Optimal vortex formation as an index of cardiac health

Evaluation of hemodynamics in patients with hypertrophic cardiomyopathy by vector flow mapping: Comparison with healthy subjects

The present study investigated the role of energy loss assessed by vector flow mapping (VFM) in patients with hypertrophic cardiomyopathy (HCM). VFM analysis was performed in 42 patients with HCM and in 40 control subjects, which were matched for age, sex and left ventricular (LV) ejection fraction. The intra-LV and left atrial blood flow were obtained from the apical 3-chamber view, and the energy loss (EL) during the systolic and diastolic phases was calculated. The measurements were averaged over three cardiac cycles and indexed to body surface area. Compared with the controls, the left ventricular energy loss (LVEL)-total value was significantly decreased in patients with HCM during the diastolic phase (P1, P2 and P3; all P<0.05). A tendency for increased systolic LVEL-total values was observed in the patients with HCM compared with the controls (P>0.05). LVEL-base values were decreased in the patients with HCM during P1 and P2 (slow filling time). Compared with the controls, patients with HCM had lower LVEL-mid values during the diastolic phases (P0, P1, P2 and P3; all P<0.05). However, the LVEL-mid value of patients with HCM was higher compared with that of the controls during systolic P5 (P<0.05). LVEL-apex was decreased in patients with HCM during P0, P2 and P3. Compared with the controls, the left atrial energy loss (LAEL) of all three phases in patients with HCM were lower (each P<0.01). The diastolic LVEL values were significantly lower in patients with HCM compared with the controls; however, the systolic LVEL levels tended to be higher in HCM. The LAEL of the reservoir phase, conduit phase and atrial systolic phase were decreased in HCM compared with controls. The present study demonstrated that measurement of EL by VFM is a sensitive method of determining subclinical LV dysfunction in patients with HCM. The value of EL has been considered to be a quantitative parameter for the estimation of the efficiency of intraventricular blood flow.

Simultaneous coherent structure coloring facilitates interpretable clustering of scientific data by amplifying dissimilarity

The clustering of data into physically meaningful subsets often requires assumptions regarding the number, size, or shape of the subgroups. Here, we present a new method, simultaneous coherent structure coloring (sCSC), which accomplishes the task of unsupervised clustering without a priori guidance regarding the underlying structure of the data. sCSC performs a sequence of binary splittings on the dataset such that the most dissimilar data points are required to be in separate clusters. To achieve this, we obtain a set of orthogonal coordinates along which dissimilarity in the dataset is maximized from a generalized eigenvalue problem based on the pairwise dissimilarity between the data points to be clustered. This sequence of bifurcations produces a binary tree representation of the system, from which the number of clusters in the data and their interrelationships naturally emerge. To illustrate the effectiveness of the method in the absence of a priori assumptions, we apply it to three exemplary problems in fluid dynamics. Then, we illustrate its capacity for interpretability using a high-dimensional protein folding simulation dataset. While we restrict our examples to dynamical physical systems in this work, we anticipate straightforward translation to other fields where existing analysis tools require ad hoc assumptions on the data structure, lack the interpretability of the present method, or in which the underlying processes are less accessible, such as genomics and neuroscience.

