Review of Systemic Mock Circulation Loops for Evaluation of Implantable Cardiovascular Devices and Biological Tissues

CLINICAL IMPACT

On needs-based ex vivo monitoring of implantable devices or tissues/organs in cardiovascular simulators provides new insights and paves new paths for device prototypes. The insights gained could not only support the needs of patients, but also inform engineers, scientists and clinicians about undiscovered aspects of diseases (during routine monitoring). We analyze seminal and current work and highlight a variety of opportunities for developing preclinical tools that would improve strategies for future implantable devices. Holistically, mock circulation loop studies can bridge the gap between in vivo and in vitro approaches, as well as clinical and laboratory settings, in a mutually beneficial manner.

Type III aortic arch angulation increases aortic stiffness: Analysis from an ex vivo porcine model

Objective

The relationship among increased aortic arch angulation, aortic flow dynamics, and vessel wall stiffness remains unclear. This experimental ex vivo study investigated how increased aortic arch angulation affects aortic stiffness and stent-graft induced aortic stiffening, assessed by pulse wave velocity (PWV).

Methods

Porcine thoracic aortas were connected to a circulatory mock loop in a Type I and Type III aortic arch configuration. Baseline characteristics and blood pressures were measured. Proximal and distal flow curves were acquired to calculate PWV in both arch configurations. After that, a thoracic stent-graft (VAMF2626C100TU) was deployed in aortas with adequate proximal landing zone diameters to reach 10% t0 20% oversizing. Acquisitions were repeated for both arch configurations after stent-graft deployment.

Results

Twenty-four aortas were harvested, surgically prepared, and mounted. Cardiac output was kept constant for both arch configurations (Type I: 4.74 ± 0.40 and Type III: 4.72 ± 0.38 L/minute; P = .703). Compared with a Type I arch, aortic PWV increased significantly in the Type III arch (3.53 ± 0.40 vs 3.83 ± 0.40 m/second; P < .001), as well as blood pressures. A stent-graft was deployed in 15 aortas. After deployment, Type I arch PWV increased (3.55 ± 0.39 vs 3.81 ± 0.44 m/second; P < .001) and Type III arch PWV increased although not significantly (3.86 ± 0.42 vs 4.03 ± 0.46 m/second; P = .094). Type III arch PWV resulted the highest and significantly higher compared with the Type I arch after stent-graft deployment (3.81 ± 0.44 vs 4.03 ± 0.46 m/second; P = .023).

Conclusions

Increased aortic arch angulation-as in a Type III arch-is associated with higher aortic PWV and blood pressures and this may negatively influence cardiovascular health.

Depressed Ejection Fraction Does Not Affect Perioperative Mortality After Thoracic Endovascular Aortic Repair for Type B Aortic Dissection

BACKGROUND

Despite the expanded application of thoracic endovascular aortic repair (TEVAR) in patients with significant cardiac comorbidities, the effect of decreased left ventricular ejection fraction (EF) on outcomes remains unknown. The aim of this study was to compare outcomes in patients with normal and abnormal EFs undergoing TEVAR for type-B aortic dissection (TBAD).

METHODS

The Vascular Quality Initiative database was reviewed from 2012 to 2020. Patients were categorized into severely reduced (EF ≤ 30%), reduced (EF 30-50%) and normal EF (EF>50%). Baseline characteristics, procedural details and 18-month outcomes were compared. Multivariable logistic regression identified factors associated with mortality, major adverse cardiac events (MACEs), and aortic-related reintervention.

RESULTS

Of 1,993 patients, 38 (2%) and 208 (10%) patients had severely reduced ejection fraction (SREF) and reduced ejection fraction (REF). Patients with abnormal EF were more likely to have cardiac comorbidities and be prescribed angiotensin-converting enzyme inhibitors and anticoagulants. Perioperatively, patients with SREF were more likely to experience mortality (13.2% vs. 6.7% vs. 4.4%, P = 0.018), MACE (26.3% vs. 11.5% vs. 8%, P < 0.001), hemodialysis (13.5% vs. 5% vs. 2.9%, P = 0.001) and aortic related reintervention (21.1% vs. 13% vs. 10%, P = 0.041), compared to REF and normal ejection fraction (NEF) patients. However, these associations were not present on multivariable analysis. At 18 months, mortality was significantly higher in patients with SREF, which was confirmed on multivariable analysis, but depressed EF was not associated with increased aortic reintervention compared to NEF.

