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

False lumen hemodynamics and partial thrombosis in chronic aortic dissection of the descending aorta

OBJECTIVES

Partial thrombosis of the false lumen (FL) in patients with chronic aortic dissection (AD) of the descending aorta has been associated with poor outcomes. Meanwhile, the fluid dynamic and biomechanical characteristics associated with partial thrombosis remain to be elucidated. This retrospective, single-center study tested the association between FL fluid dynamics and biomechanics and the presence and extent of FL thrombus.

METHODS

Patients with chronic non-thrombosed or partially thrombosed FLs in the descending aorta after an aortic dissection underwent computed tomography angiography, cardiovascular magnetic resonance (CMR) angiography, and a 4D flow CMR study. A comprehensive quantitative analysis was performed to test the association between FL thrombus presence and extent (percentage of FL with thrombus) and FL anatomy (diameter, entry tear location and size), fluid dynamics (inflow, rotational flow, wall shear stress, kinetic energy, and flow acceleration and stasis), and biomechanics (pulse wave velocity).

RESULTS

Sixty-eight patients were included. In multivariate logistic regression FL kinetic energy (p = 0.038) discriminated the 33 patients with partial FL thrombosis from the 35 patients with no thrombosis. Similarly, in separated multivariate linear correlations kinetic energy (p = 0.006) and FL inflow (p = 0.002) were independently related to the extent of the thrombus. FL vortexes, flow acceleration and stasis, wall shear stress, and pulse wave velocity showed limited associations with thrombus presence and extent.

CONCLUSION

In patients with chronic descending aorta dissection, false lumen kinetic energy is related to the presence and extent of false lumen thrombus.

CLINICAL RELEVANCE STATEMENT

In patients with chronic aortic dissection of the descending aorta, false lumen hemodynamic parameters are closely linked with the presence and extent of false lumen thrombosis, and these non-invasive measures might be important in patient management.

KEY POINTS

• Partial false lumen thrombosis has been associated with aortic growth in patients with chronic descending aortic dissection; therefore, the identification of prothrombotic flow conditions is desirable. • The presence of partial false lumen thrombosis as well as its extent was related with false lumen kinetic energy. • The assessment of false lumen hemodynamics may be important in the management of patients with chronic aortic dissection of the descending aorta.

An efficient procedure for the blood flow computer simulation of patient-specific aortic dissections

In this work we present a novel methodology for the numerical simulation of patient-specific aortic dissections. Our proposal, which targets the seamless virtual prototyping of customized scenarios, combines an innovative two-step segmentation procedure with a CutFEM technique capable of dealing with thin-walled bodies such as the intimal flap. First, we generate the fluid mesh from the outer aortic wall disregarding the intimal flap, similarly to what would be done in a healthy aorta. Second, we create a surface mesh from the approximate midline of the intimal flap. This approach allows us to decouple the segmentation of the fluid volume from that of the intimal flap, thereby bypassing the need to create a volumetric mesh around a thin-walled body, an operation widely known to be complex and error-prone. Once the two meshes are obtained, the original configuration of the dissection into true and false lumen is recovered by embedding the surface mesh into the volumetric one and calculating a level set function that implicitly represents the intimal flap in terms of the volumetric mesh entities. We then leverage the capabilities of unfitted mesh methods, specifically relying on a CutFEM technique tailored for thin-walled bodies, to impose the wall boundary conditions over the embedded intimal flap. We tested the method by simulating the flow in four patient-specific aortic dissections, all involving intricate geometrical patterns. In all cases, the preprocess is greatly simplified with no impact on the computational times. Additionally, the obtained results are consistent with clinical evidence and previous research.

Inconsistent False Lumen Enhancement Predicts Late Aortic Events After Hemiarch Replacement in Acute Type A Aortic Dissection

The impact of inconsistent enhancement within the patent false lumen on the occurrence of late aortic events remains uncertain. We enrolled 55patients who exhibited a patent false lumen after hemiarch replacement. The Hounsfield unit (HU) measurements in the patent false lumen were obtained at 2 specific locations: the aortic arch (a) and the descending aorta (b). The false lumen HU score was calculated as the absolute value of 1 - a/b, representing the discrepancy in HUs within the patent false lumen. We investigated the cut-off value of the false lumen HU score with the receiver operating characteristics curve to predict the incidence of late aortic events. We divided the patients based on the cut-off value and compared the cumulative incidence of the late aortic events. The analysis of the receiver operating characteristics curve showed that the cut-off value of the false lumen HU score was 0.345. Based on this cut-off value, we divided them into 2 groups: Group A (score <0.345, n = 26) and Group B (score ≥0.345, n = 29). The baseline characteristics were similar between the 2 groups. The cumulative incidence of the late aortic events was significantly lower in Group A (7.8% at 5 years) than in Group B (39.9% at 5 years) (p = 0.02). The false lumen HU score might be useful to predict the incidence of late aortic events after hemiarch replacement.

Predicting adverse events after thoracic endovascular aortic repair for patients with type B aortic dissection

The potential of adverse events (AEs) after thoracic endovascular aortic repair (TEVAR) in patients with type B aortic dissection (TBAD) has been reported. To avoid the occurrence of AEs, it is important to recognize high-risk population for prevention in advance. The data of 261 patients with TBAD who received TEVAR between June 2017 and June 2021 at our medical center were retrospectively reviewed. After the implementation of exclusion criteria, 172 patients were finally included, and after 2.8 years (range from 1 day to 5.8 years) of follow up, they were divided into AEs (n = 41) and non-AEs (n = 131) groups. We identified the predictors of AEs, and a prediction model was constructed to calculate the specific risk of postoperative AEs at 1, 2, and 3 years, and to stratify patients into high-risk (n = 78) and low-risk (n = 94) group. The prediction model included seven predictors: Age > 75 years, Lower extremity malperfusion (LEM), NT-proBNP > 330 pg/ml, None distal tear, the ratio between the diameter of the ascending aorta and descending aorta (A/D ratio) > 1.2, the ratio of the area of the false lumen to the total aorta (FL ratio) > 64%, and acute TEVAR, which exhibited excellent predictive accuracy performance and discriminatory ability with C statistic of 82.3% (95% CI 77.3-89.2%). The prediction model was contributed to identify high-risk patients of postoperative AEs, which may serve to achievement of personalized treatment and follow-up plans for patients.

The Role of Multiple Re-Entry Tears in Type B Aortic Dissection Progression: A Longitudinal Study Using a Controlled Swine Model

PURPOSE

False lumen (FL) expansion often occurs in type B aortic dissection (TBAD) and has been associated with the presence of re-entry tears. This longitudinal study aims to elucidate the role of re-entry tears in the progression of TBAD using a controlled swine model, by assessing aortic hemodynamics through combined imaging and computational modeling.

MATERIALS AND METHODS

A TBAD swine model with a primary entry tear at 7 cm distal to the left subclavian artery was created in a previous study. In the current study, reintervention was carried out in this swine model to induce 2 additional re-entry tears of approximately 5 mm in diameter. Computed tomography (CT) and 4-dimensional (4D) flow magnetic resonance imaging (MRI) scans were taken at multiple follow-ups before and after reintervention. Changes in aortic volume were measured on CT scans, and hemodynamic parameters were evaluated based on dynamic data acquired with 4D-flow MRI and computational fluid dynamics simulations incorporating all available in vivo data.

RESULTS

Morphological analysis showed FL growth of 20% following the initial TBAD-growth stabilized after the creation of additional tears and eventually FL volume reduced by 6%. Increasing the number of re-entry tears from 1 to 2 caused flow redistribution, with the percentage of true lumen (TL) flow increasing from 56% to 78%; altered local velocities; reduced wall shear stress surrounding the tears; and led to a reduction in FL pressure and pressure difference between the 2 lumina.

CONCLUSION

This study combined extensive in vivo imaging data with sophisticated computational methods to show that additional re-entry tears can alter dissection hemodynamics through redistribution of flow between the TL and FL. This helps to reduce FL pressure, which could potentially stabilize aortic growth and lead to reversal of FL expansion. This work provides a starting point for further study into the use of fenestration in controlling undesirable FL expansion.

CLINICAL IMPACT

Aortic growth and false lumen (FL) patency are associated with the presence of re-entry tears in type B aortic dissection (TBAD) patients. Guidelines on how to treat re-entry tears are lacking, especially with regards to the control and prevention of FL expansion. Through a combined imagining and computational hemodynamics study of a controlled swine model, we found that increasing the number of re-entry tears reduced FL pressure and cross lumen pressure difference, potentially stabilising aortic growth and leading to FL reduction. Our findings provide a starting point for further study into the use of fenestration in controlling undesirable FL expansion.

Prognostic Implications of Initial Focal Contrast Enhancement in Acute Type B Intramural Hematoma

BACKGROUND

The prognostic implication of initial focal contrast enhancement (FCE), including focal intimal disruption (FID) and intramural blood pool (IBP), in acute type B intramural hematoma (IMH) remain unclear.

OBJECTIVES

The purpose of this study was to compare the prognostic implications in IMH with or without FCE.

