The loss of helical flow in the thoracic aorta might be an identifying marker for the risk of acute type B aortic dissection.

BACKGROUND AND OBJECTIVE: The occurrence of acute type B aortic dissection (TBAD) remained unclear. This study aimed to investigate the association between flow features and hemodynamic parameters in aortas that demonstrated the risk of TBAD occurrence. METHODS: The geometries of 15 hyperacute TBAD and 12 control patients (with healthy aorta) were reconstructed from computed tomography angiography images. Pre-TBAD models were then obtained by eliminating the dissection flaps. Flow features and hemodynamic parameters, including wall shear stress-related parameters and helicities, were compared between pre-TBAD and control models using computational fluid dynamics. RESULTS: There were no significant differences in baseline characteristics and anatomical parameters between the two groups. Significant contralateral helical blood flow was present in the healthy thoracic aorta, while almost no helical flow was observed in the pre-TBAD group. In addition, the mean normal transverse wall shear stress (NtransWSS) was significantly higher in the pre-TBAD group (aortic arch 0.49±0.09 vs. 0.40±0.05, P = 0.04; descending aorta: 0.46±0.05 vs. 0.33±0.02, P<0.01). Moreover, a significantly negative correlation was found between helicity and NtransWSS in the descending aorta. Moreover, the location of primary tears in 12 pre-TABD subjects matched well with regions of high NtransWSS. CONCLUSIONS: Loss of helical flow in the aortic arch and descending aorta may be a major flow feature in patients with underlying TBAD, resulting in increased flow disturbance and wall lesions.

A Hemodynamic Analysis of the Thrombosis Within Occluded Coronary Arterial Fistulas With Terminal Aneurysms Using a Blood Stasis Model.

Objective: The aim of this study is to numerically evaluate thrombosis risk within occluded coronary arterial fistulas (CAF) with terminal aneurysms, and provide guidance in choosing occlusion positions, with clinical observations as reference. Method: Four patients with CAF were studied, with different occlusion positions in actual treatments. Hemodynamics simulations were conducted, with blood residue predicted using the blood stasis model. Three types of models (untreated model, aneurysm-reserved model and aneurysm-removed model) were studeid for each patient. Four metrics, i.e., proportion of high oscillatory shear index (OSI), area of high OSI, old blood volume fraction (OBVF)) and old blood volume (OBV) was obtained to distinguish the thrombosis risk of different treatments (proximal or distal occlusion), comparing with the follow-up CTA. Results: For all the postopertive models, the high OBVF, high OSI(>0.3) and low time-averaged wall shear stress (TAWSS) regions were mainly at the distal fistula, indicating these regions were prone to thrombosis. The regions where blood residue remains are roughly regions of high OSI, corresponding well with clinical observations. In contrast, TAWSS failed to distinguish the difference in thrombosis risk. Absolute values (area of high OSI, OBV) can better reflect the degree of thrombosis risk between treatment types compared with percentage values (proportion of high OSI, OBVF). By comparing with the actual clinical treatments and observations, the OBV is superior to the area of high OSI in determining treatment type. Conclusion: The OBV, a volumetric parameter for blood stasis, can better account for the CAF thrombosis and reflect the degree of blood stasis compared with OSI or TAWSS, is a more appropriate metric for thrombosis in the fistula. Together with morphological parameters, the OBV could guide clinicians to formulate more appropriate surgical plans, which is of great significance for the preoperative evaluation and treatment prognosis of CAF patients.

Hemodynamic Characteristics of Patients With Suspected Coronary Heart Disease at Their Initial Visit.

PURPOSE: It is difficult for doctors to decide whether patients with suspected coronary heart disease classified as Coronary Artery Disease Reporting and Data System (CAD-RADS) < 3 should be administered preventive treatment, or whether non-atherosclerotic chest pain should be considered. The aim of the current study was to investigate coronary hemodynamic characteristics in such patients, which may provide more information on their stenosis and be helpful for initial diagnoses. METHODS: Two patient-specific models were reconstructed based on the coronary computed tomographic angiography underwent in 2012. Patient 1 was classified as CAD-RADS 0, and was readmitted to hospital due to coronary artery disease within 5 years. Patient 2 was classified as CAD-RADS 2, and has experienced no adverse events to date. Computational fluid dynamics (CFD) analysis was used to obtain hemodynamic parameters including flow rate waveform, flow streamlines, time-average wall shear stress (TAWSS), and oscillatory shear index (OSI). RESULTS: Patient 1 exhibited no physiological characteristics of right coronary artery flow waveform, large areas of low TAWSS, and slow blood flow in the proximal and middle segments of the left anterior descending branch. Patient 2 exhibited reduced coronary supply, small and separate areas of abnormal TAWSS, and a higher left anterior descending branch OSI than patient 1. CONCLUSION: Hemodynamic abnormalities may play an important role in the prognosis of patients with coronary stenosis, and patient-specific hemodynamic characteristics may facilitate more accurate initial diagnosis, and better management. Overall hemodynamics (along the whole vessel) warranted attention at the time of the initial visit in patients classified as CAD-RADS < 3.