CONCLUSIONS

SREF was not independently associated with perioperative mortality or MACE compared to NEF. REF had similar risk of morbidity and mortality compared to NEF in both the perioperative and early postoperative periods. TEVAR-related complications were similar among the cohorts. As such, TEVAR may be offered to appropriately selected patients regardless of EF.

Impact of thoracic endovascular aortic repair on aortic biomechanics: Integration of in silico and ex vivo analysis using porcine model

Thoracic endovascular aortic repair (TEVAR) is widespread in clinical practice for treating aortic diseases but it has relevant systemic complications, such as increase of the cardiac workload due to post-TEVAR aortic stiffening, and local issues such as re-entry tears due to the tissue damage caused by endograft interaction. The present study aims to elucidate these aortic biomechanical mechanisms by coupling ex vivo and in silico analysis. By ex vivo tests, the pulse wave velocity before and after TEVAR is measured. Uni-axial tensile tests are performed to measure regional mechanical response of tissue samples, supplied as input data for the in silico analysis. Numerical analysis is finally performed to compute the wall stress induced by the stent-graft deployment and the arterial pressurization. The ex vivo results highlight an increase of baseline PWV by a mean .78 m/s or 12% after TEVAR with a 100 mm stent-graft (p <.013). In the in silico analysis, the average von Mises stress in the landing zone increases of about 15% and 20% using, respectively stent-graft with radial oversizing of 10% and 20%. This work shows the effectiveness of integrated framework to analyze the biomechanical post TEVAR mechanisms. Moreover, the obtained results quantify the effect of prosthesis selection on the stiffening of the aorta after TEVAR and on the local increase of the aortic wall stress that is proportional to the stent-graft oversizing.

Global and local stiffening of ex vivo-perfused stented human thoracic aortas: A mock circulation study

The effects of thoracic endovascular repair (TEVAR) on the biomechanical properties of aortic tissue have not been adequately studied. Understanding these features is important for the management of endograft-triggered complications of a biomechanical nature. This study aims to examine how stent-graft implantation affects the elastomechanical behavior of the aorta. Non-pathological human thoracic aortas (n=10) were subjected to long-standing perfusion (8h) within a mock circulation loop under physiological conditions. To quantify compliance and its mismatch in the test periods without and with a stent, the aortic pressure and the proximal cyclic circumferential displacement were measured. After perfusion, biaxial tension tests (stress-stretch) were carried out to examine the stiffness profiles between non-stented and stented tissue, followed by a histological assessment. Experimental evidence shows: (i) a significant reduction in aortic distensibility after TEVAR, indicating aortic stiffening and compliance mismatch, (ii) a stiffer behavior of the stented samples compared to the non-stented samples with an earlier entry into the nonlinear part of the stress-stretch curve and (iii) strut-induced histological remodeling of the aortic wall. The biomechanical and histological comparison of the non-stented and stented aortas provides new insights into the interaction between the stent-graft and the aortic wall. The knowledge gained could refine the stent-graft design to minimize the stent-induced impacts on the aortic wall and the resulting complications. STATEMENT OF SIGNIFICANCE: Stent-related cardiovascular complications occur the moment the stent-graft expands on the human aortic wall. Clinicians base their diagnosis on the anatomical morphology of CT scans while neglecting the endograft-triggered biomechanical events that compromise aortic compliance and wall mechanotransduction. Experimental replication of endovascular repair in cadaver aortas within a mock circulation loop may have a catalytic effect on biomechanical and histological findings without an ethical barrier. Demonstrating interactions between the stent and the wall can help clinicians make a broader diagnosis such as ECG-triggered oversizing and stent-graft characteristics based on patient-specific anatomical location and age. In addition, the results can be used to optimize towards more aortophilic stent grafts.

