Tear size and location impacts false lumen pressure in an ex vivo model of chronic type B aortic dissection

Vertebral Artery Stump Syndrome Due to Chronic Complicated Aortic Dissection

BACKGROUND

Vertebral artery (VA) stump syndrome arises when thrombi of an occluded proximal VA propagate to the brain and cause posterior circulation strokes. This phenomenon has been described in limited reports to date.

CASE DESCRIPTION

A 39-year-old man with a remote history of endovascular repair of a type B aortic dissection experienced type Ia endoleak causing expansion of the false lumen associated with the dissection. This required combined open debranching and endovascular reconstruction of the thoracic aortic arch. He experienced recurrent posterior circulation strokes 6 months postoperatively. The left VA origin was occluded and remained sequestered to the proximal subclavian artery, in continuity with the false lumen of the dissection. We suspected the aortic dissection extended into the VA and caused the occlusion, while pressure from the false lumen propelled thrombi from the occluded VA stump into the posterior circulation. Repeat imaging shortly after symptom onset showed spontaneous recanalization of the VA. Open surgical ligation of the proximal left VA led to symptom resolution.

CONCLUSIONS

We describe a unique mechanism of VA stump syndrome due to VA occlusion and pressure waves from an aortic dissection and present the first report of VA stump syndrome treatment by surgical exclusion of the VA.

Role of proximal and distal tear size ratio in hemodynamic change of acute type A aortic dissection

Background

Acute type A aortic dissection (ATAAD) is a life-threatening disease. The aim of this study was to examine the role of tear size in the hemodynamic change and help improve the treatment level of this extremely dangerous disease.

Methods

A total of 120 ATAAD patients treated in our institution from November 2014 to December 2016 were divided into three groups according to proximal and distal tear size ratio (PDTSR). There were 35 patients in group A (PDTSR ≥2:1), 44 patients in group B (1:2< PDTSR <2:1), and 41 patients in Group C (PDTSR ≤1:2). Three computational fluid dynamics (CFD) models with different PDTSRs were established to investigate the hemodynamic difference in the three groups.

Results

The mean age (± SD) of the 120 patients included in this study was 47.7±10.1 years. Patients in Group A had a significantly larger proximal tear size (219.1±76.5 vs. 127.7±70.1 vs. 75.7±49.7 mm²; P<0.001). The mortality of the patients in group A was significantly higher than those in group B and group C in the acute phase (37.1% vs. 2.3% vs. 2.4%, respectively; P<0.001). A proximal tear larger than a distal tear was found to be significantly associated with preoperative death in logistic regression analysis (odds ratio: 15.89; 95% confidence interval, 2.702-93.477; P=0.002).

Conclusions

A proximal tear larger than a distal tear was associated with a significantly high-pressure difference between false and true lumens and more blood flow into the false lumen. In such cases, patients would experience extremely high mortality and morbidity.

The Influence of Aortic Wall Elasticity on the False Lumen in Aortic Dissection: An In Vitro Study

BACKGROUND

Hemodynamics, dissection morphology, and aortic wall elasticity have a major influence on the pressure in the false lumen. In contrast to aortic wall elasticity, the influence of hemodynamics and dissection morphology have been investigated often in multiple in vitro and ex vivo studies. The purpose of this study was to evaluate the influence of aortic wall elasticity on the diameter and pressure of the false lumen in aortic dissection.

METHODS

An artificial dissection was created in 3 ex vivo porcine aortas. The aorta models were consecutively positioned in a validated in vitro circulatory system with physiological pulsatile flow. Each model was imaged with ultrasound on 4 positions along the aorta and the dissection. At these 4 locations, pressure measurement was also performed in the true and false lumen with an arterial catheter. After baseline experiments, the aortic wall elasticity was adjusted with silicon and the experiments were repeated.

RESULTS

The aortic wall elasticity was decreased in all 3 models after siliconizing. In all 3 siliconized models, the diameters of the true and false lumen increased at proximal, mid, and distal location, while the mean arterial pressure did not significantly change.

CONCLUSIONS

In this in vitro study, we showed that aortic wall elasticity is an important parameter altering the false lumen. An aortic wall with reduced elasticity results in an increased false lumen diameter in the mid and distal part of the false lumen. These results can only be transferred to corresponding clinical situations to a limited extent.

The effect of the entry and re-entry size in the aortic dissection: a two-way fluid-structure interaction simulation

Aortic dissection (AD) is one of the most catastrophic cardiovascular diseases. AD occurs when a layer inside the aorta is disrupted and gives rise to the formation of a true lumen and a false lumen. These lumens can be connected through tears in the intimal flap which are known as entries. Despite being known for about two centuries, the effects of many factors on the morbidity and mortality of this disease are still unknown. As the blood interaction with the aorta is crucial in the severity and the progression of the aortic dissection, a biomechanical approach is chosen to investigate the influence of different morphologies on the severity of this disease. Using the finite element method (FEM) and the fluid-structure interaction (FSI) approach, we have evaluated the blood flow characteristics along the diseased aorta, in conjunction with the deformation of the aortic wall. In this study, an idealized geometry of a dissected descending aorta (type B) with two entries has been studied. The values for the diameter of the entry tear were chosen to be 5 mm and 10 mm. Therefore, a total of four conditions were investigated. According to our results, the retrograde flow through the proximal tear is dependent on the size of the distal re-entry and vice versa. Our results revealed that when both entry and re-entry tears are 10 mm in diameter, the flow passes through the true and false lumens with smaller resistance, resulting in a smaller flutter of the intimal flap, and therefore more stable intimal flap. Major oscillation frequencies of 2.5 Hz and 7.4 Hz were observed for the oscillation of the intimal flap, and amplitudes of the waves with higher frequencies were negligible.

CT Angiography Findings Predictive of Kidney Injury in Chronic Aortic Dissection

OBJECTIVE. The purpose of this study was to compare the volume alteration and effective renal plasma flow of kidneys supplied by false lumens (FLs) with those of kidneys supplied by true lumens (TLs), to show the discrepancy in perfusion between the two lumens. We sought to corroborate malperfusion of FL-supplied kidneys with imaging characteristics observed on CT angiography. MATERIALS AND METHODS. A retrospective analysis was conducted using prospectively collected data for 87 patients with a diagnosis of residual chronic aortic dissection between 2005 and 2013 who had one kidney perfused by a TL and the other kidney perfused by a FL. RESULTS. Overall, at follow-up, FL-supplied kidneys had a mean (± SD) effective renal plasma flow (117.5 ± 42.6 vs 146.6 ± 41.0 mL/min; p = 0.004) and volume (131.1 ± 37.1 vs 146.5 ± 33.3 cm³; p = 0.004) that were lower than those of TL-supplied kidneys. Multivariate analysis revealed the presence of a proximal major inlet (odds ratio, 0.306; 95% CI, 0.103-0.910; p = 0.033) and large FL area (odds ratio, 0.104; CI, 0.012-0.880; p = 0.038) as factors protecting against malperfusion of FL-supplied kidneys. In patients with dissected renal arteries, the FL-supplied kidney had low effective renal plasma flow (mean, 88.5 ± 26.8 vs 149.6 ± 43.5 mL/min; p = 0.004) and diminished volume (mean, 120.4 ± 30.4 vs 152.3 ± 24.6 cm³; p = 0.001). CONCLUSION. In the present study, kidneys perfused by FLs showed decreased volume and reduced effective renal plasma flow during follow-up, particularly those kidneys with dissected renal arteries, a small FL area at the renal level, and lack of a proximal major inlet. Further studies are warranted to identify the clinical relevance of malperfusion in FL-supplied kidneys.