METHODS

A total of 574 patients were enrolled. FID was defined as an intimal disruption with contrast-filled out-pouching from the aorta lumen with a communicating orifice of >3 mm, and IBP was defined as a localized contrast medium-filled pool inside the IMH.

RESULTS

A total of 207 (36.1%) patients with initial FCE, including 132 (63.8%) FIDs and 75 (36.2%) IBPs, were identified. Patients with FCE accompanying IMH were more likely to have hypertension (P = 0.001), pleural effusion (P = 0.006), fewer aortic segments involved (P < 0.001), more adverse aortic events (AAEs) (P < 0.001), and fewer freedom from intervention (P = 0.002). Pleural effusion (HR: 1.79; 95% CI: 1.25-2.55; P = 0.001) and FCE (HR: 1.51; 95% CI: 1.12-2.02; P = 0.006) were identified to be the independent risk factors of AAEs. In the subgroup analysis, IMH with initial FID were more likely to progress than those with initial IBP (P < 0.001). FIDs located at the proximal descending aorta (HR: 2.95; 95% CI: 1.65-5.29; P < 0.001) were associated with AAEs.

CONCLUSIONS

Patients with FCE accompanying IMH were more likely to progress, especially in those initial FID localized at the proximal descending aorta. (Nature course and predictors of progression of intramural hematoma: A retrospective, multicenter study; ChiCTR2300073829).

The Role of Location, Length, and Thickness of the Intimal Flap in the Propagation of Stanford Type B Aortic Dissection Based on Ex Vivo Porcine Aorta Models

PURPOSE

To explore the role of location, length, and thickness of the intimal flap in the propagation of Stanford type B aortic dissection (TBAD) based on ex vivo porcine aorta models based on ex vivo porcine aorta models.

MATERIALS AND METHODS

The porcine aortas were harvested and randomly divided into 6 groups to create various TBAD aortic models. We constructed intimal flaps for different locations (group A [entry tear on outer curvature] and group B [entry tear on inner curvature]), lengths (group C [long] and group D [short]), and thicknesses (group E [thick] and group F [thin]). For the ex vivo perfusion experiments conducted on model aortas, an experimental circulation loop (ECL) was employed. The pressure in false lumen (FL) was constantly monitored. A comparison was made between the morphological data collected before and after the experiment to quantify the changes in the FL after the experiment.

RESULTS

Compared the results with group B, the mean peak pressures of the FL in group A were lower (106.87±15.55 vs. 124.01±22.75 mm Hg, p=0.028). The mean axial propagation length in group A was shown to be shorter than that of group B (88.14±33.38 vs. 197.43±41.65 mm, p<0.001). The mean peak pressure was higher in group C than in group D (144.04±19.37 vs. 92.51±26.70 mm Hg, p<0.001). The mean peak pressure of group E was higher than that of group F (160.83±32.83 vs. 109.33±15.62 mm Hg, p<0.001), as was the mean axial propagation length of group E (143.11±39.73 vs. 100.45±35.44 mm, p=0.021). According to the results of multivariable linear regression, axial propagation length=45.873-0.703×length of initial FL+0.863× peak pressure (p<0.001).

CONCLUSION

There was a relationship between FL propagation and the location, length, and thickness of the intimal flap. The axial propagation length was related to the length of the intimal flap and the peak pressure of propagation. It may be helpful to evaluate the risk of propagation in patients with TBAD.

CLINICAL IMPACT

This study found that the locations, lengths, and thickness of the intimal flap significantly contributed to propagation pressure of FL. Using dissection flap characteristics, a physician can predict FL development in a patient and formulate a treatment plan.The purpose was to investigate the relationship between the dissection flap characteristics (location, length, and thickness) and the propagation of the FL, which is not clear at present. This study employed porcine models to create an experimental circulation loop. The perfusion experiment was conducted using a FL without distal re-entry and a non-pulsating flow.

Finite-element simulation of in-plane tear propagation in the dissected aorta: Implications for the propagation mechanism

Computer modeling and numerical simulation are essential for understanding the progression of aortic dissection. However, tear propagation has not been properly modeled and simulated. The in-plane dissection propagation between concentrically distributed elastic lamellae is modeled using the cohesive zone method with a bilinear traction-separation law. The parameters of cohesive elements are calibrated for the three modes of interfacial damage in the media, enabling quantitative predictions of in-plane tear propagation. An idealized cylindrical tube-shaped bilayer thick-wall model of the aorta is employed to elucidate the influence of geometrical parameters, loading conditions and residual stress on the tear propagation. While the model is capable of replicating that deeper, larger tears are associated with lower critical pressure, new findings include: (i) Larger axial stretch leads to lower critical pressure; (ii) Increased magnitude of residual stress is associated with higher critical pressure; (iii) Pressure difference between true and false lumen alters the critical pressure; (iv) The interfacial damage is mostly opening mode in the axial direction, but shear-dominated in the circumferential direction; (v) Damage due to the opening mode is associated with smaller fracture energy, which makes it easier to propagate than the shear and the mixed modes. (vi) The deformed shape of the tear, which is related to its geometrical features and loading conditions, modulates the critical pressure via two pathways: (a) deformed shapes are associated with specific modes of damage, which influences the critical pressure, and (b) deformed shapes modulate the critical pressure directly via geometrical constraints.

A computational study of the effects of size, location, and number of tears on haemodynamics in surgically repaired type A aortic dissection

Objective

This study aimed to comprehensively examine the roles of size, location, and number of tears in the progression of surgically repaired type A aortic dissection (TAAD) by assessing haemodynamic changes through patient-specific computational fluid dynamic (CFD) simulations.

Methods

Two patient-specific TAAD geometries with replaced ascending aorta were reconstructed based upon computed 15 tomography (CT) scans, after which 10 hypothetical models (5 per patient) with different tear configurations were artificially created. CFD simulations were performed on all the models under physiologically realistic boundary conditions.

Results

Our simulation results showed that increasing either the size or number of the re-entry tears reduced the luminal pressure difference (LPD) and maximum time-averaged wall shear stress (TAWSS), as well as areas exposed to abnormally high or low TAWSS values. Models with a large re-entry tear outperformed the others by reducing the maximum LPD by 1.88 mmHg and 7.39 mmHg, for patients 1 and 2, respectively. Moreover, proximally located re-entry tears in the descending aorta were more effective at reducing LPD than distal re-entry tears.

Discussion

These computational results indicate that the presence of a relatively large re-entry tear in the proximal descending aorta might help stabilize post-surgery aortic growth. This finding has important implications for the management and risk stratification of surgically repaired TAAD patients. Nevertheless, further validation in a large patient cohort is needed.

Progression of distal aorta after endovascular fenestration/stenting in acute type A aortic dissection with malperfusion syndrome

Objective

The study objective was to evaluate the progression of dissected distal aorta in patients with acute type A aortic dissection with malperfusion syndrome treated with endovascular fenestration/stenting and delayed open aortic repair.

Methods

From 1996 to 2021, 927 patients presented with acute type A aortic dissection. Of these, 534 had DeBakey I dissection with no malperfusion syndrome and underwent emergency open aortic repair (no malperfusion syndrome group), whereas 97 patients with malperfusion syndrome underwent fenestration/stenting and delayed open aortic repair (malperfusion syndrome group). Sixty-three patients with malperfusion syndrome treated with fenestration/stenting were excluded due to no open aortic repair, including death from organ failure (n = 31), death from aortic rupture (n = 16), and discharged alive (n = 16).

Results

Compared with the no malperfusion syndrome group, the malperfusion syndrome group had more patients with acute renal failure (60% vs 4.3%, P < .001). Both groups had similar aortic root and arch procedures. Postoperatively, the malperfusion syndrome group had similar operative mortality (5.2% vs 7.9%, P = .35) and permanent dialysis (4.7% vs 2.9%, P = .50), but more new-onset dialysis (22% vs 7.7%, P < .001) and prolonged ventilation (72% vs 49%, P < .001). The growth rate of the aortic arch (0.38 vs 0.35 mm/year, P = .81) was similar between the malperfusion syndrome and no malperfusion syndrome groups. The descending thoracic aorta growth rate (1.03 vs 0.68 mm/year, P = .001) and abdominal aorta growth rate (0.76 vs 0.59 mm/year, P = .02) were significantly higher in the malperfusion syndrome group. The cumulative incidence of reoperation over 10 years (18% vs 18%, P = .81) and 15-year survival outcome (50% vs 48%, P = .43) were similar between the malperfusion syndrome and no malperfusion syndrome groups.

Conclusions

Endovascular fenestration/stenting followed by delayed open aortic repair was a valid approach for patients with malperfusion syndrome.

Factors affecting distal false lumen enlargement after thoracic endovascular aortic repair for type B aortic dissection

Objective

To investigate the factors influencing distal false lumen enlargement after thoracic endovascular aortic repair (TEVAR) for type B aortic dissection.

Materials and methods

Data were collected on patients with type B aortic dissection who underwent TEVAR from January 2008 to August 2022. Patients were divided into a distal aortic segmental enlargement (DSAE) group and a non-DSAE group based on whether the distal false lumen was dilated more than 5 mm on computed tomographic angiography (CTA) images. To analyze the independent influences on distal false lumen dilatation after TEVAR, the variables with a P value < 0.05 during univariate analysis were included in the binary logistic regression analysis model.

