Elective endovascular treatment of descending thoracic aortic aneurysms and chronic dissections with stent-grafts

PURPOSE: To report our experience of endovascular stent-graft placement in patients with descending thoracic aortic dissections and aneurysms and to evaluate the feasibility, safety, and clinical outcomes of the treatment. MATERIALS AND METHODS: Stent-grafts were placed in the descending thoracic aortas of 23 patients with saccular aneurysms (n = 11) and Stanford type B chronic aortic dissections of the descending thoracic and abdominal aorta (n = 12). All stent-grafts were individually constructed of self-expandable stainless steel stents covered with polytetrafluoroethylene. Vascular access was achieved through the femoral artery in all patients. Clinical status of each patient was monitored and postoperative CT was performed within 1 month of the procedure and at 3-12-month intervals after the procedures. RESULTS: Successful exclusion of the primary entry tears of dissections and the inlets of saccular aneurysms was achieved in all but two patients with aortic dissection. The overall technical success rate was 91.3% (dissection: 10 of 12 = 83%; aneurysm: 11 of 11 = 100%). All patients in whom technical success was achieved showed complete thrombosis and significant decrease in diameter of the thoracic false lumen (preoperative: 5.3 cm +/- 0.9; postoperative: 4.3 cm +/- 0.9; P = .004) or aneurysm sac (preoperative: 5.3 cm +/- 1.7; postoperative: 2.8 cm +/- 2.5; P = .001). In addition, five patients demonstrated complete resolution of the dissected thoracic false lumen (n = 2) and aneurysm sac (n = 3). However, in all patients with aortic dissection, the abdominal aorta was not significantly changed in size (P = .302) and shape and their false lumen flows remained persistent. Immediate postoperative complications were detected in 12 patients (52%); 10 had fever, leukocytosis, and elevation of C-reactive protein, another had wound infection, and another had transient abdominal pain. Three patients died 2, 3, and 12 months after the procedure: one from septic shock, another from underlying mediastinitis, and the other from an unexplained cause. The remaining 20 patients were well after the procedure (1-9 days; mean, 3 days), without any stent-graft-related complications or discomfort (follow up period: 10-65 mo; mean: 25.1 mo +/- 15.6). The cumulative survival rate after the stent graft was 100% at 30 days and 91% at 12 months. CONCLUSIONS: For treatment of aortic dissection and saccular aneurysm of the descending thoracic aorta, endovascular stent-graft repair may be a technically feasible and effective treatment modality.     

The "Carpentier" thoracic aortic by-pass technique for management of descending aortic aneurysms and dissections--a radiological perspective

The "Carpentier" thoracic aortic bypass procedure is a recently described and, until now, little used surgical technique for the treatment of descending thoracic aortic aneurysms and dissections. It involves the placement of a large conduit from the ascending aorta to the distal abdominal aorta through a midline sternotomy incision extended to the umbilicus and the subsequent interruption of the aorta just distal to the left subclavian artery via a left postero-lateral thoracotomy. As radiologists we should be aware of this alternative surgical option so that, in addition to diagnosing and classifying these aneurysms and dissections, we can assist our surgical colleagues in:-- a. The pre-operative assessment of the aorta for bypass grafting including the distal abdominal aorta b. The post-operative monitoring of the anticipated thrombotic occlusion of the descending thoracic aorta to the coeliac axis.     

Coil embolization of an anastomotic leak after ascending aorta replacement

Surgical treatment of diseases of the thoracic aorta (aneurysms, dissections, and ruptures) may be associated with serious postoperative complications. Endovascular repair of thoracic aorta pathology is less invasive and offers a therapeutic alternative in high-surgical-risk patients, particularly in the presence of previous surgical repair of the thoracic aorta. The endovascular procedure, however, is almost only possible in the descending thoracic aorta, although advances have also been made in the aortic arch as well as in the ascending aorta with branched stent grafts. We report a case of a surgically treated aneurysm in the ascending thoracic aorta complicated with an anastomotic leak. If a short prosthesis (6 cm) had been available, the anastomotic leak would have been treated with endovascular repair. In lack of this prosthesis, we were forced to treat the patient with a method not generally accepted--embolization with endovascular coils--successfully resulting in occlusion of the leakage.     

Descending thoracic aneurysm rupture with a known abdominal aortic aneurysm.