Pre-emptive thoracic endovascular aortic repair is unnecessary in extended type A (DeBakey type I) aortic dissections

OBJECTIVE

Pre-emptive thoracic endovascular aortic repair (TEVAR) improves late survival and limits progression of disease after type B aortic dissection, but the potential value of pre-emptive TEVAR has not been evaluated after type A dissection extending beyond the aortic arch (DeBakey type I). The purpose of this study was to compare disease progression and need for aortic intervention in survivors of acute, extended type A (ExTA) dissections after initial repair of the ascending aorta versus acute type B aortic dissections.

METHODS

Consecutive patients presenting with ExTA or type B dissections between 2011 and 2018 were studied. Forty-three patients with ExTA and 44 with type B dissections who survived to discharge and had follow-up imaging studies were included in the analysis. Study end points included progression of aortic disease (>5 mm growth or extension), need for intervention, and death.

RESULTS

The groups were not different for age, sex, atherosclerotic risk factors, or extent of dissection distal to the left subclavian artery. Following emergent ascending aortic repair, five ExTA patients (12%) underwent TEVAR within 4 months after discharge. Despite optimal medical treatment, 29 type B patients (66%) underwent early or late TEVAR (P < .001). During a mean follow-up of 38 ± 30 months, 38 ExTA patients (88%) did not require intervention-23 (53%) of whom showed no disease progression. In comparison, during a mean follow-up of 18 ± 6 months, 14 type B patients (32%) did not require intervention-nine (20%) of whom showed no disease progression (P = .003). There was one aortic-related late death in the ExTA group and two in the type B group. Compared with ExTA patients, type B patients had significantly worse intervention-free survival and intervention/growth-free survival (log rank, P < .001).

CONCLUSIONS

In contrast with type B dissections, these midterm results demonstrate that one-half of ExTA aortic dissections show no disease progression in the thoracic or abdominal aorta, and few require additional interventions. After initial repair of the ascending aorta, pre-emptive TEVAR does not seem to be justified in patients with acute, ExTA dissections.

Fluid-structure interaction simulations of patient-specific aortic dissection

Credible computational fluid dynamic (CFD) simulations of aortic dissection are challenging, because the defining parallel flow channels-the true and the false lumen-are separated from each other by a more or less mobile dissection membrane, which is made up of a delaminated portion of the elastic aortic wall. We present a comprehensive numerical framework for CFD simulations of aortic dissection, which captures the complex interplay between physiologic deformation, flow, pressures, and time-averaged wall shear stress (TAWSS) in a patient-specific model. Our numerical model includes (1) two-way fluid-structure interaction (FSI) to describe the dynamic deformation of the vessel wall and dissection flap; (2) prestress and (3) external tissue support of the structural domain to avoid unphysiologic dilation of the aortic wall and stretching of the dissection flap; (4) tethering of the aorta by intercostal and lumbar arteries to restrict translatory motion of the aorta; and a (5) independently defined elastic modulus for the dissection flap and the outer vessel wall to account for their different material properties. The patient-specific aortic geometry is derived from computed tomography angiography (CTA). Three-dimensional phase contrast magnetic resonance imaging (4D flow MRI) and the patient's blood pressure are used to inform physiologically realistic, patient-specific boundary conditions. Our simulations closely capture the cyclical deformation of the dissection membrane, with flow simulations in good agreement with 4D flow MRI. We demonstrate that decreasing flap stiffness from [Formula: see text] to [Formula: see text] kPa (a) increases the displacement of the dissection flap from 1.4 to 13.4 mm, (b) decreases the surface area of TAWSS by a factor of 2.3, (c) decreases the mean pressure difference between true lumen and false lumen by a factor of 0.63, and (d) decreases the true lumen flow rate by up to 20% in the abdominal aorta. We conclude that the mobility of the dissection flap substantially influences local hemodynamics and therefore needs to be accounted for in patient-specific simulations of aortic dissection. Further research to accurately measure flap stiffness and its local variations could help advance future CFD applications.

Computational modeling of the fluid flow in type B aortic dissection using a modified finite element embedded formulation

This work explores the use of an embedded computational fluid dynamics method to study the type B aortic dissection. The use of the proposed technique makes it possible to easily test different intimal flap configurations without any need of remeshing. To validate the presented methodology, we take as reference test case an in vitro experiment present in the literature. This experiment, which considers several intimal flap tear configurations (number, size and location), mimics the blood flow in a real type B aortic dissection. We prove the correctness and suitability of the presented approach by comparing the pressure values and waveform. The obtained results exhibit a remarkable similarity with the experimental reference data. Complementary, we present a feasible surgical application of the presented computer method. The aim is to help the clinicians in the decision making before the type B aortic dissection surgical fenestration. The capabilities of the proposed technique are exploited to efficiently create artificial reentry tear configurations. We highlight that only the radius and center of the reentry tear need to be specified by the clinicians, without any need to modify neither the model geometry nor the mesh. The obtained computational surgical fenestration results are in line with the medical observations in similar clinical studies.

The application of computational modeling for risk prediction in type B aortic dissection

OBJECTIVE

New tools are urgently needed to help with surgical decision-making in type B aortic dissection (TBAD) that is uncomplicated at the time of initial presentation. This narrative review aims to answer the clinical question, Can computational modeling be used to predict risk in acute and chronic Stanford TBAD?

METHODS

The review (PROSPERO 2018 CRD42018104472) focused on risk prediction in TBAD. A comprehensive search of the Ovid MEDLINE database, using terms related to computational modeling and aortic dissection, was conducted to find studies of any form published between 1998 and 2018. Cohort studies, case series, and case reports of adults (older than 18 years) with computed tomography or magnetic resonance imaging diagnosis of TBAD were included. Computational modeling was applied in all selected studies.

