4D MDCT in the assessment of the tricuspid valve and its spatial relationship with the right coronary artery: A customized tool based on computed tomography for the planning of percutaneous procedures.

Multidetector computed tomography (MDCT) is currently the imaging technique of choice for the assessment of tricuspid valve (TV) annulus geometry and relationship with the right coronary artery (RCA). However, standardized protocols with a full 3D analysis are still lacking to plan percutaneous procedures for functional tricuspid regurgitation (FTR). A novel customized 4-dimensional tool based on MDCT data was developed and provided accurate information on TV annulus morphology (3D-perimeter, 2D-Area, maximum and minimum diameters, eccentricity index), function and distance to the RCA, crucial for patient selection of percutaneous TV procedures.

Aortic Root Dynamics in Sleeve Aortic Sparing Procedure: Echocardiographic and Computational Studies.

In Sleeve procedure, the leaflets-sinus unit is maintained. We hypothesized that this feature partially preserves aortic root (AR) dynamics and leaflets kinematics and limits tensions in the leaflets. We tested our hypothesis based on in vivo and computational assessment of leaflets and AR dynamics. AR and aortic leaflet kinematics was assessed by transthoracic echocardiography in 10 patients treated with the Sleeve procedure and in 10 healthy patients. Numerical calculations with the Finite Element Method were performed to support the analysis of the clinical results and provide a better understanding of the behavior of the AR treated via the Sleeve procedure. Echocardiographic evidence showed that AR expansion in the Sleeve group was partially preserved as compared to the Control group (2.9 ± 2.5% vs 7.7 ± 6.3%, P = 0.038) and of the sinotubular junction (2.9 ± 1.5% vs 7.3 ± 3.8%, P = 0.003), and significantly preserved at the Valsalva sinuses level (6.7 ± 2.6% vs 9.5 ± 4.3%) with not statistically significant differences (P = 0.11). In none of the cardiac phases, differences in aortic valve leaflets kinematics were measured between the 2 groups; computational results were rather consistent with this evidence. Computational results well matched echocardiographic evidences, allowing for their mechanistic interpretation. Near-normal opening and closing characteristics can be accomplished by a technique that preserves the shape and the dynamics of the Valsalva sinuses. Whether the substantial preservation of the AR distensibility and leaflets kinematics observed in this study will favorably affect long-term valve durability it remains to be ascertained.

Mixed impact of torsion on LV hemodynamics: A CFD study based on the Chimera technique.

Image-based patient-specific Computational Fluid Dynamics (CFD) models of the Left Ventricle (LV) can be used to quantify hemodynamics-based biomarkers that can support the clinicians in the early diagnosis, follow-up and treatment planning of patients, beyond the capabilities of the current imaging modalities. We propose a workflow to build patient-specific CFD models of the LV with moving boundaries based on the Chimera technique to overcome the convergence issues previously encountered by means of the Arbitrarian Lagrangian Eulerian approach. The workflow was tested while investigating whether the torsional motion has an impact on LV fluid dynamics. Starting from 3D cine MRI scans of a healthy volunteer, six cardiac cycles were simulated in three CFD LV models: with no, physiological, and exaggerated torsion. The Chimera technique was robust in handling the impulsive motion of the LV endocardium, allowing to notice cycle-to-cycle variations in every simulated case. Torsion affected slightly velocity, vorticity, WSS. It did not affect energy loss and induced a double-sided effect in terms of residence time: the particles ejected in one beat decreased, whereas the motility of the particles remaining in the LV was affected only in the exaggerated torsion case, indicating that implementation of torsion can be discarded in case of physiological levels. Nonetheless, caution is warranted when interpreting these results given the absence of the mitral valve, the papillary muscles, and the trabeculae. The effects of the mitral valve will be evaluated within an Fluid Structure Interaction simulation framework as further development of the current model.

Blood damage in Left Ventricular Assist Devices: Pump thrombosis or system thrombosis?

INTRODUCTION:: Despite significant technical advancements in the design and manufacture of Left Ventricular Assist Devices, post-implant thrombotic and thromboembolic complications continue to affect long-term outcomes. Previous efforts, aimed at optimizing pump design as a means of reducing supraphysiologic shear stresses generated within the pump and associated prothrombotic shear-mediated platelet injury, have only partially altered the device hemocompatibility. METHODS:: We examined hemodynamic mechanisms that synergize with hypershear within the pump to contribute to the thrombogenic potential of the overall Left Ventricular Assist Device system. RESULTS:: Numerical simulations of blood flow in differing regions of the Left Ventricular Assist Device system, that is the diseased native left ventricle, the pump inflow cannula, the impeller, the outflow graft and the anastomosed downstream aorta, reveal that prothrombotic hemodynamic conditions might occur at these specific sites. Furthermore, we show that beyond hypershear, additional hemodynamic abnormalities exist within the pump, which may elicit platelet activation, such as recirculation zones and stagnant platelet trajectories. We also provide evidences that particular Left Ventricular Assist Device implantation configurations and specific post-implant patient management strategies, such as those allowing aortic valve opening, are more hemodynamically favorable and reduce the thrombotic risk. CONCLUSION:: We extend the perspective of pump thrombosis secondary to the supraphysiologic shear stress environment of the pump to one of Left Ventricular Assist Device system thrombosis, raising the importance of comprehensive characterization of the different prothrombotic risk factors of the total system as the target to achieve enhanced hemocompatibility and improved clinical outcomes.

