Differences in the Area of Proximal and Distal Entry Tears at CT Angiography Predict Long-term Clinical Outcomes in Aortic Dissection

Mechanisms of aortic dissection: From pathological changes to experimental and in silico models

Aortic dissection continues to be responsible for significant morbidity and mortality, although recent advances in medical data assimilation and in experimental and in silico models have improved our understanding of the initiation and progression of the accumulation of blood within the aortic wall. Hence, there remains a pressing necessity for innovative and enhanced models to more accurately characterize the associated pathological changes. Early on, experimental models were employed to uncover mechanisms in aortic dissection, such as hemodynamic changes and alterations in wall microstructure, and to assess the efficacy of medical implants. While experimental models were once the only option available, more recently they are also being used to validate in silico models. Based on an improved understanding of the deteriorated microstructure of the aortic wall, numerous multiscale material models have been proposed in recent decades to study the state of stress in dissected aortas, including the changes associated with damage and failure. Furthermore, when integrated with accessible patient-derived medical data, in silico models prove to be an invaluable tool for identifying correlations between hemodynamics, wall stresses, or thrombus formation in the deteriorated aortic wall. They are also advantageous for model-guided design of medical implants with the aim of evaluating the deployment and migration of implants in patients. Nonetheless, the utility of in silico models depends largely on patient-derived medical data, such as chosen boundary conditions or tissue properties. In this review article, our objective is to provide a thorough summary of medical data elucidating the pathological alterations associated with this disease. Concurrently, we aim to assess experimental models, as well as multiscale material and patient data-informed in silico models, that investigate various aspects of aortic dissection. In conclusion, we present a discourse on future perspectives, encompassing aspects of disease modeling, numerical challenges, and clinical applications, with a particular focus on aortic dissection. The aspiration is to inspire future studies, deepen our comprehension of the disease, and ultimately shape clinical care and treatment decisions.

Predicting Late Adverse Events in Uncomplicated Stanford Type B Aortic Dissection: Results From the ROADMAP Validation Study

BACKGROUND

Risk stratification is highly desirable in patients with uncomplicated Stanford type B aortic dissection but inadequately supported by evidence. We sought to validate externally a published prediction model for late adverse events (LAEs), consisting of 1 clinical (connective tissue disease) and 4 imaging variables: maximum aortic diameter, false lumen circumferential angle, false lumen outflow, and number of identifiable intercostal arteries.

METHODS

We assembled a retrospective multicenter cohort (ROADMAP [Registry of Aortic Diseases to Model Adverse Events and Progression]) of 401 patients with uncomplicated Stanford type B aortic dissection presenting to 1 of 8 aortic centers between 2001 and 2013, followed until 2020. LAEs were defined as fatal or nonfatal aortic rupture, new refractory hypertension or pain, organ or limb ischemia, aortic aneurysm formation (≥6 cm), or rapid growth (≥1 cm per year). We applied the original model parameters to the validation cohort and examined the effect on risk categorization using LAE end points.

RESULTS

One hundred and seventy-six patients (44%) with incomplete imaging or clinical data were excluded. Of 225 patients in the final cohort, 90 (40%) developed LAEs, predominantly driven by aneurysm formation. Baseline maximum aortic diameter was significantly larger in patients with (42.6 [95% CI, 39.1-45.8] mm) compared with patients without LAEs (39.9 [95% CI, 36.3-44.2] mm; P=0.001). A multivariable Cox regression model indicated that only maximum diameter was associated with LAEs (hazard ratio, 1.07 [95% CI, 1.03-1.11] per mm; P<0.001), while the other parameters were not (P>0.05). Applying the original prediction model to the validation cohort resulted in a poor 5-year sensitivity (38%) and specificity (69%).

CONCLUSIONS

A clinical and imaging-based prediction model performed poorly in the ROADMAP cohort. Maximum aortic diameter remains the strongest predictor of LAEs in uncomplicated Stanford type B aortic dissection.

False lumen hemodynamics and partial thrombosis in chronic aortic dissection of the descending aorta

OBJECTIVES

Partial thrombosis of the false lumen (FL) in patients with chronic aortic dissection (AD) of the descending aorta has been associated with poor outcomes. Meanwhile, the fluid dynamic and biomechanical characteristics associated with partial thrombosis remain to be elucidated. This retrospective, single-center study tested the association between FL fluid dynamics and biomechanics and the presence and extent of FL thrombus.