RESULTS

There were 37 studies about computational modeling of TBAD identified from the search, and the findings were synthesized into a narrative review. Computational modeling can produce numerically calculated values of stresses, pressures, and flow velocities that are difficult to measure in vivo. Hemodynamic parameters-high or low wall shear stress, high pressure gradient between lumens during the cardiac cycle, and high false lumen flow rate-have been linked to the pathogenesis of branch malperfusion and aneurysm formation by numerous studies. Considering the major outcomes of end-organ failure, aortic rupture, and stabilization and remodeling, hypotheses have been generated about inter-relationships of measurable parameters in computational models with observable anatomic and pathologic changes, resulting in specific clinical outcomes.

CONCLUSIONS

There is consistency in study findings about computational modeling in TBAD, although a limited number of patients have been analyzed using various techniques. The mechanistic patterns of association found in this narrative review should be investigated in larger cohort prospective studies to further refine our understanding. It highlights the importance of patient-specific computational hemodynamic parameters in clinical decision-making algorithms. The current challenge is to develop and to test a risk assessment method that can be used by clinicians for TBAD.

Effects of circulating levels of Th17 cells on the outcomes of acute Stanford B aortic dissection patients after thoracic endovascular aortic repair: A 36-month follow-up study a cohort study

T helper 17 (Th17) cells are related to the progression of aortic dissection. This study aimed to determine whether circulating Th17 levels are associated with the prognosis of acute Stanford type B aortic dissection (STBAD) after thoracic endovascular aortic repair (TEVAR).A cohort study was performed and STBAD patients (n = 140) received TEVAR were enrolled, the circulating Th17 levels were measured and the patients were divided into low and high Th17 groups, and 36 months of follow-up was performed. The data for mortality, survival outcomes, heart structure and function changes, aortic regurgitation prevalence, and aortic remodeling outcomes were recorded.Lower mortality and fewer complications were observed in the low Th17 group than in the high Th17 group in the third year of follow-up. In addition, the low Th17 group exhibited better cardiac remodeling and cardiac function when compared with that in the high Th17 group in the second to third year after TEVAR. Aortic reflux was improved in both groups but was more pronounced in the low Th17 group. During follow-up, the true lumen of the proximal thoracic aorta at the level of the celiac trunk in both the low and high Th17 groups continuously enlarged and was more pronounced in the low Th17 group.Circulating Th17 cells were related to cardiac and aortic remodeling and prognosis during STBAD after TEVAR. Anti-inflammatory therapy may be useful for STBAD patients who have undergone TEVAR.

Highly integrated workflows for exploring cardiovascular conditions: Exemplars of precision medicine in Alzheimer's disease and aortic dissection

For precision medicine to be implemented through the lens of in silico technology, it is imperative that biophysical research workflows offer insight into treatments that are specific to a particular illness and to a particular subject. The boundaries of precision medicine can be extended using multiscale, biophysics-centred workflows that consider the fundamental underpinnings of the constituents of cells and tissues and their dynamic environments. Utilising numerical techniques that can capture the broad spectrum of biological flows within complex, deformable and permeable organs and tissues is of paramount importance when considering the core prerequisites of any state-of-the-art precision medicine pipeline. In this work, a succinct breakdown of two precision medicine pipelines developed within two Virtual Physiological Human (VPH) projects are given. The first workflow is targeted on the trajectory of Alzheimer's Disease, and caters for novel hypothesis testing through a multicompartmental poroelastic model which is integrated with a high throughput imaging workflow and subject-specific blood flow variability model. The second workflow gives rise to the patient specific exploration of Aortic Dissections via a multi-scale and compliant model, harnessing imaging, computational fluid-dynamics (CFD) and dynamic boundary conditions. Results relating to the first workflow include some core outputs of the multiporoelastic modelling framework, and the representation of peri-arterial swelling and peri-venous drainage solution fields. The latter solution fields were statistically analysed for a cohort of thirty-five subjects (stratified with respect to disease status, gender and activity level). The second workflow allowed for a better understanding of complex aortic dissection cases utilising both a rigid-wall model informed by minimal and clinically common datasets as well as a moving-wall model informed by rich datasets.

Computational modeling of the fluid flow and the flexible intimal flap in type B aortic dissection via a monolithic arbitrary Lagrangian/Eulerian fluid-structure interaction model

In the present work, we perform numerical simulations of the fluid flow in type B aortic dissection (AD), accounting for the flexibility of the intimal flap. The interaction of the flow with the intimal flap is modeled using a monolithic arbitrary Lagrangian/Eulerian fluid-structure interaction model. The model relies on choosing velocity as the kinematic variable in both domains (fluid and solid) facilitating the coupling. The fluid flow velocity and pressure evolution at different locations is studied and compared against the experimental evidence and the formerly published numerical simulation results. Several tear configurations are analyzed. Details of the fluid flow in the vicinity of the tears are highlighted. Influence of the tear size upon the fluid flow and the flap deformation is discussed.

Intramural hematoma and penetrating atherosclerotic ulcers of the aorta: uncertainties and controversies

The natural histories of intramural hematoma (IMH) and penetrating atherosclerotic ulcer (PAU) are highly variable as they may progress to aneurysm formation, rupture, or dissection, or even resolve, in the specific case of IMH. Imaging plays an increasingly important role in clinical and surgical management of IMH and PAU. In contrast to ulcer-like projections, images of intramural blood pools have not been widely reported in CT studies of patients with IMH. Understanding the imaging characteristics and the natural course of each of these entities would help clinicians and surgeons to identify patients at greatest risk for bad prognosis and may improve outcomes. This paper discusses the pathophysiology of these entities, the controversies regarding their natural history, and the prognostic factors that should be identified in CT scans.

Intermediate fenestrations reduce flow reversal in a silicone model of Stanford Type B aortic dissection

Pulsatile, three-dimensional hemodynamic forces influence thrombosis, and may dictate progression of aortic dissection. Intimal flap fenestration and blood pressure are clinically relevant variables in this pathology, yet their effects on dissection hemodynamics are poorly understood. The goal of this study was to characterize these effects on flow in dissection models to better guide interventions to prevent aneurysm formation and false lumen flow. Silicone models of aortic dissection with mobile intimal flap were fabricated based on patient images and installed in a flow loop with pulsatile flow. Flow fields were acquired via 4-dimensional flow MRI, allowing for quantification and visualization of relevant fluid mechanics. Pulsatile vortices and jet-like structures were observed at fenestrations immediately past the proximal entry tear. False lumen flow reversal was significantly reduced with the addition of fenestrations, from 19.2 ± 3.3% in two-tear dissections to 4.67 ± 1.5% and 4.87 ± 1.7% with each subsequent fenestration. In contrast, increasing pressure did not cause appreciable differences in flow rates, flow reversal, and vortex formation. Increasing the number of intermediate tears decreased flow reversal as compared to two-tear dissection, which may prevent false lumen thrombosis, promoting persistent false lumen flow. Vortices were noted to result from transluminal fluid motion at distal tear sites, which may lead to degeneration of the opposing wall. Increasing pressure did not affect measured flow patterns, but may contribute to stress concentrations in the aortic wall. The functional and anatomic assessment of disease with 4D MRI may aid in stratifying patient risk in this population.