Numerical simulation of transapical off-pump mitral valve repair with neochordae implantation.

BACKGROUND: Transapical off-pump mitral valve (MV) repair is a novel minimally-invasive surgical technique, allowing to correct mitral regurgitation (MR) caused by chordae tendineae rupture. While numerical simulation of the MV structure has proven to be useful to evaluate the effects of the MV surgical repair techniques, no numerical simulation studies on the outcomes of transapical MV repair have been done up to now. OBJECTIVE: The purpose of this study is to evaluate the transapical MV repair using finite element modeling and to determine the effect of the neochordal length on the function of the prolapsing MV. METHODS: The reconstruction of the MV geometry based on the patient-specific data was performed. In order to simulate prolapse, chordae inserted into the middle segment of the posterior leaflet (P2) were ruptured. A total of four virtual transapical repairs using neochordae of different length were performed. The function of the MV before and after virtual repairs was simulated. RESULTS: The evaluation of the effect of the neochordal length on post-repair MV function showed that the length of the implanted neochordae has a significant impact on the correction of MR caused by chordae tendineae rupture. CONCLUSIONS: The presented results can improve the understanding of the effects of transapical MV repair.

Dynamic and quantitative evaluation of degenerative mitral valve disease: a dedicated framework based on cardiac magnetic resonance imaging.

BACKGROUND: Accurate quantification of mitral valve (MV) morphology and dynamic behavior over the cardiac cycle is crucial to understand the mechanisms of degenerative MV dysfunction and to guide the surgical intervention. Cardiac magnetic resonance (CMR) imaging has progressively been adopted to evaluate MV pathophysiology, although a dedicated framework is required to perform a quantitative assessment of the functional MV anatomy. METHODS: We investigated MV dynamic behavior in subjects with normal MV anatomy (n=10) and patients referred to surgery due to degenerative MV prolapse, classified as fibro-elastic deficiency (FED, n=9) and Barlow's disease (BD, n=10). A CMR-dedicated framework was adopted to evaluate prolapse height and volume and quantitatively assess valvular morphology and papillary muscles (PAPs) function over the cardiac cycle. Multiple comparison was used to investigate the hallmarks associated to MV degenerative prolapse and evaluate the feasibility of anatomical and functional distinction between FED and BD phenotypes. RESULTS: On average, annular dimensions were significantly (P<0.05) larger in BD than in FED and normal subjects while no significant differences were noticed between FED and normal. MV eccentricity progressively decreased passing from normal to FED and BD, with the latter exhibiting a rounder annulus shape. Over the cardiac cycle, we noticed significant differences for BD during systole with an abnormal annular enlargement between mid and late systole (LS) (P<0.001 vs. normal); the PAPs dynamics remained comparable in the three groups. Prolapse height and volume highlighted significant differences among normal, FED and BD valves. CONCLUSIONS: Our CMR-dedicated framework allows for the quantitative and dynamic evaluation of MV apparatus, with quantifiable annular alterations representing the primary hallmark of severe MV degeneration. This may aid surgeons in the evaluation of the severity of MV dysfunction and the selection of the appropriate MV treatment.

Aortic Root Biomechanics After Sleeve and David Sparing Techniques: A Finite Element Analysis.

BACKGROUND: Aortic root aneurysm can be treated with valve-sparing procedures. The David and Yacoub techniques have shown excellent long-term results but are technically demanding. Recently, a new and simpler procedure, the Sleeve technique, was proposed with encouraging results. We aimed to quantify the biomechanics of the initially aneurysmal aortic root (AR) after the Sleeve procedure to assess whether it induces abnormal stresses, potentially undermining its durability. METHODS: Two finite element (FE) models of the physiologic and aneurysmal AR were built, accounting for the anatomical asymmetry and the nonlinear and anisotropic mechanical properties of human AR tissues. On the aneurysmal model, the Sleeve and David techniques were simulated based on the corresponding published technical features. Aortic root biomechanics throughout 2 consecutive cardiac cycles were computed in each simulated configuration. RESULTS: Both sparing techniques restored physiologic-like kinematics of aortic valve (AV) leaflets but induced different leaflets stresses. The time course averaged over the leaflets' bellies was 35% higher in the David model than in the Sleeve model. Commissural stresses, which were equal to 153 and 318 kPa in the physiologic and aneurysmal models, respectively, became 369 and 208 kPa in the David and Sleeve models, respectively. CONCLUSIONS: No intrinsic structural problems were detected in the Sleeve model that might jeopardize the durability of the procedure. If corroborated by long-term clinical outcomes, the results obtained suggest that using this new technique could successfully simplify the surgical repair of AR aneurysms and reduce intraoperative complications.