The association of abdominal aortic aneurysms with aneurysmal disease of the thoracic aorta is well established. However, rupture of a descending atherosclerotic thoracic aortic aneurysm in association with an infrarenal abdominal aortic aneurysm can present a difficult diagnostic and therapeutic problem to the treating physician. This article presents a case of rupture of an atherosclerotic descending thoracic aortic aneurysm in the face of what clinically appeared to be a leaking or ruptured abdominal aortic aneurysm.     

多层螺旋CT造影在主动脉病变腔内修复术后随访的价值

目的:探讨多层螺旋CT血管造影(multi-detector rowspiral computed tomography angiography,MDCTA)及后处理技术在主动脉覆膜支架腔内修复术(transluminal stent-graft placement,TSGP)术后随访的临床应用价值。方法:21例接受TSGP主动脉疾病患者,包括:Stanford B型夹层13例,真性动脉瘤3例,假性动脉瘤2例,弓降部穿透性溃疡1例,胸主动脉瘤合并局限性夹层1例,胸主动脉瘤合并Stanford B型夹层1例,术后采用MDCTA进行随访,平均随访13个月(1~24个月)。采用轴位图像与多种重建图像相结合来显示支架形态、术前术后主动脉管腔情况的变化和有无并发症。结果:13例主动脉夹层覆膜支架置入后:所有患者均真腔扩大,假腔减小或消失并伴血栓形成,支架未发现移位或断裂;共3例(14%)随访中发现内漏,1例Ⅱ型内漏,建议随访观察;1例术后8个月复查新发现支架近端Ⅰ型内漏,密切随访2个月后患者出现胸痛,复查CT内漏增多,转外科治疗。1例腹主动脉瘤术后1月复查发现Ⅲ型内漏。所有患者介入术后CT随访图像均满足临床诊断需要。结论:MDCTA对主动脉覆膜支架置入术后随访较其他检查手段具有多方面的优越性,能及时观察术后疗效、发现并发症,对主动脉疾病覆膜支架腔内修复术后随访具有重要价值。     

Endovascular treatment in diseases of the thoracic aorta

PURPOSE: To determine whether endovascular treatment of thoracic aorta conditions can be an effective alternative approach to surgical repair. MATERIAL AND METHODS: July 1997 to February 1999, eighteen patients (16 men and 2 women; 58.6 +/- 14.8 years) presenting with different kinds of descending aorta conditions were selected for the endovascular treatment. All patients exhibited severe comorbid pulmonary and/or cardiovascular medical conditions which increased surgical risk. All implants were performed in the operating room under fluoroscopic and TEE guidance. Clinical and imaging follow-up was performed 1, 3, 6 and 12 months later. RESULTS: The endovascular treatment was successful in 17 cases. No deaths or major complications occurred. No leakage was evident at post-procedure angiography. The patients were discharged after 6 +/- 4 days. MRI or CT study performed before hospital discharge showed aneurysms exclusion in 16 patients. In the four cases of dissection, thrombosis of the false lumen was evident since the first follow-up study. In the group of patients (11 cases) with 6 months follow-up, the diameters of stented aortic segments decreased. No late leakage was observed and thrombosis was complete in all cases. DISCUSSION: The natural history of aortic aneurysms and dissection is progressive toward dilation and aortic rupture. Surgery of descending thoracic aorta is burdened with a mortality of 8-12% in elective cases and over 50% in emergency cases or aortic dissection. The endovascular treatment of aortic conditions was introduced in clinical practice in 1991 and literature data show that it is effective, with lower mortality and morbidity rates than surgical treatment. CONCLUSION: Our results stress the feasibility and effectiveness of endovascular procedure in the treatment of complex thoracic aorta conditions even in high risk patients. Thus, endovascular treatment of thoracic aorta can be considered an effective alternative approach to conventional surgery.     