Experimental and theoretical investigation of aortic wall tissue in tensile tests

BACKGROUND

Understanding the mechanical properties of aortic tissue is essential for developing numerical computation tools and assessing the risk of aortic aneurysm fractures. Tensile tests using aortic wall specimens allow for the determination of stress and strain depending on the location and direction of the sample.

OBJECTIVE

The aim of this study was to perform a mechanical tensile test using canine aorta samples and create a numerical model of aortic tissue tension from the processed data.

METHODS

Dogbone-shaped samples were dissected from canine aortic segments. The initial measurements were made at zero tension and the tensile tests were conducted at 10 mm/min until rupture. Force and stretch data were used to obtain engineering and true stress-strain curves. The true stress-strain curves were taken until the maximum strength was obtained, after which they were smoothed and fitted using a logistic function with three coefficients. These curves were then used as material mechanical properties for a numerical model of the aortic tissue tension. A simplified rectangle form was used to mimic the middle of the dogbone-shaped portion of the tissue specimen. Experimental displacement data were collected for the boundary conditions of the finite element 3D model.

RESULTS

The experimental data processing revealed that the logistic function described the nonlinear behaviour of the aorta soft tissue with an accuracy of 95% from the start of the tension to the media layer rupture. By applying numerical simulations, we obtained a correspondence of the load curve with an RMSE = 0.069 for the theoretical and experimental external tension data.

CONCLUSION

The numerical investigation confirmed that the non-linear soft tissue was validated by applying a logistic function approach to the mechanical properties of the aortic wall.

Comparison of Two Generations of Thoracic Aortic Stent Grafts and Their Impact on Aortic Stiffness in an Ex Vivo Porcine Model

Objective

Little is known about the cardiovascular changes after TEVAR and regarding the impact on aortic stiffness for different stent graft generations specifically, following changes in device design. The present study evaluated the stent graft induced aortic stiffening of two generations of the Valiant thoracic aortic stent graft.

Methods

This was an ex vivo porcine investigation using an experimental mock circulatory loop. Thoracic aortas of young healthy pigs were harvested and connected to the mock circulatory loop. At a 60 bpm heart rate and stable mean arterial pressure, baseline aortic characteristics were obtained. Pulse wave velocity (PWV) was calculated before and after stent graft deployment. Paired and independent sample t tests or their non-parametric alternatives were performed to test for differences where appropriate.

Results

Twenty porcine thoracic aortas were divided into two equal subgroups, in which a Valiant Captivia or a Valiant Navion stent graft was deployed. Both stent grafts were similar in diameter and length. Baseline aortic characteristics did not differ between the subgroups. Mean arterial pressure values did not change after either stent graft, while pulse pressures increased statistically significantly after Captivia (mean 44 ± 10 mmHg to 51 ± 13 mmHg, p = .002) but not after Navion. Mean baseline PWV increased after both Captivia (4.4 ± 0.6 m/s to 4.8 ± 0.7 m/s, p = .007) and Navion (4.6 ± 0.7 m/s to 4.9 ± 0.7 m/s, p = .002). There was no statistically significant difference in the mean percentage increase in PWV for either subgroup (8 ± 4% vs. 6 ± 4%, p = .25).

Conclusion

These experimental findings showed no statistically significant difference in the percentage increase of aortic PWV after either stent graft generation and confirm that TEVAR increases aortic PWV. As a surrogate for aortic stiffness, this calls for further improvements in future thoracic aortic stent graft designs regarding device compliance.

Cardiac Stress in High-Risk Patients Undergoing Major Endovascular Surgery-Focus on Diastolic Function

OBJECTIVES

The purpose of this study was to determine the relationship between the changes in diastolic function and their association with cardiac biomarkers in the perioperative period in patients undergoing complex endovascular aortic repair.

DESIGN

Prospective observational study.

SETTING

Single-center academic hospital, central teaching hospital in Warsaw, Poland.

PARTICIPANTS

The study comprised 27 high-risk patients scheduled for elective endovascular repair of aortic aneurysm.