Results

A total of 335 patients were included in this study, with 85 in the DSAE group and 250 in the non-DSAE group. The mean age was 52.40 ± 11.34 years, 289 (86.27%) were male patients, and the median follow-up time was 6.41 (11.99-29.99) months. There were significant differences in Marfan syndrome, chronic obstructive pulmonary disease (COPD), and follow-up time between the two groups. In terms of morphology, there were statistically significant differences in the number of tears, the size of the primary tear, and the length of dissection between the two groups. Binary logistic regression analysis indicated that Marfan syndrome, COPD, and the primary tear size were associated with distal false lumen dilatation.

Conclusions

Marfan syndrome, COPD, and the primary tear size influence distal aortic segmental enlargement after TEVAR in type B aortic dissection patients.

Uncomplicated Type B Aortic Dissection: Challenges in Diagnosis and Categorisation

BACKGROUND

Acute type B aortic dissection (TBAD) is a rare disease that is likely under-diagnosed in the UK. As a progressive, dynamic clinical entity, many patients initially diagnosed with uncomplicated TBAD deteriorate, developing end-organ malperfusion and aortic rupture (complicated TBAD). An evaluation of the binary approach to the diagnosis and categorisation of TBAD is needed.

METHODS

A narrative review of the risk factors predisposing patients to progression from unTBAD to coTBAD was undertaken.

RESULTS

Key high-risk features predispose the development of complicated TBAD, such as maximal aortic diameter > 40 mm and partial false lumen thrombosis.

CONCLUSION

An appreciation of the factors that predispose to complicated TBAD would aid clinical decision-making surrounding TBAD.

Monitoring of false lumen thrombosis in type B aortic dissection by impedance cardiography - A multiphysics simulation study

Aortic dissection is caused by a tear on the aortic wall that allows blood to flow through the wall layers. Usually, this tear involves the intimal and partly the medial layer of the aortic wall. As a result, a new false lumen develops besides the original aorta, denoted then as the true lumen. The local hemodynamic conditions such as flow disturbances, recirculations and low wall shear stress may cause thrombus formation and growth in the false lumen. Since the false lumen status is a significant predictor for late-dissection-related deaths, it is of great importance in the medical management of patients with aortic dissection. The hemodynamic changes in the aorta also alter the electrical conductivity of blood. Since the blood is much more conductive than other tissues in the body, such changes can be identified with non-invasive methods such as impedance cardiography. Therefore, in this study, the capability of impedance cardiography in monitoring thrombosis in the false lumen is studied by multiphysics simulations to assist clinicians in the medical management of patients under treatment. To tackle this problem, a 3D computational fluid dynamics simulation has been set up to model thrombosis in the false lumen and its impact on the blood flow-induced conductivity changes. The electrical conductivity changes of blood have been assigned as material properties of the blood-filled aorta in a 3D finite element electric simulation model to investigate the impact of conductivity changes on the measured impedance from the body's surface. The results show remarkable changes in the electrical conductivity distribution in the measurement region due to thrombosis in the false lumen, which significantly impacts the morphology of the impedance cardiogram. Thus, frequent monitoring of impedance cardiography signals may allow tracking the thrombus formation and growth in the false lumen.

Morphological parameters affecting false lumen thrombosis following type B aortic dissection: a systematic study based on simulations of idealized models

Type B aortic dissection (TBAD) carries a high risk of complications, particularly with a partially thrombosed or patent false lumen (FL). Therefore, uncovering the risk factors leading to FL thrombosis is crucial to identify high-risk patients. Although studies have shown that morphological parameters of the dissected aorta are related to FL thrombosis, often conflicting results have been reported. We show that recent models of thrombus evolution in combination with sensitivity analysis methods can provide valuable insights into how combinations of morphological parameters affect the prospect of FL thrombosis. Based on clinical data, an idealized geometry of a TBAD is generated and parameterized. After implementing the thrombus model in computational fluid dynamics simulations, a global sensitivity analysis for selected morphological parameters is performed. We then introduce dimensionless morphological parameters to scale the results to individual patients. The sensitivity analysis demonstrates that the most sensitive parameters influencing FL thrombosis are the FL diameter and the size and location of intimal tears. A higher risk of partial thrombosis is observed when the FL diameter is larger than the true lumen diameter. Reducing the ratio of the distal to proximal tear size increases the risk of FL patency. In summary, these parameters play a dominant role in classifying morphologies into patent, partially thrombosed, and fully thrombosed FL. In this study, we point out the predictive role of morphological parameters for FL thrombosis in TBAD and show that the results are in good agreement with available clinical studies.

Acute aortic syndromes: An internist's guide to the galaxy

Acute aortic syndromes (AASs) are severe conditions defined by dissection, hemorrhage, ulceration or rupture of the thoracic aorta. AASs share etiological and pathophysiological features, including long-term aortic tissue degeneration and mechanisms of acute aortic damage. The clinical signs and symptoms of AASs are unspecific and heterogeneous, requiring large differential diagnosis. When evaluating a patient with AAS-compatible symptoms, physicians need to integrate clinical probability assessment, bedside imaging techniques such as point-of-care ultrasound, and blood test results such as d-dimer. The natural history of AASs is dominated by engagement of ischemic, coagulative and inflammatory pathways at large, causing multiorgan damage. Medical treatment, multiorgan monitoring and outcome prognostication are therefore paramount, with internal medicine playing a key role in non-surgical management of AASs.

Fate and Consequences of the False Lumen after TEVAR in Type B Aortic Dissection

BACKGROUND

Type B aortic dissection (TBAD) occurs due to an entry tear in the intimal layer of the aorta distal to the origin of the left subclavian artery where blood enters the newly formed false lumen (FL) and extends distally or proximally to form a dissection over an indeterminate length of the aorta which, over time, may eventually rupture. Thoracic endovascular aortic repair (TEVAR) aims to seal off the entry tear proximally with the stent-graft, occluding the origin of the dissection and excluding the FL. Nevertheless, in some cases, the perfusion to the FL is maintained, hindering the aortic remodelling process and increasing the risk of aneurysmal degeneration and rupture, particularly in the abdominal aorta where evidence suggest that remodelling is slower. This review examines the long-term effects of a patent or partially thrombosed FL on clinical outcomes following TEVAR in TBAD, also highlighting the pathological processes behind negative aortic remodelling. Another aim of this review is to provide an overview and appraisal of the currently available techniques for managing a patent or partially thrombosed FL to prevent long-term morbidity occurring.

METHODS

A comprehensive literature search was performed using several search engines including PubMed, Ovid, Google Scholar, Scopus, and Embase to identify and extract relevant studies.

RESULTS

Evidence in the literature show that a partially thrombosed FL is more dangerous than a patent FL due to the occlusion of the distal re-entry tears, impeding outflow and increasing mean arterial and diastolic pressures, whereas the latter is decompressed via distal re-entry sites. FL thrombosis and satisfactory remodelling is sometimes achieved in as few as 40% of patients after TEVAR due to the maintained perfusion of the FL either at the level of the thoracic or abdominal aorta. However, although the thoracic aorta is predominantly covered by the TEVAR stent-graft, poorer remodelling and more dilation is seen in the abdominal aorta. Several techniques are available to embolize the FL, including the Provisional Extension to Induce Complete Attachment, Stent Assisted Balloon Induced Intimal Disruption and Relamination in Aortic Dissection Repair, candy-plug, and Knickerbocker techniques.

CONCLUSIONS

The management of TBAD is invariably TEVAR to seal off the proximal entry tear while extending the repair distally to completely exclude the FL. A risk of aortic wall dilatation distal to TEVAR stent-graft remains; hence, regular monitoring and accurate imaging are essential. At present, a patent FL can be treated using a range of different endovascular techniques.

False Lumen Flow Assessment by Magnetic Resonance Imaging and Long-Term Outcomes in Uncomplicated Aortic Dissection

BACKGROUND

Despite the absence of clinical complications after an acute aortic dissection (AD) with persistent patent false lumen (FL), a high risk for clinical events may persist.

OBJECTIVES

The aim of this study was to assess the natural evolution of noncomplicated AD and ascertain whether different FL flow patterns by magnetic resonance imaging (MRI) have independent prognostic value for AD-related events beyond established morphologic parameters.

METHODS

One hundred thirty-one consecutive patients, 78 with surgically treated type A dissections and 53 with medically treated type B dissections, were followed up prospectively after acute AD with persistent patent FL in the descending aorta. Maximum aortic diameter, true lumen compression, entry tear, and partial FL thrombosis by computed tomography were assessed. Systolic antegrade true lumen and FL flow volumes and diastolic antegrade and retrograde flows were analyzed by MRI during the first year after AD.

RESULTS

After a median follow-up period of 8.0 years (IQR: 4.6-10.9 years), 43 patients presented aorta-related events (25 died and 18 required endovascular treatment). FL systolic antegrade flow ≥30% with respect to total systolic antegrade flow and retrograde diastolic flow ≥80% with respect to total diastolic FL flow were predictors of aortic events. In multivariate analysis, aortic diameter >45 mm (HR: 2.91), type B dissection (HR: 2.44), and MRI flow pattern (HR: 16.87) were independent predictors of AD-related events.

