Endografting of the Descending Thoracic Aorta Increases Ascending Aortic Input Impedance and Attenuates Pressure Transmission in Dogs

Ascending Geometry After Thoracic Endovascular Aortic Repair for Descending Aortic Dissection

BACKGROUND

This study aimed to assess geometry changes of the ascending aorta after thoracic endovascular aortic repair (TEVAR) for descending aortic dissection and identify potential risk factors for diameter and length change.

METHODS

Between April 2009 and July 2021, 102 patients were treated for acute descending aortic dissections (type B and non-A non-B) with TEVAR and were included in this analysis. Computed tomography angiographic scans were transferred to a dedicated imaging software and detailed aortic measurements (including length, diameter and area) were taken in multiplanar reconstruction postoperatively, after 6 months and annually thereafter.

RESULTS

Sixty-five (58%) patients were male, with a mean age of 66 (±11). Four (4%) patients were diagnosed with connective tissue disease. Before TEVAR, 79% of our patients were treated with a mean of 1.5 (±1.2) different classes of antihypertensive medications. This number rose to 98% after TEVAR and 2.7 (±1.0) different antihypertensive drugs. There was no significant change in length, diameter, cross-sectional area, or volume of the ascending aorta during the follow-up of 3 years after TEVAR. Body height was a negative predictor for mean ascending aortic diameter (P value = -0.013; B = -8.890) and mean aortic diameter at the level of the brachiocephalic trunk (P value = 0.039; B = -14.763).

CONCLUSIONS

Our data suggest no significant changes in the ascending aorta following TEVAR of the descending thoracic aorta during mid-term follow-up when under stringent blood pressure medication. Additionally, we did not find any modifiable risk factors for geometry parameter increase.

Classification and hemodynamic characteristics of delayed intracerebral hemorrhage following stent-assisted coil embolism in unruptured intracranial aneurysms

Background and objective

Stent-assisted coil (SAC) embolization is a commonly used endovascular treatment for unruptured intracranial aneurysms (UIAs) but can be associated with symptomatic delayed intracerebral hemorrhage (DICH). Our study aimed to investigate the hemodynamic risk factors contributing to DICH following SAC embolization and to establish a classification for DICH predicated on hemodynamic profiles.

Methods

This retrospective study included patients with UIAs located in the internal carotid artery (ICA) treated with SAC embolization at our institution from January 2021 to January 2022. We focused on eight patients who developed postoperative DICH and matched them with sixteen control patients without DICH. Using computational fluid dynamics, we evaluated the hemodynamic changes in distal arteries [terminal ICA, the anterior cerebral artery (ACA), and middle cerebral artery (MCA)] pre-and post-embolization. We distinguished DICH-related arteries from unrelated ones (ACA or MCA) and compared their hemodynamic alterations. An imbalance index, quantifying the differential in flow velocity changes between ACA and MCA post-embolization, was employed to gauge the flow distribution in distal arteries was used to assess distal arterial flow distribution.

Results

We identified two types of DICH based on postoperative flow alterations. In type 1, there was a significant lower in the mean velocity increase rate of the DICH-related artery compared to the unrelated artery (-47.25 ± 3.88% vs. 42.85 ± 3.03%; p < 0.001), whereas, in type 2, there was a notable higher (110.58 ± 9.42% vs. 17.60 ± 4.69%; p < 0.001). Both DICH types demonstrated a higher imbalance index than the control group, suggesting an association between altered distal arterial blood flow distribution and DICH occurrence.

Conclusion

DICH in SAC-treated UIAs can manifest as either a lower (type 1) or higher (type 2) in the rate of velocity in DICH-related arteries. An imbalance in distal arterial blood flow distribution appears to be a significant factor in DICH development.

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.

Endovascular aortic repair impact on myocardial contractility: A prospective study

BACKGROUND

This study aimed to estimate if the altered sphygmic wave transmission may affect the left ventricular (LV) contractile function in patients undergoing endovascular aortic repair (EVAR).

METHODS

A prospective single-centre study was carried out on consecutive patients undergoing EVAR for abdominal aortic aneurysm. A preoperative and 6-month single photon emission computed tomography (SPECT) with arterial stiffness measurement were performed to evaluate variations in pressure wave curve and myocardial perfusion parameters.

RESULTS

From 2018 to 2020 a total of 16 patients were included in the study. Among the parameters evaluated, we found a measurable reduction of the reflected wave transit time from pre- to postoperative period, for both stress (115.13 ± 7.2 ms-111.1 ± 7.0 ms, p = .08) and rest SPECT acquisitions (115.3 ± 6.2 ms-112.2 ± 5.6 ms, p = .1). Unidirectional increase of both LV end-systolic volume (34 ± 9 mL-39 ± 8 mL, p = .02) and end-diastolic volume (85 ± 34 mL-89 ± 29 mL, p = .6) was also observed. Lastly, the ratio between the end-systolic pressure and the end-systolic volume (maximal systolic myocardial stiffness) decreased from 3.6 ± 1.5 mmHg/mL to 2.66 ± .74 mmHg/mL (p = .03).

CONCLUSIONS

Our data showed that EVAR induced an altered transmission of the sphygmic wave associated with an early LV contractile impairment.

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.

