Wall Stress and Geometry of the Thoracic Aorta in Patients With Aortic Valve Disease

The role of 4-dimensional flow in the assessment of bicuspid aortic valve and its valvulo-aortopathies

Bicuspid aortic valve is the most common congenital cardiac malformation and the leading cause of aortopathy and aortic stenosis in younger patients. Aortic wall remodelling secondary to altered haemodynamic flow patterns, changes in peak velocity, and wall shear stress may be implicated in the development of aortopathy in the presence of bicuspid aortic valve and dysfunction. Assessment of these parameters as potential predictors of disease severity and progression is thus desirable. The anatomic and functional information acquired from 4D flow MRI can allow simultaneous visualisation and quantification of the pathological geometric and haemodynamic changes of the aorta. We review the current clinical utility of haemodynamic quantities including velocity, wall sheer stress and energy losses, as well as visual descriptors such as vorticity and helicity, and flow direction in assessing the aortic valve and associated aortopathies.

Does the Leaflet Fusion Subtype Affect Pattern and Rate of Growth in BAV Aortopathy?: A Study of 102 BAV Aortopathy Cases With A Literature Review

BACKGROUND

Bicuspid aortic valves (BAV) and related aortopathy remain an intriguing topic. Not all BAVs get diseased and around 40% would develop aortic dilatation in their lifetime. If haemodynamic theory is to be believed, then leaflet fusion pattern should have an impact. This study sought to compare the association of aortic morphologies and rate of growth in a set of 102 BAV acropathies operated at a single centre, based on the fusion patterns.

METHODS

Data on aortic valve replacements over a 10-year period was analysed from a prospectively maintained database. Of the 198 BAV undergoing surgery, 102 had aortic dilatation above 40 mm on echocardiogram. These underwent computed tomography (CT) aortograms and were followed up as a part of a database. The impact of leaflet fusion patterns on aortic dilatation pattern and rate was analysed.

RESULTS

Of the 102, two patients had type 0 pathology and one had left-noncoronary (LN) leaflet fusion. Seventy-four (74) had type 1A or left-right (RL) fusion and 25 had type 1B right-noncoronary (RN) fusion. RL fusion had more males, were taller, bigger and had more proportion of aortic stenosis (AS). Aortic diameters, angles and growth rates at root, ascending/descending aorta and arch were not different. Regression analyses for size or growth did not show any significant impact of fusion pattern.

CONCLUSIONS

Left-right fusion pattern comprised three-quarters of BAV in this cohort and these patients were bigger, taller and had a greater proportion of males with increased rate of aortic stenosis. Despite these differences, there was no significant impact of fusion pattern on aortic size or rate of growth.

Influence of Material Model and Aortic Root Motion in Finite Element Analysis of Two Exemplary Cases of Proximal Aortic Dissection

The risk of type-A dissection is increased in subjects with connective tissue disorders and dilatation of the proximal aorta. The location and extents of vessel wall tears in these patients could be potentially missed during prospective imaging studies. The objective of this study is to estimate the distribution of systolic wall stress in two exemplary cases of proximal dissection using finite element analysis (FEA) and evaluate the sensitivity of the distribution to the choice of anisotropic material model and root motion. FEA was performed for predissection aortas, without prior knowledge of the origin and extents of vessel wall tear. The stress distribution was evaluated along the wall tear in the postdissection aortas. The stress distribution was compared for the Fung and Holzapfel models with and without root motion. For the subject with spiral dissection, peak stress coincided with the origin of the tear in the sinotubular junction. For the case with root dissection, maximum stress was obtained at the distal end of the tear. The FEA predicted tear pressure was 20% higher for the subject with root dissection as compared to the case with spiral dissection. The predicted tear pressure was higher (9-11%) for root motions up to 10 mm. The Holzapfel model predicted a tear pressure that was lower (8-15%) than the Fung model. The FEA results showed that both material response and root motion could potentially influence the predicted dissection pressure of the proximal aorta at least for conditions tested in this study.

New indicators for systematic assessment of aortic morphology: a narrative review

In order to prevent the occurrence of aortic adverse events in ascending thoracic aortic aneurysm patients, preventive surgery is the sole option in case of large aneurysm. Identifying high-risk patients timely and accurately requires effective predictive indicators of aortic adverse events and accurate risk stratification thresholds. Absolute diameter measured after a single imaging examination, which has been used as the predictive indicator for decades, has been proved to be ineffective for risk stratification in moderately dilated aorta. Previously, new indicators combining absolute diameters with personalized parameters have been reported to show better predictive power of aortic adverse events than absolute diameters by correcting the effect of these parameters on the diameters. Meanwhile, combining three-dimensional parameters to formulate risk stratification thresholds not only may characterize the aortic risk morphology more precisely, but also predict aortic adverse events more accurately. These new indicators may provide more systematic assessment methods of patients’ risk, formulate more personalized intervention strategies for ascending thoracic aortic aneurysm patients, and also provide a basis for researchers to develop more accurate and effective risk thresholds. We also highlight that the algorithm obtained by combining multiple indicators may be a better choice compared with single indicator, but this still requires the support of more evidence. Due to the particularity of syndromic aortic disease, whether these new indicators can be used for its risk stratification is still uncertain. Therefore, the scope of this manuscript does not include this kind of disease.

Certain aortic geometries and hemodynamics are associated with FID development and impact the evolution of uncomplicated type B intramural hematoma during the acute phase

OBJECTIVES

It is difficult to predict the evolution of uncomplicated type B intramural hematoma (IMHB) with a focal intimal disruption (FID) in the acute phase. The aims of this study were to investigate the predictors of FIDs and summarize the risk factors for the evolution of uncomplicated IMHB in the acute phase.

METHODS

Eighty-six patients with uncomplicated IMHB were included and were divided according to the development of an FID during the acute phase: the FID group (n = 32) and the no-FID group (n = 54). Geometric measurements and computed fluid dynamic calculations were based on a computed tomography scan performed on admission. Multivariate logistic regression analysis was used to estimate the predictors of FID development.

RESULTS

Thirty-two (37%) patients developed an FID. Patients with an FID had higher C-reactive protein levels (18.6 ± 2.3 vs 8.1 ± 0.2 mg/dL, P < 0.001) and white blood cell counts (10.3 ± 2.1 vs 7.5 ± 1.7 10⁹ /L, P < 0.001). The no-FID group had lower occurrences of disease progression (15% vs 64%, P < 0.001) and aorta-related mortality (6% vs 25%, P = 0.016). Multivariate logistic regression analysis indicated a significant risk for the occurrence of an FID with a larger maximum aortic diameter (OR, 1.35; 95% CI, 1.05-1.73, P = 0.020), thicker hematoma (OR, 2.20; 95% CI, 1.40-3.48, P = 0.001), and higher oscillatory shear index (per 0.01 unit, OR, 1.74; 95% CI, 1.21-2.49, P = 0.003). The aorta-related mortality during the acute phase was 25% (n = 8).

CONCLUSIONS

Certain aortic conditions, including ta larger aortic diameter, thicker hematoma and higher oscillatory shear stress, are associated with the FID development and result in worse clinical outcomes.