CONCLUSIONS

High systolic antegrade flow volume in the FL with significant diastolic retrograde flow assessed by MRI and aortic diameter >45 mm identify patients with higher risk for complications in whom more aggressive management would be indicated.

Risk profile analysis of uncomplicated type B aortic dissection patients undergoing thoracic endovascular aortic repair: Laboratory and radiographic predictors

BACKGROUND

There is emerging evidence to support pre-emptive thoracic endovascular aortic repair (TEVAR) intervention for uncomplicated type B aortic dissection (unTBAD). Pre-emptive intervention would be particularly beneficial in patients that have a higher baseline risk of progressing to complicated TBAD (coTBAD). There remain debate on the optimal clinical, laboratory, morphological, and radiological parameters, which would identify the highest-risk patients that would benefit most from pre-emptive TEVAR.

AIM

This review summarizes evidence on the clinical, laboratory, and morphological parameters that increase the risk profiles of unTBAD patients.

METHODS

A comprehensive literature search was carried out on multiple electronic databases including PubMed, EMBASE, Ovid, and Scopus to collate all research evidence on the clinical, laboratory, and morphological parameters that increase the risk profiles of unTBAD patients RESULTS: At present, there are no clear clinical guidelines using risk-stratification to inform the selection of unTBAD patients for TEVAR. However, there are noticeable literature trends that can assist with the identification of the most at-risk unTBAD patients. Patients are at particular risk when they have refractory pain and/or hypertension, elevated C-reactive protein (CRP), larger aortic diameter, and larger entry tears. These risks should be considered alongside factors that increase the procedural risk of TEVAR to create a well-balanced approach. Advances in biomarkers and imaging are likely to identify more pertinent parameters in the future to optimize the development of balanced, risk-stratified treatment protocols.

CONCLUSION

There are a variety of risk profiling parameters that can be used to identify the high-risk unTBAD patient, with novel biomarkers and imaging parameters emerging. Longer-term evidence verifying these parameters would be ideal. Further randomized controlled trials and multicentre registry analyses are also warranted to guide risk-stratified selection protocols.

Ratio of the false lumen to the true lumen is associated with long-term prognosis after surgical repair of acute type A aortic dissection

Objectives

The aim of this study was to assess potential predictors of aortic events after an emergency surgery for acute type A aortic dissection, especially paying attention to the findings of computed tomography (CT) performed immediately after the surgery.

Methods

Between January 2001 and December 2015, 72 patients, who were diagnosed as having Stanford type A acute aortic dissection with a patent false lumen in the descending thoracic aorta, survived the emergency operation, and had postoperative CT scan data, were included in this study (mean follow-up, 8.2 ± 3.8 years; range 0.8-17.4 years). From the CT scan data, the diameter of the false lumen (FL-D) and true lumen (TL-D) were measured, and the FL-D:TL-D ratio was calculated. Long-term outcomes of the FL-D > TL-D group (n = 30) and the FL-D < TL-D group (n = 42) were compared.

Results

In the late follow-up, 17 aortic events in the downstream aorta were observed. The FL-D:TL-D ratio (P = .01) was an adjusted risk of aortic events in multivariable analysis. The rates of freedom from aortic events at 5 and 9 years were superior in the FL-D < TL-D group than in the FL-D > TL-D group (92.0% and 88.6% vs 81% and 60.7%; log rank P < .05).

Conclusions

Our results suggest that the false lumen:true lumen ratio predicts long-term prognosis after surgical repair of acute type A aortic dissection.

The STABILISE technique to address malperfusion on acute-subacute type B aortic dissections

Endovascular treatment is the current standard of care for complicated acute and subacute type B aortic dissection. Closure of the primary entry tear with thoracic endovascular aneurysm repair (TEVAR) is often insufficient to induce complete false lumen thrombosis and a positive aortic remodeling. Moreover, TEVAR does not solve all the cases of malperfusion. The Provisional ExTension to Induce COmplete ATtachment (PETTICOAT) technique (deploying self-expandable bare metal stents in the true lumen in addition to TEVAR) can re-expand the true lumen, stabilize the lamella and promote aortic remodeling, but it does not recreate a single-lumen aorta and long-term aneurysmal degeneration of the aorta is frequent. Endovascular treatment by means of TEVAR + PETTICOAT does not recreate a single-lumen aorta so long-term aneurysmal degeneration of the aorta is frequent. The stent-assisted, balloon-induced intimal disruption and relamination of aortic dissection (STABILISE) technique may help to this purpose disrupting the intimal lamella and creating a relaminated uni-luminal aorta.

An in vitro Assessment of the Haemodynamic Features Occurring Within the True and False Lumens Separated by a Dissection Flap for a Patient-Specific Type B Aortic Dissection

One of the highest mortality rates of cardiovascular diseases is aortic dissections with challenging treatment options. Currently, less study has been conducted in developing in vitro patient-specific Type B aortic dissection models, which mimic physiological flow conditions along the true and false lumens separated by a dissection flap with multiple entry and exit tears. A patient-specific Stanford Type B aortic dissection scan was replicated by an in-house manufactured automatic injection moulding system and a novel modelling technique for creating the ascending aorta, aortic arch, and descending aorta incorporating arterial branching, the true/false lumens, and dissection flap with entry and exit intimal tears. The physiological flowrates and pressure values were monitored, which identified jet stream fluid flows entering and exiting the dissection tears. Pressure in the aorta’s true lumen region was controlled at 125/85 mmHg for systolic and diastolic values. Pressure values were obtained in eight sections along the false lumen using a pressure transducer. The true lumen systolic pressure varied from 122 to 128 mmHg along the length. Flow patterns were monitored by ultrasound along 12 sections. Detailed images obtained from the ultrasound transducer probe showed varied flow patterns with one or multiple jet steam vortices along the aorta model. The dissection flap movement was assessed at four sections of the patient-specific aorta model. The displacement values of the flap varied from 0.5 to 3 mm along the model. This model provides a unique insight into aortic dissection flow patterns and pressure distributions. This dissection phantom model can be used to assess various treatment options based on the surgical, endovascular, or hybrid techniques.

Outer Media Thickness at False Lumen and Secondary Aortic Dilatation After Acute Aortic Dissection

BACKGROUND

This study measured the outer media thickness (OMT) at the false lumen by using microscopic images of specimens collected intraoperatively and assessed the impact of OMT on secondary dilatation of the downstream aorta.

METHODS

Of 238 patients undergoing surgical procedures for acute type A dissection between 2007 and 2016, 129 patients fulfilled the inclusion criteria for this study: DeBakey type I dissection with a patent false lumen, histopathologic examination of full-thickness aortic wall, and at least 1 follow-up computed tomographic scan at more than 3 months after surgical procedures. On average, 5.1 scans were obtained per patient, and median follow-up was 4.3 years.

RESULTS

Considerable variation was observed in OMT (median, 0.21 mm; range, 0.04-0.51 mm). The aortic diameter growth rate was inversely correlated with the OMT, and in the lowest tertile of OMT the aortic diameter dilated significantly faster in the first year than later and faster than in the other tertiles. Multivariable Fine-Gray analysis, with death as the competing risk, identified OMT as an independent variable for aortic-related events. Patients with OMT of 0.04 to 0.15 mm had a 3.54-fold higher risk of aortic-related events and those with 0.16 to 0.31 mm had a 1.56-fold higher risk of aortic-related events than did patients with OMT of 0.32 to 0.51 mm. Multivariable Cox regression analyses revealed OMT of 0.04 to 0.15 mm as an independent variable for all-cause mortality.

CONCLUSIONS

In patients with DeBakey type I aortic dissection with a patent false lumen, the growth rate of the distal residual dissecting aorta was inversely correlated with the OMT. The risk of aortic-related events was significantly higher in patients with OMT of 0.04 to 0.15 mm.

Prediction of aortic dilatation in surgically repaired type A dissection: A longitudinal study using computational fluid dynamics

OBJECTIVE

To examine the role of a key hemodynamic parameter, namely the true and false lumen pressure difference, to predict progressive aortic dilatation following type A aortic dissection (TAAD) repair.

METHODS

Four patients with surgically repaired TAAD with multiple follow-up computed tomography angiography scans (4-5 scans per patient; N = 18) were included. Through-plane diameter of the residual native thoracic aorta was measured in various aortic segments during the follow up period (mean follow-up: 49.6 ± 31.2 months). Computational flow analysis was performed to estimate true and false lumen pressure difference at the same locations and the correlation with aortic size change was studied using a linear mixed effects model.

RESULTS

Greater pressure difference between the true and false lumen was consistent with greater aortic diameter expansion during the follow up period (linear mixed effects analysis; coefficient, 0.26; 95% confidence interval, 0.15-0.37; P < .001). Based on our limited data points, a pressure difference higher than 5 mm Hg might cause unstable aortic growth.

CONCLUSIONS

Computational fluid dynamic assessment of standard aortic computed tomography angiography offers a noninvasive technique that predicts the risk of aortic dilatation following TAAD. The technique may be used to plan closer observation or intervention in high-risk patients.