The Effect of Ascending Aortic Repair on Left Ventricular Remodeling

Left ventricular (LV) hypertrophy is common in patients with thoracic aortic diseases and is associated with increased long-term mortality. Thoracic aortic aneurysms are reported to increase LV afterload because of kinetic energy loss within the aneurysm sac, which may improve after surgical repair. However, LV afterload may also increase because of the stiffness of prosthetics used for aortic repair. We sought to investigate the long-term effect of surgical aortic repair with prostheses on postsurgical LV mass. We reviewed patients who underwent ascending aortic replacement with a prosthesis at our institution from January 2008 to December 2018. We calculated the LV mass index based on pre- and postoperative echocardiogram measurements. The primary outcome was the change in LV mass index 6 months after aortic repair. Patients aged <18 years and those who had concomitant cardiac operations, severe aortic valve disease, or who had no echocardiographic data were excluded. Of 1,008 patients who underwent ascending aortic replacement, 134 (51 with acute aortic dissections) were included. The median baseline and follow-up LV mass index were 107 (90 to 135) g/m² and 101 (83 to 123) g/m², respectively. Overall, there was a significant reduction of LV mass index over time (p = 0.03). LV mass index decreased in 77 patients (59%). Presentation due to acute aortic dissection (p = 0.03) and baseline LV mass index (p <0.001) were significant predictors of LV mass reduction. In conclusion, LV mass index may significantly decrease over time after the aortic repair, but the course is highly variable. The largest decrease occurred in patients who presented because of aortic dissections rather than for elective repair of aneurysms.

Aortic Biomechanics and Clinical Applications

The aorta contributes to cardiovascular physiology and function. Understanding biomechanics in health, disease, and after aortic interventions will facilitate optimization of perioperative patient care.

Functional Evaluation of Embedded Modular Single-Branched Stent Graft: Application to Type B Aortic Dissection With Aberrant Right Subclavian Artery

Background

Endovascular repair of type B aortic dissection (TBAD) with aberrant right subclavian artery (ARSA) is challenging due to anatomical complexity. The embedded modular single-branched stent graft (EMSBSG) could solve this problem. However, the hemodynamic efficacy of this innovative technique has not been fully assessed. This study aimed to propose morphometric and functional indicators to quantify the outcomes of EMSBSG in treating TBAD with ARSA.

Material and Methods

A patient who had TBAD with ARSA underwent EMSBSG implantation was admitted. Computational fluid dynamics (CFD) and three-dimensional structural analyses were conducted based on CTA datasets before the operation (Pre-1) and at 4 and 25 days after EMSBSG implantation (Post-1 and Post-2). Quantitative and qualitative functional analyses were conducted via pressure-, velocity- and wall shear stress (WSS) -based parameters, such as the luminal pressure difference (LPD), total energy loss, and flow distribution ratio. By precisely registering the aortas at the three time points, parameter variations in the EMSBSG region were also computed to investigate the prognostic improvement after EMSBSG implantation.

Results

The first balance point of LPD distally shifted to the abdominal aorta in Post-1 by a distance of 20.172 cm, and shifted out of the dissected region in Post-2, indicating positive pressure recovery post EMSBSG. The flow distribution ratios of all aortic arch branches increased after EMSBSG implantation. A positive normal deformation index in the EMSBSG region confirmed true lumen expansion; dominant AR_N (area ratio of negative value) of pressure and WSS-based parameters indicated an improved prognosis from Post-1 to Post-2.

Conclusions

The short-term results of EMSBSG in treating TBAD with ARSA proved to be promising, especially in EMSBSG region. Comprehensive evaluation could provide new insight into the therapy of TBAD with ARSA. Thus, it might guide the further management of complex aortic arch lesions.

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.

Cardiac remodelling following thoracic endovascular aortic repair for descending aortic aneurysms

OBJECTIVES

Current endografts for thoracic endovascular aortic repair (TEVAR) are much stiffer than the aorta and have been shown to induce acute stiffening. In this study, we aimed to estimate the impact of TEVAR on left ventricular (LV) stroke work (SW) and mass using a non-invasive image-based workflow.

METHODS

The University of Michigan database was searched for patients treated with TEVAR for descending aortic pathologies (2013-2016). Patients with available pre-TEVAR and post-TEVAR computed tomography angiography and echocardiography data were selected. LV SW was estimated via patient-specific fluid-structure interaction analyses. LV remodelling was quantified through morphological measurements using echocardiography and electrocardiographic-gated computed tomography angiography data.

RESULTS

Eight subjects were included in this study, the mean age of the patients was 68 (73, 25) years, and 6 patients were women. All patients were prescribed antihypertensive drugs following TEVAR. The fluid-structure interaction simulations computed a 26% increase in LV SW post-TEVAR [0.94 (0.89, 0.34) J to 1.18 (1.11, 0.65) J, P = 0.012]. Morphological measurements revealed an increase in the LV mass index post-TEVAR of +26% in echocardiography [72 (73, 17)  g/m2 to 91 (87, 26)  g/m2, P = 0.017] and +15% in computed tomography angiography [52 (46, 29)  g/m2 to 60 (57, 22)  g/m2, P = 0.043]. The post- to pre-TEVAR LV mass index ratio was positively correlated with the post- to pre-TEVAR ratios of SW and the mean blood pressure (ρ = 0.690, P = 0.058 and ρ = 0.786, P = 0.021, respectively).