Left ventricular vortex formation time in elite athletes

Vortex formation time (VFT) is a continuous measure of the left ventricular (LV) filling that integrates all phases of diastole. This has been previously studied in patients with heart failure. This study examined the differences in VFT between healthy controls and elite athletes. We compared echocardiographic indices between elite male athletes (n = 41) and age-, weight- and sex-matched sedentary volunteers (n = 22). VFT was obtained using the validated formula: 4 × (1 - β)/π × α³ × LVEF, where β is the fraction of total transmitral diastolic stroke volume contributed by atrial contraction (assessed by time velocity integral of the mitral E- and A-waves) and α is the biplane end-diastolic volume (EDV)^1/3 divided by mitral annular diameter during early diastole. Diastolic function was measured by the ratio of mitral peak velocity of early filling (E) to early diastolic mitral annular velocity (e') (E/e' ratio) and the ratio of E to mitral peak velocity of late filling (A) (E/A ratio). The heart rate was lower (63 ± 10 vs. 74 ± 6 beats per minute, p < 0.001) and the LV end diastolic diameter was larger in athletes as compared to controls (56 ± 3 vs. 50 ± 4 mm, p < 0.001). The VFT was lower in the sedentary group compared to athletes (3.1 ± 0.4 vs. 4.0 ± 0.8, p < 0.001). Similarly, E/e' was higher in sedentary controls compared to athletes (7.5 ± 1.8 vs 4.2 ± 1.0, p < 0.001). Furthermore, there was a modest correlation between VFT and E/A (r = 0.47, p < 0.001) as well as E/e' (r = - 0.33, p = 0.012). In conclusion, the VFT was elevated among elite athletes compared to healthy sedentary controls.

High Frame Rate Ultrasound Particle Image Velocimetry for Estimating High Velocity Flow Patterns in the Left Ventricle

Echocardiographic determination of multicomponent blood flow dynamics in the left ventricle remains a challenge. In this paper, we compare contrast enhanced, high frame rate (HFR) (1000 frames/s) echo-particle image velocimetry (ePIV) against optical particle image velocimetry (oPIV, gold standard), in a realistic left ventricular (LV) phantom. We find that ePIV compares well to oPIV, even for the high velocity inflow jet (normalized RMSE = 9% ± 1%). In addition, we perform the method of proper orthogonal decomposition, to better qualify and quantify the differences between the two modalities. We show that ePIV and oPIV resolve very similar flow structures, especially for the lowest order mode with a cosine similarity index of 86%. The coarser resolution of ePIV does result in increased variance and blurring of smaller flow structures when compared to oPIV. However, both modalities are in good agreement with each other for the modes that constitute the bulk of the kinetic energy. We conclude that HFR ePIV can accurately estimate the high velocity diastolic inflow jet and the high energy flow structures in an LV setting.

Intraventricular Vortex Interaction between Transmitral Flow and Paravalvular Leak

Paravalvular leak (PVL) is a complication of transcatheter aortic valve replacement. Despite its marked clinical impact, no previous study has reported how PVL affects the intraventricular fluid dynamics. This study aims to delineate vortex interaction between PVL and transmitral flow and the influence of PVL orifice location on intraventricular fluid dynamics using Echocardiographic Particle Image Velocimetry. Three different conditions of no PVL, anterior PVL and posterior PVL were experimentally studied and clinically compared. Circulation, impulse, kinetic energy (KE) and change in KE (ΔKE) were calculated. As well, vortex formation analyses and streamline description were performed to study vortex interactions. The anterior PVL jet streamed into the LV and interfered with the transmitral flow. Posterior PVL jet formed a large clockwise vortex and collided with transmitral flow, which resulted in flow disturbance. Compared to no PVL condition, average circulation, impulse, KE and ΔKE increased in presence of PVL. In conclusion, we found that PVL jets lead to abnormal vortex formation that interfere with natural advancement of transmitral flow, and negatively affect the LV fluid dynamics parameters. PVL orifice location strongly affects the intraventricular vortex formation, and posterior PVL may have more negative effects compared to anterior PVL.

Assessment of human left ventricle flow using statistical shape modelling and computational fluid dynamics

Blood flow patterns in the human left ventricle (LV) have shown relation to cardiac health. However, most studies in the literature are limited to a few patients and results are hard to generalize. This study aims to provide a new framework to generate more generalized insights into LV blood flow as a function of changes in anatomy and wall motion. In this framework, we studied the four-dimensional blood flow in LV via computational fluid dynamics (CFD) in conjunction with a statistical shape model (SSM), built from segmented LV shapes of 150 subjects. We validated results in an in-vitro dynamic phantom via time-resolved optical particle image velocimetry (PIV) measurements. This combination of CFD and the SSM may be useful for systematically assessing blood flow patterns in the LV as a function of varying anatomy and has the potential to provide valuable data for diagnosis of LV functionality.

