Effects of Aortic Graft Implantation on Heart and Downstream Vessels: An Artery is not a Rigid Pipe

Total Arch Replacement Versus Hemiarch Replacement in Hemodynamic Performance: A Simulation Study

Acute type A aortic dissection (ATAAD) is a life-threatening aortic emergency with high mortality. Currently, hemiarch replacement (HAR) and total arch replacement (TAR) are the primary surgeries for ATAAD, but their long-term outcomes remain debated, possibly due to the influence of clinical factors in multicenter studies. This study aims to evaluate the long-term outcomes of HAR and TAR by in silico analysis, mitigating the impact of clinical factors. A personalized model was reconstructed to simulate HAR and TAR by altering the material properties at the replacement regions, obtaining hemodynamic and wall response parameters through two-way fluid-structure interaction analysis. HAR exhibits a higher increase in von Mises stress at the anastomosis compared to pre-operation levels (HAR: 4.39 times normal, TAR: 2.42 times normal), increasing the risk of pseudoaneurysm formation. TAR induced more severe streamline absence in the arch branches, potentially resulting in intermittent blood flow to the upper limbs and brain. HAR poses a higher risk of pseudoaneurysm formation at the anastomosis, while TAR carries increased risks of upper limb and cerebral ischemia. Enhanced monitoring of the anastomosis in HAR patients and vigilance for upper limb fatigue and cerebral ischemic events in TAR patients are recommended. This study offers effective guidance for managing postoperative HAR and TAR patients, contributing to the prevention of complications and enhancing their postoperative quality of life.

Elective root replacement increases the risk of type B dissection in patients with Marfan syndrome

OBJECTIVE

Marfan syndrome is a genetic disorder with increased risk of aortic dissection. Currently, type A aortic dissection risk is mitigated by aortic root replacement with Dacron. It is unclear if root replacement increases the risk of distal aortic disease given the noncompliant nature of Dacron.

METHODS

All adult patients with a diagnosis of Marfan syndrome at a single academic center, excluding those with history of dissection or concomitant arch repair, were studied (n = 322). Student t test or Wilcoxon Mann-Whitney test was used for continuous variables; chi-square or Fisher exact test was used for categorical variables. Propensity matching used age, sex, hypertension, race, body mass index, family history of Marfan syndrome, and genetic mutational class. Differences in freedom from type B aortic dissection were determined using the log-rank test.

RESULTS

A total of 124 patients underwent root replacement compared with 198 patients with no prior aortic surgery. Median follow-up time was 9.90 years. Male sex, weight, and hypertension prevalence were higher in the root replacement group (P < .05). Distribution of fibrillin-1 mutations was homogenous (P > .9). Type B aortic dissection frequency in the root replacement group was higher (21% [n = 20] vs 4.2% [n = 4], P < .001). Aortic-related mortality was higher in the root replacement group (11% [n = 14] vs 3.5% [n = 7], P < .01). Distal aortic intervention frequency was higher in the root replacement group (P = .009).

CONCLUSIONS

Patients with Marfan syndrome who undergo elective aortic root replacement appear to have a higher incidence of subsequent type B aortic dissection, independent of other risk factors. Careful consideration must be made to the management of the distal aorta in patients with Marfan syndrome who undergo root replacement.

Comparison of Biomechanical and Microstructural Properties of Aortic Graft Materials in Aortic Repair Surgeries

Mechanical mismatch between native aortas and aortic grafts can induce graft failure. This study aims to compare the mechanical and microstructural properties of different graft materials used in aortic repair surgeries with those of normal and dissected human ascending aortas. Five types of materials including normal aorta (n = 10), dissected aorta (n = 6), human pericardium (n = 8), bovine pericardium (n = 8) and Dacron graft (n = 5) were collected to perform uniaxial tensile testing to determine their material stiffness, and ultimate strength/stretch. The elastin and collagen contents in four tissue groups except for Dacron were quantified by histological examinations, while the material ultrastructure of five material groups was visualized by scanning electron microscope. Statistical results showed that three graft materials including Dacron, human pericardium and bovine pericardium had significantly higher ultimate strength and stiffness than both normal and dissected aortas. Human and bovine pericardia had significantly lower ultimate stretch than native aortas. Histological examinations revealed that normal and diseased aortic tissues had a significantly higher content of elastic fiber than two pericardial tissues, but less collagen fiber content. All four tissue groups exhibited lamellar fiber ultrastructure, with aortic tissues possessing thinner lamella. Dacron was composed of densely coalesced polyethylene terephthalate fibers in thick bundles. Aortic graft materials with denser fiber ultrastructure and/or higher content of collagen fiber than native aortic tissues, exhibited higher ultimate strength and stiffness. This information provides a basis to understand the mechanical failure of aortic grafts, and inspire the design of biomimetic aortic grafts.