CONCLUSIONS

TEVAR was associated with increased LV SW and mass during follow-up. Medical device manufacturers should develop more compliant devices to reduce the stiffness mismatch with the aorta. Additionally, intensive antihypertensive management is needed to control blood pressure post-TEVAR.

Influence of TEVAR on blood pressure in subacute type B aortic dissection (TBAD) patients with refractory and non-refractory arterial hypertension

BACKGROUND

Aim of this study was to compare the modifications of systemic blood pressure in patients with subacute type b aortic dissection (TBAD) and refractory (rHTN) and non-refractory arterial hypertension (N-rHTN) treated by thoracic endovascular aortic repair (TEVAR).

METHODS

Patients were divided into two groups, rHTN defined as blood pressure >140/90 mmHg with ≥5 antihypertensive drugs and patients with N-rHTN. Primary endpoint was the variation of mean systolic, diastolic and overall pressure (MSP, MDP and MAP) before and after antihypertensive treatment or TEVAR. Secondary endpoints were the 30-days mortality. Fifty-seven patients were included in this study.

RESULTS

Of the 44 Patients of the TEVAR group 21 were included in the N-rHTN group. The MSP before and after surgery for the N-rHTN group was 130 (±10 SD) and 111 (±22 SD) mmHg, P=0.01. In the rHTN group 164 (±17 SD) and 118 (±17 SD) mmHg (P=0.01). The reduction of MSP was greater in the rHTN group (P=0.01). The MAP before and after the TEVAR for the N-rHTN group was 90 (±10 SD) and 74 (±12 SD) mmHg (P=0.01), in the rHTN group 111 (±14 SD) and 70 (±9 SD) mmHg (P=0.01). The overall mortality rate group was 2.2% (1/44).

CONCLUSIONS

TEVAR for TBAD appears to positively affect blood pressure in patients with rHTN and N-rHTN.

Preoperative distal aortic diameter is a significant predictor of late aorta-related events after endovascular repair for chronic type B aortic dissection

OBJECTIVES

Long-term therapeutic effects of thoracic endovascular aortic repair (TEVAR) for chronic type B aortic dissection remain controversial. This study aimed to evaluate the possible predictors of late aortic rupture and re-interventions after TEVAR.

METHODS

We retrospectively reviewed the operative outcomes of 40 patients who underwent TEVAR for chronic type B aortic dissection at Kyushu University Hospital. During a mean follow-up period of 39.2 months, we assessed aortic morphology via computed tomography and then employed a multivariable Cox regression analysis in an attempt to identify the predictors of late aorta-related events.

RESULTS

The early success rate of TEVAR was 100%. During the follow-up, however, three patients died from aortic rupture. Eight patients required aortic re-intervention, including thoraco-abdominal aortic graft replacement, repeated TEVAR, total arch replacement and EVAR. Multivariable Cox regression analysis revealed that the preoperative maximum distal aortic diameter was a significant predictor of late aorta-related events. The cutoff value of the distal aortic diameter was 40 mm. Freedom from aorta-related events was 94.6% at 1 year and 78.3% at 3 years. The survival rate was not significantly different despite the re-intervention.

CONCLUSIONS

TEVAR is an effective treatment for chronic type B dissection, with acceptable mid-term results. The preoperative distal aortic diameter is a significant risk factor for late aorta-related events. When the maximum distal aortic diameter is ≥ 40 mm, a therapeutic strategy should be developed taking into consideration the possible need for aortic re-intervention.

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.

In silico study of vessel and stent-graft parameters on the potential success of endovascular aneurysm repair

The variety of stent-graft (SG) design variables (eg, SG type and degree of SG oversizing) and the complexity of decision making whether a patient is suitable for endovascular aneurysm repair (EVAR) raise the need for the development of predictive tools to assist clinicians in the preinterventional planning phase. Recently, some in silico EVAR methods have been developed to predict the deployed SG configuration. However, only few studies investigated how to assess the in silico EVAR outcome with respect to EVAR complication likelihoods (eg, endoleaks and SG migration). Based on a large literature study, in this contribution, 20 mechanical and geometrical parameters (eg, SG drag force and SG fixation force) are defined to evaluate the quality of the in silico EVAR outcome. For a cohort of n = 146 realizations of parameterized vessel and SG geometries, the in silico EVAR results are studied with respect to these mechanical and geometrical parameters. All degrees of SG oversizing in the range between 5% and 40% are investigated continuously by a computationally efficient parameter continuation approach. The in silico investigations have shown that the mechanical and geometrical parameters are able to indicate candidates at high risk of postinterventional complications. Hence, this study provides the basis for the development of a simulation-based metric to assess the potential success of EVAR based on engineering parameters.