Advanced Age Attenuates Left Ventricular Filling Efficiency Quantified Using Vortex Formation Time: A Study of Octogenarians With Normal Left Ventricular Systolic Function Undergoing Coronary Artery Surgery

OBJECTIVE

Blood flow across the mitral valve during early left ventricular (LV) filling produces a 3-dimensional rotational fluid body, known as a vortex ring, that enhances LV filling efficiency. Diastolic dysfunction is common in elderly patients, but the influence of advanced age on vortex formation is unknown. The authors tested the hypothesis that advanced age is associated with a reduction in LV filling efficiency quantified using vortex formation time (VFT) in octogenarians undergoing coronary artery bypass graft (CABG) surgery.

DESIGN

Observational study.

SETTING

Veterans Affairs medical center.

PARTICIPANTS

After institutional review board approval, octogenarians (n = 7; 82 ± 2 year [mean ± standard deviation]; ejection fraction 56% ± 7%) without valve disease or atrial arrhythmias undergoing CABG were compared with a younger cohort (n = 7; 55 ± 6 year; ejection fraction 57% ± 7%) who were undergoing coronary revascularization.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

All patients were monitored using radial and pulmonary arterial catheters and transesophageal echocardiography. Peak early LV filling (E) and atrial systole (A) blood flow velocities and their corresponding velocity-time integrals were obtained using pulse-wave Doppler echocardiography to determine E/A, atrial filling fraction (β), and E wave deceleration time. Pulse-wave Doppler also was used to measure pulmonary venous blood flow during systole and diastole. Mitral valve diameter (D) was calculated as the average of major and minor axis lengths obtained in the midesophageal LV bicommissural and long-axis transesophageal echocardiography imaging planes, respectively. VFT was calculated as 4 × (1 - β) × SV/(πD³), where SV is the stroke volume measured using thermodilution. Systemic and pulmonary hemodynamics, LV diastolic function, and VFT were determined during steady-state conditions 30 minutes before cardiopulmonary bypass. A delayed relaxation pattern of LV filling (E/A 0.81 ± 0.16 v 1.29 ± 0.19, p = 0.00015; β 0.44 ± 0.05 v 0.35 ± 0.03, p = 0.0008; E wave deceleration time 294 ± 58 v 166 ± 28 ms, p < 0.0001; ratio of peak pulmonary venous systolic and diastolic blood flow velocity 1.42 ± 0.23 v 1.14 ± 0.20, p = 0.0255) was observed in octogenarians compared with younger patients. Mitral valve diameter was similar between groups (2.7 ± 0.2 and 2.6 ± 0.2 cm, respectively, in octogenarians v younger patients, p = 0.299). VFT was reduced in octogenarians compared with younger patients (3.0 ± 0.9 v 4.5 ± 1.2; p = 0.0171). An inverse correlation between age and VFT was shown using linear regression analysis (VFT = -0.0627 × age + 8.24; r² = 0.408; p = 0.0139).

CONCLUSION

The results indicate that LV filling efficiency quantified using VFT is reduced in octogenarians compared with younger patients undergoing coronary artery bypass grafting.

Cardiac fluid dynamics meets deformation imaging

Cardiac function is about creating and sustaining blood in motion. This is achieved through a proper sequence of myocardial deformation whose final goal is that of creating flow. Deformation imaging provided valuable contributions to understanding cardiac mechanics; more recently, several studies evidenced the existence of an intimate relationship between cardiac function and intra-ventricular fluid dynamics. This paper summarizes the recent advances in cardiac flow evaluations, highlighting its relationship with heart wall mechanics assessed through the newest techniques of deformation imaging and finally providing an opinion of the most promising clinical perspectives of this emerging field. It will be shown how fluid dynamics can integrate volumetric and deformation assessments to provide a further level of knowledge of cardiac mechanics.

