Evaluation of intraventricular flow by multimodality imaging: a review and meta-analysis

Background The aim of this systematic review was to evaluate current inter-modality agreement of noninvasive clinical intraventricular flow (IVF) assessment with 3 emerging imaging modalities: echocardiographic particle image velocimetry (EPIV), vector flow mapping (VFM), and 4-dimensional flow cardiovascular magnetic resonance imaging (4D flow CMR). Methods We performed a systematic literature review in the databases EMBASE, Medline OVID and Cochrane Central for identification of studies evaluating left ventricular (LV) flow patterns using one of these flow visualization modalities. Of the 2224 initially retrieved records, 10 EPIV, 23 VFM, and 25 4D flow CMR studies were included in the final analysis. Results Vortex parameters were more extensively studied with EPIV, while LV energetics and LV transport mechanics were mainly studied with 4D flow CMR, and LV energy loss and vortex circulation were implemented by VFM studies. Pooled normative values are provided for these parameters. The meta- analysis for the values of two vortex morphology parameters, vortex length and vortex depth, failed to reveal a significant change between heart failure patients and healthy controls. Conclusion Agreement between the different modalities studying intraventricular flow is low and different methods of measurement and reporting were used among studies. A multimodality framework with a standardized set of flow parameters is necessary for implementation of noninvasive flow visualization in daily clinical practice. The full potential of noninvasive flow visualization in addition to diagnostics could also include guiding medical or interventional treatment.

Intraventricular Flow Simulations in Singular Right Ventricles Reveal Deteriorated Washout and Low Vortex Formation

Purpose Patients with a functionally univentricular heart represent one of the most common severe cardiac lesions with a prevalence of 3 per 10,000 live births. Hemodynamics of the singular ventricle is a major research topic in cardiology and there exists a relationship between fluid dynamical features and cardiac behavior in health and disease. The aim of the present work was to compare intraventricular flow in single right ventricle (SRV) patients and subjects with healthy left hearts (LV) through patient-specific CFD simulations. Methods Three-dimensional real-time echocardiographic images were obtained for five SRV patients and two healthy subjects and CFD simulations with a moving mesh methodology were performed. Intraventricular vortex formation and vortex formation time (VFT) as well as the turbulent kinetic energy (TKE) and ventricular washout were evaluated. Results The results show significantly lower values for the VFT and the TKE in SRV patients compared with healthy LV subjects. Furthermore, vortex formation does not progress to the apex in SRV patients. These findings were confirmed by a significantly lower washout in SRV patients. Conclusions The study pinpoints the intriguing role of intraventricular flows to characterize performance of SRVs that goes beyond standard clinical metrics such as ejection fraction.

Effects of the atrium on intraventricular flow patterns during mechanical circulatory support

Simulations of the ventricular flow patterns during left ventricular assist device (LVAD) support are mainly performed with idealized cylindrical inflow, neglecting the influence of the atrial vortex. In this study, the influence of the left atrium (LA) on the intra-ventricular flow was investigated via Computational Fluid Dynamics (CFD) simulations. Ventricular flow was simulated by a combined Eulerian (carrier flow)/Lagrangian (particles) approach taking into account either the LA or a cylindrical inflow section to mimic a fully support condition. The flow deviation at the mitral valve, the blood low-velocity volume as well as the residence time and shear stress history of the particles were calculated. Inclusion of the LA deflects the flow at the mitral valve by 25°, resulting in an asymmetric flow jet entering the left ventricle. This reduced the ventricular low-velocity volume by 40% (from 6.4 to 3.9 cm3), increased (40%) the shear stress experienced by particles and correspondingly increased (27%) their residence time. Under the studied conditions, the atrial geometry plays a major role in the development of intraventricular flow patterns. A reliable prediction of blood flow dynamics and consequently thrombosis risk analysis within the ventricle requires the consideration of the LA in computational simulations.

Intraventricular flow visualization in different heart failure stages with blood pump support in a mock circulatory loop

The intraventricular blood flow changed by blood pump flow dynamics may correlate with thrombosis and ventricular suction. The flow velocity, distribution of streamlines, vorticity, and standard deviation of velocity inside a left ventricle failing to different extents throughout the cardiac cycle when supported by an axial blood pump were measured by particle image velocimetry (PIV) in this study. The results show slower and static flow velocities existed in the central region of the left ventricle near the mitral valve and aortic valve and that were not sensitive to left ventricular (LV) failure degree or LV pressure. Strong vorticity located near the inner LV wall around the LV apex and the blood pump inlet was not sensitive to LV failure degree or LV pressure. Higher standard deviation of the blood velocity at the blood pump inlet decreased with increasing LV failure degree, whereas the standard deviation of the velocity near the atrium increased with increasing intraventricular pressure. The experimental results demonstrated that the risk of thrombosis inside the failing left ventricle is not related to heart failure degree. The “washout” performance of the strong vorticity near the inner LV wall could reduce the thrombotic potential inside the left ventricle and was not related to heart failure degree. The vorticity near the aortic valve was sensitive to LV failure degree but not to LV pressure. We concluded that the risk of blood damage caused by adverse flow inside the left ventricle decreased with increasing LV pressure.