Locational impact of luminal communication on aortic diameter changes and reintervention in acute type I aortic dissection

OBJECTIVES

The aim of this study is to evaluate the locational impact of a luminal communication on aortic diameter changes and reintervention after surgical repair of acute type I aortic dissection.

METHODS

Between 2009 and 2017, 304 patients underwent operation for acute type I aortic dissection. Among them, 93 patients were enrolled. The luminal communications were analysed in segment 1 (the proximal descending thoracic aorta), segment 2 (the distal descending thoracic aorta) and segment 3 (the abdominal aorta). The aortic diameter was measured at the pulmonary artery bifurcation, coeliac axis, maximal abdominal aorta and maximal thoraco-abdominal aorta using serial follow-up computed tomography scans. The linear mixed model was used, and the rate of freedom from reintervention was analysed.

RESULTS

In the adjusted analysis, the initial diameter of the maximal abdominal aorta and the first luminal communication in segment 1 was statistically significant. However, the slope value of the maximal abdominal aorta was smaller than that of the first luminal communication in segment 1 (0.024 vs 0.198). The 3-year freedom from reintervention rate was significantly higher in patients without a luminal communication than in those with an initial luminal communication in segment 1 (96% vs 47%, log rank, P = 0.003).

CONCLUSIONS

A luminal communication at the proximal descending thoracic aorta (segment 1) is a significant factor for an increasing aortic diameter and reintervention after surgical repair of acute type I aortic dissection.

Proposed classification of endoleaks after endovascular treatment of Stanford type-B aortic dissections

Objectives

Despite two decades of experience, no dedicated classification system exists to document and prognosticate patterns of endoleak encountered after endovascular therapy of type-B aortic dissection. This nomenclature gap has led to inconsistent management and underreporting of significant findings associated with adverse outcomes after endovascular treatment of type-B aortic dissection. Our goal was to propose a reproducible and prognostically relevant classification.

Methods

A multidisciplinary team of seven experienced open and endovascular aortic surgeons was assembled to provide consensus opinion. Extensive literature review was conducted. Deficiencies in the current classification approach of the various patterns of persistent filling of false lumen after endovascular therapy were identified.

Results

Our focus was to categorize high-risk and low-risk subgroups within endoleaks after endovascular treatment of type-B aortic dissection. In this classification, type-Ia endoleak refers to persistent filling of the false lumen in an antegrade manner. Causes include failure to cover the primary entry tear and sizing or technical related proximal seal failure. False lumen filling via distal entry tears is classified as type Ib endoleak, which is further sub-classified into b1 (major branch-related tears), and b2 (multiple small branches related tears). Retrograde ascending aortic dissection and stent graft-induced new entry were classified as type-I endoleaks (type-Ir and type-Is, respectively). Another focus was reclassification type-II endoleaks, with type-IIa endoleak referring to conventional retroleak from one or more posterior branches and type-IIx referring to retroleak from major branches (visceral or left subclavian arteries).

Conclusions

The majority of endoleaks after endovascular treatment of type-B aortic dissection are related to persistent or new filling of the false lumen. We propose a new false lumen-based classification schema for endoleaks occurring after endovascular therapy of type-B aortic dissection.

Experimental Insight into the Hemodynamics and Perfusion of Radiological Contrast in Patent and Non-patent Aortic Dissection Models

PURPOSE

In a curved vessel such as the aortic arch, the velocity profile closer to the aortic root is normally skewed towards the inner curvature wall, while further downstream along the curve, the velocity profile becomes skewed towards the outer wall. In an aortic dissection (AD) disease, blood velocities in the true lumen (TL) and false lumen (FL) are hypothesized to depend on the proximity of the entry tear to the root of aortic arch. Faster velocity in the FL can lead to higher hemodynamic loading, and pose tearing risk. Furthermore, the luminal velocities control the perfusion rate of radiological contrast media during diagnostic imaging. The objective in this study is to investigate the effect of AD disease morphology and configuration on the blood velocity field in the TL and FL, and on the relative perfusion of radiological enhancement agents through the dissection.

METHODS

Eight in vitro models were studied, including patent and non-patent FL configurations. Particle image velocimetry (PIV) was used to quantify the AD velocity field, while laser-induced fluorescence (LIF) was implemented to visualize dynamical flow phenomena and to quantify the perfusion of injected dye, in mimicry of contrast-enhanced computed tomography (CT).

RESULTS

The location of the proximal entry tear along the aortic arch in a patent FL had a dramatic impact on whether the blood velocity was higher in the TL or FL. The luminal velocities were dependent on the entry/reentry tear size combination, with the smaller tear (whether distal or proximal) setting the upper limit on the maximal flow velocity in the FL. Upon merging near the distal reentry tear, the TL/FL velocity differential gave rise to the roll up and shedding of shear layer vortices that convected downstream in close proximity to the wall of the non-dissected aorta. In a non-patent FL, the flow velocity was practically null with all the blood passing through the TL. LIF imaging showed much slower perfusion of contrast dye in the FL compared to the TL. In a patent FL, however, dye had a comparable perfusion rate appearing around the same time as in the TL.

CONCLUSIONS

Blood velocities in the TL and FL were highly sensitive to the exact dissection configuration. Geometric case A1R, which had its proximal entry tear located further downstream along the aortic arch, and had its entry and reentry tears sufficiently sized, exhibited the highest FL flow velocity among the tested models, and it was also higher than in the TL, which suggest that this configuration had elevated hemodynamic loading and risk for tearing. In contrast-enhanced diagnostic imaging, a time-delayed acquisition protocol is recommended to improve the detection of suspected cases with a non-patent FL.

A Novel Pulse Damper for Endothelial Cell Flow Bioreactors

PURPOSE

Peristaltic pumps (PP) are favored in flow bioreactors for their non-contact sterile design. But they produce pulsatile flow, which is consequential for the cultured cells. A novel pulse damper (PD) is reported for pulsatility elimination.

METHODS

The PD design was implemented to target static pressure pulsatility and flow rate (velocity) pulsatility from a PP. Damping effectiveness was tested in a macro-scale, closed-loop recirculating bioreactor mimicking the aortic arch at flow rates up to (4 L/min). Time-resolved particle image velocimetry was used to characterize the velocity field. Endothelial cells (EC) were grown in the bioreactor, and subjected to continuous flow for 15 min with or without PD.