Early Results of Endovascular Treatment of the Thoracic Aorta Using the Valiant Endograft

Endovascular repair of the thoracic aorta has been adopted as the first-line therapy for much pathology. Initial results from the early-generation endografts have highlighted the potential of this technique. Newer-generation endografts have now been introduced into clinical practice and careful assessment of their performance should be mandatory. This study describes the initial experience with the Valiant endograft and makes comparisons with similar series documenting previous-generation endografts. Data were retrospectively collected on 180 patients treated with the Valiant endograft at seven European centers between March 2005 and October 2006. The patient cohort consisted of 66 patients with thoracic aneurysms, 22 with thoracoabdominal aneurysms, 19 with an acute aortic syndrome, 52 with aneurysmal degeneration of a chronic dissection, and 21 patients with traumatic aortic transection. The overall 30-day mortality for the series was 7.2%, with a stroke rate of 3.8% and a paraplegia rate of 3.3%. Subgroup analysis demonstrated that mortality differed significantly between different indications; thoracic aneurysms (6.1%), thoracoabdominal aneurysms (27.3%), acute aortic syndrome (10.5%), chronic dissections (1.9%), and acute transections (0%). Adjunctive surgical procedures were required in 63 patients, and 51% of patients had grafts deployed proximal to the left subclavian artery. Comparison with a series of earlier-generation grafts demonstrated a significant increase in complexity of procedure as assessed by graft implantation site, number of grafts and patient comorbidity. The data demonstrate acceptable results for a new-generation endograft in series of patients with diverse thoracic aortic pathology. Comparison of clinical outcomes between different endografts poses considerable challenges due to differing case complexity.     

Urgent thoracic aortal dissection and aneurysm: treatment with stent-graft implantation in an angiographic suite

The aim of this study was to evaluate the feasibility of endoluminal stent-graft placement in an angiographic suite for the treatment of emergent type-B aortic dissections and ruptured thoracic aortal aneurysms. Twenty-six patients with either urgent type-B dissection (n=8) or aneurysms (n=18) of the descending thoracic aorta were chosen for stent-graft implantation. All patients received a multidetector-row CT angiography of the whole aorta and pelvic arteries prior to stent-graft implantation. All procedures were performed in a fully equipped digital subtraction angiography (DSA) suite under general anesthesia. In 20 patients Talent LPS tube grafts and in 4 patients an Excluder graft were used. Access was achieved via surgical cut-down in the left (n=7) or right (n=19) groin. Sealing was successful in 24 patients. The proximal covered portion of the stent graft was placed across the left subclavian artery in 2 patients. Procedural success was achieved in 23 of 24 patients. One patient required a second stent-graft placement before the aneurysm was sealed. One patient with an acute perforation of the descending aorta died due to cardiac failure prior to stent-graft implantation. In 1 patient stent-graft delivery failed due to severe calcification of both common iliac arteries. Endoluminal treatment of both urgent type-B aortic dissections and thoracic aortal aneurysms with stent graft is an attractive alternative treatment to surgical repair. The placement of stent grafts in an angiographic suite is a safe and feasible method with good clinical effectiveness and, so far, good clinical outcome.     

Aneurysm shrinkage after endovascular repair of aortic diseases

BACKGROUND: There are two graft materials for endovascular repair of aortic diseases, i.e., polyester and expanded polytetrafluoroethylene (ePTFE). The latest reports have suggested that there is graft-specific difference in outcomes. The purpose of this article was to evaluate the difference in terms of aneurysm shrinkage. PATIENTS AND METHODS: Eighty-six patients who underwent endovascular repair of aortic diseases were included. Forty patients had true aortic aneurysms, 8 had aortic pseudoaneurysms, and 38 had aortic dissections. Eighteen patients with true aortic aneurysms were treated with stent grafts fabricated with polyester, while the other 68 patients, including 22 patients with true aneurysms, 8 patients with pseudoaneurysms, and 38 patients with aortic dissections, were treated with stent grafts fabricated with ePTFE. All patients were followed-up by computed tomography (CT) for more than 1 year. The mean follow-up term was 28 months. Computed tomography confirmed that there were sufficiently long necks, and the aneurysm or the entry tear was completely excluded without any endoleak in all patients. The diameter of the preoperative lesion was compared with that measured on follow-up CT at 1 year and at the end of the follow-up term. Increase or decrease in the diameter by more than 5 mm was defined as a significant diameter change. RESULTS: Aneurysm shrinkage was observed in 40% of patients with true aneurysms, 88% of patients with pseudoaneurysms, and 55% of patients with aortic dissections at 1 year. There was no significant increase in patients with aneurysm shrinkage at the end of follow-up in any groups. In the case of true aortic aneurysms, shrinkage of aneurysms was observed more frequently with polyester-fabricated stent grafts (67%, 13/18) than with ePTFE-fabricated ones (18%, 4/22) at 1 year (P<.01). In contrast, expansion of aneurysms was observed only in patients treated with ePTFE (14%, 3/22). Shrinkage of the descending aorta was observed in 55% of patients with acute aortic dissections and 36% of patients with chronic aortic dissections. There was no case with aortic enlargement in either group. There was no significant difference between acute and chronic dissection in terms of shrinkage of the descending aorta. CONCLUSION: Expanded polytetrafluoroethylene appears to be effective for the treatment of pseudoaneurysms and aortic dissections. However, polyester seems to be more effective than ePTFE when true aneurysms are to be treated.     