Exploiting light-based 3D-printing for the fabrication of mechanically enhanced, patient-specific aortic grafts

Despite polyester vascular grafts being routinely used in life-saving aortic aneurysm surgeries, they are less compliant than the healthy, native human aorta. This mismatch in mechanical behaviour has been associated with disruption of haemodynamics contributing to several long-term cardiovascular complications. Moreover, current fabrication approaches mean that opportunities to personalise grafts to the individual anatomical features are limited. Various modifications to graft design have been investigated to overcome such limitations; yet optimal graft functionality remains to be achieved. This study reports on the development and characterisation of an alternative vascular graft material. An alginate:PEGDA (AL:PE) interpenetrating polymer network (IPN) hydrogel has been produced with uniaxial tensile tests revealing similar strength and stiffness (0.39 ± 0.05 MPa and 1.61 ± 0.19 MPa, respectively) to the human aorta. Moreover, AL:PE tubular conduits of similar geometrical dimensions to segments of the aorta were produced, either via conventional moulding methods or stereolithography (SLA) 3D-printing. While both fabrication methods successfully demonstrated AL:PE hydrogel production, SLA 3D-printing was more easily adaptable to the fabrication of complex structures without the need of specific moulds or further post-processing. Additionally, most 3D-printed AL:PE hydrogel tubular conduits sustained, without failure, compression up to 50% their outer diameter and returned to their original shape upon load removal, thereby exhibiting promising behaviour that could withstand pulsatile pressure in vivo. Overall, these results suggest that this AL:PE IPN hydrogel formulation in combination with 3D-printing, has great potential for accelerating progress towards personalised and mechanically-matched aortic grafts.

TEVAR and EVAR, the unknown knowns of the cardiovascular hemodynamics; and the immediate and long-term consequences of fabric material on major adverse clinical outcome

This review discusses the impact of endovascular aneurysm repair on cardiovascular (CV) hemodynamics and the role of stent-graft material, i.e., polytetrafluoroethylene (PTFE) vs. polyester in post-procedural outcomes. Endovascular aneurysm repair has been widely employed in the last decades for thoracic and abdominal aneurysm repair. However, aortic endografts are stiff and alter the native flow hemodynamics. This failure to simulate the native aorta could lead to added strain on the heart, manifesting as increased left ventricular strain, higher pulse pressure, and congestive heart failure later. This could result in adverse CV outcomes. Also, evidence is mounting to support the implication of stent-graft materials, i.e., PTFE vs. polyester, in adverse post-procedural outcomes. However, there is an absence of level one evidence. Therefore, the only way forward is to plan and perform a randomised controlled trial to demonstrate the alterations in the CV hemodynamics in the short and long run and compare the available stent-graft materials regarding procedural and clinical outcomes. We believe the best solution, for now, would be to reduce the stented length of the aorta. At the same time, in the longer term, encourage continuous improvement in stent-graft materials and design.

Aortic distensibility in Marfan syndrome: a potential predictor of aortic events?

Objectives

Patients with Marfan syndrome (MFS) are prone to develop aortic aneurysms due to fragmentation of elastic fibres, resulting in reduced distensibility of the aorta. Reduced distensibility was previously shown to predict progressive descending aorta dilatation. Here, we investigated longitudinal changes in distensibility, as a potential predictor of aortic events.

Methods

This retrospective study included all patients with MFS with at least four cardiac magnetic resonance examinations performed between 1996 and 2012. Aortic distensibility was assessed, in the ascending (level 1), proximal descending (level 2) and distal descending (level 3) aorta. Changes in distensibility were studied using linear mixed-effects regression models.