INTERVENTIONS

Complex endovascular procedure using branched endograft of the thoracoabdominal aorta. Branches of the stent grafts included renal arteries, the superior mesenteric artery, and the celiac trunk.

MEASUREMENTS AND MAIN RESULTS

The primary outcome was to evaluate changes in diastolic function parameters assessed with transthoracic echocardiography at two and 24 hours postoperatively. The major secondary outcomes were changes in N-terminal pro-B-type natriuretic peptide (NT-proBNP) and troponin I concentrations, systolic function parameters, hemodynamic parameters at two and 24 hours, length of hospital stay, and 30-day mortality. There was a reduction in e' wave velocity on both the septal and lateral sides at two hours compared with the baseline (p = 0.041 and p = 0.05, respectively). There was an increase in both NT-proBNP and troponin I concentrations after surgery (p = 0.002 and p = 0.034, respectively), with troponin I peaking two hours after surgery and NT-proBNP peaking 24 hours after surgery.

CONCLUSIONS

Patients undergoing a branched endovascular aortic repair of a thoracoabdominal aortic aneurysm experience a cardiac insult that manifests with deterioration in diastolic parameters and concomitant increases of troponin and NT-proBNP concentrations. Additional large-scale prospective studies are required to confirm this phenomenon.

Exercise stress echocardiogram for the evaluation of change in the ventricular-arterial interaction after thoracic endovascular aortic repair

OBJECTIVES

The aim of this study was to explore, with exercise echocardiography, the potential impact of thoracic endovascular aortic repair (TEVAR) on the ventricle-aorta coupling, based on the hypothesis that the interaction between the ventricle and aorta may be influenced by an increase in aortic stiffness due to the stent graft.

METHODS

Of the patients who underwent isolated TEVAR for thoracic aortic diseases between April 2016 and December 2016, changes found in haemodynamic and echocardiographic parameters between the control (n = 17) and TEVAR (n = 30) groups were analysed by a stress echocardiogram.

RESULTS

The end-systolic elastance significantly increased with stress in both groups [from 3.0 (2.5-4.5) mmHg/ml to 4.8 (3.7-6.5) mmHg/ml, P < 0.001, in the control group and from 2.9 (2.0-3.5) mmHg/ml to 3.4 (2.6-4.2) mmHg/ml, P < 0.001, in the TEVAR group]. The arterial elastance significantly elevated only in the TEVAR group [from 1.6 (1.3-1.8) mmHg/ml to 1.7 (1.5-2.0) mmHg/ml, P = 0.007] and arterial elastance/end-systolic elastance (ventricular-arterial coupling) significantly decreased only in the control group [from 0.5 (0.4-0.7) to 0.4 (0.3-0.5), P = 0.002, in the control group and from 0.6 (0.4-0.8) to 0.5 (0.4-0.6), P = 0.10, in the TEVAR group]. In the control group, the change in end-systolic elastance and ventricular-arterial coupling tended to be greater (P = 0.002 and 0.07).

CONCLUSIONS

An exercise echocardiogram showed the underlying influences of TEVAR on the interaction between the heart and aorta. TEVAR may have the potential to suppress left ventricular contractile capacity and increase cardiac afterload during exercise.

CLINICAL TRIAL REGISTRATION NUMBER

A201770-01.

Is the Risk of Aorta Injury or Impingement Higher During Correction Surgery in Patients with Severe and Rigid Scoliosis?

OBJECTIVE

To evaluate the position of the aorta relative to the spine and the risk of aortic injury during correction surgery in patients with idiopathic severe and rigid scoliosis (main curve Cobb angle >90° and flexibility <30%).

METHODS

Twenty-seven patients with severe right thoracic/thoracolumbar scoliosis were recruited. The entry point-aorta distance (EAD), the left pedicle-aorta angle (α), the left aorta angle (β), and the vertebral rotation angle (γ) were measured from 4 vertebrae above (A4) to 4 below (B4) the apical vertebra (Apex) to quantify the spatial relationship between aorta and spine. We simulated the pedicle screw misplacement with variable direction error, length, and diameter to analyze the potential risk of aortic injury.