Analysis of imaging characteristics of blunt traumatic aortic dissection: an 8-year experience

BACKGROUND

Traumatic aortic dissection (TAD) has a low incidence but extremely high mortality. It always presents atypical clinical manifestations that are easily missed or misdiagnosed. This study mainly aims to describe the imaging characteristics and management of TAD patients.

METHODS

A retrospective analysis of 27 blunt TAD patients was performed between 2013 and 2020. Demographic features, imaging characteristics, and management were analyzed.

RESULTS

Twenty-seven patients with type B aortic dissection (age 56.04±16.07 years, 20 men) were included. Aortic intimal tears were mostly initiated from the aortic isthmus. The sizes of the proximal intimal tears in the greater curvature were larger than those in the lesser curvature (1.78±0.56 cm vs. 1.24±0.52 cm, P=0.031). Compared with those in the control group, the maximum diameters of the aortic arch, thoracic aorta, and abdominal aorta in the TAD patients were all significantly widened (all P<0.050). Multivariate logistic regression analysis showed that the maximum diameter of the thoracic aorta was an independent risk factor for TAD, with a predictive value with an area under the receiver operating characteristic curve (AUC) of 0.673. Finally, 26 patients successfully underwent delayed thoracic endovascular aortic repair (TEVAR), and the remaining one patient was treated conservatively. No progression of aortic dissection or death occurred during the six-month follow-up period.

CONCLUSIONS

In blunt trauma, the aortic isthmus is the most common site of proximal intimal tears. An accurate diagnosis of TAD requires an overall consideration of medical history and imaging characteristics. Delayed TEVAR might be an effective therapeutic option for TAD.

Differences in the Area of Proximal and Distal Entry Tears at CT Angiography Predict Long-term Clinical Outcomes in Aortic Dissection

Purpose

To identify entry tear variables that are related to adverse clinical events by using CT angiography (CTA) performed during the subacute phase of aortic dissection.

Materials and Methods

In this prospective study conducted from January 2000 to December 2013, participants with an aortic dissection with a patent false lumen and no comorbidities underwent CTA during the subacute phase. Participants were followed up for a survival analysis to assess the time to an adverse aortic event (AAE). The maximum aortic diameter (MAD), proximal and distal tear areas and difference between these areas, and partial false-lumen thrombosis were assessed by using Cox regression for adverse events.

Results

Seventy-two participants (mean age, 55 years ± 12 [standard deviation]; 55 men) were evaluated: 47 were surgically treated (type A aortic dissection) and 25 were medically treated (type B aortic dissection). Twenty-two participants had an AAE manifest during follow-up (9.22 years ± 5.78): There were 18 elective surgeries for aneurysmal degeneration, two emergent surgeries for acute aortic syndrome, and two aortic condition-related deaths. A categorical model composed of genetic aortic disease (GAD) (hazard ratio [HR], 3.4 [95% CI: 1.2, 9.9]; P = .02), MAD greater than 45 mm (HR, 6.1 [95% CI: 2.4, 15.8]; P < .001), and tear dominance (HR, 5.2 [95% CI: 2.1, 13]; P < .001), defined as an absolute tear area difference of greater than 1.2 cm², was used to stratify participants into three risk groups: low, without any risk factors (57% [41 of 72] and 7% [three of 41] had events); intermediate, with one risk factor (31% [22 of 72] and 50% [11 of 22] had events); and high, with two or more risk factors (13% [nine of 72] and 89% [eight of nine] had events; log rank P < .001).

Conclusion

Tear dominance demonstrated at CTA performed in the subacute phase of aortic dissection was related to long-term adverse events. Participants without GAD, dominant tears, or MAD greater than 45 mm had conditions that were safely managed with optimal medical treatment and imaging follow-up.Keywords: CT Angiography, Vascular, Aorta, Dissection Supplemental material is available for this article. © RSNA, 2021See also commentary by Fleischmann and Burris in this issue.

Descending Aorta Diameters as Predictor of Late Adverse Outcomes in Patients with Uncomplicated Type B Aortic Dissection: A Systematic Review and Meta-Analysis

BACKGROUND

A subset of patients with uncomplicated type B aortic dissection (uTBAD) has been shown to possess higher risk of experiencing late adverse outcomes. Therefore, we conducted an analysis to investigate the role of descending aorta diameters, including total descending aorta diameter and false lumen diameter, as predictor of late adverse outcomes in patients with uTBAD.

METHODS

A systematic search was performed through Pubmed, ClinicalKey, ScienceDirect, and Cochrane Library to identify relevant studies. Our primary outcome was the composite late adverse events following their first episode of hospitalization. All meta-analyses were performed using Review Manager version 5.4.

RESULTS

A total of 2,339 (male 68.8%) patients from a total of 15 cohorts were included in our analysis. During follow-up period, there were 655 (27.3%) and 149 (6.3%) cases of late adverse events and mortality, respectively. Patients with higher initial descending aorta diameter were at higher risk of developing late adverse events (RR 2.99 [2.60, 3.44]; P < 0.001) and mortality (RR 3.15 [2.34, 4.25]; P <0.001) throughout follow-up period. Maximum false lumen diameter at the initial presentation seemed to significantly be associated with late adverse events (RR 1.87 [1.46, 2.39]; P <0.001) but not with mortality (RR 2.55 [0.81-8.00; P = 0.11).

CONCLUSION

Descending aorta diameters, particularly maximum initial descending aorta diameter, is a good and helpful predictor of late adverse outcomes in patients with uTBAD.

Proximal False Lumen Thrombosis is Associated with Low False Lumen Pressure and Fewer Complications in Type B Aortic Dissection

BACKGROUND

Improved risk stratification is a key priority for type B aortic dissection (TBAD). Partial false lumen thrombus morphology is an emerging predictor of complications however, partial thrombosis is poorly defined and its evaluation in clinical studies is inconsistent.

PURPOSE

This work aims to characterise hemodynamic pressure in TBAD and determine how pressure relates to false lumen thrombus morphology and clinical events.

METHODS

Retrospective admission computed tomography angiography of 69 patients with acute TBAD was used to construct three-dimensional computational models for simulation of cyclical blood flow and calculation of pressure. Patients were categorised based on false lumen thrombus morphology: minimal; proximal; distal; or extensive thrombosis. Linear regression analysis compared the luminal pressure difference between the true and false lumen for each morphology group. The impact of morphology classification on acute complications within 14 days was studied using logistic regression adjusted for clinical parameters. A survival analysis for adverse aortic events at one-year was also performed using Cox regression.

RESULTS

44 patients experienced acute complications and 45 had an adverse aortic event at one-year. Mean (±standard deviation) age was 62.6 (±12.6) years and 75.4% were male. Compared to patients with minimal thrombosis, those with proximal thrombosis had reduced false lumen pressure by 10.1mmHg (95% CI 4.3-15.9mmHg, p=.001). Individuals that did not experience an acute complication had reduced relative false lumen pressure (-6.35mmHg vs -0.62mmHg, p=.03). Proximal thrombosis was associated with fewer acute complications (OR 0.17, 95% CI 0.04-0.60 p=.01) and one-year adverse aortic events (HR 0.36, 95% CI 0.16-0.80, p=.01).

CONCLUSIONS

Proximal false lumen thrombosis is a marker of reduced false lumen pressure. This may explain how proximal false lumen thrombosis appears protective of acute complications (refractory hypertension or pain, aortic rupture, visceral or limb malperfusion and acute expansion) and adverse aortic events within the first year.

Before and after Endovascular Aortic Repair in the Same Patients with Aortic Dissection: A Cohort Study of Four-Dimensional Phase-Contrast Magnetic Resonance Imaging

(1) Background: We used four-dimensional phase-contrast magnetic resonance imaging (4D PC-MRI) to evaluate the impact of an endovascular aortic repair (TEVAR) on aortic dissection. (2) Methods: A total of 10 patients received 4D PC-MRI on a 1.5-T MR both before and after TEVAR. (3) Results: The aortas were repaired with either a GORE TAG Stent (Gore Medical; n = 7) or Zenith Dissection Endovascular Stent (Cook Medical; n = 3). TEVAR increased the forward flow volume of the true lumen (TL) (at the abdominal aorta, p = 0.047). TEVAR also reduced the regurgitant fraction in the TL at the descending aorta but increased it in the false lumen (FL). After TEVAR, the stroke distance increased in the TL (at descending and abdominal aorta, p = 0.018 and 0.015), indicating more effective blood transport per heartbeat. Post-stenting quantitative flow revealed that the reductions in stroke volume, backward flow volume, and absolute stroke volume were greater when covered stents were used than when bare stents were used in the FL of the descending aorta. Bare stents had a higher backward flow volume than covered stents did. (4) Conclusions: TEVAR increased the stroke volume in the TL and increased the regurgitant fraction in the FL in patients with aortic dissection.

