Jiaxuan Feng

Endovascular Repair of Ascending Aortic Dissection : A Novel Treatment Option for Patients Judged Unfit for Direct Surgical Repair

OBJECTIVES This paper sought to report the outcomes of patients who are considered unfit for urgent surgical repair of ascending aortic dissections (AADs) who were treated using a novel endovascular repair strategy. BACKGROUND AAD is best treated by direct surgical repair. Patients who are unable to undergo this form of treatment have poor prognoses. Previously, clinical case reports related to endovascular repair of AAD have been controversial. METHODS Between May 2009 and January 2011, 41 consecutive patients with AAD were treated in our institution. Fifteen patients were considered poor candidates for direct surgical repair and subsequently underwent the endovascular repair. RESULTS The nature of the referral process to our tertiary care facility made the median time from aortic dissection onset to treatment 25.5 days (range: 6 to 353 days). Dissections in 5 patients (33.3%) were considered acute, and those in 10 patients (66.7%) were considered chronic. The rate of successful stent-graft deployment was 100%, and there were no major morbidities or deaths in the perioperative period. Median follow-up was 26 months (range: 16 to 35 months). One new dissection occurred in the aortic arch at 3 months and was treated with a branched endograft. Significant enlargements of true lumens and decreases of false lumens and overall thoracic aorta were noted after the procedures. CONCLUSIONS Endovascular repair of AAD was an appropriate treatment option in patients who were considered poor candidates for traditional direct surgical repair by the clinical criteria used in our institution. A larger series of cases with longer follow-up is needed to substantiate these results.

Material properties of components in human carotid atherosclerotic plaques: A uniaxial extension study

Graphical abstract Fibrous cap and media in the carotid atherosclerotic plaques are much stiffer than either lipid, intraplaque haemorrhage or thrombus.

Endovascular repair by customized branched stent-graft: A promising treatment for chronic aortic dissection involving the arch branches

OBJECTIVE There is no approved special endovascular device for use in preventing entry tears in the distal part of ascending aorta or in the aortic arch and preserving the arch branch arteries. Thus, we have designed a novel branched stent-graft, and herein report the initial clinical outcomes. METHODS Between August 2009 and January 2014, 51 patients with aortic dissections involving the aortic arch were treated by endovascular branched stent-grafts. There were 7 Stanford type A aortic dissections, 22 retrograde type A aortic dissections, and 22 Stanford type B aortic dissections (including 4 localized aortic arch dissections). All patients were treated while in the chronic phase (>2 weeks). RESULTS All of the proximal entry tears in the arch were successfully excluded, and all of the treated branch arteries remained patent. No new cerebral infarction occurred. There was 1 death from a retrograde type A dissection, occurring 6 days after the endovascular procedure. The median follow-up period was 44 months (range, 14-66 months). No additional complications or mortality occurred. Complete thrombosis in the false lumen of the aortic arch was formed in all patients, and significant true lumen recovery and false lumen shrinkage were demonstrated in different levels of the thoracic aorta according to computed tomography angiography at 1 year postsurgery (P < .001). CONCLUSIONS In patients with aortic dissection involving the arch branches, the customized branched stent-graft may provide a feasible endovascular treatment option. A larger series of cases with longer follow-up is needed to substantiate these results.

Restrictive bare stent for prevention of stent graft-induced distal redissection after thoracic endovascular aortic repair for type B aortic dissection.