RESULTS

The aorta shifted laterally and posteriorly as it descended from A4 and moved back medially and anteriorly from Apex. The potential risk of aortic injury increased with the augment of direction error and/or length of the screw, but the tendency was not significant with the augment of diameter. The risk peaked at A4, A3, and B2, when the screw length was 40 mm and diameter was 5.0 mm, and the direction error was 30°, whereas the risk was lowest at the apical level 14.3% (0%-40.7%) in any scenarios.

CONCLUSIONS

In patients with severe and rigid scoliosis, the aorta shifted more laterally and posteriorly, and the injury risk was lower at the apical level, compared with moderate scoliosis. Most potential risks can be minimized by careful preoperative planning and the assistance of intraoperative navigation or robotics.

Decreased biventricular function following thoracic endovascular aortic repair

OBJECTIVES

Preclinical studies have suggested acute stiffening of the aorta following experimental thoracic endovascular aortic repair (TEVAR), resulting in acute elevated pulse pressure, hypertension and possibly heart failure. The aim of this study was to evaluate cardiac remodelling following TEVAR.

METHODS

From 2005 to 2018, 519 TEVAR procedures were performed at a single centre. Transthoracic echocardiography was performed pre- and post-TEVAR in 31 patients without previous replacement of the thoracic aorta. Patient characteristics, drug information, radiographic and follow-up data were evaluated. Aortic details were measured in multiplanar reconstruction.

RESULTS

Transthoracic echocardiography was performed 2 ± 2 years after TEVAR. At this time, patients received significantly more antihypertensive drugs compared to the pre-TEVAR intake (beta-blocker therapy: P = 0.037; calcium channel blocker: P = 0.022). Compared to pre-TEVAR, there was a significant reduction in the left ventricular ejection fraction (P = 0.008) and tricuspid annular plane systolic excursion (P = 0.013) post-TEVAR. A significant increase in the left ventricular mass was not detected in this study (P = 0.95). The mean distance of 163 ± 66 mm of the descending aorta was covered.

CONCLUSIONS

This study suggests negative cardiac remodelling with a decrease in the left and right ventricular function following TEVAR despite an increase in oral antihypertensive medication. The impact of stiffer endovascular grafts compared with the native aortic wall should be considered by endovascular specialists and manufacturers.

Aortic Curvature Remodeling after Thoracic Endovascular Aortic Repair: Assessing Device Conformability, Using Image Vector Analysis

BACKGROUND

Aortic arch curvature can be straightened by endograft placement. However, different measurement methods with dissimilar follow-up and endografts have been published. The aim of this study was to corroborate, for the first time, the pliability of the Conformable Gore TAG Thoracic Endoprosthesis (W.L. Gore and Associates, Flagstaff, AZ, USA) into the aortic arch, using different image vector analysis.

MATERIAL AND METHODS

We, retrospectively, analyzed patients primarily treated for thoracic aortic aneurysms and blunt traumatic aortic injuries by means of a Conformable Gore TAG Thoracic Endoprosthesis endograft proximally sealed into the aortic arch (zones Z1-Z3) in five different Spanish centers, between 2010 and 2017. The preoperative, one-month and six-month postoperative, computed tomography angiographies (CTAs) were obtained, creating accurate 3D center lumen line and external lumen line from the aortic valve to the renal arteries. Three different image analysis methods were used to compare modifications of the aortic curvature: first, segment analysis (angulations of the center lumen line when divided into seven precise segments, examining anterior-posterior, right-left, and cranial-caudal displacement), second, center lumen line analysis (bending of the center lumen line itself in seven definite points), and third, expected behavior (length of the endograft in the external lumen line). Two independent observers performed a blind analysis of all CTAs. Changes between preoperative and postoperative CTAs at one and six months are compared, and differences are viewed between cases sealed proximally (Z1-Z2) and distally (Z3) into the aortic arch.