Computational Fluid Dynamic Technique for Assessment of How Changing Character of Blood Flow and Different Value of Hct Influence Blood Hemodynamic in Dissected Aorta

Using computer tomography angiography (CTA) and computational structural analysis, we present a non-invasive method of mass flow rate/velocity and wall stress analysis in type B aortic dissection. Three-dimensional (3D) computer models of the aorta were calculated using pre-operative (baseline) and post-operative CT data from 12 male patients (aged from 51 to 64 years) who were treated for acute type B dissection. A computational fluid dynamics (CFD) technique was used to quantify the displacement forces acting on the aortic wall in the areas of endografts placement. The mass flow rate and wall stress were measured and quantified using the CFD technique. The CFD model indicated the places with a lower value of blood velocity and shear rate, which corelated with higher blood viscosity and a probability of thrombus appearance. Moreover, with the increase in Hct, blood viscosity also increased, while the intensity of blood flow provoked changing viscosity values in these areas. Furthermore, the velocity gradient near the tear surface caused high wall WSS; this could lead to a decreased resistance in the aorta’s wall with further implications to a patient.

Utility of 4D Flow MRI in Thoracic Aortic Diseases: A Literature Review of Clinical Applications and Current Evidence

Despite the recent technical developments, surgery on the thoracic aorta remains challenging and is associated with significant mortality and morbidity. Decisions about when and if to operate are based on a balance between surgical risk and the hazard of aortic rupture. These decisions are sometimes difficult in elective cases of thoracic aortic diseases, including aneurysms and dissections. Abnormal wall stress derived from flow alterations influences disease progression. Therefore, a better understanding of the complex hemodynamic environment inside the aortic lumen will facilitate patient-specific risk assessments of complications, which enable clinicians to provide timely prophylactic interventions. Time-resolved 3D phase-contrast (4D flow) MRI has many advantages for the in vivo assessment of flow dynamics. Recent developments in 4D flow imaging techniques has led to significant advances in our understanding of physiological flow dynamics in healthy subjects and patients with thoracic aortic diseases. In this clinically focused review of thoracic aortic diseases, we demonstrate the clinical advances acquired with 4D flow MRI from published studies. We provide a systematic overview of key evidences and considerations regarding normal thoracic aortas, thoracic aortic aneurysms, aortic dissections, and thoracic aortas with prosthetic graft replacement.

Distal Aortic Remodeling after Type A Dissection Repair: An Ongoing Mirage

Remodeling is a commonly encountered term in the field of cardiothoracic surgery that is often used to describe various pathophysiological changes in the dimension, structure, and function of various cardiac chambers, including the aorta. Stanford type A or DeBakey type 1 aortic dissection (TAAD) is a perplexing pathologic condition that can present surgical teams with the need to navigate a maze of complex decision-making. Ascending or hemi-arch replacement leaves behind a significant amount of distal diseased aortic tissue, which might have a persistent false lumen or primary or secondary intimal tears (or communications between lumina), which can lead to dilatation of the aortic arch. Unfavorable aortic remodeling is a major cause of distal aortic deterioration after the index surgery. Cardiac surgeons are aware of post-surgical cardiac chamber remodeling, but the concept of distal aortic remodeling is still idealized. The contemporary literature from established aortic centers supports aggressive management of the residual aortic pathology during the index surgery, and with continuing technical advancements, endovascular stenting options are readily available for patients with TAAD or for complicated type B aortic dissection cases. This review discusses the pathophysiology and treatment options for favorable distal aortic remodeling, as well as its impact on mid- to long-term outcomes following TAAD repair.

A Mock Circulation Loop for In Vitro Hemodynamic Evaluation of Aorta: Application in Aortic Dissection

PURPOSE

Aortic dissection (AD) is a catastrophic disease with complex hemodynamic conditions, however, understandings regarding its perfusion characteristics were not sufficient. In this study, a mock circulation loop (MCL) that integrated the Windkessel element and patient-specific silicone aortic phantoms was proposed to reproduce the aortic flow environment in vitro.

MATERIALS AND METHODS

Patient-specific normal and dissected aortic phantoms with 12 branching vessels were established and embedded into this MCL. Velocities for aortic branches based on 20 healthy volunteers were regarded as the standardized data for flow division. By altering boundary conditions, the proposed MCL could mimic normal resting and left-sided heart failure (LHF) conditions. Flow rates and pressure status of the aortic branches could be quantified by separate sensors.

RESULTS

In normal resting condition, the simulated heart rate and systemic flow rate were 60 bpm and 4.85 L/minute, respectively. For the LHF condition, the systolic and diastolic blood pressures were 75.94±0.77 mmHg and 57.65±0.35 mmHg, respectively. By tuning the vascular compliance and peripheral resistance, the flow distribution ratio (FDR) of each aortic branch was validated by the standardized data in the normal aortic phantom (mean difference 2.4%±1.70%). By comparing between the normal and dissected aortic models under resting condition, our results indicated that the AD model presented higher systolic (117.82±0.60 vs 108.75±2.26 mmHg) and diastolic (72.38±0.58 vs 70.46±2.33 mmHg) pressures, the time-average velocity in the true lumen (TL; 36.95 cm/s) was higher than that in the false lumen (FL; 22.95 cm/s), and the blood transport direction between the TL and FL varied in different re-entries.

CONCLUSIONS

The proposed MCL could be applied as a research tool for in vitro hemodynamic analysis of the aorta diseases under various physical conditions.

Retrospective analysis of factors associated with aortic remodeling in patients with Stanford type B aortic dissection after thoracic endovascular aortic repair

Objective

Acute aortic dissection is a life-threatening condition. Thoracic endovascular aortic repair (TEVAR), together with optimized medical treatment, is currently the first line treatment for acute Stanford type B aortic dissection. TEVAR can close the entry tear and reduce mortality. Aortic remodeling after TEVAR can directly affect the patient’s long-term prognosis. The factors that influence aortic remodeling have, however, received insufficient clinical attention and remain unclear. It is very important to identify these factors.

Methods

A total of 100 patients were continuously enrolled from 2011 to 2018 in 2 centers. Relevant data, including time from hospital admission to surgery, medicine use and aortic computed tomography angiography images obtained before and 6 months after surgery were collected. Patients were divided into favorable and adverse aortic remodeling groups, according to the degree of aortic remodeling. Analysis of variance and the chi-square test were performed using SPSS software to compare differences between groups and to determine the factors that influence postoperative aortic remodeling.

Results

The proportion of single-stent implantations was higher in the favorable remodeling group than in the adverse remodeling group (79.5% vs. 53.8% in distal end of stent-graft level and 81.3% vs. 56.4% in diaphragm level, respectively, p < 0.05). The earlier the TEVAR procedure was performed, the better the aortic remodeling (3.4 days vs. 4.8 days in distal stent graft levels, and 3.6 days vs. 4.9 days in diaphragm level, respectively, p < 0.05), the presence of residual distal entry tears in the abdominal aorta also improved aortic remodeling after TEVAR (85.7% vs. 55.1% in the celiac trunk level, and 92.0% vs. 48.9% in the right renal artery level, respectively, p < 0.05).

Conclusion

Single stent-graft implantation and early surgery were associated with favorable aortic remodeling. Distal entry tears were also conducive to aortic remodeling after surgery for aortic dissection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13019-021-01571-2.

Noninvasive Morphologic and Hemodynamic Evaluation of Type B Aortic Dissection: State of the Art and Future Perspectives

Stanford type B aortic dissection (TBAD) is associated with relatively high rates of morbidity and mortality, and appropriate treatment selection is important for optimizing patient outcomes. Depending on individualized risk factors, clinical presentation, and imaging findings, patients are generally stratified to optimal medical therapy anchored by antihypertensives or thoracic endovascular aortic repair (TEVAR). Using standard anatomic imaging with CT or MRI, several high-risk features including aortic diameter, false lumen (FL) features, size of entry tears, involvement of major aortic branch vessels, or evidence of visceral malperfusion have been used to select patients likely to benefit from TEVAR. However, even with these measures, the number needed to treat for TEVAR remains, and improved risk stratification is needed. Increasingly, the relationship between FL hemodynamics and adverse aortic remodeling in TBAD has been studied, and evolving noninvasive techniques can measure numerous FL hemodynamic parameters that may improve risk stratification. In addition to summarizing the current clinical state of the art for morphologic TBAD evaluation, this review provides a detailed overview of noninvasive methods for TBAD hemodynamics characterization, including computational fluid dynamics and four-dimensional flow MRI. Keywords: CT, Image Postprocessing, MRI, Cardiac, Vascular, Aorta, Dissection © RSNA, 2021.

False lumen ejection fraction predicts growth in type B aortic dissection: preliminary results

OBJECTIVES

Current risk assessment strategies in type B aortic dissection are focused on anatomic parameters, although haemodynamic abnormalities that result in false lumen (FL) pressurization are thought to play a significant role in aortic growth. The objective of this study was to evaluate blood flow of the FL using 4D flow magnetic resonance imaging (MRI) and identify haemodynamic and anatomic factors that independently predict the rate of aortic growth.

METHODS

Patients with dissection of the descending thoraco-abdominal aorta (n = 18) were enrolled in a prospective observational study and underwent 4D flow MRI for haemodynamic assessment of the entry tear and FL. Anatomic parameters were obtained by magnetic resonance angiography and baseline computed tomography. False lumen ejection fraction (FL EF) was defined the ratio of retrograde flow rate at the dominant entry tear during diastole over the antegrade systolic flow rate.