METHODS

Patients with chronic non-thrombosed or partially thrombosed FLs in the descending aorta after an aortic dissection underwent computed tomography angiography, cardiovascular magnetic resonance (CMR) angiography, and a 4D flow CMR study. A comprehensive quantitative analysis was performed to test the association between FL thrombus presence and extent (percentage of FL with thrombus) and FL anatomy (diameter, entry tear location and size), fluid dynamics (inflow, rotational flow, wall shear stress, kinetic energy, and flow acceleration and stasis), and biomechanics (pulse wave velocity).

RESULTS

Sixty-eight patients were included. In multivariate logistic regression FL kinetic energy (p = 0.038) discriminated the 33 patients with partial FL thrombosis from the 35 patients with no thrombosis. Similarly, in separated multivariate linear correlations kinetic energy (p = 0.006) and FL inflow (p = 0.002) were independently related to the extent of the thrombus. FL vortexes, flow acceleration and stasis, wall shear stress, and pulse wave velocity showed limited associations with thrombus presence and extent.

CONCLUSION

In patients with chronic descending aorta dissection, false lumen kinetic energy is related to the presence and extent of false lumen thrombus.

CLINICAL RELEVANCE STATEMENT

In patients with chronic aortic dissection of the descending aorta, false lumen hemodynamic parameters are closely linked with the presence and extent of false lumen thrombosis, and these non-invasive measures might be important in patient management.

KEY POINTS

• Partial false lumen thrombosis has been associated with aortic growth in patients with chronic descending aortic dissection; therefore, the identification of prothrombotic flow conditions is desirable. • The presence of partial false lumen thrombosis as well as its extent was related with false lumen kinetic energy. • The assessment of false lumen hemodynamics may be important in the management of patients with chronic aortic dissection of the descending aorta.

Radiology: Cardiothoracic Imaging Highlights 2023

Radiology: Cardiothoracic Imaging publishes novel research and technical developments in cardiac, thoracic, and vascular imaging. The journal published many innovative studies during 2023 and achieved an impact factor for the first time since its inaugural issue in 2019, with an impact factor of 7.0. The current review article, led by the Radiology: Cardiothoracic Imaging trainee editorial board, highlights the most impactful articles published in the journal between November 2022 and October 2023. The review encompasses various aspects of coronary CT, photon-counting detector CT, PET/MRI, cardiac MRI, congenital heart disease, vascular imaging, thoracic imaging, artificial intelligence, and health services research. Key highlights include the potential for photon-counting detector CT to reduce contrast media volumes, utility of combined PET/MRI in the evaluation of cardiac sarcoidosis, the prognostic value of left atrial late gadolinium enhancement at MRI in predicting incident atrial fibrillation, the utility of an artificial intelligence tool to optimize detection of incidental pulmonary embolism, and standardization of medical terminology for cardiac CT. Ongoing research and future directions include evaluation of novel PET tracers for assessment of myocardial fibrosis, deployment of AI tools in clinical cardiovascular imaging workflows, and growing awareness of the need to improve environmental sustainability in imaging. Keywords: Coronary CT, Photon-counting Detector CT, PET/MRI, Cardiac MRI, Congenital Heart Disease, Vascular Imaging, Thoracic Imaging, Artificial Intelligence, Health Services Research © RSNA, 2024.

Relationship between false lumen morphology and entry tear in acute type A aortic dissection

OBJECTIVES

This study aimed to investigate the relationship between false lumen morphology and the size, aortic segment and position of the entry tear for acute type A aortic dissection.

METHODS

The records of patients who underwent emergency operation for acute type A aortic dissection in our institution between April 2011 and May 2022 were examined. Data regarding size, location and position of the entry tear and preoperative computed tomography findings were reviewed. The relationship of these variables with false lumen morphology was examined and retrospectively compared according to tear size.

RESULTS

Of 243 cases, characteristics of the entry tear, visualized during surgery, were confirmed in 134 cases (age = 70.9 ± 12.6 years, male = 45.5%). Tear sizes at different aortic segments were not significantly different (P = 0.376). Tears posterior to the lesser curvature were significantly smaller than those anterior to the greater curvature (P = 0.004). A thrombosed false lumen was associated with a significantly smaller tear size and position on the posterior to the lesser curvature side in aortic cross-section (all P < 0.001). Multivariate analysis showed that tear size, the presence of re-entry and tear position anterior to the greater curvature were independent predictors of a patent false lumen.