RESULTS

We analyzed 37 cases. At 1- and 6-month follow-ups, minimal changes occurred first in segment analysis (only a slight decrease of -2.0° in the XY plane at 10 cm from the brachiocephalic trunk at six-month follow-up was seen, P = 0.027). Second, center lumen line analysis again only showed negligible aortic curvature straightening (+3.5° at 10 cm from the brachiocephalic trunk at one month, P = 0.006, disappearing at six-month follow-up). Finally, good device length predictability was shown (interclass correlation coefficients: 0.995 and 0.994 at one and six months, P > 0.001). No differences were seen between cases proximally sealed into the proximal and distal aortic arch.

CONCLUSIONS

Conformable Gore TAG Thoracic Endoprosthesis thoracic endograft showed a good pliability into the aortic arch and proximal thoracic aorta, with minimal changes in the aortic curvature after endograft placement in the short-term follow-up (up to six months). In addition, final endograft length into outer aortic curvature is highly predictable.

Comparative Analysis of Porcine and Human Thoracic Aortic Stiffness

OBJECTIVES

To compare porcine and human thoracic aortic stiffness using the available literature.

METHODS

The available literature was searched for studies reporting data on porcine or human thoracic aortic mechanical behaviour. A four fibre constitutive model was used to transform the data from included studies. Thus, equi-biaxial stress stretch curves were generated to calculate circumferential and longitudinal aortic stiffness. Analysis was performed separately for the ascending and descending thoracic aorta. Data on human aortic stiffness were divided by age <60 or ≥60 years. Porcine and human aortic stiffness were compared.

RESULTS

Eleven studies were included, six reported on young porcine aortas, four on human aortas of various ages, and one reported on both. In the ascending aorta, circumferential and longitudinal stiffness were 0.42±0.08 MPa and 0.37±0.06 MPa for porcine aortas (4-9 months) versus 0.55±0.15 MPa and 0.45±0.08 MPa for humans <60 years, and 1.02±0.59 MPa and 1.03±0.54 MPa for humans ≥60 years. In the descending aorta, circumferential and longitudinal stiffness were 0.46±0.03 MPa and 0.44±0.01 MPa for porcine aortas (4-10 months) versus 1.04±0.70 MPa and 1.24±0.76 MPa for humans <60 years, and 3.15±3.31 MPa and 1.17±0.31 MPa for humans ≥60 years.

CONCLUSIONS

The stiffness of young porcine aortic tissue shows good correspondence with human tissue aged <60 years, especially in the ascending aorta. Young porcine aortic tissue is less stiff than human aortic tissue aged ≥60 years.

Reversed Auxiliary Flow to Reduce Embolism Risk During TAVI: A Computational Simulation and Experimental Study

INTRODUCTION

Endovascular treatments, such as transcatheter aortic valve implantation (TAVI), carry a risk of embolization due to debris dislodgement during various procedural steps. Although embolic filters are already available and marketed, mechanisms underlying cerebral embolism still need to be elucidated in order to further reduce cerebrovascular events.

METHODS

We propose an experimental framework with an in silico duplicate allowing release of particles at the level of the aortic valve and their subsequent capture in the supra-aortic branches, simulating embolization under constant inflow and controlled hemodynamic conditions. The effect of a simple flow modulation, consisting of an auxiliary constant flow via the right subclavian artery (RSA), on the amount of particle entering the brachiocephalic trunk was investigated. Preliminary computational fluid dynamics (CFD) simulations were performed in order to assess the minimum retrograde flow-rate from RSA required to deviate particles.

RESULTS

Our results show that a constant reversed auxiliary flow of 0.5 L/min from the RSA under a constant inflow of 4 L/min from the ascending aorta is able to protect the brachiocephalic trunk from particle embolisms. Both computational and experimental results also demonstrate that the distribution of the bulk flow dictates the distribution of the particles along the aortic branches. This effect has also shown to be independent of release location and flow rate.

CONCLUSIONS

The present study confirms that the integration of in vitro experiments and in silico analyses allows designing and benchmarking novel solutions for cerebral embolic protection during TAVI such as the proposed embo-deviation technique based on an auxiliary retrograde flow from the right subclavian artery.