Aortic Arch Vessel Geometries and Deformations in Patients with Thoracic Aortic Aneurysms and Dissections

PurposeTo quantify aortic arch geometry and in vivo cardiac-induced and respiratory-induced arch translations and arch branch angulations using three-dimensional geometric modeling techniques.Materials and MethodsScanning with electrocardiogram-gated computed tomography angiography during inspiratory and expiratory breath holds was performed in 15 patients (age, 64 y ± 14) with thoracic aortic aneurysms or dissections. From the lumen models, centerlines of the thoracic aorta, brachiocephalic artery, left common carotid artery, and left subclavian artery and their branching ostia positions were quantified. Three-dimensional translation of vessel ostia, branching angles, and their changes secondary to cardiac pulsation and respiration were computed.ResultsDuring expiration, all ostia translated rightward from systole to diastole (P < .035). Regardless of cardiac phase, all ostia translated posteriorly and superiorly from inspiration to expiration (P < .05). Respiration induced greater posterior and superior translations than cardiac pulsation (P < .03). The left common carotid artery branch angled significantly more toward the aortic arch compared with the brachiocephalic artery and left subclavian artery (P < .03). No significant changes in branching angle were found from systole to diastole or inspiration to expiration.ConclusionsIn patients with thoracic aortic aneurysms or dissections, the thoracic aortic arch translated significantly secondary to inspiration and expiration and to a lesser extent secondary to cardiac pulsation. Insignificant branching angle changes suggest that the aortic arch and its branch origins move predominantly in unison.     

Localised aneurysms of the descending thoracic aorta.

The clinical, roentgenographic and aortographic data were reviewed in 12 patients with localised descending, thoracic aortic aneurysms. The current study indicates that arteriosclerotic peripheral vascular disease not infrequently produced localised saccular aneurysms of the descending thoracic aorta. Characteristic symptomatology was unusual; most aneurysms were detected as incidental roentgenographic findings. The aneurysms projected from the posteroloteral aspect of the aorta and roentgenographically appeared as left hilar masses or left retrocardiac masses when located in the mid and lower descending thoracic aorta, respectively. Specific rim calcification or vertebral erosion was not encountered in any case. During aortography only a small portion of the aneurysm was outlined with contrast material due to partial obliteration of the aneurysmal cavity with thrombus.     

Placement of endovascular stent-grafts for emergency treatment of acute disease of the descending thoracic aorta

OBJECTIVE: The aim of this study was to evaluate the feasibility, safety, and effectiveness of endovascular stent-graft placement for the emergency treatment of acute descending thoracic aortic disease. MATERIALS AND METHODS: From January 1996 through November 2001, 18 patients underwent emergency endovascular stent-graft placement for various types of acute descending thoracic aortic disease. Five patients had Stanford type B aortic dissection, six had traumatic ruptures of the thoracic aorta, five had ruptured aortic aneurysms, and two had penetrating atherosclerotic aortic ulcers. All patients presented with life-threatening symptoms requiring treatment with stent-grafts from the emergency kit. All were at high surgical risk due to serious comorbidities. The efficacy of the procedure was assessed at follow-up studies before discharge and at 3, 6, and 12 months after intervention and yearly thereafter. RESULTS: The primary technical success rate was 78%. Four patients had primary perigraft leaks. The secondary technical success rate was 83%. One patient died 20 hr after intervention from stent-graft-related causes. Follow-up studies revealed stent-graft migration in one patient. Progression of disease was observed in one patient treated for dissection and in both patients treated for penetrating ulcers. One patient died 7 months after intervention of unknown reasons; all other patients are alive. The mean follow-up time was 17.4 months (range, 0-38 months). CONCLUSION: Emergency repair of acute descending thoracic aortic disease with stent-graft placement can be successfully accomplished and may be a promising alternative to open-chest surgery, especially in patients at high risk.     