Optimized Time-Resolved Echo Particle Image Velocimetry– Particle Tracking Velocimetry Measurements Elucidate Blood Flow in Patients With Left Ventricular Thrombus

Contrast ultrasound is a widely used clinical tool to obtain real-time qualitative blood flow assessments in the heart, liver, etc. Echocardiographic particle image velocimetry (echo-PIV) is a technique for obtaining quantitative velocity maps from contrast ultrasound images. However, unlike optical particle image velocimetry (PIV), routine echo images are prone to nonuniform spatiotemporal variations in tracer distribution, making analysis difficult for standard PIV algorithms. This study introduces optimized procedures that integrate image enhancement, PIV, and particle tracking velocimetry (PTV) to obtain reliable time-resolved two-dimensional (2D) velocity distributions. During initial PIV analysis, multiple results are obtained by varying processing parameters. Optimization involving outlier removal and smoothing is used to select the correct vector. These results are used in a multiparameter PTV procedure. To demonstrate their clinical value, the procedures are implemented to obtain velocity and vorticity distributions over multiple cardiac cycles using images acquired from four left ventricular thrombus (LVT) patients. Phase-averaged data elucidate flow structure evolution over the cycle and are used to calculate penetration depth and strength of left ventricular (LV) vortices, as well as apical velocity induced by them. The present data are consistent with previous time-averaged results for the minimum vortex penetration depth associated with LVT occurrence. However, due to decay and fragmentation of LV vortices, as they migrate away from the mitral annulus, in two cases with high penetration, there is still poor washing near the resolved clot throughout the cycle. Hence, direct examination of entire flow evolution may be useful for assessing risk of LVT relapse before prescribing anticoagulants.

Development and Validation of a Phase-Filtered Moving Ensemble Correlation for Echocardiographic Particle Image Velocimetry

A new processing method for echocardiographic particle image velocimetry (EchoPIV) using moving ensemble (ME) correlation with dynamic phase correlation filtering was developed to improve velocity measurement accuracy for routine clinical evaluation of cardiac function. The proposed method was tested using computationally generated echocardiogram images. Error analysis indicated that ME EchoPIV yields a twofold improvement in bias and random error over the current standard correlation method (β_Pairwise = -0.15 vs. β_ME = -0.06; σ_Pairwise = 1.00 vs. σ_ME = 0.49). Subsequently a cohort of eight patients with impaired diastolic filling underwent similar evaluation. Comparison of patient EchoPIV velocity time series with corresponding color M-mode velocity time series revealed better agreement for ME EchoPIV compared with standard PIV processing (R_ME = 0.90 vs. R_Pairwise = 0.70). Further time series analysis was performed to measure filling propagation velocity and 1-D intraventricular pressure gradients. Comparison against CMM values indicated that both measurements are completely decorrelated for pairwise processing (R²_Vp = 0.15, R²_IVPD = 0.07), whereas ME processing correlates decently (R²_Vp = 0.69, R²_IVPD = 0.69). This new approach enables more robust processing of routine clinical scans and can increase the utility of EchoPIV for the assessment of left ventricular function.

Accelerating fishes increase propulsive efficiency by modulating vortex ring geometry

Swimming animals need to generate propulsive force to overcome drag, regardless of whether they swim steadily or accelerate forward. While locomotion strategies for steady swimming are well characterized, far less is known about acceleration. Animals exhibit many different ways to swim steadily, but we show here that this behavioral diversity collapses into a single swimming pattern during acceleration regardless of the body size, morphology, and ecology of the animal. We draw on the fields of biomechanics, fluid dynamics, and robotics to demonstrate that there is a fundamental difference between steady swimming and forward acceleration. We provide empirical evidence that the tail of accelerating fishes can increase propulsive efficiency by enhancing thrust through the alteration of vortex ring geometry. Our study provides insight into how propulsion can be altered without increasing vortex ring size and represents a fundamental departure from our current understanding of the hydrodynamic mechanisms of acceleration. Our findings reveal a unifying hydrodynamic principle that is likely conserved in all aquatic, undulatory vertebrates.