The most relevant unmet needs in endovascular management of descending thoracic aorta

Endovascular repair of descending thoracic aorta (DTA) is considered as first interventional option for most part of the aortic disorders. However, many unmet needs and issues are still limiting its applicability. One of the major limitations is related to the existing gaps in evidence. Clear and robust evidence is still needed in many aspects of the management of DTA pathologies. In numerous clinical scenarios, adequate trials are lacking. Besides those gaps in evidence, it is well recognized that thoracic endografting (TEVAR) is technically evolving in order to overcome technical and device-related complications and limitations. We can deploy endografts in any aortic segment: in the descending, in the ascending, in the arch, even preserving aortic branches. Nevertheless, from the pure technical point of view, current generations of endografts still need more development and improvement. Durability remains the major concern for any endovascular treatment, and thoracic endografting is not an exception. As Galenus said, the physician is only nature's assistant, thoracic endograft should also follow the natural anatomy instead of fighting against it. We will focus the following pages on the graft conformability and compliance, both related to durability and safety of thoracic endografting. We will review the current knowledge and concerns associated with the anatomical and hemodynamic modifications induced by the thoracic endograft strength, stiffness and straightness and their implications for the future thoracic endograft designs.

Endovascular stent-induced alterations in host artery mechanical environments and their roles in stent restenosis and late thrombosis

Cardiovascular stent restenosis remains a major challenge in interventional treatment of cardiovascular occlusive disease. Although the changes in arterial mechanical environment due to stent implantation are the main causes of the initiation of restenosis and thrombosis, the mechanisms that cause this initiation are still not fully understood. In this article, we reviewed the studies on the issue of stent-induced alterations in arterial mechanical environment and discussed their roles in stent restenosis and late thrombosis from three aspects: (i) the interaction of the stent with host blood vessel, involve the response of vascular wall, the mechanism of mechanical signal transmission, the process of re-endothelialization and late thrombosis; (ii) the changes of hemodynamics in the lumen of the vascular segment and (iii) the changes of mechanical microenvironment within the vascular segment wall due to stent implantation. This review has summarized and analyzed current work in order to better solve the two main problems after stent implantation, namely in stent restenosis and late thrombosis, meanwhile propose the deficiencies of current work for future reference.

Changes in Geometry and Cardiac Deformation of the Thoracic Aorta after Thoracic Endovascular Aortic Repair

BACKGROUND

Thoracic endovascular aortic repair (TEVAR) has dramatically expanded treatment options for patients with thoracic aortic pathology. The interaction between endografts and the dynamic anatomy of the thoracic aorta is not well characterized for repetitive physiologic stressors and subsequent issues related to long-term durability. Through three-dimensional (3D) modeling we sought to quantify cardiac-induced aortic deformation before and after TEVAR to assess the impact of endografts on dynamic aortic anatomy.

METHODS

Eight patients with acute (n = 4) or chronic (n = 3) type B dissections, or chronic arch aneurysm (n = 1), underwent TEVAR with a single (n = 5) or multiple (n = 3) Gore C-TAG(s). Cardiac-resolved thoracic CT images were acquired pre- and post-TEVAR. 3D models of thoracic aorta and branch vessels were constructed in systole and diastole. Axial length, mean, and peak curvature of the ascending aorta, arch, and stented lumens were computed from the aortic lumen centerline, delineated with branch vessel landmarks. Cardiac-induced deformation was computed from mid-diastole to end-systole.

RESULTS

Pre-TEVAR, there were no significant cardiac-induced changes for aortic axial length or mean curvature. Post-TEVAR, the ascending aorta increased in axial length (2.7 ± 3.1%, P < 0.05) and decreased in mean curvature (0.38 ± 0.05 → 0.36 ± 0.05 cm^-1, P < 0.05) from diastole to systole. From pre- to post-TEVAR, axial length change increased in the ascending aorta (P < 0.02), mean curvature decreased in the arch and stented aorta (P < 0.03), and peak curvature decreased in the stented aorta (P < 0.05).

CONCLUSIONS

TEVAR for a range of indications not only causes direct geometric changes to the stented aorta but also results in dynamic changes to the ascending and stented aorta. In our cohort, endograft placement straightens the stented aorta and mutes cardiac-induced bending due to longitudinal stiffness. This is compensated by greater length and curvature changes from diastole to systole in the ascending aorta, relative to pre-TEVAR.

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.

Impact of Thoracic Endovascular Aortic Repair on Pulsatile Circumferential and Longitudinal Strain in Patients With Aneurysm

Purpose: To quantify both pulsatile longitudinal and circumferential aortic strains before and after thoracic endovascular aortic repair (TEVAR), potentially clarifying TEVAR-related complications. Methods: This retrospective study assessed the impact of TEVAR on pulsatile aortic strains through custom developed software and cardiac-gated computed tomography imaging of 8 thoracic aneurysm patients (mean age 71.0±8.2 years; 6 men) performed before TEVAR and during follow-up (median 0.1 months, interquartile range 0.1–5.8). Lengths of the ascending aorta, the aortic arch, and the descending aorta were measured. Diameters and areas were computed at the sinotubular junction, brachiocephalic trunk, left subclavian artery, and the celiac trunk. Pulsatile longitudinal and circumferential strains were quantified as systolic increments of length and circumference divided by the corresponding diastolic values. Results: Average pulsatile longitudinal strain ranged from 1.4% to 7.1%, was highest in the arch (p<0.001), and increased after TEVAR by 77% in the arch (7.1%±2.5% vs 12.5%±5.1%, p=0.04) and by 69% in the ascending aorta (5.6±2.3% vs 9.4±4.4%, p=0.06). Average pulsatile circumferential strain ranged from 3.6% to 5.0% before TEVAR and did not differ significantly throughout the thoracic aorta; there was a nonsignificant increase after TEVAR at the unstented sinotubular junction (5.0%±1.4% vs 6.3%±1.0%, p=0.18), with a significant increase at the celiac trunk (3.6%±1.8% vs 6.2%±1.8%, p=0.02). Pulsatile circumferential strains within stented segments were deemed unreliable due to image artifacts. Conclusion: TEVAR was associated with an increase of pulsatile longitudinal strains (in the arch) and circumferential strains (at the celiac trunk) in unstented aortic segments. These observations suggest increased pulsatile wall stress after TEVAR in segments adjacent to the device, which may contribute to the understanding of stent-graft–related complications such as retrograde dissection, aneurysm formation, and rupture.