BACKGROUND Stent graft-induced distal redissection (SIDR) is one of the major concerns in the durability of endovascular repair for complicated Stanford type B aortic dissection. The characteristics and means of prevention of this complication remain unknown. METHODS From April 1997 to March 2010, 674 patients with type B aortic dissections were treated primarily by thoracic endovascular aortic repair (TEVAR) at our center. Criteria for inclusion in this study were treatment primarily with TEVAR and an estimated mismatch rate (ratio of distal diameter of stent graft to long diameter of true lumen) greater than 120%. By this protocol, 465 patients were included in this study and were retrospectively analyzed. Among them, 266 patients were treated in the acute phase, and 199 were treated in the chronic phase. RESULTS A total of 311 patients were treated with standard TEVAR and 154 patients with TEVAR + restrictive bare stent (RBS). The preoperative mismatch rate (measured as the preoperative long diameter of the true lumen at the level of the intended distal end of the stent graft) of the SIDR was significantly higher than that of the non-SIDR (192.7 ± 54.9% vs 131.9 ± 10.4%; P ＜ .05). The follow-up mismatch rate of the SIDR was significantly higher than that of the non-SIDR (145.4 ± 34.6 vs 120.3 ± 16.1; P ＜ .05). Compared with the standard TEVAR, TEVAR + RBS was associated with a lower incidence of SIDR (0% vs 2.9%; P = .033) and less secondary intervention (3.9% vs 9.3%; P = .040). Placement of the RBS significantly expanded the true lumen at the level of the descending aorta with the narrowest true lumen and at the level of the distal end of the stent graft. CONCLUSIONS The mismatch between the distal diameter of the stent graft and the diameter of the compressed true lumen seems to be the major factor in the occurrence of SIDR. Placement of an RBS, as an adjunctive technique to TEVAR, could reduce the incidence of SIDR. On the basis of early- to midterm observations, RBSs may improve morphological remodeling of the dissected aorta at certain levels.

Endovascular management of pararenal aortic aneurysms with multiple overlapping uncovered stents

OBJECTIVE This study aims at evaluating the safety and efficacy of a porous stent system consisting of multiple overlapping uncovered stents in the treatment of complex aortic aneurysms with vital branches. METHODS Data of all patients with aortic aneurysms treated in our center with multiple overlapping uncovered stents between February 2010 and December 2011 were retrospectively reviewed. Preoperative characteristics, intraoperative details, and follow-up outcomes were documented. Technical success was defined as successful deployment of the stents to target locations without procedure-related complications. Clinical success was characterized by complete shrinkage or stabilization of the aneurysm, preservation of vital branches, and absence of major complications. Patients were grouped, according to rapidity of aneurysm thrombosis, into fast-thrombosis group (complete thrombosis of aneurysmal sac was achieved in ≤6 months) and a delayed-thrombosis group (>6 months required for complete thrombosis). Possible factors affecting the speed of thrombosis were analyzed statistically with the Fisher exact test and the t-test. RESULTS This porous stent system was used to treat 34 patients (23 men, 11 women; mean age, 65.7 years). Technical success was achieved in all patients (100%). Regular follow-up over 6 months was achieved in 29 patients (mean length of follow-up, 11.4 months). Complete thrombosis of the aneurysm sac within 12 months was observed in 24 patients (83%). Aneurysm shrinkage was documented in seven patients (24%) and stabilization in 21 (72%). All branch arteries covered by bare stents stayed patent during follow-up. The overall clinical success rate reached 97% in the follow-up group. Risk factors for delayed thrombosis included fewer stents implanted (P = .013), longer sac entrance (P = .043), and use of antiplatelet medication (P = .040). CONCLUSIONS An alternative method of management of complicated aortic aneurysm appears to be feasible using overlapping bare stents, which may prevent aneurysm growth while preserving vital branches. The short-term outcome of our study seems encouraging but is not sufficient to draw a robust conclusion. Further hemodynamic and clinical studies are warranted to evaluate long-term efficacy.

