Atlas-Based Evaluation of Hemodynamic in Ascending Thoracic Aortic Aneurysms

Atlas-based analyses of patients with cardiovascular diseases have recently been explored to understand the mechanistic link between shape and pathophysiology. The construction of probabilistic atlases is based on statistical shape modeling (SSM) to assess key anatomic features for a given patient population. Such an approach is relevant to study the complex nature of the ascending thoracic aortic aneurysm (ATAA) as characterized by different patterns of aortic shapes and valve phenotypes. This study was carried out to develop an SSM of the dilated aorta with both bicuspid aortic valve (BAV) and tricuspid aortic valve (TAV), and then assess the computational hemodynamic of virtual models obtained by the deformation of the mean template for specific shape boundaries (i.e., ±1.5 standard deviation, σ). Simulations demonstrated remarkable changes in the velocity streamlines, blood pressure, and fluid shear stress with the principal shape modes such as the aortic size (Mode 1), vessel tortuosity (Mode 2), and aortic valve morphologies (Mode 3). The atlas-based disease assessment can represent a powerful tool to reveal important insights on ATAA-derived hemodynamic, especially for aneurysms which are considered to have borderline anatomies, and thus challenging decision-making. The utilization of SSMs for creating probabilistic patient cohorts can facilitate the understanding of the heterogenous nature of the dilated ascending aorta.

Cardiac and aortic size measures in adult echocardiography should be indexed by body surface area regardless of body mass index

BACKGROUNDBody size indexation is a foundation of the diagnostic interpretation of cardiac size measures used in imaging assessment of cardiovascular health. Body surface area (BSA) is the most commonly used metric for body size indexation of echocardiographic measures, but its use in patients who are underweight or obese is questioned (body mass index (BMI) <18·5 kg/m2 or ≥30 kg/m2, respectively). We hypothesized that mortality can be used to identify an optimal body size indexation metric for echocardiographic measures that would be a better predictor of survival than BSA regardless of BMI.METHODSIn this big data, cohort study, adult patients with no prior valve replacement were selected from the National Echo Database Australia. Survival analysis was performed for echocardiographic measures both unindexed and indexed to different body size metrics, with 5-year cardiovascular mortality as the primary endpoint.FINDINGSIndexation of echocardiographic measures (left ventricular diameter [n=337,481] and mass [n=330,959], left atrial area [n=136,989], aortic sinus diameter [n=125,130], right atrial area [n=81,699], right ventricular diameter [n=3,575], right ventricular outflow tract diameter [n=2,841]) by BSA had better prognostic performance vs unindexed measures (healthy/overweight: C-statistic 0·656 vs 0·618, average change in Akaike Information Criteria (ΔAIC) 800; underweight: C-statistic 0·669 vs 0·654, ΔAIC 15; obese: C-statistic 0·630 vs 0·612, ΔAIC 113). Indexation by other body size metrics (lean body mass or height and/or weight raised to various powers) did not improve prognostic performance versus BSA by a clinically relevant magnitude (average C-statistic increase ≤0·01), with smaller differences in higher BMI subgroups. Similar results were obtained using sex-disaggregated analysis, for indexation of other aortic or cardiac dimension or volume measures, and for all-cause mortality.INTERPRETATIONIndexing measures of cardiac and aortic size by BSA improves prognostic performance regardless of BMI, and no other body size metric has a clinically meaningful better performance.FUNDINGThis research was supported in part by grants (PI Ugander) from New South Wales Health, Heart Research Australia, and the University of Sydney.

Hemodynamic Characteristics of Dilated Ascending Aorta in Patients with Bicuspid Aortic Valve

Objective: Aim of this study is to investigate the influence of aortic diameter on hemodynamic environment characteristics in patient with the bicuspid aortic valve (BAV) and dilated ascending aorta (AAo) .Methods: In this study, an MRI of one BAV patient with 4.5 cm AAo was collected and numerical model was constructed. Based on the images，the other three numerical models were constructed with different ascending aortic size with 4.0cm, 5.0cm and 5.5cm respectively while the size and the geometry of other parts were fixed. Then hemodynamics in these four models was simulated numerically and the flow patterns and loading distributions were investigated.Results: Hemodynamics environments in the AAo were simulated with different aortic size. As the aortic diameter increases, we find: 1. the blood flow becomes more disturbing;2.the wall pressure at ascending aortic is higher; 3. the wall shear stress at the ascending aortic decreases; 4.oscillatory shear index of the outer part on the proximal AAo increases;5. all these hemodynamic parameters described above are asymmetrically distributed in dilated AAo and more parts of aorta would be affected as the AAo dilatation progresses.Conclusions: The study revealed that the diameter of ascending aortic can significantly influence the magnitude and distribution of the dynamics. There are altered flow patterns, pressure difference, WSS and OSI distribution features in bicuspid aortic valve patients with vascular dilatation. As the extent of aortic dilatation increases especially exceed 5.5cm,this study support the recent guideline that aortic replacement should be considered .

Two-Dimensional Aortic Size Normalcy: A Novelty Detection Approach

Background: To develop a tool for assessing normalcy of the thoracic aorta (TA) by echocardiography, based on either a linear regression model (Z-score), or a machine learning technique, namely one-class support vector machine (OC-SVM) (Q-score). Methods: TA diameters were measured in 1112 prospectively enrolled healthy subjects, aging 5 to 89 years. Considering sex, age and body surface area we developed two calculators based on the traditional Z-score and the novel Q-score. The calculators were compared in 198 adults with TA > 40 mm, and in 466 patients affected by either Marfan syndrome or bicuspid aortic valve (BAV). Results: Q-score attained a better Area Under the Curve (0.989; 95% CI 0.984–0.993, sensitivity = 97.5%, specificity = 95.4%) than Z-score (0.955; 95% CI 0.942–0.967, sensitivity = 81.3%, specificity = 93.3%; p < 0.0001) in patients with TA > 40 mm. The prevalence of TA dilatation in Marfan and BAV patients was higher as Z-score > 2 than as Q-score < 4% (73.4% vs. 50.09%, p < 0.00001). Conclusions: Q-score is a novel tool for assessing TA normalcy based on a model requiring less assumptions about the distribution of the relevant variables. Notably, diameters do not need to depend linearly on anthropometric measurements. Additionally, Q-score can capture the joint distribution of these variables with all four diameters simultaneously, thus accounting for the overall aortic shape. This approach results in a lower rate of predicted TA abnormalcy in patients at risk of TA aneurysm. Further prognostic studies will be necessary for assessing the relative effectiveness of Q-score versus Z-score.