Aneurysms of the ascending aorta and arch: the role of imaging in diagnosis and surgical management

Repair of an ascending aortic aneurysm associated with an anomalous right coronary artery origin

BACKGROUND

Anomalous right coronary artery (RCA) origin off the ascending aorta, above the level of the sinus of Valsalva, is rare and can be associated with altered hemodynamics, decreased coronary perfusion, and presents unique considerations during intraoperative management in the surgical treatment of concomitant ascending aneurysmal disease.

CASE PRESENTATION

A 58-year-old female with prior symptomatic visceral aneurysmal rupture and cerebrovascular disease presented with a 5 cm ascending aortic aneurysm, elevated aortic index, and increased rupture risk factors. She was preoperatively diagnosed with an anomalous, high RCA origin off the ascending aorta 15 mm above the sinotubular junction. She underwent successful ascending aortic repair using a 28 mm Dacron hemiarch graft with reimplantation of an RCA button.

CONCLUSION

Our successful reconstructive surgical repair using an RCA button is effective management for high anomalous RCA take-offs from the ascending aorta and presents the first documented case of this rare coronary anomaly in the context of ascending aortic aneurysmal disease.

Computational predictions of damage propagation preceding dissection of ascending thoracic aortic aneurysms

Dissections of ascending thoracic aortic aneurysms (ATAAs) cause significant morbidity and mortality worldwide. They occur when a tear in the intima-media of the aorta permits the penetration of the blood and the subsequent delamination and separation of the wall in 2 layers, forming a false channel. To predict computationally the risk of tear formation, stress analyses should be performed layer-specifically and they should consider internal or residual stresses that exist in the tissue. In the present paper, we propose a novel layer-specific damage model based on the constrained mixture theory, which intrinsically takes into account these internal stresses and can predict appropriately the tear formation. The model is implemented in finite-element commercial software Abaqus coupled with user material subroutine. Its capability is tested by applying it to the simulation of different exemplary situations, going from in vitro bulge inflation experiments on aortic samples to in vivo overpressurizing of patient-specific ATAAs. The simulations reveal that damage correctly starts from the intimal layer (luminal side) and propagates across the media as a tear but never hits the adventitia. This scenario is typically the first stage of development of an acute dissection, which is predicted for pressures of about 2.5 times the diastolic pressure by the model after calibrating the parameters against experimental data performed on collected ATAA samples. Further validations on a larger cohort of patients should hopefully confirm the potential of the model in predicting patient-specific damage evolution and possible risk of dissection during aneurysm growth for clinical applications.

Prefailure and failure mechanics of the porcine ascending thoracic aorta: experiments and a multiscale model

Ascending thoracic aortic aneurysms (ATAA) have a high propensity for dissection, which occurs when the hemodynamic load exceeds the mechanical strength of the aortic media. Despite our recognition of this essential fact, the complex architecture of the media has made a predictive model of medial failure-even in the relatively simple case of the healthy vessel-difficult to achieve. As a first step towards a general model of ATAA failure, we characterized the mechanical behavior of healthy ascending thoracic aorta (ATA) media using uniaxial stretch-to-failure in both circumferential (n = 11) and axial (n = 11) orientations and equibiaxial extensions (n = 9). Both experiments demonstrated anisotropy, with higher tensile strength in the circumferential direction (2510 ± 439.3 kPa) compared to the axial direction (750 ± 102.6 kPa) for the uniaxial tests, and a ratio of 1.44 between the peak circumferential and axial loads in equibiaxial extension. Uniaxial tests for both orientations showed macroscopic tissue failure at a stretch of 1.9. A multiscale computational model, consisting of a realistically aligned interconnected fiber network in parallel with a neo-Hookean solid, was used to describe the data; failure was modeled at the fiber level, with an individual fiber failing when stretched beyond a critical threshold. The best-fit model results were within the 95% confidence intervals for uniaxial and biaxial experiments, including both prefailure and failure, and were consistent with properties of the components of the ATA media.

Computed tomography angiography of hybrid thoracic endovascular aortic repair of the aortic arch

Endovascular repair of the aorta has traditionally been limited to the abdominal aorta and, more recently, the descending thoracic aorta. However, recently hybrid repairs (a combination of open surgical and endovascular repair) have made endovascular repair of the aortic arch possible. Hybrid repair of the aortic arch typically involves an open surgical debranching procedure that allows for revascularization of the aortic arch vessels and subsequent endovascular stent placement. These approaches avoid the deep hypothermic circulatory arrest required for full, open surgical repair of the aortic arch. In hybrid repairs, the stent landing zone determines which branch vessels will be covered and therefore need revascularization. This article will review the preprocedure assessment with computed tomography angiography, techniques for revascularization and postprocedure complications.