Investigation of Atrial Vortices Using a Novel Right Heart Model and Possible Implications for Atrial Thrombus Formation

The main aim of this paper is to characterize vortical flow structures in the healthy human right atrium, their impact on wall shear stresses and possible implications for atrial thrombus formation. 3D Particle Tracking Velocimetry is applied to a novel anatomically accurate compliant silicone right heart model to study the phase averaged and fluctuating flow velocity within the right atrium, inferior vena cava and superior vena cava under physiological conditions. We identify the development of two vortex rings in the bulk of the right atrium during the atrial filling phase leading to a rinsing effect at the atrial wall which break down during ventricular filling. We show that the vortex ring formation affects the hemodynamics of the atrial flow by a strong correlation (ρ = 0.7) between the vortical structures and local wall shear stresses. Low wall shear stress regions are associated with absence of the coherent vortical structures which might be potential risk regions for atrial thrombus formation. We discuss possible implications for atrial thrombus formation in different regions of the right atrium.

High-speed, high-frequency ultrasound, in utero vector-flow imaging of mouse embryos

Real-time imaging of the embryonic murine cardiovascular system is challenging due to the small size of the mouse embryo and rapid heart rate. High-frequency, linear-array ultrasound systems designed for small-animal imaging provide high-frame-rate and Doppler modes but are limited in regards to the field of view that can be imaged at fine-temporal and -spatial resolution. Here, a plane-wave imaging method was used to obtain high-speed image data from in utero mouse embryos and multi-angle, vector-flow algorithms were applied to the data to provide information on blood flow patterns in major organs. An 18-MHz linear array was used to acquire plane-wave data at absolute frame rates ≥10 kHz using a set of fixed transmission angles. After beamforming, vector-flow processing and image compounding, effective frame rates were on the order of 2 kHz. Data were acquired from the embryonic liver, heart and umbilical cord. Vector-flow results clearly revealed the complex nature of blood-flow patterns in the embryo with fine-temporal and -spatial resolution.

New echocardiographic parameters in the diagnosis of heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is a serious clinical disease. The pathophysiology of HFpEF is complex, and specific diagnostic criteria have evolved over time. Limited data are available on the quantification of diastolic function using two-dimensional real-time echocardiography, and a simple parameter has not yet been established. The aim of this work is to evaluate new echocardiographic parameters-the diastolic wall strain of the posterior wall (DWS PW) and the vortex formation time (VFT). Echocardiographic data from 111 subjects with exertional dyspnea and normal left ejection fraction (Group A) and 20 healthy volunteers (Group B) were retrospectively evaluated. In addition to the standard parameters used in the diagnosis of HFpEF, DWS PW and VFT were assessed in all patients. HFpEF was diagnosed in 38 patients with dyspnea (Group A1). The remaining 73 patients did not meet the established criteria for a positive diagnosis of HFpEF (Group A2). We discovered that both observed parameters were significantly lower in patients with HFpEF than in other groups. Multivariate analysis revealed that both DWS PW and VFT independently predicted the presence of HFpEF. DWS PW and VFT are simple parameters in the evaluation of diastolic function and may play a potential role as a part of an integrated approach to the assessment of HFpEF.