Assessment of ventricular flow dynamics by 4D-flow MRI in patients following surgical repair of d-transposition of the great arteries

Objectives To use 4D-flow MRI to describe systemic and non-systemic ventricular flow organisation and energy loss in patients with repaired d-transposition of the great arteries (d-TGA) and normal subjects. Methods Pathline tracking of ventricular volumes was performed using 4D-flow MRI data from a 1.5-T GE Discovery MR450 scanner. D-TGA patients following arterial switch (n = 17, mean age 14 ± 5 years) and atrial switch (n = 15, 35 ± 6 years) procedures were examined and compared with subjects with normal cardiac anatomy and ventricular function (n = 12, 12 ± 3 years). Pathlines were classified by their passage through the ventricles as direct flow, retained inflow, delayed ejection flow, and residual volume and visually and quantitatively assessed. Additionally, viscous energy losses (ELv) were calculated. Results In normal subjects, the ventricular flow paths were well ordered following similar trajectories through the ventricles with very little mixing of flow components. The flow paths in all atrial and some arterial switch patients were more irregular with high mixing. Direct flow and delayed ejection flow were decreased in atrial switch patients’ systemic ventricles with a corresponding increase in residual volume compared with normal subjects (p = 0.003 and p < 0.001 respectively) and arterial switch patients (p < 0.0001 and p < 0.001 respectively). In non-systemic ventricles, arterial switch patients had increased direct flow and decreased delayed ejection fractions compared to normal (p = 0.007 and p < 0.001 respectively) and atrial switch patients (p = 0.01 and p < 0.001 respectively). Regions of high levels of mixing of ventricular flow components showed elevated ELv. Conclusions 4D-flow MRI pathline tracking reveals disordered ventricular flow patterns and associated ELv in d-TGA patients. Key Points • 4D-flow MRI can be used to assess intraventricular flow dynamics in d-TGA patients. • d-TGA arterial switch patients mostly show intraventricular flow dynamics representative of normal subjects, while atrial switch patients show increased flow disorder and different proportions of intraventricular flow volumes. • Flow disruption and disorder increase viscous energy losses.

Evaluation of patients with a HeartMate 3 left ventricular assist device using echocardiographic particle image velocimetry

Purpose Poor left ventricular (LV) function may affect the physiological intraventricular blood flow and physiological vortex formation. The aim of this study was to investigate the pattern of intraventricular blood flow dynamics in patients with LV assist devices (LVADs) using echocardiographic particle image velocimetry. Materials and methods This prospective study included 17 patients (mean age 57 ± 11 years, 82% male) who had received an LVAD (HeartMate 3, Abbott Laboratories, Chicago, Illinois, USA) because of end-stage heart failure and poor LV function. Eleven (64%) patients had ischemic cardiomyopathy, and six patients (36%) had nonischemic cardiomyopathy. All patients underwent echocardiography, including intravenous administration of an ultrasound-enhancing agent (SonoVue, Bracco, Milan, Italy). Echocardiographic particle image velocimetry was used to quantify LV blood flow dynamics, including vortex formation (Hyperflow software, Tomtec imaging systems Gmbh, Unterschleissheim, Germany). Results Contrast-enhanced ultrasound was well tolerated in all patients and was performed without adverse reactions or side effects. The LVAD function parameters did not change during or after the ultrasound examination. The LVAD flow was on average 4.3 ± 0.3 L/min, and the speed was 5247 ± 109 rotations/min. The quantification of LV intraventricular flow demonstrated substantial impairment of vortex parameters. The energy dissipation, vorticity, and kinetic energy fluctuation indices were severely impaired. Conclusions Echo particle velocimetry is safe and feasible for the quantitative assessment of intraventricular flow in patients with an LVAD. The intraventricular LV flow and vortex parameters are severely impaired in these patients.

Intraventricular flow features and cardiac mechano-energetics after mitral valve interventions – feasibility of an isolated heart model

The aim of this work was the development of an isolated heart setup to delineate the interactions between intraventricular flow features, hemodynamic parameters and mechano-energetics after certain mitral valve therapies. Five porcine hearts were explanted and prepared for (i) edge-to-edge mitral valve repair, (ii) implantation of a rotatable biscupid mechanical valve prosthesis. Flow structures were visualized using echocardiography while hemodynamics was recorded in terms of pressures, flow rates and ventricular volume. Hemodynamic and cardiac mechano-energetics implied a marginal effect (<5%) of alternating leaflet orientation on ventricular pre-load and stroke work. After edge-to-edge repair, substantial variations in flow structures were observed. Beside promoting profound insights into fundamental physiologic mechanisms, the setup may be used for validation of computer aided therapy planning tools.