RESULTS

The PD was found to be nearly 90% effective at reducing pulsatility. The EC exposed to low PP flow without PD exhibited distress signaling in the form of increased ERK1/2 phosphorylation (2.5 folds) when compared to those exposed to the same flow with PD. At high pump flow without PD, the cells detached and did not survive, while they were perfectly healthy with PD.

CONCLUSIONS

Flow pulsatility from PP causes EC distress at low flow and cell detachment at high flow. Elevated temporal shear stress gradient combined with elevated shear stress magnitude at high flow are believed to be the cause of cell detachment and death. The proposed PD design was effective at minimizing the hemodynamic stressors in the pump's output, demonstrably reducing cell distress. Adoption of the proposed PD design in flow bioreactors should improve experimental protocols.

Should the distal tears of aortic dissection be treated? The risk of distal tears after proximal repair of aortic dissection

BACKGROUND

Patients with distal residual after proximal repair of aortic dissection (AD) have shown unsatisfactory long-term prognosis. However, possible mechanisms and risk factors for distal aortic segmental enlargement (DSAE) have been poorly understood.

METHODS

We analyzed 962 AD patients repaired to the descending aorta between 1999 and 2014. Aortic morphological characteristics of 419 patients (including 75 DSAE and 344 non-DSAE patients) were investigated and compared. Potential risk factors associated with DSAE were explored using logistic regression analysis or natural logarithmic transformation. Logistic multi regress equations were performed to identify independent risk factors.

RESULTS

Independent risk factors of DSAE are listed as follow: more tears in the thoracic descending aorta (odds ratio [OR], 1.65; 95% confidence interval [CI],1.24 to 2.19; P = .0005); fewer tears in the infra-renal abdominal aorta (OR, 3.00; 95% CI,2.04 to 4.55; P < .0001); closer distance of the first intimal tear to the left subclavian artery (OR, 1.51; 95% CI,1.28 to 1.69; P < .0001); larger average distance between tears (OR, 11.81; 95% CI,3.39 to 41.08; P = .0001); larger maximum distance between two tears (OR, 1.79; 95% CI,1.48 to 2.16; P < .0001), and larger area of remained tears (OR, 1.56; 95% CI, 1.38 to 1.76; P < .0001).

CONCLUSIONS

The location and size of remained tears are the key risk factors of DSAE patients. Long-segment aortic repair and aggressive exclusion of all distal tears located on the thoracic descending aorta in their initial therapy will be an optimal strategy.

Differential impact of intimal tear location on aortic dilation and reintervention in acute type I aortic dissection after total arch replacement

OBJECTIVE

The study objective was to evaluate the differential impact of intimal tear location on aortic dilation and reintervention after total arch replacement for acute type I aortic dissection.

METHODS

From 2009 to 2016, 85 patients underwent total arch replacement for acute type I aortic dissection with residual dissected thoracoabdominal aorta. Forty patients (47%) underwent serial computed tomography scans that were sufficient for analysis. Among these, 14 (35%) underwent total arch replacement via the frozen elephant trunk procedure. Intimal tears were analyzed (size and number) at 3 different levels (level 1, proximal descending thoracic aorta; level 2, distal descending thoracic aorta; level 3, abdominal aorta). Aortic diameter was measured at 4 levels (pulmonary artery bifurcation, celiac axis, maximal abdominal aorta, and maximal thoracoabdominal aorta) using serial follow-up computed tomography scans. The linear mixed model for a repeated-measures random intercept and slope model was used. The rate of freedom from reintervention was analyzed.

RESULTS

In the unadjusted analysis, initial diameter of pulmonary artery bifurcation level, number of intimal tears, presence of 3- or 5-mm intimal tears, and frozen elephant trunk were not significant factors for aortic dilation or shrinking. The significant factors for aortic dilation were intimal tear location and number of visceral branches from the false lumen. The 3-year freedom from reintervention rate was significantly higher in patients with intimal tears 3 mm or greater at level 3 than in those with tears at level 1 (94.1% vs 37.5%, log-rank, P < .001).

CONCLUSIONS

Intimal tear in the proximal descending thoracic aorta is the most important factor for aortic dilation and reintervention in acute type I aortic dissection after total arch replacement.

Computational tools for clinical support: a multi-scale compliant model for haemodynamic simulations in an aortic dissection based on multi-modal imaging data

Aortic dissection (AD) is a vascular condition with high morbidity and mortality rates. Computational fluid dynamics (CFD) can provide insight into the progression of AD and aid clinical decisions; however, oversimplified modelling assumptions and high computational cost compromise the accuracy of the information and impede clinical translation. To overcome these limitations, a patient-specific CFD multi-scale approach coupled to Windkessel boundary conditions and accounting for wall compliance was developed and used to study a patient with AD. A new moving boundary algorithm was implemented to capture wall displacement and a rich in vivo clinical dataset was used to tune model parameters and for validation. Comparisons between in silico and in vivo data showed that this approach successfully captures flow and pressure waves for the patient-specific AD and is able to predict the pressure in the false lumen (FL), a critical variable for the clinical management of the condition. Results showed regions of low and oscillatory wall shear stress which, together with higher diastolic pressures predicted in the FL, may indicate risk of expansion. This study, at the interface of engineering and medicine, demonstrates a relatively simple and computationally efficient approach to account for arterial deformation and wave propagation phenomena in a three-dimensional model of AD, representing a step forward in the use of CFD as a potential tool for AD management and clinical support.

The prognostic impact of distal anastomotic new entry after acute type I aortic dissection repair

OBJECTIVES

Distal anastomotic new entry (DANE) is considered to be one of the causes of patent false lumen (PFL) after acute type I aortic dissection repair. However, there have been few articles with regard to this important issue. We assessed the influence of PFL caused by DANE on long-term outcomes.

METHODS

One hundred twenty-two patients underwent emergency surgery for acute type I aortic dissection (2007-12). The in-hospital mortality was 8% (10 patients). Among the survivors, 93 patients (mean age 67 years) underwent enhanced computed tomography within 2 weeks after the operation. These patients were divided into 3 groups according to the status of the residual FL: those with a PFL with DANE (n = 19) or without DANE (n = 27) and those with a thrombosed FL (n = 47). Changes in descending aortic diameter were analysed between early and last follow-up images.

RESULTS

Aortic growth rate in the PFL with DANE group was greater than that of the other 2 groups (P < 0.05). The PFL with DANE group demonstrated a lower rate of freedom from dissection-related event of distal aorta (66% at 5 years) and enlargement of distal aortic lesions (62% at 5 years). There were no significant differences in late survival among the groups. PFL with DANE was one of the significant risk factors for distal aortic events.

CONCLUSIONS

PFL caused by DANE after acute type I aortic dissection repair showed greater aortic growth rate of the descending aorta and was one of the significant risk factors for distal aortic events.