RESULTS

The median aortic growth rate was 3.5 mm/year (interquartile range 0.5-8.1 mm/year). Entry tear peak velocity was lower in patients with enlarging aortic dimensions (95.5 ± 24.1 vs 128.1 ± 37.4 cm/s, P = 0.039). After adjusting for co-variates FL EF (β = 0.15, P = 0.004), baseline maximal aortic diameter (β = 0.37, P = 0.001) and the entry tear distance from the left subclavian artery (β = 0.07, P = 0.016) were significant predictors of aortic growth rate.

CONCLUSIONS

Beyond standard anatomic risk factors, FL EF is an independent predictor of aortic growth rate and may represent an intuitive, non-invasive method to estimate FL pressurization and improve patient-specific risk assessment in patients with type B aortic dissection.

The characteristics of distal tears affect false lumen thrombosis rate after thoracic endovascular aortic repair for acute type B dissection

OBJECTIVES

A low false lumen thrombosis rate (FLTR) is common in patients with type B aortic dissection after they have undergone thoracic endovascular aortic repair, which indicates a poor long-term prognosis. This study aimed to establish a quantitative linear regression model to predict false lumen (FL) thrombosis accurately using morphological parameters.

METHODS

In this retrospective study, we included 59 patients diagnosed with acute type B aortic dissection between 2014 and 2017. Morphological parameters were measured. Univariable and multivariable linear regression analyses were performed, and a linear regression model relating FLTR with the number of re-entry tears was proposed. Ten patients were further chosen to validate the linear relationship, and idealized aortic dissection models were adopted for haemodynamic analysis.

RESULTS

Only the total area and number of re-entry tears were negatively correlated with FL thrombosis (P < 0.001). Moreover, based on the univariable regression, the number of re-entry tears played a more crucial role in FLTR (R2 = 0.509 vs R2 = 0.298), and the linear relationship model was created as follows: thrombosis rate (%) = -11.25 × distal tear number + 105.24. This model was perfectly matched in 10 patients (concordance correlation coefficient = 0.880, P = 0.947). Moreover, when the total area of re-entry tears was constant, the net blood flow increased rapidly with an increase in the tear count.

CONCLUSIONS

The number of re-entry tears could be a crucial related factor of FL thrombosis; the larger the number of re-entry tears is, the lower the possibility of thrombosis is.

Wall Shear Stress Assessment of the False Lumen in Acute Type B Aortic Dissection Visualized by 4-Dimensional Flow Magnetic Resonance Imaging: An Ex-Vivo Study

BACKGROUND

Four-dimensional flow magnetic resonance imaging (4D flow MRI) can accurately visualize and quantify flow and provide hemodynamic information such as wall shear stress (WSS). This imaging technique can be used to obtain more insight in the hemodynamic changes during cardiac cycle in the true and false lumen of uncomplicated acute Type B Aortic Dissection (TBAD). Gaining more insight of these forces in the false lumen in uncomplicated TBAD during optimal medical treatment, might result in prediction of adverse outcomes.

METHODS

A porcine aorta dissection model with an artificial dissection was positioned in a validated ex-vivo circulatory system with physiological pulsatile flow. 4D flow MR images with 3 set heartrates (HR; 60 bpm, 80 bpm and 100 bpm) were acquired. False lumen volume per cycle (FLV), mean and peak systolic WSS were determined from 4D flow MRI data. For validation, the experiment was repeated with a second porcine aorta dissection model.

RESULTS

During both experiments an increase in FLV (initial experiment: ΔFLV = 2.05 ml, p < 0.001, repeated experiment: ΔFLV = 1.08 ml, p = 0.005) and peak WSS (initial experiment: ΔWSS = 1.2 Pa, p = 0.004, repeated experiment: ΔWSS = 1.79 Pa, p = 0.016) was observed when HR increased from 60 to 80 bpm. Raising the HR from 80 to 100 bpm, no significant increase in FLV (p = 0.073, p = 0.139) was seen during both experiments. The false lumen mean WSS increased significant during initial (2.71 to 3.85 Pa; p = 0.013) and non-significant during repeated experiment (3.22 to 4.00 Pa; p = 0.320).

CONCLUSION

4D flow MRI provides insight into hemodynamic dimensions including WSS. Our ex-vivo experiments showed that an increase in HR from 60 to 80 bpm resulted in a significant increase of FLV and WSS of the false lumen. We suggest that strict heart rate control is of major importance to reduce the mean and peak WSS in uncomplicated acute TBAD. Because of the limitations of an ex-vivo study, 4D flow MRI will have to be performed in clinical setting to determine whether this imaging model would be of value to predict the course of uncomplicated TBAD.

Association of hemodynamic factors and progressive aortic dilatation following type A aortic dissection surgical repair

Type A aortic dissection (TAAD) involves the ascending aorta or the arch. Acute TAAD usually requires urgent replacement of the ascending aorta. However, a subset of these patients develops aortic rupture due to further dilatation of the residual dissected aorta. There is currently no reliable means to predict the risk of dilatation following TAAD repair. In this study, we performed a comprehensive morphological and hemodynamic analysis for patients with and without progressive aortic dilatation following surgical replacement of the ascending aorta. Patient-specific models of repaired TAAD were reconstructed from post-surgery computed tomography images for detailed computational fluid dynamic analysis. Geometric and hemodynamic parameters were evaluated and compared between patients with stable aortic diameters (N = 9) and those with aortic dilatation (N = 8). Our results showed that the number of re-entry tears and true/false lumen pressure difference were significantly different between the two groups. Patients with progressive aortic dilatation had higher luminal pressure difference (6.7 [4.6, 10.9] vs. 0.9 [0.5, 2.3] mmHg; P = 0.001) and fewer re-entry tears (1.5 [1, 2.8] vs. 5 [3.3, 7.5]; P = 0.02) compared to patients with stable aortic diameters, suggesting that these factors may serve as potential predictors of aneurysmal dilatation following surgical repair of TAAD.

Four-dimensional flow analysis reveals mechanism and impact of turbulent flow in the dissected aorta

 

OBJECTIVES

This study aimed to explore the flow dynamics factors affecting turbulence formation in the false lumen (FL) of aortic dissection using four-dimensional flow magnetic resonance imaging (4D flow MRI). This study also aimed to uncover risk factors affecting late complications of aortic dissection.

METHODS

Thirty-three aortic dissection patients were examined using 4D flow MRI for quantitative flow dynamics (gross flow, velocity and regurgitant fraction) and turbulence visualization (helix and vortex with three-point visual grading) in the FL. The incidence of late complications (rupture or prophylactic intervention) was also obtained prospectively.

RESULTS

The helix grade was correlated with FL gross flow (rS = 0.55, P < 0.001) and FL velocity (rS = 0.45, P = 0.008). The vortex grade was also correlated with FL gross flow (rS = 0.70, P < 0.001) and FL velocity (rS = 0.67, P < 0.001). Comparative analysis of patients with complications and stable patients revealed that patients with complications exhibited higher FL gross flow [41.7 (interquartile range, IQR 29.1-59.7) vs 17.7 (IQR 9.0-42.0) ml/s; P = 0.01], higher helix grade [2 (IQR 1.25-2) vs 0 (IQR 0-1); P = 0.001] and higher vortex grade [2 (IQR 1-2) vs 0 (IQR 0-2); P = 0.01].

CONCLUSIONS

Using 4D flow MRI analysis, we showed that turbulence formation depends on flow volume and velocity in the FL. Patients with high-volume turbulent flow in their FL are at higher risk of late complications; therefore, close follow-up and aggressive prophylactic intervention may improve their survival.

CLINICAL TRIAL REGISTRATION NUMBER

Nippon Medical School Hospital Institutional Review Board approved this observational study in September 2018 (No. 30-08-986).

False lumen pressure estimation in type B aortic dissection using 4D flow cardiovascular magnetic resonance: comparisons with aortic growth

BACKGROUND

Chronic type B aortic dissection (TBAD) is associated with poor long-term outcome, and accurate risk stratification tools remain lacking. Pressurization of the false lumen (FL) has been recognized as central in promoting aortic growth. Several surrogate imaging-based metrics have been proposed to assess FL hemodynamics; however, their relationship to enlarging aortic dimensions remains unclear. We investigated the association between aortic growth and three cardiovascular magnetic resonance (CMR)-derived metrics of FL pressurization: false lumen ejection fraction (FLEF), maximum systolic deceleration rate (MSDR), and FL relative pressure (FL ΔPmax).

METHODS

CMR/CMR angiography was performed in 12 patients with chronic dissection of the descending thoracoabdominal aorta, including contrast-enhanced CMR angiography and time-resolved three-dimensional phase-contrast CMR (4D Flow CMR). Aortic growth rate was calculated as the change in maximal aortic diameter between baseline and follow-up imaging studies over the time interval, with patients categorized as having either 'stable' (< 3 mm/year) or 'enlarging' (≥ 3 mm/year) growth. Three metrics relating to FL pressurization were defined as: (1) FLEF: the ratio between retrograde and antegrade flow at the TBAD entry tear, (2) MSDR: the absolute difference between maximum and minimum systolic acceleration in the proximal FL, and (3) FL ΔPmax: the difference in absolute pressure between aortic root and distal FL.

