Patient-Specific Haemodynamic Analysis of Virtual Grafting Strategies in Type-B Aortic Dissection: Impact of Compliance Mismatch

INTRODUCTION

Compliance mismatch between the aortic wall and Dacron Grafts is a clinical problem concerning aortic haemodynamics and morphological degeneration. The aortic stiffness introduced by grafts can lead to an increased left ventricular (LV) afterload. This study quantifies the impact of compliance mismatch by virtually testing different Type-B aortic dissection (TBAD) surgical grafting strategies in patient-specific, compliant computational fluid dynamics (CFD) simulations.

MATERIALS AND METHODS

A post-operative case of TBAD was segmented from computed tomography angiography data. Three virtual surgeries were generated using different grafts; two additional cases with compliant grafts were assessed. Compliant CFD simulations were performed using a patient-specific inlet flow rate and three-element Windkessel outlet boundary conditions informed by 2D-Flow MRI data. The wall compliance was calibrated using Cine-MRI images. Pressure, wall shear stress (WSS) indices and energy loss (EL) were computed.

RESULTS

Increased aortic stiffness and longer grafts increased aortic pressure and EL. Implementing a compliant graft matching the aortic compliance of the patient reduced the pulse pressure by 11% and EL by 4%. The endothelial cell activation potential (ECAP) differed the most within the aneurysm, where the maximum percentage difference between the reference case and the mid (MDA) and complete (CDA) descending aorta replacements increased by 16% and 20%, respectively.

CONCLUSION

This study suggests that by minimising graft length and matching its compliance to the native aorta whilst aligning with surgical requirements, the risk of LV hypertrophy may be reduced. This provides evidence that compliance-matching grafts may enhance patient outcomes.

Ascending Aortic Endograft and Thoracic Aortic Deformation After Ascending Thoracic Endovascular Aortic Repair

PURPOSE

We aim to quantify multiaxial cardiac pulsatility-induced deformation of the thoracic aorta after ascending thoracic endovascular aortic repair (TEVAR) as a part of the GORE ARISE Early Feasibility Study.

MATERIALS AND METHODS

Fifteen patients (7 females and 8 males, age 73±9 years) with ascending TEVAR underwent computed tomography angiography with retrospective cardiac gating. Geometric modeling of the thoracic aorta was performed; geometric features including axial length, effective diameter, and centerline, inner surface, and outer surface curvatures were quantified for systole and diastole; and pulsatile deformations were calculated for the ascending aorta, arch, and descending aorta.

RESULTS

From diastole to systole, the ascending endograft exhibited straightening of the centerline (0.224±0.039 to 0.217±0.039 cm^-1, p<0.05) and outer surface (0.181±0.028 to 0.177±0.029 cm^-1, p<0.05) curvatures. No significant changes were observed for inner surface curvature, diameter, or axial length in the ascending endograft. The aortic arch did not exhibit any significant deformation in axial length, diameter, or curvature. The descending aorta exhibited small but significant expansion of effective diameter from 2.59±0.46 to 2.63±0.44 cm (p<0.05).

CONCLUSION

Compared with the native ascending aorta (from prior literature), ascending TEVAR damps axial and bending pulsatile deformations of the ascending aorta similar to how descending TEVAR damps descending aortic deformations, while diametric deformations are damped to a greater extent. Downstream diametric and bending pulsatility of the native descending aorta was muted compared with that in patients without ascending TEVAR (from prior literature). Deformation data from this study can be used to evaluate the mechanical durability of ascending aortic devices and inform physicians about the downstream effects of ascending TEVAR to help predict remodeling and guide future interventional strategies.

CLINICAL IMPACT

This study quantified local deformations of both stented ascending and native descending aortas to reveal the biomechanical impact of ascending TEVAR on the entire thoracic aorta, and reported that the ascending TEVAR muted cardiac-induced deformation of the stented ascending aorta and native descending aorta. Understanding of in vivo deformations of the stented ascending aorta, aortic arch and descending aorta can inform physicians about the downstream effects of ascending TEVAR. Notable reduction of compliance may lead to cardiac remodeling and long-term systemic complications. This is the first report which included dedicated deformation data regarding ascending aortic endograft from clinical trial.

In Vivo Quantification of Cardiac-Pulsatility-Induced Motion Before and After Double-Branched Endovascular Aortic Arch Repair

The Relay^®Branch stent-graft (Terumo Aortic, Sunrise, FL, USA) offers a custom-made endovascular solution for complex aortic arch pathologies. In this technical note, a modified electrocardiography (ECG)-gated computed tomography (CT)-based algorithm was applied to quantify cardiac-pulsatility-induced changes of the aortic arch geometry and motion before and after double-branched endovascular repair (bTEVAR) of an aortic arch aneurysm. This software algorithm has the potential to provide novel and clinically relevant insights in the influence of bTEVAR on aortic anatomy, arterial compliance, and stent-graft dynamics.

