Anatomic features in SCAD assessed by CCT: A propensity score matching case control study.

PURPOSE: Spontaneous coronary artery dissection (SCAD) may occur in middle age population without any cardiovascular risk factor. We retrospectively evaluated anatomic features of 11 patients with SCAD using a coronary arteries computed tomography (CCT), compared to age and sex balanced patients who underwent CCT. MATERIAL AND METHODS: CCT was performed in 11 patients (7 females and 4 males) as follow-up in patients with SCAD (left anterior descending - LAD or circumflex artery - Cx) and compared, using the propensity score matching analysis, with 11 healthy patients. Several anatomic features were evaluated: Left main (LM) length, angle between descending coronary artery (LAD) and its first branch, angle between LAD and LM, distance from the annulus to RCA (a-RCA distance) and LM (a-LM distance) ostia and their ratio; ratio between LM length and length a-LM and tortuosity score of the vessel with SCAD. A fluid dynamic analysis has been performed to evaluate the effects on shear stress of vessels wall. RESULTS: LM length was significantly shorter in patients with SCAD versus healthy subjects (P=0.01) as well as LM length/a-LM (P=0.03) and the angle between LAD and the first adjacent branch was sharper (P<0.01). Tortuosity score showed a statistically significant difference between groups (P<0.001). Fluid dynamic analysis demonstrates that, in SCAD group, an angle<90 degree is present at the first bifurcation and it can be a cause of increased strain on vessel wall in patients with high tortuosity of coronary artery. CONCLUSION: Tortuosity and angle between the LAD and the adjacent arterial branch combined may determine increased shear stress on the vessel wall that increases the risk of SCAD.

Evaluation of prosthetic-valved devices by means of numerical simulations.

The in vivo evaluation of prosthetic device performance is often difficult, if not impossible. In particular, in order to deal with potential problems such as thrombosis, haemolysis, etc., which could arise when a patient undergoes heart valve replacement, a thorough understanding of the blood flow dynamics inside the devices interacting with natural or composite tissues is required. Numerical simulation, combining both computational fluid and structure dynamics, could provide detailed information on such complex problems. In this work, a numerical investigation of the mechanics of two composite aortic prostheses during a cardiac cycle is presented. The numerical tool presented is able to reproduce accurately the flow and structure dynamics of the prostheses. The analysis shows that the vortical structures forming inside the two different grafts do not influence the kinematics of a bileaflet valve or the main coronary flow, whereas major differences are present for the stress status near the suture line of the coronaries to the prostheses. The results are in agreement with in vitro and in vivo observations found in literature.

Fluid-structure interaction of deformable aortic prostheses with a bileaflet mechanical valve.

Two different aortic prostheses can be used for performing the Bentall procedure: a standard straight graft and the Valsalva graft that better reproduces the aortic root anatomy. The aim of the present work is to study the effect of the graft geometry on the blood flow when a bileaflet mechanical heart valve is used, as well as to evaluate the stress concentration near the suture line where the coronary arteries are connected to graft. An accurate three-dimensional numerical method is proposed, based on the immersed boundary technique. The method accounts for the interactions between the flow and the motion of the rigid leaflets and of the deformable aortic root, under physiological pulsatile conditions. The results show that the graft geometry only slightly influences the leaflets dynamics, while using the Valsalva graft the stress level near the coronary-root anastomoses is about half that obtained using the standard straight graft.

Numerical and experimental investigation of structure-function scaling in turbulent Rayleigh-Bénard convection.

Direct numerical simulation and stereoscopic particle image velocimetry of turbulent convection are used to gather spatial data for the calculation of structure functions. We wish to add to the ongoing discussion in the literature whether temperature acts as an active or passive scalar in turbulent convection, with consequences for structure-function scaling. The simulation results show direct confirmation of the scalings derived by Bolgiano and Obukhov for turbulence with an active scalar for both velocity and temperature statistics. The active-scalar range shifts to larger scales when the forcing parameter (Rayleigh number) is increased. Furthermore, a close inspection of local turbulent length scales (Kolmogorov and Bolgiano lengths) confirms conjectures from earlier studies that the oft-used global averages are not suited for the interpretation of structure functions. In the experiment, a characterization of the domain-filling large-scale circulation of confined convection is carried out for comparison with other studies. The measured velocity fields are also used to calculate velocity structure functions, further confirming the Bolgiano-Obukhov scalings when interpreted with the local turbulent length scales found in the simulations. An extended self-similarity analysis shows that the relative scalings are different for the Kolmogorov and Bolgiano-Obukhov regimes.