CONCLUSIONS

In acute type A aortic dissection, larger tear size, the presence of re-entry and tear position anterior to the greater curvature are risk factors for a patent false lumen. Although the results of this study are valid only for patients in whom intimal tears were detected during aortic surgery, this trend may provide information for pathophysiology of the disease.

Hemodynamic effects of entry and exit tear size in aortic dissection evaluated with in vitro magnetic resonance imaging and fluid-structure interaction simulation

Understanding the complex interplay between morphologic and hemodynamic features in aortic dissection is critical for risk stratification and for the development of individualized therapy. This work evaluates the effects of entry and exit tear size on the hemodynamics in type B aortic dissection by comparing fluid-structure interaction (FSI) simulations with in vitro 4D-flow magnetic resonance imaging (MRI). A baseline patient-specific 3D-printed model and two variants with modified tear size (smaller entry tear, smaller exit tear) were embedded into a flow- and pressure-controlled setup to perform MRI as well as 12-point catheter-based pressure measurements. The same models defined the wall and fluid domains for FSI simulations, for which boundary conditions were matched with measured data. Results showed exceptionally well matched complex flow patterns between 4D-flow MRI and FSI simulations. Compared to the baseline model, false lumen flow volume decreased with either a smaller entry tear (- 17.8 and - 18.5%, for FSI simulation and 4D-flow MRI, respectively) or smaller exit tear (- 16.0 and - 17.3%). True to false lumen pressure difference (initially 11.0 and 7.9 mmHg, for FSI simulation and catheter-based pressure measurements, respectively) increased with a smaller entry tear (28.9 and 14.6 mmHg), and became negative with a smaller exit tear (- 20.6 and - 13.2 mmHg). This work establishes quantitative and qualitative effects of entry or exit tear size on hemodynamics in aortic dissection, with particularly notable impact observed on FL pressurization. FSI simulations demonstrate acceptable qualitative and quantitative agreement with flow imaging, supporting its deployment in clinical studies.

A Comparison of Retrospective ECG-Gated CT and Surgical or Angiographical Findings in Acute Aortic Syndrome

The best cardiac phases in retrospective ECG-gated CT for detecting an intimal tear (IT) in aortic dissection (AD) and an ulcer-like projection (ULP) in an intramural hematoma (IMH) have not been established. This study aimed to compare the detection accuracy of diastolic-phase and systolic-phase ECG-gated CT for IT in AD and ULP in IMH, with subsequent surgical or angiographical confirmation as the reference standard.In total, 81 patients (67.6 ± 11.8 years; 41 men) who underwent emergency ECG-gated CT and subsequent open surgery or thoracic endovascular aortic repair for AD (n = 52) or IMH (n = 29) were included. The accuracies of detecting IT and ULP were compared among only diastolic-phase, only systolic-phase, and both diastolic-phase and systolic-phase methods of retrospective ECG-gated CT; surgical or angiographical findings were used as the reference standard. The detection accuracy for IT and ULP using only diastolic-phase, only systolic-phase, and both diastolic-phase and systolic-phase methods of ECG-gated CT was 93% [95% CI: 87-97], 94% [95% CI: 88-97], and 95% [95% CI: 90-97], respectively. There were no significant differences in detection accuracy among the 3 acquisition methods (P = 0.55). Similarly, there were no significant differences in the accuracy of detecting IT in AD (P = 0.55) and ULP in IMH (P > 0.99) among only diastolic-phase, only systolic-phase, and both diastolic- and systolic-phase ECG-gated CT.Retrospective ECG-gated CT for detecting IT in AD and ULP in IMH yields highly accurate findings. There were no significant differences seen among only diastolic-phase, only systolic-phase, and both diastolic-phase and systolic-phase ECG-gated CT.

