Equations for Estimating the Predissected Diameter of the Descending Aorta From Computed Tomographic Images at the Onset of Aortic Dissection

Growth and remodeling of the dissected membrane in an idealized dissected aorta model

While transitioning from the acute to chronic phase, the wall of a dissected aorta often expands in diameter and adaptations in thickness and microstructure take place in the dissected membrane. Including the mechanisms, leading to these changes, in a computational model is expected to improve the accuracy of predictions of the long-term complications and optimal treatment timing of dissection patients. An idealized dissected wall was modeled to represent the elastin and collagen production and/or degradation imposed by stress- and inflammation-mediated growth and remodeling, using the homogenized constrained mixture theory. As no optimal growth and remodeling parameters have been defined for aortic dissections, a Latin hypercube sampling with 1000 parameter combinations was assessed for four inflammation patterns, with a varying spatial extent (full/local) and temporal evolution (permanent/transient). The dissected membrane thickening and microstructure was considered together with the diameter expansion over a period of 90 days. The highest success rate was found for the transient inflammation patterns, with about 15% of the samples leading to converged solutions after 90 days. Clinically observed thickening rates were found for 2-4% of the transient inflammation samples, which represented median total diameter expansion rates of about 5 mm/year. The dissected membrane microstructure showed an elastin decrease and, in most cases, a collagen increase. In conclusion, the model with the transient inflammation pattern allowed the reproduction of clinically observed dissected membrane thickening rates, diameter expansion rates and adaptations in microstructure, thus providing guidance in reducing the parameter space in growth and remodeling models of aortic dissections.

Uncertainty quantification of the wall thickness and stiffness in an idealized dissected aorta

Personalized treatment informed by computational models has the potential to markedly improve the outcome for patients with a type B aortic dissection. However, existing computational models of dissected walls significantly simplify the characteristic false lumen, tears and/or material behavior. Moreover, the patient-specific wall thickness and stiffness cannot be accurately captured non-invasively in clinical practice, which inevitably leads to assumptions in these wall models. It is important to evaluate the impact of the corresponding uncertainty on the predicted wall deformations and stress, which are both key outcome indicators for treatment optimization. Therefore, a physiology-inspired finite element framework was proposed to model the wall deformation and stress of a type B aortic dissection at diastolic and systolic pressure. Based on this framework, 300 finite element analyses, sampled with a Latin hypercube, were performed to assess the global uncertainty, introduced by 4 uncertain wall thickness and stiffness input parameters, on 4 displacement and stress output parameters. The specific impact of each input parameter was estimated using Gaussian process regression, as surrogate model of the finite element framework, and a δ moment-independent analysis. The global uncertainty analysis indicated minor differences between the uncertainty at diastolic and systolic pressure. For all output parameters, the 4th quartile contained the major fraction of the uncertainty. The parameter-specific uncertainty analysis elucidated that the material stiffness and relative thickness of the dissected membrane were the respective main determinants of the wall deformation and stress. The uncertainty analysis provides insight into the effect of uncertain wall thickness and stiffness parameters on the predicted deformation and stress. Moreover, it emphasizes the need for probabilistic rather than deterministic predictions for clinical decision making in aortic dissections.

Aortic Dilatation on the Edge of Dissection-Do We Operate Too Late? The Ratio between Ascending and Descending Aorta DiameteR (RADAR)

(1) Background: There is a need for a novel surrogate marker to ease decision making when facing ascending aortic dilatation. In this article, we study the ratio between ascending and descending aorta diameters as a potential one. (2) Methods: Retrospective observational cohort study, including all the patients who underwent surgery for acute type A aorta dissection (aTAAD) between January 2014 and September 2020 at our center. A total of 50 patients were included. Clinical and demographic data were collected. The anatomical measurements were made including orthogonal maximal diameters of the ascending and descending aorta, post-dissection whole circumference length (post-wCL), post-dissection true lumen circumference length (post-tCL), and surface and sphericity indices of the ascending and descending aorta. Pre-dissection ascending aorta diameter (pre-AAD) and pre-dissection descending aorta diameter (pre-DAD) were calculated as well as the ratio between them and compared with reference values. (3) Results: Of the pre-AAD patients, 96% had smaller than the recommended 55 mm. The ratio between the descending and ascending aorta pre-dissection diameters was significantly smaller compared to the reference value (0.657 ± 0.125 versus 0.745 ± 0.016 with a mean difference of -0.088 and a p < 0.001). (4) Conclusions: The 55 mm threshold for aorta maximal diameter is an insufficient criterion when assessing the risk of dissection. The ratio between DAD and AAD is a parameter worthy of analysis as a tool to stratify the risk of dissection.