Assessment of CardiOvascular Remodelling following Endovascular aortic repair through imaging and computation: the CORE prospective observational cohort study protocol

INTRODUCTION

Thoracic aortic stent grafts are orders of magnitude stiffer than the native aorta. These devices have been associated with acute hypertension, elevated pulse pressure, cardiac remodelling and reduced coronary perfusion. However, a systematic assessment of such cardiovascular effects of thoracic endovascular aortic repair (TEVAR) is missing. The CardiOvascular Remodelling following Endovascular aortic repair (CORE) study aims to (1) quantify cardiovascular remodelling following TEVAR and compare echocardiography against MRI, the reference method; (2) validate computational modelling of cardiovascular haemodynamics following TEVAR using clinical measurements, and virtually assess the impact of more compliant stent grafts on cardiovascular haemodynamics; and (3) investigate diagnostic accuracy of ECG and serum biomarkers for cardiac remodelling compared to MRI.

METHODS AND ANALYSIS

This is a prospective, nonrandomised, observational cohort study. We will use MRI, CT, echocardiography, intraluminal pressures, ECG, computational modelling and serum biomarkers to assess cardiovascular remodelling in two groups of patients with degenerative thoracic aneurysms or penetrating aortic ulcers: (1) patients managed with TEVAR and (2) control patients managed with medical therapy alone. Power analysis revealed a minimum total sample size of 20 patients (α=0.05, power=0.97) to observe significant left ventricular mass increase following TEVAR after 1 year. Consequently, we will include 12 patients in both groups. Advanced MRI sequences will be used to assess myocardial and aortic strain and distensibility, myocardial perfusion and aortic flow. ECG, echocardiography and serum biomarkers will be collected and compared against the imaging data. Computational models will be constructed from each patient imaging data, analysed and validated. All measurements will be collected at baseline (prior to TEVAR) and 1-year follow-up. The expected study period is 3 years.

ETHICS AND DISSEMINATION

This study has been approved by the University of Michigan IRB. The results will be disseminated through scientific journals and conference presentations.

TRIAL REGISTRATION NUMBER

NCT02735720.

Incidence and Characteristics of Remote Intracerebral Hemorrhage After Endovascular Treatment of Unruptured Intracranial Aneurysms

OBJECTIVE

The purpose of this study was to investigate the incidence and characteristics of remote intracerebral hemorrhage (ICH) after endovascular treatment (EVT) of unruptured intracranial aneurysms (UIAs).

METHODS

Between March 2007 and September 2015, 11 patients with remote ICH from a series of 2258 consecutive patients with 2597 UIAs treated via EVT were identified. Baseline demographic characteristics, medical history, radiologic imaging data, characteristics of remote ICH, and clinical outcomes were retrospectively reviewed. The characteristics of patients with remote ICH were compared with those of patients without remote ICH.

RESULTS

All hematomas were single lesions located in the subcortical white matter as lobar-type in 9 patients (81.8%) and in the basal ganglia in 2 patients (18.2%). Events occurred mostly within 1 week and up to 3 weeks after EVT. Hematoma was located on the ipsilateral side in 8 patients (72.7%) and in the contralateral side in 3 patients (27.3%). Compared with patients without remote ICH, there were more aneurysms located on the internal carotid artery (ICA) (P = 0.041), more patients treated with stents (P < 0.001), more patients with hypertension (P = 0.026), and poorer clinical outcomes at discharge (P < 0.001) for patients with remote ICH.

CONCLUSIONS

The incidence of remote ICH after EVT of UIAs was 0.46%. This event occurred mostly in patients with stents, hypertension, and UIAs on the ICA. It presented mostly as an ipsilateral lobar-type hemorrhage within 1 week after the procedure. This complication should not be neglected because of its poor clinical outcomes.

In Vitro Evaluation of Upstream and Downstream Influences on Blood Pressure of the Hybrid Treatment of Thoracoabdominal Aortic Aneurysms

BACKGROUND

The aim of our study was to assess, by means of an experimental model, whether different geometries in retrograde bypass and stent-graft deployment may affect upstream and downstream blood pressure in hybrid treatment.

METHODS

An in vitro model of the arterial circulation has been prepared, which consists of a peristaltic pump, silicon tubes with geometrical and mechanical properties close to realistic arteries, a terminal reservoir kept at constant pressure, and a sequence of pressure transducers. The system allows us to study the pressure wave propagation in physiological conditions and simulate the patient's conditions as a result of debranching in 2 different configurations.

