811.

Shimono

Kato

Yasuda

et al . Transluminal stent-graft placements for the treatments of acute onset and chronic aortic dissections. Circulation 2002; 106: I241–I247.

Feng

Zhou

et al . Endovascular repair of ascending aortic dissection: a novel treatment option for patients judged unfit for direct surgical repair. J Am Coll Cardiol 2013; 61: 1917–1924.

Fillinger

Greenberg

McKinsey

et al . Reporting standards for thoracic endovascular aortic repair (TEVAR). J Vasc Surg 2010; 52: 1022–1033, 1033. e15.

Hirst

Johns

Kime

SW.

Dissecting aneurysm of the aorta: a review of 505 cases. Med (Baltimore) 1958; 37: 217–279.

Crawford

Beaulieu

Ehlert

et al . Malperfusion syndromes in aortic dissections. Vasc Med 2016; 21: 264–273.

Rosen

Green

RM.

Endoleak management following endovascular aneurysm repair. J Vasc Interv Radiol 2008; 19: S37–S43.

Melissano

Civilini

Bertoglio

et al . Initial clinical experience with the modified Zenith “Pro-Form” TX2 thoracic endograft. J Endovasc Ther 2010; 17: 463–470.

Boufi

Guivier-Curien

Deplano

et al . Risk factor analysis of bird beak occurrence after thoracic endovascular aortic repair. Eur J Vasc Endovasc Surg 2015; 50: 37–43.

10.

Rengier

Weber

Giesel

et al . Centerline analysis of aortic CT angiographic examinations: benefits and limitations. AJR Am J Roentgenol 2009; 192: W255–W263.

11.

Boskamp

Rinck

Link

et al . New vessel analysis tool for morphometric quantification and visualization of vessels in CT and MR imaging data sets. Radiographics 2004; 24: 287–297.

12.

Dake

Miller

Semba

et al . Transluminal placement of endovascular stent-grafts for the treatment of descending thoracic aortic aneurysms. N Engl J Med 1994; 331: 1729–1734.

13.

Nienaber

Fattori

Lund

et al . Nonsurgical reconstruction of thoracic aortic dissection by stent-graft placement. N Engl J Med 1999; 340: 1539–1545.

14.

Müller-Eschner

Rengier

Partovi

et al . Accuracy and variability of semiautomatic centerline analysis versus manual aortic measurement techniques for TEVAR. Eur J Vasc Endovasc Surg 2013; 45: 241–247.

15.

Rengier

Weber

Partovi

et al . Reliability of semiautomatic centerline analysis versus manual aortic measurement techniques for TEVAR among non-experts. Eur J Vasc Endovasc Surg 2011; 42: 324–331.

16.

Boufi

Aouini

Guivier-Curien

et al . Examination of factors in type I endoleak development after thoracic endovascular repair. J Vasc Surg 2015; 61: 317–323.

17.

Sze

van den Bosch

Dake

et al . Factors portending endoleak formation after thoracic aortic stent-graft repair of complicated aortic dissection. Circ Cardiovasc Interv 2009; 2: 105–112.

18.

Zhang

Zhou

et al . Potential risk factors of re-intervention after endovascular repair for type B aortic dissections. Cathet Cardiovasc Intervent 2015; 86: E11–E10.

19.

Mestres

Capoccia

Riambau

Secondary procedures in thoracic aorta. J Cardiovasc Surg (Torino) 2014; 55: 731–740.

20.

Oberhuber

Schabhasian

Kohlschmitt

et al . The bird beak configuration has no adverse effect in a magnetic resonance functional analysis of thoracic stent grafts after traumatic aortic transection. J Vasc Surg 2015; 61: 365–373.

21.

Hiratzka

Bakris

Beckman

et al . 2010 ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM guidelines for the diagnosis and management of patients with thoracic aortic disease: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines, American Association for Thoracic Surgery, American College of Radiology, American Stroke Association, Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, Society of Interventional Radiology, Society of Thoracic Surgeons, and Society for Vascular Medicine. Circulation 2010; 121: e266–e369.

22.

Boodhwani

Andelfinger

Leipsic

et al . Canadian Cardiovascular Society position statement on the management of thoracic aortic disease. Can J Cardiol 2014; 30: 577–589.

23.

Iezzi

Dattesi

Pirro

et al . CT angiography in stent-graft sizing: impact of using inner vs. outer wall measurements of aortic neck diameters. J Endovasc Ther 2011; 18: 280–288.

24.

Mongeon

Marcotte

Terrone

DG.

Multimodality noninvasive imaging of thoracic aortic aneurysms: time to standardize. Can J Cardiol 2016; 32: 48–59.

25.

Huang

et al . A study of aortic dimension in type B aortic dissection. Interact Cardiovasc Thorac Surg 2008; 7: 244–248.

26.

Qing

Yiu

Cheng

SW.

A morphologic study of chronic type B aortic dissections and aneurysms after thoracic endovascular stent grafting. J Vasc Surg 2012; 55: 1268–1275. Discussion 1275–1276.

27.

Hagan

Nienaber

Isselbacher

et al . The International Registry of Acute Aortic Dissection (IRAD): new insights into an old disease. JAMA 2000; 283: 897–903.

28.

Imamura

Sekiguchi

Iwashita

et al . Painless acute aortic dissection – diagnostic, prognostic and clinical implications. Circ J 2011; 75: 59–66.

29.

Wooley

Sparks

Boudoulas

Aortic pain. Prog Cardiovasc Dis 1998; 40: 563–589.

30.

Rahmatullah

Khan

Nair

et al . Painless limited dissection of the ascending aorta presenting with aortic valve regurgitation. Am J Emerg Med 1999; 17: 700–701.

31.

Park

Hutchison

Mehta

et al . Association of painless acute aortic dissection with increased mortality. Mayo Clin Proc 2004; 79: 1252–1257.

32.

Kamman

de Beaufort

van Bogerijen

et al . Contemporary management strategies for chronic type B aortic dissections: a systematic review. PLoS One 2016; 11: e0154930.