Changes in aortic pulse wave velocity of four thoracic aortic stent grafts in an ex vivo porcine model

Objectives

Thoracic endovascular aortic repair (TEVAR) has been shown to lead to increased aortic stiffness. The aim of this study was to investigate the effect of stent graft type and stent graft length on aortic stiffness in a controlled, experimental setting.

Methods

Twenty porcine thoracic aortas were connected to a pulsatile mock loop system. Intraluminal pressure was recorded at two sites in order to measure pulse wave velocity (PWV) for each aorta: before stent graft deployment (t₁); after deployment of a 100-mm long stent graft (t₂); and after distal extension through deployment of a second 100-mm long stent graft (t₃). Four different types of stent grafts (Conformable Gore^® TAG^® Device, Bolton Relay^® Device, Cook Zenith Alpha^™, and Medtronic Valiant^®) were evaluated.

Results

For the total cohort of 20 aortas, PWV increased by a mean 0.6 m/s or 8.9% of baseline PWV after deployment of a 100-mm proximal stent graft (P<0.001), and by a mean 1.4 m/s or 23.0% of baseline PWV after distal extension of the stent graft (P<0.001). Univariable regression analysis showed a significant correlation between aortic PWV and extent of stent graft coverage, (P<0.001), but no significant effect of baseline aortic length, baseline aortic PWV, or stent graft type on the percentual increase in PWV at t₂ or at t₃.

Conclusions

In this experimental set-up, aortic stiffness increased significantly after stent graft deployment with each of the four types of stent graft, with the increase in aortic stiffness depending on the extent of stent graft coverage.

Appearance and rapid evolution of thoraco-abdominal intramural hematoma after TEVAR

Some studies consider the different physical properties of the stent graft when compared with the blood vessel on the basis of vascular lesions that may require further intervention. We present a case in which a patient developed an intramural hematoma at the distal landing of previous thoracic endovascular aortic repair (TEVAR) that required the relining with a flared prosthesis. During follow-up, we observed the appearance of more caudal hematoma. We decided to observe this lesion with close radiological controls. In order to prevent serious complication after the induction of TEVAR, accurate planning of the procedure is very important to study the impact of the prosthesis implanted in the cardiovascular system. In particular, oversize, radial forces and length of coverage have been taken into account. The adherence to follow-up is very important to precociously detect the lesions to avoid the onset of complication.

Impact of thoracic endovascular aortic repair on radial strain in an ex vivo porcine model

Objectives

To quantify the impact of thoracic endovascular aortic repair (TEVAR) on radial aortic strain with the aim of elucidating stent-graft-induced stiffening and complications.

Methods

Twenty fresh thoracic porcine aortas were connected to a mock circulatory loop driven by a centrifugal flow pump. A high-definition camera captured diameters at five different pressure levels (100, 120, 140, 160, and 180 mmHg), before and after TEVAR. Three oversizing groups were created: 0-9% ( n  = 7), 10-19% ( n  = 6), and 20-29% ( n  = 6). Radial strain (or deformation) derived from diameter amplitude divided by baseline diameter at 100 mmHg. Uniaxial tensile testing evaluated Young's moduli of the specimens.

Results

Radial strain was reduced after TEVAR within the stented segment by 49.4 ± 24.0% ( P  < 0.001). As result, a strain mismatch was observed between the stented segment and the proximal non-stented segment (7.0 ± 2.5% vs 11.8 ± 3.9%, P  < 0.001), whereas the distal non-stented segment was unaffected ( P  = 0.99). Stent-graft oversizing did not significantly affect the amount of strain reduction ( P  = 0.30). Tensile testing showed that the thoracic aortas tended to be more elastic proximally than distally ( P  = 0.11).

Conclusions

TEVAR stiffened the thoracic aorta by 2-fold. Such segmental stiffening may diminish the Windkessel function considerably and might be associated with TEVAR-related complications, including stent-graft-induced dissection and aneurysmal dilatation. These data may have implications for future stent-graft design, in particular for TEVAR of the highly compliant proximal thoracic aorta.