RESULTS

In configuration 1, the mean pressure value (Kpa) was 4.72 in silicone tube before stent graft and debranching, 4.59 in visceral and renal bypass, and 4.38 in silicone tube after stent graft and debranching. In configuration 2, the mean pressure value (Kpa) was 5.22 in silicone tube before stent graft and debranching, 4.48 in visceral and renal bypass, and 4.99 in silicone tube after stent graft and debranching.

CONCLUSION

The experimental data suggest that the debranching geometry and the material of the grafts and stent grafts change significantly the physiological arterial pressure possibly leading to an augmented pressure upstream of the stent grafts, owing to retrograde pressure waves toward the heart, and a decreased pressure downstream visceral and renal arteries.

Changes in Coronary Flow Reserve following Stent Implantation in the Swine Descending Thoracic Aorta

Purpose:

To evaluate coronary flow reserve (CFR) changes following stent implantation in the descending thoracic aorta (DTA) of a porcine model.

Methods:

Six pigs (3 males; 40 to 44 kg) were anesthetized and kept on mechanical ventilation. A 6-F guiding right Judkins catheter was advanced under fluoroscopy to the right coronary artery, and a pressure wire with a temperature sensor was placed within the vessel lumen at a distance of 4 cm from the ostium. CFR was estimated by the thermodilution method before and after maximal coronary vasodilation with 20 mg of intracoronary papaverine. Aortography was also performed to measure aortic diameter. Subsequently, a self-expanding vascular stent was deployed into the DTA just below the left subclavian artery (LSA), and CFR was measured again. All animals were maintained for 3 weeks; at the end of this period, a further CFR was calculated using the same procedure.

Results:

The mean aortic diameter below the LSA was 12.15±0.15 mm. Following stent deployment, the mean aortic diameter measured at the stented segment was 12.58±0.11 (p=0.001 versus baseline). The mean CFR value was 4.7062.00 before stent implantation, 2.6860.86 immediately after, and 4.0561.15 at 3 weeks after stenting. Accordingly, CFR values were significantly depressed immediately after stent placement compared with baseline (p=0.027). However, CFR values obtained 3 weeks following stent deployment were similar to the initial values (p=0.59).

Conclusion:

Stent deployment in the normal swine DTA produces a significant immediate decrease in CFR, which is attenuated 3 weeks later. The clinical impact of CFR changes following DTA endografting remain to be elucidated.

Radial force measurement of endovascular stents: Influence of stent design and diameter

Background and purpose

Angioplasty and endovascular stent placement is used in case to rescue the coverage of main branches to supply blood to brain from aortic arch in thoracic endovascular aortic repair. This study assessed mechanical properties, especially differences in radial force, of different endovascular and thoracic stents.

Material and methods

We analyzed the radial force of three stent models (Epic™, E-Luminexx® and SMART®) stents using radial force-tester method in single or overlapping conditions. We also analyzed radial force in three thoracic stents using Mylar® film testing method: conformable Gore®-TAG®, Relay®, and Valiant® Thoracic Stent Graft.

Results

Overlapping SMART stents had greater radial force than overlapping Epic or Luminexx stents ( P < 0.01). The radial force of the thoracic stents was greater than that of all three endovascular stents ( P < 0.01).

Conclusions

Differences in radial force depend on types of stents, site of deployment, and layer characteristics. In clinical settings, an understanding of the mechanical characteristics, including radial force, is important in choosing a stent for each patient.

Arterial Stiffness Alterations and Inflammatory Response Following Endovascular Aortic Repair: Based on a Presentation at the 2013 VEITH Symposium, November 19-23, 2013 (New York, NY, USA)

Endovascular abdominal aortic aneurysm repair (EVAR) and thoracic aortic aneurysm repair (TEVAR) have been widely incorporated into clinical practice. However, changes in arterial stiffness and post-implantation syndrome after aortic endografting remain important issues under investigation. The aneurysm sac wall motion after successful EVAR and TEVAR reflects complex interactions between all the components of the excluded aneurysm, including true compliance of the aneurysm wall itself, intra-aneurysm sac pressure, remodeling of the thrombus, and mechanical characteristics of the endograft. Experimental and clinical studies have shown that aortic endografting results in increased arterial stiffness in animal models. It can be assumed that the alterations of aortic mechanical properties can have a direct impact on heart output. The long-term impact of these mechanical changes on cardiovascular outcomes and the potential effects of different endografts on hemodynamics are important issues under investigation. Post-implantation syndrome (PIS) is a systemic inflammatory response frequently observed after endovascular treatment of aortic pathologies. The main features of PIS include fever, leukocytosis, elevated C-reactive protein levels, and coagulation disturbances. Endograft design appears to influence this inflammatory response following aortic endografting; woven polyester endografts have been shown to be associated with greater inflammatory response compared to PTFE stent grafts. The purpose of this paper is to review the literature to elucidate arterial stiffness alterations and inflammatory response after EVAR and TEVAR and the impact of endograft design on aortic stiffness and the post-inflammatory response.

Can the Windkessel Hypothesis Explain Delayed Intraparenchymal Haemorrhage After Flow Diversion? A Case Report and Model-Based Analysis of Possible Mechanisms

BACKGROUND

Delayed ipsilateral intraparenchymal haemorrhage is a recently recognised complication after endovascular flow diversion for intracranial aneurysms. Although the mechanism of this phenomenon is not understood, one proposed explanation (the windkessel hypothesis) is that removal of aneurysmal compliance increases distal pulse pressure.