Layer- and Direction-Specific Material Properties, Extreme Extensibility and Ultimate Material Strength of Human Abdominal Aorta and Aneurysm: A Uniaxial Extension Study

Abstract Mechanical analysis has the potential to provide complementary information to aneurysm morphology in assessing its vulnerability. Reliable calculations require accurate material properties of individual aneurysmal components. Quantification of extreme extensibility and ultimate material strength of the tissue are important if rupture is to be modelled. Tissue pieces from 11 abdomen aortic aneurysm (AAA) from patients scheduled for elective surgery and from 8 normal aortic artery (NAA) from patients who scheduled for kidney/liver transplant were collected at surgery and banked in liquid nitrogen with the use of Cryoprotectant solution to minimize frozen damage. Prior to testing, specimen were thawed and longitudinal and circumferential tissue strips were cut from each piece and adventitia, media and thrombus if presented were isolated for the material test. The incremental Young’s modulus of adventitia of NAA was direction-dependent at low stretch levels, but not the media. Both adventitia and media had a similar extreme extensibility in the circumferential direction, but the adventitia was much stronger. For aneurysmal tissues, no significant differences were found when the incremental moduli of adventitia, media or thrombus in both directions were compared. Adventitia and media from AAA had similar extreme extensibility and ultimate strength in both directions and thrombus was the weakest material. Adventitia and media from AAA were less extensible compared with those of NAA, but the ultimate strength remained similar. The material properties, including extreme extensibility and ultimate strength, of both healthy aortic and aneurysmal tissues were layer-dependent, but not direction-dependent.

Treatment of type I endoleak after endovascular repair of infrarenal abdominal aortic aneurysm: success of fibrin glue sac embolization.

Purpose: To analyze a single-center experience of fibrin glue sac embolization to eliminate type I endoleaks after endovascular aneurysm repair (EVAR), assessing the feasibility and effectiveness of the technique in long-term follow-up. Methods: A retrospective study was conducted involving 783 EVAR patients treated between August 2002 and February 2009. Under a standardized protocol, 42 (5.4%) patients (37 men; mean age 73±8 years) underwent intraoperative transcatheter fibrin glue sac embolization to resolve type I endoleak persisting after initial intraoperative maneuvers to close the leak or in necks too short or angulated for cuff placement. Intrasac pressure was measured before and after glue injection. Computed tomographic angiography was performed to assess the outcome after 3, 6, and 12 months and annually thereafter. Results: In this type I endoleak cohort, 16 (38.1%) patients had proximal necks <10 mm long, and 5 (11.9%) patients had proximal neck angulation >60°; 22 additional devices (8 stents, 14 cuffs) had been placed in the initial attempts to resolve the endoleaks. After fibrin glue injection, 41 (97.6%) of the 42 endoleaks were resolved using a mean 15±10 mL of glue. Intrasac pressure decreased significantly in successfully treated cases. The patient who failed embolotherapy was converted to open surgery (2.4%); he died 2 months later from multiorgan failure. Two (4.8%) patients died in the perioperative period from myocardial infarction. One (2.4%) patient developed right lower extremity ischemia unrelated to the fibrin glue treatment. There were no allergic reactions. Over a median follow-up of 39.9 months (range 10–88), 3 (7.1%) patients died (1 aneurysm-related). Cumulative survival was 90.5% at 1 year, 87.0% at 3 years, and 82.6% at 5years. The mean maximal aneurysm diameter fell from the baseline 59.5±14.7 mm to 49.0±11.6 mm (p<0.001). Of the 4 patients with increased aneurysm diameter during follow-up, 1 was converted, 2 are being observed due to advanced age, and 1 died of renal failure. No recurrent type I endoleak or glue-related complications were observed in follow-up. Conclusion: Fibrin glue sac embolization to eliminate type I endoleak after EVAR yielded excellent results in our experience, effectively and durably resolving the leaks. Balloon occlusion of the proximal aorta must be done during glue injection to block proximal flow and facilitate formation of a structured fibrin clot.

A uni-extension study on the ultimate material strength and extreme extensibility of atherosclerotic tissue in human carotid plaques.