In Vitro Validation of Regional Circumferential Strain Assessment in a Phantom Aortic Model Using Cine Displacement Encoding With Stimulated Echoes MRI

BACKGROUND

A novel application of cine Displacement ENcoding with Stimulated Echoes Magnetic Resonance Imaging (DENSE MRI) has recently been described to assess regional heterogeneities in circumferential strain around the aortic wall in vivo; however, validation is first required for successful clinical translation.

PURPOSE

To validate the quantification of regional circumferential strain around the wall of an aortic phantom using DENSE MRI.

STUDY TYPE

In vitro phantom study.

POPULATION

Three polyvinyl alcohol aortic phantoms with eight axially oriented nitinol wires embedded evenly around the walls.

FIELD STRENGTH/SEQUENCE

3 T; gradient-echo aortic DENSE MRI with spiral cine readout, gradient-echo phase-contrast MRI (PCMR) with Cartesian cine readout.

ASSESSMENT

Phantoms were connected to a pulsatile flow loop and peak DENSE-derived regional circumferential Green strains at 16 equally spaced sectors around the wall were assessed according to previously published algorithms. "True" regional circumferential strains were calculated by manually tracking displacements of the nitinol wires by two independent observers. Normalized circumferential strains (NCS) were calculated by dividing regional strains by the mean strain. Finally, DENSE-derived regional strain was corrected by multiplying regional DENSE NCS by the mean strain calculated from the diameter change on the PCMR.

STATISTICAL TESTS

One-sample t-test, Paired-sample t-test, and analysis of variance with Bonferroni correction, coefficient of variation (CoV), Bland-Altman analysis; P < 0.05 was considered statistically significant.

RESULTS

Aortic DENSE MRI significantly overestimated circumferential strain compared to the wire-tracking method (mean difference and SD 0.030 ± 0.014, CoV 0.31). However, NCS demonstrated good agreement between DENSE and wire-tracking data (mean difference 0.000 ± 0.172, CoV 0.15). After correcting the DENSE-derived regional strain, the mean difference in regional circumferential strain between DENSE and wire-tracking was significantly reduced to 0.006 ± 0.008, and the CoV was reduced to 0.18.

DATA CONCLUSION

For aortic phantoms with mild spatial heterogeneity in circumferential strain, the previously published aortic DENSE MRI technique successfully assessed the regional NCS distribution but overestimated the mean strain. This overestimation is correctable by computing a more accurate mean circumferential strain using a separate cine scan.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 2.

Endovascular repair of the aortic arch: State of the art

BACKGROUND

Open total arch replacement remains the gold standard treatment for aneurysms and dissections involving the aortic arch. However, high-risk surgical candidates may benefit from endovascular techniques to reduce the risk of perioperative mortality and morbidity, especially neurologic complications. Numerous endografts are available for investigational use in the aortic arch as part of investigational device exemption (IDE) programs. Some devices are fenestrated or scalloped, while others are branched, ranging from single branch to triple branch stent-grafts. Furthermore, chimney techniques and in situ fenestration may be utilized in bailout or emergent situations.

RESULTS

Initial results describing outcomes of complete endovascular repair of the aortic arch are encouraging, with current data estimating that technical success ranges from 84.2% to 100%. Moreover, operative mortality may be as high as 13.2%, while neurologic complications also remain common, with stroke rates being as high as 20% and spinal cord ischemia being as high as 3.1%. However, more data are necessary to determine the comparative treatment effect of endovascular stent-grafting of the aortic arch, compared with conventional open and hybrid repairs. Longitudinal follow-up is also lacking, which will determine the long-term durability of endografts in the aortic arch. Nevertheless, endovascular repair represents an important opportunity for improving outcomes in patients with complex and potentially devastating pathologies of the aortic arch.

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.

Open Conversion for Recurrent Endograft Occlusion after Endovascular Treatment of Blunt Traumatic Aortic Injury: A Peculiar Case Report

BACKGROUND

We report a rare case of delayed, symptomatic thoracic endograft thrombosis after the initial thoracic endovascular aortic repair (TEVAR) for blunt thoracic aortic injury which was successfully retreated with a redo TEVAR, followed by open conversion due to recurrent partial occlusion of the distal edge of the endografts.

METHODS

Two years ago, a 22-year-old man had undergone an emergency TEVAR for blunt thoracic aortic injury. A Zenith Cook 22 × 100 mm (Cook Incorporated, Bloomington, IN) endograft was used. Six months later, he underwent an emergency endovascular relining of the endograft using the same type of device. The multiorgan perfusion was completely restored except for the spinal cord injury. After 8 months, a recurrent partial occlusion of the distal edge of the second graft was documented. The thoracic aorta was replaced with a 22-mm silver-coated graft (Maquet Spain, SLU).

RESULTS

Histology examination showed a neointimal formation and thickening and fibrosis of the inner 1/3 of the media with loss of smooth muscle cells and increase of the elastic fibers.

CONCLUSIONS

The need for secondary interventions or open conversion because of potential complications after TEVAR for traumatic aortic injury is an additional consideration when weighing the risks and benefits of endovascular repair and subsequent surveillance strategies.

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.