Distal stent graft-induced new entry (dSINE) after frozen elephant trunk: a scoping review

Background

The introduction of hybrid total arch replacement with the frozen elephant trunk (FET) technique has improved the field of aortic surgery by allowing single-stage treatment of complex aortic pathologies. Although FET has been associated with favorable aortic remodeling, it is also associated with the potential development of distal stent graft-induced new entries (dSINEs). The aim of our review is to collect data about the incidence and the supposed conditions for the occurrence of dSINE after total hybrid arch replacement with FET technique.

Methods

The literature review was performed using PubMed databases from inception to January 2022. A descriptive approach to detect and display supposed risk factors and predictors for dSINE occurrence has been adopted.

Results

Eight studies summarized the state-of-the-art of dSINE in a total number of 544 FET procedures performed to treat acute and chronic aortic dissections. The scoping review showed dSINEs occurrence in 69 patients (12.7%). The mean time between surgery and the diagnosis ranged from 12.6 to 30.6 months. Most patients that developed dSINE received endovascular treatment, whereas a couple of them needed open surgery. According to our experience, from January 2007 to December 2021, in 225 FET procedures a total of 54 cases of dSINE, both with Thoraflex and E-vita grafts have been detected. The mean time between the surgical procedure and the diagnosis was 27.2±33.6 months.

Conclusions

dSINEs are frequent complications after FET. Although not emergent, they require proper treatment. Due to dSINE's asymptomatic nature and potential harm, a rigorous follow-up including angio-computed tomography (CT) should be planned.

A machine learning approach for predicting descending thoracic aortic diameter

Background

To establish models for predicting descending thoracic aortic diameters and provide evidence for selecting the size of the stent graft for TBAD patients.

Methods

A total of 200 candidates without severe deformation of aorta were included. CTA information was collected and 3D reconstructed. In the reconstructed CTA, a total of 12 cross-sections of peripheral vessels were made perpendicular to the axis of flow of the aorta. Parameters of the cross sections and basic clinical characteristics were used for prediction. The data was randomly split into the training set and the test set in an 8:2 ratio. To fully describe diameters of descending thoracic aorta, three predicted points were set based quadrisection, and a total of 12 models at three predicted points were established using four algorithms included linear regression (LR), support vector machine (SVM), Extra-Tree regression (ETR) and random forest regression (RFR). The performance of models was evaluated by mean square error (MSE) of the prediction value, and the ranking of feature importance was given by Shapley value. After modeling, prognosis of five TEVAR cases and stent oversizing were compared.

Results

We identified a series of parameters which affect the diameter of descending thoracic aorta, including age, hypertension, the area of proximal edge of superior mesenteric artery, etc. Among four predictive models, all the MSEs of SVM models at three different predicted position were less than 2 mm², with approximately 90% predicted diameters error less than 2 mm in the test sets. In patients with dSINE, stent oversizing was about 3 mm, while only 1 mm in patients without complications.

Conclusion

The predictive models established by machine learning revealed the relationship between basic characteristics and diameters of different segment of descending aorta, which help to provide evidence for selecting the matching distal size of the stent for TBAD patients, thereby reducing the incidence of TEVAR complications.