Data-driven Modeling of Hemodynamics and its Role on Thrombus Size and Shape in Aortic Dissections

Aortic dissection is a pathology that manifests due to microstructural defects in the aortic wall. Blood enters the damaged wall through an intimal tear, thereby creating a so-called false lumen and exposing the blood to thrombogenic intramural constituents such as collagen. The natural history of this acute vascular injury thus depends, in part, on thrombus formation, maturation, and possible healing within the false lumen. A key question is: Why do some false lumens thrombose completely while others thrombose partially or little at all? An ability to predict the location and extent of thrombus in subjects with dissection could contribute significantly to clinical decision-making, including interventional design. We develop, for the first time, a data-driven particle-continuum model for thrombus formation in a murine model of aortic dissection. In the proposed model, we simulate a final-value problem in lieu of the original initial-value problem with significantly fewer particles that may grow in size upon activation, thus representing the local concentration of blood-borne species. Numerical results confirm that geometry and local hemodynamics play significant roles in the acute progression of thrombus. Despite geometrical differences between murine and human dissections, mouse models can provide considerable insight and have gained popularity owing to their reproducibility. Our results for three classes of geometrically different false lumens show that thrombus forms and extends to a greater extent in regions with lower bulk shear rates. Dense thrombi are less likely to form in high-shear zones and in the presence of strong vortices. The present data-driven study suggests that the proposed model is robust and can be employed to assess thrombus formation in human aortic dissections.

The impact of development of atherosclerosis on delamination resistance of the thoracic aortic wall

The aim of this work is to determine the impact of development of atherosclerosis on dissection of the human thoracic aorta on the basis of an analysis of the mechanical properties of the interfaces between its layers. The research material consisted of 17 pathologically unchanged aortae and 74 blood vessels with atherosclerotic lesions, which were classified according to the histological classification by Stary. The subject of the analysis were the interfaces between the adventitia and the media-intima complex (A-MIC) and between the intima and the media-adventitia complex (I-MAC). The mechanical properties of the above interfaces were determined by the peeling test in the longitudinal and circumferential directions. The results indicate that development of atherosclerosis reduces vessel wall resistance to delamination. The greatest risk of dissection occurs at stage IV of the disease. In this case, energy values are lower by about 28% for the I-MAC interface and by 39% for the A-MIC interface compared with normal tissues. Lower values of mean force and energy were obtained for the I-MAC interface, indicating that this interface is more susceptible to delamination. The mechanical properties of the A-MIC interfaces are directional.

Cluster analysis of acute ascending aortic dissection provides novel insight into mechanisms of distal progression

Background

Whether primary tear size impacts extent of type A dissection is unclear. Using statistical groupings based on dissection morphology, we examined its relationship to primary tear area.

Methods

We retrospectively reviewed 108 patients who underwent acute ascending dissection repair from 2000-2016. Dissection morphology was characterized using 3-dimensional (3D) reconstructions of computed tomography (CT) scan images. Two-step cluster analysis was performed to group the dissections by examining the true lumen area as a fraction of the total aortic area at various levels.

Results

Cluster analysis defined two distinct categories. This first grouping corresponds to DeBakey type I (n=71, 65.7%) with a dissection extending from the ascending aorta to the aortic bifurcation. The second grouping conforms more closely to DeBakey type II dissection (n=37, 34.3%). It differs however from the classic type II definition as the dissection may extend up to the distal arch from the ascending aorta. Compared to type I, this "extended" DeBakey type II had no malperfusion (P<0.05), a larger primary tear area (6.6 vs. 3.7 cm², P=0.009), and a greater burden of atherosclerotic coronary artery disease (P<0.05). A smaller aortic valve annulus (P=0.025) and a smaller root false lumen area (P=0.017) may explain less aortic valve insufficiency (P<0.05) in extended type II dissections. No differences in complications or survival were seen.

Conclusions

In this series, limited distal extension of DeBakey type II dissections appears to be related to a larger primary tear area and greater atherosclerotic disease burden. It is also associated with less malperfusion and aortic valve insufficiency.

Role of Re-entry Tears on the Dynamics of Type B Dissection Flap

Mortality during follow-up after acute Type B aortic dissection is substantial with aortic expansion observed in over 59% of the patients. Lumen pressure differential is considered a prime contributing factor for aortic dilation after propagation. The objective of the study was to evaluate the relationship between changes in vessel geometry with and without lumen pressure differential post propagation in an ex vivo porcine model with comparison with patient clinical data. A pulse duplicator system was utilized to propagate the dissection within descending thoracic porcine aortic vessels for set proximal (%circumference of the entry tear: 40%, axial length: 2 cm) and re-entry (50% of distal vessel circumference) tear geometry. Measurements of lumen pressure differential were made along with quantification of vessel geometry (n = 16). The magnitude of mean lumen pressure difference measured after propagation was low (~ 5 mmHg) with higher pressures measured in false lumen and as anticipated the pressure difference approached zero after the creation of distal re-entry tear. False lumen Dissection Ratio (FDR) defined as arc length of dissected wall divided by arc length of dissection flap, had mean value of 1.59 ± 0.01 at pressure of 120/80 mmHg post propagation with increasing values with increase in pulse pressure that was not rescued with the creation of distal re-entry tear (p < 0.01). An average FDR of 1.87 ± 0.27 was measured in patients with acute Type B dissection. Higher FDR value (FDR = 1 implies zero dissection) in the presence of distal re-entry tear demonstrates an acute change in vessel morphology in response to the dissection independent of local pressure changes challenges the re-apposition of the aortic wall.

Editor's Choice - Occurrence and Classification of Proximal Type I Endoleaks After EndoVascular Aneurysm Sealing Using the Nellix™ Device

OBJECTIVE/BACKGROUND

Proximal type I endoleaks are associated with abdominal aortic aneurysm (AAA) growth and rupture and necessitate repair. The Nellix™ EndoVascular Aneurysm Sealing (EVAS) system is a unique approach to AAA repair, where the appearance and treatment of endoleaks is also different. This study aimed to analyse and categorise proximal endoleaks in an EVAS treated cohort.

METHODS

All patients, treated from February 2013 to December 2015, in 15 experienced EVAS centres, presenting with proximal endoleak were included. Computed tomography scans were analysed by a core laboratory. A consensus meeting was organised to discuss and qualify each case for selection, technical aspects, and possible causes of the endoleak. Endoleaks were classified using a novel classification system for EVAS.

RESULTS

During the study period 1851 patients were treated using EVAS at 15 centres and followed for a median of 494 ± 283 days. Among these, 58 cases (3.1%) developed a proximal endoleak (1.5% early and 1.7% late); of these, 84% of 58 patients were treated outside the original and 96% outside the current, refined, instructions for use. Low stent positioning was the most likely cause in 44.6%, a hostile anatomy in 16.1%, and a combination of both in 33.9%. Treatment, by embolisation or proximal extension, was performed in 47% of cases, with a technical success of 97%.