RESULTS

FLEF was higher in enlarging TBAD (49.0 ± 17.9% vs. 10.0 ± 11.9%, p = 0.002), whereas FL ΔPmax was lower (32.2 ± 10.8 vs. 57.2 ± 12.5 mmHg/m, p = 0.017). MSDR and conventional anatomic variables did not differ significantly between groups. FLEF showed positive (r = 0.78, p = 0.003) correlation with aortic growth rate whereas FL ΔPmax showed negative correlation (r = - 0.64, p = 0.026). FLEF and FL ΔPmax remained as independent predictors of aortic growth rate after adjusting for baseline aortic diameter.

CONCLUSION

Comparative analysis of three 4D flow CMR metrics of TBAD FL pressurization demonstrated that those that focusing on retrograde flow (FLEF) and relative pressure (FL ΔPmax) independently correlated with growth and differentiated patients with enlarging and stable descending aortic dissections. These results emphasize the highly variable nature of aortic hemodynamics in TBAD patients, and suggest that 4D Flow CMR derived metrics of FL pressurization may be useful to separate patients at highest and lowest risk for progressive aortic growth and complications.

False lumen enhancement characteristics on computed tomography angiography predict risk of aneurysm formation in acute type B aortic dissection

OBJECTIVES

Differential luminal enhancement [between true lumen (TL) and false lumen (FL)] results from differential flow patterns, most likely due to outflow restriction in the FL. We aimed to assess the impact of differential luminal enhancement at baseline computed tomography angiography on the risk of adverse events in patients with acute type B aortic dissection (TBAD).

METHODS

Baseline computed tomography angiographies of patients with acute TBAD between 2007 and 2016 (n = 48) were analysed using three-dimensional software at multiple sites along the descending thoraco-abdominal aorta. At each location, we measured contrast density in TL and FL [Houndsfield unit (HU)], maximal diameter (cm) and circumferential FL extent (°). Outcome data were collected via retrospective chart review. Multivariable logistic regression models were employed to determine the independent risk of TL-FL differential luminal enhancement on aneurysm formation (maximal diameter ≥55 mm) and medical treatment failure.

RESULTS

Patients were predominately male (75%) and 52.8±12.9 years at diagnosis. The mean follow-up was 5.9±2.6 years, and 42% (n = 20/48) patients were diagnosed with thoraco-abdominal aortic aneurysm. The baseline absolute difference between FL and TL contrast density measured at 2 cm distal to primary entry tear (TL-FLabs-Tear) was significantly higher among patients who developed aneurysm (26 HU, IQR: 15-53 vs 13 HU, IQR: 4-24, P = 0.001). Aneurysm development during follow-up was predicted by TL-FLabs-Tear (odds ratio 1.07, P = 0.012) and baseline maximal aortic diameter (odds ratio 1.90, P < 0.001). High (≥18 HU) differential luminal enhancement was associated with lower rates of aneurysm-free survival and higher rates of medical treatment failure.

CONCLUSIONS

Differential luminal enhancement may be a novel predictor of aneurysm formation among patients with acute TBAD.

Thoracic Endovascular Aortic Repair With Additional Distal Bare Stents in Type B Aortic Dissection Does Not Prevent Long-Term Aneurysmal Degeneration

PURPOSE

TEVAR (thoracic endovascular aortic repair) + PETTICOAT (Provisional ExTension to Induce COmplete ATtachment) technique has been selectively employed since 2005 at our institution during endovascular treatment of type B aortic dissection (TBD). The aim of this study is to evaluate the long-term (>5 years) clinical results and the evolution of aortic volume.

MATERIALS AND METHODS

All the patients receiving an endovascular treatment for TBD with the PETTICOAT technique were collected in a prospectively maintained database and follow-up computed tomography scan were retrospectively analyzed. Study endpoints included short- and long-term clinical success (absence of need for reintervention) and any major adverse event. The volumes of thoracic and abdominal aorta at long-term follow-up were also analyzed.

RESULTS

Twenty-eight patients received a TEVAR + PETTICOAT and were followed up (median follow-up 85 months). Primary 30-day clinical success rate was 82% with an adverse event rate of 31%; 4 type I endoleak and 1 retrograde dissection were recorded. Secondary mid-term clinical success was 96% while the long-term clinical success rate was 79%. Six cases (21%) received either an open repair or an endovascular repair for a significant distal aortic enlargement at follow-up. With regards to volumetric analysis, an increase of overall (thoracic and abdominal) aortic volume was observed in 8 cases mainly related to an increase (mean: +31%) of the abdominal volume that was observed in 11 cases.

CONCLUSIONS

PETTICOAT technique does not protect from long-term significant aneurysmal degeneration that may require aortic open or endovascular reinterventions. Aortic growth occurs mainly in the bare-stented aorta and thus, life-long surveillance is advisable in these patients.

Review of Current Advances in the Mechanical Description and Quantification of Aortic Dissection Mechanisms

Aortic dissection is a life-threatening event associated with a very poor outcome. A number of complex phenomena are involved in the initiation and propagation of the disease. Advances in the comprehension of the mechanisms leading to dissection have been made these last decades, thanks to improvements in imaging and experimental techniques. However, the micro-mechanics involved in triggering such rupture events remains poorly described and understood. It constitutes the primary focus of the present review. Towards the goal of detailing the dissection phenomenon, different experimental and modeling methods were used to investigate aortic dissection, and to understand the underlying phenomena involved. In the last ten years, research has tended to focus on the influence of microstructure on initiation and propagation of the dissection, leading to a number of multiscale models being developed. This review brings together all these materials in an attempt to identify main advances and remaining questions.

Optimal phase analysis of electrocardiogram-gated computed tomography angiography in patients with Stanford type A acute aortic dissection

Objective

To determine the phase that facilitates flap observation of the ascending aorta in Stanford type A acute aortic dissection with perfused false lumen.

Methods

We reconstructed retrospective Electrocardiogram-gated Computed Tomography Angiography images of the ascending aorta of all 20 patients to 20 phases of curved-multiplanar reconstruction in 5% increment. One radiologist created and randomized 10 cross-sectional images of each phase for every patient and two radiologists scored these images on a 5-point scale depending on the degree of flap stoppage. We calculated the average score for each phase of each case and compared them among the three groups.

Results

Image scores were significantly better in the 65 %-100 % R-R interval group than those in the 5%-30 % (p < 2e-16) and 35 %-60 % R-R interval groups(p = 7.2e-10). Similar scores were observed in the Heart Rate > 70 group (p = 0.00039, 2.2e-14). Moreover a similar tendency was observed in the arrhythmia group (p = 0.0035, 0.294). No difference was found in the degree of flap stoppage in the 65 %-100 % R-R interval group between the Heart Rate > 70 and Heart Rate ≤ 70 groups (p = 0.466) and between the arrhythmia and non-arrhythmia groups (p = 0.1240).

Conclusion

In observing the ascending aorta, We obtained a good image at 65 %-100 % R-R interval and similar tendency was observed in the patients with arrhythmia.

Effect of intimal flap motion on flow in acute type B aortic dissection by using fluid-structure interaction

A monolithic, fully coupled fluid-structure interaction (FSI) computational framework was developed to account for dissection flap motion in acute type B aortic dissection (TBAD). Analysis of results included wall deformation, pressure, flow, wall shear stress (WSS), von Mises stress and comparison of hemodynamics between rigid wall and FSI models. Our FSI model mimicked realistic wall deformation that resulted in maximum compression of the distal true lumen (TL) by 21.4%. The substantial movement of intimal flap mostly affected flow conditions in the false lumen (FL). Flap motion facilitated more flow entering the FL at peak systole, with the TL to FL flow split changing from 88:12 in the rigid model to 83:17 in the FSI model. There was more disturbed flow in the FL during systole (5.8% FSI vs 5.2% rigid) and diastole (13.5% FSI vs 9.8% rigid), via a λ₂ -criterion. The flap-induced disturbed flow near the tears in the FSI model caused an increase of local WSS by up to 70.0% during diastole. This resulted in a significant reduction in the size of low time-averaged WSS (TAWSS) regions in the FL (113.11 cm² FSI vs 177.44 cm² rigid). Moreover, the FSI model predicted lower systolic pressure, higher diastolic pressure, and hence lower pulse pressure. Our results provided new insights into the possible impact of flap motion on flow in aortic dissections, which are particularly important when evaluating hemodynamics of acute TBAD. NOVELTY STATEMENT: Our monolithic fully coupled FSI computational framework is able to reproduce experimentally measured range of flap deformation in aortic dissection, thereby providing novel insights into the influence of physiological flap motion on the flow and pressure distributions. The drastic flap movement increases the flow resistance in the true lumen and causes more disturbed flow in the false lumen, as visualized through the λ₂ criterion. The flap-induced luminal pressure is dampened, thereby affecting pressure measures, which may serve as potential prognostic indicators for late complications in acute uncomplicated TBAD patients.

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.