Distal Stent Graft-Induced New Entry after Total Arch Replacement with Frozen Elephant Trunk for Aortic Dissection

Objectives: Distal stent graft-induced new entry (dSINE), defined as a new tear caused by a stent graft, has been increasingly observed following total arch replacement using frozen elephant trunk (FET) for aortic dissection. We aimed to investigate the incidence and treatment of dSINE after the use of FET. Methods: This retrospective study evaluated 70 patients who underwent total arch replacement using FET for aortic dissection between August 2014 and March 2020. They were followed up for at least 6 months postoperatively. Between-group comparisons were performed between those who did and did not develop dSINE. The risk factors for the development of dSINE and the treatment of dSINE were analyzed. Results: dSINE occurred postoperatively in nine patients (12.9%) with a median time frame of 17.7±11.7 months. The incidence of dSINE did not differ significantly according to classification, phase of dissection, or oversizing. All patients in the dSINE group developed enlargement of the false lumen. dSINE closure was successfully achieved without complications via thoracic endovascular aortic repair (TEVAR) in all patients. Conclusion: No independent factors predicting the development of dSINE were noted in this study. Additional TEVAR for dSINE provides good results and achieves false lumen thrombosis in the thoracic aorta, with no complications.

Diameter change in completely remodelled proximal descending aorta after acute type I dissection repair: implications for estimating the pre-dissection size

 

OBJECTIVES

Pre-dissection diameter of the proximal descending thoracic aorta (p-DTA), if available, would be the reference for determining the size of the stent graft or elephant trunk. Acute type B dissection is known to increase p-DTA diameter by 23% (Rylski factor). This study aimed to investigate the accuracy of estimating post-remodelling diameter of the p-DTA based on the Rylski factor and other post-dissection morphological parameters in acute type I dissection, based on the assumption that the post-remodelling diameter is similar to the pre-dissection diameter.

METHODS

In 60 patients with acute type I dissection showing complete remodelling of the p-DTA false lumen after surgical repair, preoperative and post-remodelling computed tomography scans were reviewed. Parameters, including maximal true lumen diameter (TLDmax) and aortic area-derived diameter divided by the Rylski factor (AoDRylski), were measured at the p-DTA.

RESULTS

After complete remodelling, p-DTA diameter decreased by 4.1 mm (P < 0.001). The equivalent to the Rylski factor was 15%. Both TLDmax and AoDRylski frequently showed ≥2 mm discrepancy from post-remodelling aortic diameter (36.7% and 48.3%, respectively, P = 0.30). When 2 parameters coincided within 2 mm, two-third of their estimations were accurate. AoDRylski was more accurate than TLDmax in patients with a large extent of circumferential dissection, and vice versa with less circumferential dissection (P = 0.027).

CONCLUSIONS

Prediction of post-remodelling aortic diameter relying on a single morphologic parameter carries a substantial risk of overestimation and underestimation. Evaluation based on the extent of circumferential dissection together with the 2 parameters may provide a more reliable estimation.

Aortic root and ascending aorta dimensions in acute aortic dissection

Objectives:

Aim of this study was to evaluate ascending aorta and aortic root dimension at acute type A dissection (acute aortic dissection) and to identify demographics elements being allied to the acute event.

Methods:

In a period between 2009 and 2017, 225 (n = 71, 32% female, mean age = 63 ± 12 years) patients eligible for analysis of ascending aorta and 223 (n = 70, 31% female, mean age = 63 ± 13 years) of aortic root were included in this study. Aortic diameter was assessed in preoperative computed tomography scan. The predissection diameters were modeled from the diameters obtained at diagnosis, assuming 30% augmentation of the diameter at acute event.

Results:

The mean diameter of the ascending aorta at dissection was 46 ± 8 mm and the modeled diameter was 32.3 ± 5.7 mm. The diameter of the aortic root at dissection was 42 ± 8 mm and modeled diameter was 29.5 ± 5.6 mm. In multivariate analysis, female gender (p = 0.026) and history of cerebrovascular event (p = 0.001) were associated with acute aortic dissection in small aortic root. Patient age (p < 0.001) and history of inguinal hernia (p = 0.001) in ascending aorta <55 mm correlated with acute aortic dissection.

Conclusion:

Modeling indicates that more than 90% of patients had aortic root and ascending aorta diameter <45 mm. It seems that the aortic diameter expansion over the 55 mm in development of acute aortic dissection is overestimated. Parameters other than aortic size were identified, which may be considered when patients at high risk for dissection were identified.