CONCLUSION

The overall incidence of proximal endoleak after EVAS is 3.1% after a mean follow-up period of 16 months, with 1.5% occurring within 30 days. Their occurrence is related to patient selection and stent positioning. Early detection and classification is crucial to avoid the potential of sac rupture.

Influence of distal entry tears in acute type B aortic dissection after thoracic endovascular aortic repair

OBJECTIVE

This study evaluated the clinical influence of distal entry tears in acute type B aortic dissection (ATBAD) after thoracic endovascular aortic repair (TEVAR).

METHODS

From August 2009 to December 2014, the clinical outcomes of 130 patients who underwent TEVAR for ATBAD were retrospectively analyzed. According to whether distal entry tears existed after TEVAR, patients were divided into group A (n = 25, absence of distal entry tears) and group B (n = 105, presence of distal entry tears). We evaluated clinical outcomes, including mortality and morbidity in early and late follow-up, as well as aortic remolding. Late aortic events were defined as aortic dissection-related events occurring >30 days from the initial TEVAR procedures, which consisted of endoleak, retrograde type A aortic dissection, aortic enlargement, late rupture, repeat dissection, and stent-induced new entry tear.

RESULTS

The study comprised 130 patients (114 men [87.7%] and 16 women [12.3%)] with a mean age of 53.71 years. The 30-day mortality was 3.1%, and early morbidity included type I endoleak, 3.1%, organ failure, 3.8%; stroke, 3.1%; spinal cord ischemia, 0%; and early rupture 1.5%. The overall survival rate by Kaplan-Meier analysis at 1, 3, and 5 years was 93.8%, 89.5%, and 79.2%, respectively. There were no significant differences in early morbidity and 30-day mortality and late survival between group A and group B. However, group A had a significantly lower rate of late aortic events than group B (P = .028 by log-rank test). Meanwhile, group A had better aortic remolding than group B in complete thrombosis of the thoracic aorta at 12 months postoperatively (100% vs 83.5%; P = .029).

CONCLUSIONS

This study demonstrated that TEVAR for ATBAD had low perioperative morbidity and mortality and satisfactory midterm outcome. Distal entry tears increase the occurrence of late aortic events and inhibit aortic remolding but do not have a significantly negative effect on late survival. Repairing all entry tears to restore single-lumen blood flow and enhance false lumen thrombosis might benefit selected patients.

A Novel Insight into the Role of Entry Tears in Type B Aortic Dissection: Pressure Measurements in an in Vitro Model

Introduction

Predicting aortic growth in acute type B dissection is fundamental in planning interventions. Several factors are considered to be growth predictors in the literature and, among them, size and location of entry tears have been recognized to particularly influence the false lumen pressure. In this study, we develop an in vitro setting to analyze the actual impact of size and location of the entry tears on false lumen pressure, in the absence of other confounding factors such as the deformability of the aortic wall.

Methods

We formalize some indexes that synthetically describe the false lumen pressure with respect to the true lumen pressure. Then, we experimentally derive their values in several configurations of the in vitro setting, and we look for trends in the indexes with respect to the size and location of entry tears.

Results:

Results show that the tears have a relevant impact on the false lumen pressure, but that their size and location alone are not enough to explain the phenomena observed in vivo.

Conclusions

To predict the behavior of acute type B dissection, we therefore recommend not limiting to size and location, as many effects may derive from the interactions between these parameters and other patient characteristics.

False Lumen Flow Patterns and their Relation with Morphological and Biomechanical Characteristics of Chronic Aortic Dissections. Computational Model Compared with Magnetic Resonance Imaging Measurements

Aortic wall stiffness, tear size and location and the presence of abdominal side branches arising from the false lumen (FL) are key properties potentially involved in FL enlargement in chronic aortic dissections (ADs). We hypothesize that temporal variations on FL flow patterns, as measured in a cross-section by phase-contrast magnetic resonance imaging (PC-MRI), could be used to infer integrated information on these features. In 33 patients with chronic descending AD, instantaneous flow profiles were quantified in the FL at diaphragm level by PC-MRI. We used a lumped-parameter model to assess the changes in flow profiles induced by wall stiffness, tear size/location, and the presence of abdominal side branches arising from the FL. Four characteristic FL flow patterns were identified in 31/33 patients (94%) based on the direction of flow in systole and diastole: B_A = systolic biphasic flow and primarily diastolic antegrade flow (n = 6); B_R = systolic biphasic flow and primarily diastolic retrograde flow (n = 14); M_A = systolic monophasic flow and primarily diastolic antegrade flow (n = 9); M_R = systolic monophasic flow and primarily diastolic retrograde flow (n = 2). In the computational model, the temporal variation of flow directions within the FL was highly dependent on the position of assessment along the aorta. FL flow patterns (especially at the level of the diaphragm) showed their characteristic patterns due to variations in the cumulative size and the spatial distribution of the communicating tears, and the incidence of visceral side branches originating from the FL. Changes in wall stiffness did not change the temporal variation of the flows whereas it importantly determined intraluminal pressures. FL flow patterns implicitly codify morphological information on key determinants of aortic expansion in ADs. This data might be taken into consideration in the imaging protocol to define the predictive value of FL flows.

Computational Study of Anatomical Risk Factors in Idealized Models of Type B Aortic Dissection

OBJECTIVE/BACKGROUND

Several risk factors have been identified in type B aortic dissection (TBAD), namely tear size, location, patency and number, and false lumen (FL) location. However, the individual impact of each of these factors is poorly understood. The impact of these factors was investigated using computational fluid dynamics (CFD).

METHODS

Fourteen idealized models of chronic TBAD were created of different shapes (straight vs. curved vessels), different number of proximal and distal tears, tear size (4, 10, and 20 mm diameter) and shape (circular or elliptical), FL location (inner or outer arch), treated (stented), and untreated. All models had identical length, relative size of true lumen (TL) and FL, and inlet (flow) and outlet (pressure) boundary conditions. Using validated CFD tools, inlet mean pressure (MP), pulse pressure (PP), TL and FL pressures, velocities, and flows were computed for each model.

RESULTS

AD increased PP and MP relative to undissected aorta. Curvature did not change pressure and flow ratio between TL and FL. Inner curvature FL showed slightly larger pressures and tear velocities. Larger tears decreased hemodynamic differences between TL and FL. The combination of proximal and distal tear size determines the overall hemodynamics: larger proximal tears increased FL PP by up to 76%. Conversely, larger distal tears decreased FL PP and MP. Large proximal and distal tears decreased tear velocity (by up to 65%) and increased FL flow (up to 12 times). Proximal tear stenting resulted in a 54% reduction of PP. Conversely, distal occlusion tear increased FL PP and MP by 144% and 7%, respectively.