Role of Occlusion Position in Coronary Artery Fistulas with Terminal Aneurysms: A Hemodynamic Perspective.

PURPOSE: Thrombosis within an occluded coronary arterial fistula (CAF) may cause angina and myocardial infarction. This study aims to estimate how the occlusion position of CAFs with terminal aneurysm affects the risk stratification of thrombosis in the fistula in terms of hemodynamics. METHODS: Twelve CAF models were reconstructed based on patient-specific computed tomography angiogram (CTA) images. They were classified into three groups: preserved group (untreated fistula), aneurysm-reserved group (occluded at the fistula terminal: distal occlusion) and aneurysm-removed group (occluded before the aneurysm: proximal occlusion). Hemodynamics results were analyzed and compared with the clinical follow-up results. RESULTS: The results showed that: (1) Hemodynamic patterns within the fistula before and after treatment were significantly different among patients. (2) Aneurysm-removed occlusions showed better improvements with respect to the CAF blood-stealing phenomena. (3) Irrespective of whether aneurysms were removed or not, a disturbed flow pattern was observed. Areas having high OSI and low TAWSS were present in the post-occluded CAFs. The removal of the aneurysm, however, would alleviate the flow disturbance, and decrease the proportion of the area of OSI > 0.3. (4) The thrombosis region spotted in the follow-up patient CTAs was consistent with the computed high OSI area. CONCLUSIONS: A proximal occlusion, namely, removing the aneurysm of the CAF, may help in reducing the risk of thrombosis after surgery. However, follow-up studies with a larger cohort should be carried out to test and verify this speculation in the future.

Influence of Hemodialysis Catheter Insertion on Hemodynamics in the Central Veins.

Central venous catheter (CVC) related thrombosis is a major cause of CVC dysfunction in patients under hemodialysis. The aim of our study was to investigate the impact of CVC insertion on hemodynamics in the central veins and to examine the changes in hemodynamic environments that may be related to thrombus formation due to the implantation of CVC. Patient-specific models of the central veins with and without CVC were reconstructed based on computed tomography images. Flow patterns in the veins were numerically simulated to obtain hemodynamic parameters such as time-averaged wall shear stress (TAWSS), oscillating shear index (OSI), relative residence time (RRT), and normalized transverse wall shear stress (transWSS) under pulsatile flow. The non-Newtonian effects of blood flow were also analyzed using the Casson model. The insertion of CVC caused significant changes in the hemodynamic environment in the central veins. A greater disturbance and increase of velocity were observed in the central veins after the insertion of CVC. As a result, TAWSS and transWSS were markedly increased, but most parts of OSI and RRT decreased. Newtonian assumption of blood flow would overestimate the increase in TAWSS after CVC insertion. High wall shear stress (WSS) and flow disturbance, especially the multidirectionality of the flow, induced by the CVC may be a key factor in initiating thrombosis after CVC insertion. Accordingly, approaches to decrease the flow disturbance during CVC insertion may help restrain the occurrence of thrombosis. More case studies with pre-operative and postoperative modeling and clinical follow-up need to be performed to verify these findings. Non-Newtonian blood flow assumption is recommended in computational fluid dynamics (CFD) simulations of veins with CVCs.

A computational fluid dynamics study pre- and post-fistula closure in a coronary artery fistula.

This study numerically investigated the hemodynamics of a patient-specific coronary artery fistula (CAF) before and after the fistula closure. The results indicated that the dilated fistula result in inadequate perfusion to other healthy aortas. Disturbed blood flow, aberrant WSSs, local negative pressure gradients and sharp pressure changes are shown in both untreated and occluded fistula. Furthermore, extreme high WSS appeared at the fistula bending after the terminal closure. It was concluded that the fistula closure may effectively improve the phenomenon of stealing blood but worsen the unfavorable hemodyanmics predisposing the thrombosis formation due to its geometrical torturosity.