METHODS

We present a case of delayed haemorrhage after placement of a Pipeline stent, discuss the proposed mechanisms, and describe a novel electrical analogue model that was used to evaluate the likely haemodynamic effect of stent placement.

RESULTS

Model-based analysis suggests that stenting is not likely to produce a significant change in distal pulse pressure. Moreover, basic fluid dynamics principles suggest that a local reduction in disturbed flow in the region of the aneurysm could produce only a minor increase in distal pressure (a few mmHg), which is unlikely to be the main cause of the observed haemorrhage.

CONCLUSION

The windkessel hypothesis is unlikely to explain the occurrence of delayed ipsilateral intraparenchymal haemorrhage after flow diversion; however, other mechanisms involving altered haemodynamics distal to the treated aneurysm may play a role. Further studies involving the assessment of haemodynamic changes after flow diversion would be useful to understand, and eventually mitigate, this currently unpredictable risk.

Midterm results of endovascular stent grafts in the proximal aortic arch (zone 0): an imaging perspective

BACKGROUND

Endovascular options to repair the arch and ascending aorta are rapidly evolving. Little is known about the durability of endovascular devices deployed at this location. This report describes a single-centre experience with the novel application of thoracic endovascular aortic repair (TEVAR) by examining clinical and radiological outcomes.

METHODS

A retrospective review was performed for a cohort of patients undergoing TEVAR of the arch or ascending aorta, or both, at a single centre from November 2008-July 2012.

RESULTS

Sixteen patients were included in the study, with mean imaging follow-up of 38 months (range, 15-72 months). Two complications at the proximal landing zone in the ascending aorta were identified: 1 endoleak and 1 infolding identified at 3 and 24 months postoperatively, respectively. Clinically, both these complications were attributed to the bird-beak configuration at the proximal landing zone site. At up to 72 months of follow-up, there were no cases of retrograde dissection of the native sinus of Valsalva. There were no cases of stent graft migration, graft fracture, open surgical reintervention for aortic pathologic conditions, or late mortality.

CONCLUSIONS

Early outcomes suggest that the current generation of thoracic aortic endografts can be placed in the complex anatomy of the ascending aorta and aortic arch without a high incidence of early graft fracture or migration. Future endeavors will need to focus on techniques to achieve optimal apposition with the curves of the ascending aorta. These findings are important as indications for endovascular aortic therapies expand to address proximal aortic pathologic conditions.

Total aortic arch replacement: superior ventriculo-arterial coupling with decellularized allografts compared with conventional prostheses

Background

To date, no experimental or clinical study provides detailed analysis of vascular impedance changes after total aortic arch replacement. This study investigated ventriculoarterial coupling and vascular impedance after replacement of the aortic arch with conventional prostheses vs. decellularized allografts.

Methods

After preparing decellularized aortic arch allografts, their mechanical, histological and biochemical properties were evaluated and compared to native aortic arches and conventional prostheses in vitro. In open-chest dogs, total aortic arch replacement was performed with conventional prostheses and compared to decellularized allografts (n = 5/group). Aortic flow and pressure were recorded continuously, left ventricular pressure-volume relations were measured by using a pressure-conductance catheter. From the hemodynamic variables end-systolic elastance (Ees), arterial elastance (Ea) and ventriculoarterial coupling were calculated. Characteristic impedance (Z) was assessed by Fourier analysis.

Results

While Ees did not differ between the groups and over time (4.1±1.19 vs. 4.58±1.39 mmHg/mL and 3.21±0.97 vs. 3.96±1.16 mmHg/mL), Ea showed a higher increase in the prosthesis group (4.01±0.67 vs. 6.18±0.20 mmHg/mL, P<0.05) in comparison to decellularized allografts (5.03±0.35 vs. 5.99±1.09 mmHg/mL). This led to impaired ventriculoarterial coupling in the prosthesis group, while it remained unchanged in the allograft group (62.5±50.9 vs. 3.9±23.4%). Z showed a strong increasing tendency in the prosthesis group and it was markedly higher after replacement when compared to decellularized allografts (44.6±8.3dyn·sec·cm⁻⁵ vs. 32.4±2.0dyn·sec·cm⁻⁵, P<0.05).

Conclusions

Total aortic arch replacement leads to contractility-afterload mismatch by means of increased impedance and invert ventriculoarterial coupling ratio after implantation of conventional prostheses. Implantation of decellularized allografts preserves vascular impedance thereby improving ventriculoarterial mechanoenergetics after aortic arch replacement.

Study of agreement of aortic, radial and femoral blood pressures during aortic endografting

PURPOSE

To estimate the agreement between radial or femoral, and ascending aortic invasive blood pressure values.

PATIENTS AND METHODS

Prospective study on 32 patients who underwent an aortic endografting under general anesthesia. After deploying the prosthesis under controlled hypotension, a catheter was introduced in the aorta to measure the staged systolic (SAP), diastolic (DAP) and mean (MAP) arterial pressures, in particular at the level of ascending aorta and femoral artery.