Evaluation of the intraoperative specimens of the thoracic and abdominal aorta

BACKGROUND

Little is known about the histological patterns of acute and chronic aortic pathology with regard to medial degeneration, atherosclerosis and aortitis as well as their distribution in different age groups. The aim of the study was to evaluate histopathological findings of intraoperatively gained aortic specimens with regard to the incidence of medial degeneration, atherosclerosis and aortitis.

METHODS

Intraoperatively gained aortic specimens were evaluated in 151 patients including 83 (55%) aortic aneurysms (65 thoracic, 18 abdominal) and 68 (45%) acute type A aortic dissections. Histological stainings used were hematoxylin and eosin, Van Gieson as well as alcian blue. Patients were stratified according to above and below 65 years of age. High grade medial degeneration represented pooling of mucoid material in the whole aortic wall. High grade atherosclerosis represented severe intimal fibrosis, massive accumulation of macrophages and foam cells or massive calcification of the aortic wall.

RESULTS

Medial degeneration was diagnosed in 106 (70%) patients including 55 (52%) aortic aneurysms and 51 (48%) acute type A aortic dissections. High grade medial degeneration was found in 50% of patients with thoracic aortic aneurysms < 65 years of age vs. 44% in patients ≥ 65 years of age (p = 0.64) and in 36% of patients with thoracic aortic dissections < 65 years of age vs. 14% in patients ≥ 65 years of age (p = 0.07). Atherosclerosis was diagnosed in 71 (47%) patients including 46 (65%) aortic aneurysms and 25 (35%) aortic dissections. High grade atherosclerosis was found in 23% of patients with thoracic aneurysms < 65 years of age vs. 36% in patients ≥ 65 years of age (p = 0.24) and in 13% of patients with aortic dissections < 65 years of age vs. 52% in patients ≥ 65 years of age (p < 0.001). Aortitis was rare (n = 2).

CONCLUSIONS

Medial degeneration was the most frequent diagnosis in this series of aortic specimens. Medial degeneration was equally common in patients above and below 65 years of age. However in cases with acute type A aortic dissections, high grade atherosclerosis was the leading histopathological diagnosis in patients older than 65 years. Acute type A aortic dissections seem to have different underlying pathologies in different age groups.

Giant aortic pseudoaneurysm with stanford type a aortic dissection after aortic valve replacement

Giant pseudoaneurysm of the ascending aorta is a rare but dreadful complication occurring several months or years after aortic surgery. Thoracic aortic aneurysms tend to be asymptomatic and were previously often diagnosed only after a complication such as dissection or rupture. We present a rare case of giant ascending aneurysm with Stanford type A aortic dissection occurring 6 years after aortic valve replacement and also illustrate the potential dimensions the ascending aorta may reach by a pseudoaneurysm and dissection after AVR.

Effect of aneurysm on the mechanical dissection properties of the human ascending thoracic aorta

OBJECTIVES

The acute dissection of an ascending thoracic aortic aneurysm (ATAA) represents a devastating separation of elastic layers occurring when the hemodynamic loads on the diseased wall exceed the adhesive strength between layers. At present, the mechanics underlying aortic dissection are largely unclear, and the biomechanical delamination properties of the aneurysmal aorta are not defined. Individuals with bicuspid aortic valve (BAV) are particularly predisposed to ascending aortic aneurysm formation, with a marked risk of aortic dissection. The purpose of this study was to evaluate and compare the dissection properties of nonaneurysmal and aneurysmal human ascending thoracic aorta from patients with BAV morphology or normal tricuspid aortic valve (TAV) morphology using biomechanical delamination testing.

METHODS

The influence on the delamination strength (S(d)) of the aorta associated with BAV was compared with that in patients with TAV. After complete delamination of ATAA tissue samples, tensile tests were performed on each delaminated half for comparison of their tensile strengths.

RESULTS

The results showed that the aneurysmal aortas with BAV and TAV have lower S(d) than nonaneurysmal aortas and that ATAA with BAV has a lower S(d) than that with TAV. We have found a significant difference in S(d) between longitudinal and circumferential directions of the nondiseased aorta, suggesting anisotropic dissection properties.

CONCLUSIONS

The tensile testing results suggest that the weaker intimal half of the aortic wall might fail before the outer adventitial half. Scanning electron microscope analyses suggest different failure modalities of dissection between the two morphologies, and the lower S(d) in ATAAs appears to be associated with a disorganized microstructure. BAV ATAAs have a lower S(d) than TAV ATAAs, suggesting a greater propensity for aortic dissection.