Vortices Formed on the Mitral Valve Tips Aid Normal Left Ventricular Filling
For the left ventricle (LV) to function as an effective pump it must be able to fill from a low left atrial pressure. However, this ability is lost in patients with heart failure. We investigated LV filling by measuring the cardiac blood flow using 2D phase contrast magnetic resonance imaging and quantified the intraventricular pressure gradients and the strength and location of vortices. In normal subjects, blood flows towards the apex prior to the mitral valve opening, and the mitral annulus moves rapidly away after the valve opens, with both effects enhancing the vortex ring at the mitral valve tips. Instead of being a passive by-product of the process as was previously believed, this ring facilitates filling by reducing convective losses and enhancing the function of the LV as a suction pump. The virtual channel thus created by the vortices may help insure efficient mass transfer for the left atrium to the LV apex. Impairment of this mechanism contributes to diastolic dysfunction, with LV filling becoming dependent on left atrial pressure, which can lead to eventual heart failure. Better understanding of the mechanics of this progression may lead to more accurate diagnosis and treatment of this disease.
[Show abstract] [Hide abstract] ABSTRACT: As the pulsatile cardiac blood flow drives the heart valve leaflets to open and close, the flow in the vicinity of the valve resembles a pulsed jet through a non-axisymmetric orifice with dynamically changing area. As a result, three-dimensional vortex rings of intricate topology emerge that interact with the complex cardiac anatomy and give rise to shear layers, regions of recirculation, and flow instabilities that could ultimately lead to transition to turbulence. Such complex flow patterns, which are inherently valve- and patient-specific, lead to mechanical forces at scales that can cause blood cell damage and thrombosis, increasing the likelihood of stroke, and trigger the pathogenesis of various life-threatening valvular heart diseases. We summarize present day understanding of flow phenomena induced by heart valves, discuss their linkage with disease pathways, and emphasize the research advances required to translate in depth understanding of valvular hemodynamics into effective patient therapies.0Comments 0Citations
- "There is ample of evidence pointing to a relationship between LV pathology and intraventricular flow patterns, notably the dynamics of the MVR (Hong et al. 2008, Carlhäll & Bolger 2010, Charonko et al. 2013, Mangual et al. 2013). The interaction of the MV leaflets and supporting structures with the blood flow, however, is so complex (Charonko et al. 2013) that a simple correlation among those factors is unlikely to exist (Stewart et al. 2012). Therefore, "
[Show abstract] [Hide abstract] ABSTRACT: Introduction Right ventricular (RV) function has increasingly being recognized as an important predictor for morbidity and mortality in patients with pulmonary arterial hypertension (PAH). The increased RV after-load increase RV work in PAH. We used time-resolved 3D phase contrast MRI (4D flow MRI) to derive RV kinetic energy (KE) work density and energy loss in the pulmonary artery (PA) to better characterize RV work in PAH patients. Methods 4D flow and standard cardiac cine images were obtained in ten functional class I/II patients with PAH and nine healthy subjects. For each individual, we calculated the RV KE work density and the amount of viscous dissipation in the PA. Results PAH patients had alterations in flow patterns in both the RV and the PA compared to healthy subjects. PAH subjects had significantly higher RV KE work density than healthy subjects (94.7±33.7 mJ/mL vs. 61.7±14.8 mJ/mL, p = 0.007) as well as a much greater percent PA energy loss (21.1±6.4% vs. 2.2±1.3%, p = 0.0001) throughout the cardiac cycle. RV KE work density and percent PA energy loss had mild and moderate correlations with RV ejection fraction. Conclusion This study has quantified two kinetic energy metrics to assess RV function using 4D flow. RV KE work density and PA viscous energy loss not only distinguished healthy subjects from patients, but also provided distinction amongst PAH patients. These metrics hold promise as imaging markers for RV function.0Comments 0Citations
- "Vortices developed in the cardiovascular system play fundamental roles in the normal physiology, but the formation of unnatural vortices may alter the momentum transfer in the blood flow and increase energy dissipation . We observed diastolic vortex formation pattern in the RV in healthy subjects is similar with the observed LV filling pattern observed by others . The diastolic vortices are altered in some PAH subjects with additional vortices formed toward the apex of the RV or with asymmetrical vortices (Fig 1B) , which suggest abnormal energy dissipation. "
[Show abstract] [Hide abstract] ABSTRACT: A methodology for the simulation of heart function that combines an MRI-based model of cardiac electromechanics (CE) with a Navier-Stokes-based hemodynamics model is presented. The CE model consists of two coupled components that simulate the electrical and the mechanical functions of the heart. Accurate representations of ventricular geometry and fiber orientations are constructed from the structural magnetic resonance and the diffusion tensor MR images, respectively. The deformation of the ventricle obtained from the electromechanical model serves as input to the hemodynamics model in this one-way coupled approach via imposed kinematic wall velocity boundary conditions and at the same time, governs the blood flow into and out of the ventricular volume. The time-dependent endocardial surfaces are registered using a diffeomorphic mapping algorithm, while the intraventricular blood flow patterns are simulated using a sharp-interface immersed boundary method-based flow solver. The utility of the combined heart-function model is demonstrated by comparing the hemodynamic characteristics of a normal canine heart beating in sinus rhythm against that of the dyssynchronously beating failing heart. We also discuss the potential of coupled CE and hemodynamics models for various clinical applications.0Comments 1Citation
- "We first compare the time-dependent diastolic flow patterns and the vortex structures in the normal and failing LVs to qualitatively examine ventricular efficiency. It has been shown in previous studies that optimal vortex formation during diastole is a characteristic of healthy ventricles (Kilner et al., 2000; Pedrizzetti and Domenichini, 2005; Gharib et al., 2006; Watanabe et al., 2008; Pasipoularides, 2010; Sengupta et al., 2012; Charonko et al., 2013; Chnafa et al., 2014; Seo et al., 2014). The vortex structures at selected time instances during diastole are shown inFigure 6. "