RESULTS

No differences were observed between SAP, DAP or MAP measured in the aorta versus femoral or radial arteries. A better agreement was observed between the aortic and femoral MAP (bias of 1mmHg, limits of agreement between: -8.8mmHg and +10.8mmHg) than between the aortic and the radial MAP (bias of 1.7mmHg, limits of agreement between: -14.1mmHg and +17.5mmHg). The comparison between radial and femoral MAP was not satisfying (bias of -4.7mmHg and limits of agreement between -19.1mmHg and +9.7mmHg).

CONCLUSION

The femoral MAP is more accurate to predict value of the aortic MAP than the radial MAP in a hypotensive setting. The clinician should be aware of these discrepancies in conditions of hemodynamic impairment to optimize the treatment.

External aortic root support: a histological and mechanical study in sheep

OBJECTIVES

Personalized external aortic root support has completed initial evaluation and has technology appraisal in the UK for patients with Marfan syndrome for use as an alternative to root replacement. Its long-term success in preventing aortic dissection remains uncertain. Here, we report a study in sheep to establish whether the externally supporting mesh, as used clinically, is biologically incorporated. The strength of the resulting mesh/artery composite has been tested.

METHODS

The carotid artery of growing sheep (n=6) was enclosed in a mesh sleeve made of a polymer, polyethylene terephthalate. After a predefined interval of 4-6 months, a length of the artery was excised, including the sleeved and unsleeved portions, and was stress tested and examined histologically.

RESULTS

One animal died of pneumonia 7 days after implantation. Comparing sleeved with normal segments, the overall thickness was increased and there was a fibrotic sheet in the periarterial space. The overall vessel wall architecture was preserved in all specimens. Although media thickness of ensleeved arteries was smaller and in one animal mild oedema was found in one quadrant of the outer part of the media. There was a significant increase in stiffness and maximum tensile strength of the supported segments compared with normal arterial tissue.

CONCLUSIONS

Polyethylene terephthalate mesh, as used for the external support of the dilated aortic root in Marfan syndrome, becomes incorporated in the periadventitial tissue of the carotid artery of sheep. Limited thinning of the media, without any signs of inflammation or medial necrosis, was visible. There was a significantly greater tensile strength in the carotid artery/mesh composite compared with the unsleeved carotid artery.

Stent graft performance in the treatment of abdominal aortic aneurysms: the influence of compliance and geometry

The long-term success of the endovascular procedure for the treatment of Abdominal Aortic Aneurysms (AAAs ) depends on the secure fixation of the proximal end and the geometry of the stent-graft (SG) device. Variations in SG types can affect proximal fixation and SG hemodynamics. Such hemodynamic variations can have a catastrophic effect on the vascular system and may result from a SG/arterial wall compliance mismatch and the sudden decrease in cross-sectional area at the bifurcation, which may result in decreased distal perfusion, increased pressure wave reflection and increased stress at the interface between the stented and non-stented portion of the vessel. To examine this compliance mismatch, a commercial SG device was tested experimentally under a physiological pressure condition in a silicone AAA model based on computed tomography scans. There was a considerable reduction in compliance of 54% and an increase in the pulse wave velocity of 21%, with a significant amount of the forward pressure wave being reflected. To examine the SG geometrical effects, a commercial bifurcated geometry was compared computationally and experimentally with a geometrical taper in the form of a blended section, which provided a smooth transition from the proximal end to both iliac legs. The sudden contraction of commercial SG at the bifurcation region causes flow separation within the iliac legs, which is known to cause SG occlusion and increased proximal pressure. The blended section along the bifurcation region promotes a greater uniformity of the fluid flow field within the distal legs, especially, during the deceleration phase with reduced boundary layer reversal. In order to reduce the foregoing losses, abrupt changes of cross-section should be avoided. Geometrical tapers could lead to improved clinical outcomes for AAA SGs.

Delayed ipsilateral parenchymal hemorrhage following flow diversion for the treatment of anterior circulation aneurysms

BACKGROUND AND PURPOSE

The PED is a flow-diverting stent designed for the treatment of cerebral aneurysms. We report 4 cases of delayed ipsilateral IPH following the technically successful treatment of anterior circulation aneurysms with the PED.

MATERIALS AND METHODS

Clinical and imaging data from all patients undergoing aneurysm treatment with the PED at 2 institutions were analyzed to assess the incidence of delayed IPH after treatment with the PED.

RESULTS

A total of 66 patients (47 anterior circulation) with cerebral aneurysms underwent treatment with a PED between January 2008 and November 2010. Four patients experienced delayed periprocedural IPH, all after the treatment of anterior circulation aneurysms (8.5%, 4/47). The aneurysm size ranged from 5 to 21 mm. All IPHs occurred within the cerebral hemisphere, ipsilateral to the treated aneurysm, and were anatomically remote from the treated aneurysms. All procedures were uncomplicated, and patients emerged from general anesthesia at neurologic baseline. The hemorrhages became clinically evident between 1 and 6 days after the procedure. Two patients had unfavorable outcomes (mRS scores, 4 and 6).

CONCLUSIONS

Delayed IPH may occur after the treatment of anterior circulation aneurysms with flow diverters. This complication does not seem to be restricted to a specific aneurysm subtype and does not seem to be related to an intraprocedural complication or solely attributable to DAT.