Follow-up of patients with previous treatment for coarctation of the thoracic aorta: comparison between contrast-enhanced MR angiography and fast spin-echo MR imaging

Regular follow-up is required in patients with previous intervention for coarctation of the aorta to detect recoarctation or aneurysm formation. In this study we describe the findings encountered on routine follow-up exams and we compare the use of contrast-enhanced 3D MR angiography (CE MRA) with fast spin-echo MRI (FSE) to study the thoracic aorta after previous intervention. In 51 consecutive patients previously treated for aortic coarctation, 74 MR studies of the thoracic aorta were performed during a 2-year period using CE MRA and FSE MRI. The thoracic aorta was evaluated for abnormalities of course, caliber, shape, and pathology of side branches. The CE MRA and FSE MRI studies were evaluated side by side by consensus of two reviewers evaluating which MR technique depicted the abnormalities of the thoracic aorta the best. Of 74 exams, six clinically important abnormalities were found: four aneurysms and two restenoses. Two small pseudoaneurysms were missed on the FSE studies. Contrast-enhanced MRA was judged to visualize aortic abnormalities better than FSE (47 of 74 MR studies) especially for the transverse aortic arch, coarctation site, left subclavian artery, and aortic arch configuration. For the ascending aorta and distal descending aorta, CE MRA and FSE performed equally well. Aortic diameters measured at four levels in the first 18 MRI studies showed no significant differences in diameter when measured by FSE or CE MRA (p = not significant). Clinically important abnormalities, such as aneurysm formation and restenosis, can be present years after treatment for aortic coarctation. In the regular follow-up of these patients, CE MRA may provide additional diagnostic information compared with FSE and should be included as part of the routine exam. Received: 3 April 2000; Revised: 5 July 2000; Accepted: 7 July 2000     

Aortic aneurysms: growth rates measured with CT.

Because of a lack of information about the rates of growth of aortic aneurysms, such rates in thoracic and abdominal aortic aneurysms were determined. One hundred seventy-one patients with atherosclerotic aortic aneurysm managed nonoperatively were followed up for more than 6 months with sequential computed tomography (CT). There were 211 aneurysms (thoracic aortic, 82; abdominal aortic, 129). The growth rates of thoracic and abdominal aortic aneurysms were 0.42 and 0.28 cm/y, respectively. Aneurysms at the aortic arch (n = 34) grew at a faster average rate (0.56 cm/y) than aneurysms arising at other levels, even when the rate was corrected for the initial diameter. It is recommended that thoracic aortic aneurysms, especially aortic arch aneurysms, be followed frequently with CT examination of size.     

Aortobronchopulmonary fistula complicating aortic aneurysm: diagnosis in four cases

Aortobronchopulmonary fistula, a fistulous connection between the aorta and lung, is uniformly fatal in untreated cases. However, with early recognition and surgery, the survival rate exceeds 80%. We have had four patients with aortobronchopulmonary fistula, all of which resulted from thoracic aortic aneurysms (two after grafting of thoracic aortic aneurysms, one mycotic, one atherosclerotic). All four patients presented with hemoptysis. All four had a chest radiograph, which in two showed the aneurysm and in three showed airspace disease adjacent to the aorta. The aneurysm was shown by CT in one of two patients and by aortography in two of three patients. Neither CT nor aortography showed the fistula. Aortobronchopulmonary fistula was proved by surgery in two of the patients and by autopsy in the other two. A high index of suspicion is necessary to make the diagnosis of aortobronchopulmonary fistula. The diagnosis should be considered in patients who have minor or major hemoptysis, with either coexisting thoracic aortic aneurysms or history of thoracic aneurysm repair.     