CONCLUSION

Unfavorable hemodynamic conditions such as larger FL pressure occur when distal tear is small or absent, proximal tears are large, and FL is at the inner curvature, in agreement with previous clinical studies. CFD analysis is a powerful tool to understand the interplay between anatomy and hemodynamics in TBAD.

Early distal remodeling after elephant trunk repair of thoraco-abdominal aortic aneurysms

Hemodynamic alterations occur when the elephant trunk (ET) technique is adopted to treat extensive aortic aneurysms. In planning the 2nd stage operation to complete ET repair, surgeons must weigh an adequate recovery time after initial surgery against the risk of postoperative ET-related complications. The purpose of this study was to understand the mechanistic link between the flow alteration caused by the ET graft and the development of premature aortic rupture before the 2nd stage operation. Specifically, fluid-structure interaction (FSI) analysis was performed using the CT imaging data of aorta at different stages of ET repair, and then computational variables were compared to those observed in patients who underwent a prophylactic 2nd stage operation to complete aortic repair. Results show that intramural stress exerted near the distal ET anastomosis (IMS=37.5kPa) at the time of urgent intervention was comparable to that of the extensive aortic aneurysm (IMS=47.4kPa) at initial in-hospital admission, but was considerably higher than that occurring after the 1st stage procedure (IMS=3.5kPa). Pressure index suggested higher peri-graft pressurization than aortic lumen pressure during diastole, imparting an apparent risk of aortic dilatation. These critical hemodynamic and structural parameters are related to the impending rupture of descending aorta observed clinically and can thus guide prophylactic intervention and optimal timing for the 2nd stage operation of a ET technique.

Role of Pulse Pressure and Geometry of Primary Entry Tear in Acute Type B Dissection Propagation

The hemodynamic and geometric factors leading to propagation of acute Type B dissections are poorly understood. The objective is to elucidate whether geometric and hemodynamic parameters increase the predilection for aortic dissection propagation. A pulse duplicator set-up was used on porcine aorta with a single entry tear. Mean pressures of 100 and 180 mmHg were used, with pulse pressures ranging from 40 to 200 mmHg. The propagation for varying geometric conditions (%circumference of the entry tear: 15–65%, axial length: 0.5–3.2 cm) were tested for two flap thicknesses (1/3rd and 2/3rd of the thickness of vessel wall, respectively). To assess the effect of pulse and mean pressure on flap dynamics, the %true lumen (TL) cross-sectional area of the entry tear were compared. The % circumference for propagation of thin flap (47 ± 1%) was not significantly different (p = 0.14) from thick flap (44 ± 2%). On the contrary, the axial length of propagation for thin flap (2.57 ± 0.15 cm) was significantly different (p < 0.05) from the thick flap (1.56 ± 0.10 cm). TL compression was observed during systolic phase. For a fixed geometry of entry tear (%circumference = 39 ± 2%; axial length = 1.43 ± 0.13 cm), mean pressure did not have significant (p = 0.84) effect on flap movement. Increase in pulse pressure resulted in a significant change (p = 0.02) in %TL area (52 ± 4%). The energy acting on the false lumen immediately before propagation was calculated as 75 ± 9 J/m² and was fairly uniform across different specimens. Pulse pressure had a significant effect on the flap movement in contrast to mean pressure. Hence, mitigation of pulse pressure and restriction of flap movement may be beneficial in patients with type B acute dissections.

The Potential of Computational Fluid Dynamics Simulation on Serial Monitoring of Hemodynamic Change in Type B Aortic Dissection

PURPOSE

We aimed to assess the potential of computational fluid dynamics simulation (CFD) in detecting changes in pressure and flow velocity in response to morphological changes in type B aortic dissection.

MATERIALS AND METHODS

Pressure and velocity in four morphological models of type B aortic dissection before and after closure of the entry tear were calculated with CFD and analyzed for changes among the different scenarios. The control model (Model 1) was patient specific and built from the DICOM data of CTA, which bore one entry tear and three re-entry tears. Models 2-4 were modifications of Model 1, with two re-entry tears less in Model 2, one re-entry tear more in Model 3, and a larger entry tear in Model 4.

RESULTS

The pressure and velocity pertaining to each of the morphological models were unique. Changes in pressure and velocity findings were accountable by the changes in morphological features of the different models. There was no blood flow in the false lumen across the entry tear after its closure, the blood flow direction across the re-entry tears was reversed after closure of the entry tear.

CONCLUSION

CFD simulation is probably useful to detect hemodynamic changes in the true and false lumens of type B aortic dissection in response to morphological changes, it may potentially be developed into a non-invasive and patient-specific tool for serial monitoring of hemodynamic changes of type B aortic dissection before and after treatment.

Persistent Intraluminal Pressure After Endovascular Stent Grafting for Type B Aortic Dissection

OBJECTIVES

Despite technically successful thoracic endovascular stent graft repair (TEVAR) in patients with Stanford Type B aortic dissection (TBAD), long-term follow up studies have shown that the false lumen may continue to dilate. The aim of this study was to analyze the possible mechanisms leading to such changes from a hemodynamic perspective.

METHODS

Twenty-eight ex vivo fresh porcine TBAD models (Mo A: 10; Model B: 12; Model C: 6) were established to simulate three clinical situations: Model A with patent false lumen (pre-TEVAR); Model B with distal re-entry only (post-TEVAR), and Model C with thrombus filling in the false lumen and a distal re-entry (chronic stage of post-TEVAR). Synchronous pressure waveforms were taken from both the true and the false lumen. True lumen and false lumen pressure differences were calculated for each model as four indices: systolic index (SI), diastolic index (DI), mean pressure index (MPI) and area under curve index (AUCI). These indices were compared between the three models.

RESULTS

False lumen pressure and corresponding pressure-accumulating effects were significantly higher in Model A than in Model C: SI (99.9% vs. 189.4%; p < .001); MPI and AUCI (99.5% vs. 128.2%; 99.5% vs. 128%; p < .001). The SI, MPI, and AUCI were significantly higher in Model B compared with Model C. The differences between the four indices were not significant between Model A and B. The false lumen area under curve (AUC) in Model C was merely lowered by 20% compared with its true lumen (67.5 mmHg vs. 85.2 mmHg).

CONCLUSION

The false lumen pressure remained unchanged in the non-thrombosed segment with patent blood flow after the primary entry tear sealed. Intraluminal pressure reduction in the thrombosed false lumen was significant. However, nearly 80% of the pressure remained in the thrombosed false lumen. If this high intra-thrombus pressure persists, it may contribute to delayed aneurysmal formation after endovascular treatment.