Results

In total, 35 patients with MFS (age at inclusion 28 (IQR 23–32) years, 54% men) were included. Mean aortic distensibility was already low (between 2.9×10^–3/mm Hg/year and 6.4×10^–3/mm Hg/year) at all levels at baseline, and significantly decreased over time at levels 2 and 3 (respectively, p=0.012 and p=0.002). The rate of distensibility loss per year (×10^-3/mm Hg/year) was 0.01, 0.03 and 0.06×10^–3/mm Hg at levels 1, 2 and 3, respectively. At inclusion, men exhibited very low distensibility, whereas women showed moderately reduced distensibility, gradually decreasing with age.

Aortic dilatation rate at level 2 was associated with reduced aortic distensibility. However, we could not demonstrate a direct correlation between distensibility and clinical events during a follow-up of 22 years.

Conclusion

Patients with MFS display reduced aortic distensibility already at an early age, inversely relating to aortic dilatation rate. However, in this selected patient group, distensibility seems less suitable as an individual predictor of aortic events.

Combined thoracic endovascular aortic repair and endovascular aneurysm repair and the long-term consequences of altered cardiovascular haemodynamics on morbidity and mortality: case series and literature review

Background

Thoracic and abdominal aortic stent grafts are firmer and more rigid than the native aorta. Aortic implanted devices have been implicated in the development of acute systolic hypertension, elevated pulse pressure, and reduced coronary perfusion.

Case summary

We report four cases of staged thoracic endovascular aortic repair (TEVAR) and then endovascular aneurysm repair (EVAR). All patients had TEVAR first for thoracic aortic aneurysm and later on developed infra-renal abdominal aortic aneurysm (AAA) that required EVAR. There were three males and one female with a median age of 74.5 years (range 67.5-78.5). None of the patients developed aortic-related major clinical adverse effects or required any aortic intervention during their follow-up. However, within 2 years, all patients developed symptomatic left ventricular hypertrophy with diastolic dysfunction. All patients had bilateral lower limb oedema, with on and off chest pain and shortness of breath (SOB), necessitating coronary angiograms, which showed no evidence of coronary artery disease. Three patients died from cardiovascular-related morbidities, and the fourth patient is still complaining of SOB despite a normal coronary angiogram.

Discussion

Aortic-endograft compliance mismatch is an invisible enemy, with troubling consequences for the aorta proximal and distal to the endograft. Aortic stiffness due to vascular endograft could lead to cardiovascular adverse events, even in the absence of direct aortic-related complications. After combined TEVAR and EVAR, the compliance mismatch and elasticity loss are even more pronounced than with TEVAR alone, which necessitates patient monitoring for the development of cardiovascular complications.

Staged Hybrid Single Lumen Reconstruction (TIGER) in Management of Chronic Symptomatic Complex Type B Aortic Dissection, Techniques, and Literature Review

BACKGROUND

Endovascular intervention for chronic symptomatic type B aortic dissection (CS-TBAD) induces aortic wall stress with negative hemodynamic cardiovascular consequences. CS-TBAD risks increased morbidity and mortality due to septum maturation with significant impact on false lumen modulation, and partial lumen thrombosis conveying the worst outcome. The aim of the TIGER technique is total aortic remodeling with true lumen expansion, false lumen regression and complete thrombosis, and stabilization of overall aortic diameter.

METHODS

We report 5 cases of aortic dissection with a mean follow-up of 16 months (6-28 months). All had aneurysmal dilation, with 3 having acute pan aortic dissection and 2 having CS-TBAD. All were managed by sTaged HybrId sinGle lumEn Reconstruction (TIGER). Our first approach was to create one single lumen from the supraceliac, infradiaphragmatic aorta to both common iliac arteries with open surgical patching of the visceral arteries; then, we performed a TEVAR 3 months later.

RESULTS

Three patients required a left subclavian artery chimney graft and one required bilateral subclavian to carotid artery transposition. No spinal drainage was required, and all patients had intraoperative transesophageal echo for wire guidance. We had no aortic rupture or retrograde type A dissection, and we experienced no renal, visceral, cardiac, pulmonary, or spinal complications. All patients, but one, went off their antihypertensive medication. All patients had normal estimated glomerular filtration rate postoperatively, and they all demonstrated accelerated aortic modulation.

CONCLUSIONS

TIGER was not only effective at the semiacute stage to initiate remodeling and prevent malperfusion, it also facilitated a straightforward TEVAR at stage 2, which was made easier by avoiding visceral branch stenting. Moreover, it decreased the length of aortic segment, which was stented, thereby avoiding critical shattering, branch dislodgment, and visceral compromise; spinal ischemia; and negative cardiovascular consequences.