经股动脉覆膜支架植入术的临床应用

目的：总结经股动脉覆膜支架植入术治疗胸主动脉夹层动脉瘤的手术步骤和并发症处理。方法：（1）经左肱动脉置入猪尾巴导管至升主动脉,进行造影,确定动脉瘤内膜瘘口位置并作标记;（2）在透视下经股动脉将长导丝送至升主动脉;（3）沿长导丝将24F支架器放至动脉瘤瘘口位置,释放支架;（4）置入猪尾巴导管至升主动脉,造影复查。结果：6例内支架植入位置准确,主动脉瘘口被封堵,狭窄的主动脉真腔基本恢复正常。无严重心脑血管并发症。结论：与传统的胸主动脉瘤手术相比,支架植入术具有创伤小、出血少、心脑血管及肺部并发症少的特点;控制性低血压是预防和减少并发症的有力措施;导管室内必须具有良好的组织和完善的监测设备。     

Diagnosis of acute thoracic aortic dissection using combined echocardiography and computed tomography.

Acute dissection of the thoracic aorta is a life-threatening emergency requiring a diagnosis which is rapid, accurate and safe, and which will distinguish between dissections involving the ascending and descending aorta. In the absence of any general agreement on the best method of making this diagnosis we studied the use of combined echocardiography and contrast-enhanced computed tomography (CT) to diagnose acute aortic dissection. Over a 3 year period 23 patients were investigated in this way. Aortic dissection was demonstrated in 18 cases, involving the ascending aorta in 15, and the descending aorta alone in three. The diagnosis of aortic dissection was confirmed in 13 patients at surgery, in one at aortography and in one at autopsy. Three patients died without surgery or autopsy being performed to confirm the diagnosis and the subsequently which accounted for their symptoms. This combined approach has proved a valuable and safe means of investigating aortic dissection.     

Treatment of chronic aortic dissection by transluminal endovascular stent-graft placement: preliminary results.

PURPOSE: To investigate efficacy of stent-graft repair for the treatment of patients with chronic aortic dissection. MATERIALS AND METHODS: Fifteen patients with chronic aortic dissection were treated with endovascular stent-grafts. Entry tears were located in the descending thoracic aorta in all patients. The mean maximum diameter of the descending thoracic aorta was 47 mm +/- 8. The mean diameter of the true lumen at the same level was 20 mm +/- 5. The mean interval between diagnosis and stent-graft procedure was 32 months +/- 91. Stent-grafts were fabricated from expanded polytetrafluoroethylene and Z-stents. RESULTS: Stent-grafts were placed successfully in all patients. Two stent-grafts were required in one patient. Entry closure and thrombosis of the false lumen of the descending thoracic aorta were also achieved in all patients. No procedure-related complications were observed except for postimplantation syndrome, including fever and leukocytosis. The diameter of the true lumen was significantly increased (mean, 31 mm +/- 6) at the level of the descending thoracic aorta (P <.01) and the diameter of the aorta was significantly decreased (mean, 44 mm +/- 8) at the same level (P <.01). There were no deaths and no instances of aortic rupture during the subsequent average follow-up period of 24 months. Secondary stent-graft procedures were required to treat the abdominal component of dissection during follow-up in one patient. CONCLUSIONS: Stent-graft repair of chronic aortic dissection is a safe and effective method and may be an alternative to surgical graft replacement in selected patients. However, further evaluation is mandatory before this method is widely employed.     

覆膜支架腔内修复术治疗主动脉病变的价值

目的:评价覆膜支架腔内修复术治疗主动脉病变的应用价值及临床意义。方法:21例主动脉疾病患者,包括:Stanford B型夹层13例(65%),真性动脉瘤3例(15%),假性动脉瘤2例(10%),弓降部穿透性溃疡1例(5%),胸主动脉瘤合并局限性夹层1例(5%),胸主动脉瘤合并Stanford B型夹层1例(5%),全部接受TSGP。共应用3种类型大动脉覆膜支架,分别为:美国锐乐(10例)、国产先健(10例)及COOK公司血管支架(1例)。结果:17例分别置入1个支架,2例分别置入2个支架,2例分别置入主体支架1个、短支架2个,所有支架释放成功率100%。患者无截瘫及瘤体破裂等严重并发症,无围手术期死亡。支架释放后即刻造影复查,19例无明显渗漏和假腔显影(90%);2例少许内漏,其中1例术后7 d CTA复查内漏消失,1例为Ⅱ型内漏,建议随访观察;1例术后8月随访,支架近端新发内漏并逐次增多。结论:TSGP治疗主动脉夹层、真性及假性动脉瘤、穿透性溃疡成功率高、创伤小,近中期效果良好,但远期随访及效果评价有待进一步观察。