Radiology: Cardiothoracic Imaging Highlights 2022

Since its inaugural issue in 2019, Radiology: Cardiothoracic Imaging has disseminated the latest scientific advances and technical developments in cardiac, vascular, and thoracic imaging. In this review, we highlight select articles published in this journal between October 2021 and October 2022. The scope of the review encompasses various aspects of coronary artery and congenital heart diseases, vascular diseases, thoracic imaging, and health services research. Key highlights include changes in the revised Coronary Artery Disease Reporting and Data System 2.0, the value of coronary CT angiography in informing prognosis and guiding treatment decisions, cardiac MRI findings after COVID-19 vaccination or infection, high-risk features at CT angiography to identify patients with aortic dissection at risk for late adverse events, and CT-guided fiducial marker placement for preoperative planning for pulmonary nodules. Ongoing research and future directions include photon-counting CT and artificial intelligence applications in cardiovascular imaging. Keywords: Pediatrics, CT Angiography, CT-Perfusion, CT-Spectral Imaging, MR Angiography, PET/CT, Transcatheter Aortic Valve Implantation/Replacement (TAVI/TAVR), Cardiac, Pulmonary, Vascular, Aorta, Coronary Arteries © RSNA, 2023.

Thoracic Endovascular Aortic Repair for Chronic Type B Aortic Dissection: Pre- and Postprocedural Imaging

Aortic dissection is a chronic disease that requires lifelong clinical and imaging surveillance, long after the acute event. Imaging has an important role in prognosis, timing of repair, device sizing, and monitoring for complications, especially in the endovascular therapy era. Important anatomic features at preprocedural imaging include the location of the primary intimal tear and aortic zonal and branch vessel involvement, which influence the treatment strategy. Challenges of repair in the chronic phase include a small true lumen in conjunction with a stiff intimal flap, complex anatomy, and retrograde perfusion from distal reentry tears. The role of thoracic endovascular aortic repair (TEVAR) remains controversial for treatment of chronic aortic dissection. Standard TEVAR is aimed at excluding the primary intimal tear to decrease false lumen perfusion, induce false lumen thrombosis, promote aortic remodeling, and prevent aortic growth. In addition to covering the primary intimal tear with an endograft, several adjunctive techniques have been developed to mitigate retrograde false lumen perfusion. These techniques are broadly categorized into false lumen obliteration and landing zone optimization strategies, such as the provisional extension to induce complete attachment (PETTICOAT), false lumen embolization, cheese-wire fenestration, and knickerbocker techniques. Familiarity with these techniques is important to recognize expected changes and complications at postintervention imaging. The authors detail imaging options, provide examples of simple and complex endovascular repairs of aortic dissections, and highlight complications that can be associated with various techniques. Online supplemental material is available for this article. ^©RSNA, 2022.

False lumen rotational flow and aortic stiffness are associated with aortic growth rate in patients with chronic aortic dissection of the descending aorta: a 4D flow cardiovascular magnetic resonance study

BACKGROUND

Patency of the false lumen in chronic aortic dissection (AD) is associated with aortic dilation and long-term aortic events. However, predictors of adverse outcomes in this population are limited. The aim of this study was to evaluate the relationship between aortic growth rate and false lumen flow dynamics and biomechanics in patients with chronic, patent AD.

METHODS

Patients with a chronic AD with patent false lumen in the descending aorta and no genetic connective tissue disorder underwent an imaging follow-up including a contrast-enhanced 4D flow cardiovascular magnetic resonance (CMR) protocol and two consecutive computed tomography angiograms (CTA) acquired at least 1 year apart. A comprehensive analysis of anatomical features (including thrombus quantification), and false lumen flow dynamics and biomechanics (pulse wave velocity) was performed.

RESULTS

Fifty-four consecutive patients with a chronic, patent false lumen in the descending aorta were included (35 surgically-treated type A AD with residual tear and 19 medically-treated type B AD). Median follow-up was 40 months. The in-plane rotational flow, pulse wave velocity and the percentage of thrombus in the false lumen were positively related to aortic growth rate (p = 0.006, 0.017, and 0.037, respectively), whereas wall shear stress showed a trend for a positive association (p = 0.060). These results were found irrespectively of the type of AD.

CONCLUSIONS

In patients with chronic AD and patent false lumen of the descending aorta, rotational flow, pulse wave velocity and wall shear stress are positively related to aortic growth rate, and should be implemented in the follow-up algorithm of these patients. Further prospective studies are needed to confirm if the assessment of these parameters helps to identify patients at higher risk of adverse clinical events.