Atherosclerotic plaque rupture occurs when mechanical loading exceeds its material strength. Mechanical analysis has been shown to be complementary to the morphology and composition for assessing vulnerability. However, strength and stretch thresholds for mechanics-based assessment are currently lacking. This study aims to quantify the ultimate material strength and extreme extensibility of atherosclerotic components from human carotid plaques. Tissue strips of fibrous cap, media, lipid core and intraplaque hemorrhage/thrombus were obtained from 21 carotid endarterectomy samples of symptomatic patients. Uni-extension test with tissue strips was performed until they broke or slid. The Cauchy stress and stretch ratio at the peak loading of strips broken about 2 mm away from the clamp were used to characterize their ultimate strength and extensibility. Results obtained indicated that ultimate strength of fibrous cap and media were 158.3 [72.1, 259.3] kPa (Median [Inter quartile range]) and 247.6 [169.0, 419.9] kPa, respectively; those of lipid and intraplaque hemorrhage/thrombus were 68.8 [48.5, 86.6] kPa and 83.0 [52.1, 124.9] kPa, respectively. The extensibility of each tissue type were: fibrous cap – 1.18 [1.10, 1.27]; media – 1.21 [1.17, 1.32]; lipid – 1.25 [1.11, 1.30] and intraplaque hemorrhage/thrombus – 1.20 [1.17, 1.44]. Overall, the strength of fibrous cap and media were comparable and so were lipid and intraplaque hemorrhage/thrombus. Both fibrous cap and media were significantly stronger than either lipid or intraplaque hemorrhage/thrombus. All atherosclerotic components had similar extensibility. Moreover, fibrous cap strength in the proximal region (closer to the heart) was lower than that of the distal. These results are helpful in understanding the material behavior of atherosclerotic plaques.

Influence of material property variability on the mechanical behaviour of carotid atherosclerotic plaques: a 3D fluid-structure interaction analysis.

Mechanical analysis has been shown to be complementary to luminal stenosis in assessing atherosclerotic plaque vulnerability. However, patient-specific material properties are not available and the effect of material properties variability has not been fully quantified. Media and fibrous cap (FC) strips from carotid endarterectomy samples were classified into hard, intermediate and soft according to their incremental Youngs modulus. Lipid and intraplaque haemorrhage/thrombus strips were classified as hard and soft. Idealised geometry-based 3D fluid-structure interaction analyses were performed to assess the impact of material property variability in predicting maximum principal stress (Stress-P1) and stretch (Stretch-P1). When FC was thick (1000 or 600 µm), Stress-P1 at the shoulder was insensitive to changes in material stiffness, whereas Stress-P1 at mid FC changed significantly. When FC was thin (200 or 65 µm), high stress concentrations shifted from the shoulder region to mid FC, and Stress-P1 became increasingly sensitive to changes in material properties, in particular at mid FC. Regardless of FC thickness, Stretch-P1 at these locations was sensitive to changes in material properties. Variability in tissue material properties influences both the location and overall stress/stretch value. This variability needs to be accounted for when interpreting the results of mechanical modelling.

A Pilot Study Exploring the Mechanisms Involved in the Longitudinal Propagation of Acute Aortic Dissection through Computational Fluid Dynamic Analysis

Objective: This study sought to elucidate the underlying hemodynamic mechanisms involved in the longitudinal propagation of acute, type-B aortic dissections. Methods: Three-dimensional patient-specific aortic geometry was reconstructed from computed tomography images of 3 cases, followed by computational fluid dynamic analysis using finite-element analysis modeling. Three models were reconstructed; the normal-aortic model (from a healthy volunteer), the visceral-involvement model (from a patient whose visceral arteries were involved) and the progression model (from a patient whose visceral arteries were intact at admission). Wall pressure distribution was analyzed in all three models. Results: In the systolic phase of a cardiac cycle, the wall pressure dropped from the proximal to the distal aorta within the true lumen. This pressure gradient was observed in all three models. A milder pressure gradient was seen in the false lumen in the visceral-involvement model, whereas the pressure in the false lumen remained almost constant in the progression model. The dyssynchrony of the pressure gradients in the true and false lumens caused an imbalance in pressure between the two lumens. Conclusion: The interluminal pressure differential may be a contributing factor in the compression of the true lumen and the cleavage force of the aortic wall, leading to the longitudinal propagation of the dissection.