3D Experimental and Computational Analysis of Eccentric Mitral Regurgitant Jets in a Mock Imaging Heart Chamber

Mitral valve regurgitation (MR) is a disorder of the heart in which the mitral valve does not close properly. This causes an abnormal leaking of blood backwards from the left ventricle into the left atrium during the systolic contractions of the left ventricle. Noninvasive assessment of MR using echocardiography is an ongoing challenge. In particular, a major problem are eccentric or Coanda regurgitant jets which hug the walls of the left atrium and appear smaller in the color Doppler image of regurgitant flow. This manuscript presents a comprehensive investigation of Coanda regurgitant jets and the associated intracardiac flows by using a combination of experimental and computational approaches. An anatomically correct mock heart chamber connected to a pulsatile flow loop is used to generate the physiologically relevant flow conditions, and the influence of two clinically relevant parameters (orifice aspect ratio and regurgitant volume) on the onset of Coanda effect is studied. A two parameter bifurcation diagram showing transition to Coanda jets is obtained, indicating that: (1) strong wall hugging jets occur in long and narrow orifices with moderate to large regurgitant volumes, and (2) short orifices with moderate to large regurgitant volumes produce strong 3D flow features such as vortex rolls, giving rise to the velocities that are orthogonal to the 2D plane associated with the apical color Doppler views, making them "invisible" to the single plane color Doppler assessment of MR. This is the first work in which the presence of vortex rolls in the left atrium during regurgitation is reported and identified as one of the reasons for under-estimation of regurgitant volume. The results of this work can be used for better design of imaging strategies in noninvasive assessment of MR, and for better understanding of LA remodeling that may be associated with the presence of maladapted vortex dynamics. This introduces a new concept in clinical imaging, which emphasizes that the quality and not only the quantity of regurgitant flow matters in the assessment of severity of mitral valve regurgitation.

Improvements in Left Ventricular Diastolic Mechanics After Parachute Device Implantation in Patients With Ischemia Heart Failure: A Cardiac Computerized Tomographic Study

BACKGROUND

Percutaneous ventricular restoration therapy with the use of a left ventricle (LV)-partitioning Parachute device has emerged as a clinical treatment option for LV apical aneurysm after extensive anterior myocardial infarction (AMI). We assessed changes of diastolic mechanics and functional improvements following LV Parachute device implantation by means of cardiac computerized tomography (CCT).

METHODS AND RESULTS

CCT data were obtained from 28 patients before and after LV Parachute device implantation. Diastolic functional indices were determined by means of quantitative CCT assessment: 1) transmitral velocities in early (E) and late (A) diastole and ratio (E/A); 2) early diastolic mitral septal tissue velocity (Ea) and E/Ea; and 3) vortex formation time (VFT). Functional improvements were assessed with the use of New York Heart Association (NYHA) functional classification. Among the study patients, there were no significant differences in all transmitral velocities and E/A, though there was significantly increased Ea, reduced E/Ea, and greater VFT 6 months after LV Parachute device implantation. Finally, the improvement of diastolic functional indices after Parachute treatment correlated with observed clinical functional alterations (Δ E/Ea and Δ NYHA functional class:, r = 0.563; P = .002; Δ VFT and Δ NYHA functional class: r = -0.507; P = .006).

CONCLUSIONS

LV Parachute device implantation therapy in heart failure caused by AMI and LV apical aneurysm formation showed improvements in several diastolic functional mechanics according to CCT-based measures.

Flow dynamics and energy efficiency of flow in the left ventricle during myocardial infarction

Cardiovascular disease is a leading cause of death worldwide, where myocardial infarction (MI) is a major category. After infarction, the heart has difficulty providing sufficient energy for circulation, and thus, understanding the heart's energy efficiency is important. We induced MI in a porcine animal model via circumflex ligation and acquired multiple-slice cine magnetic resonance (MR) images in a longitudinal manner-before infarction, and 1 week (acute) and 4 weeks (chronic) after infarction. Computational fluid dynamic simulations were performed based on MR images to obtain detailed fluid dynamics and energy dynamics of the left ventricles. Results showed that energy efficiency flow through the heart decreased at the acute time point. Since the heart was observed to experience changes in heart rate, stroke volume and chamber size over the two post-infarction time points, simulations were performed to test the effect of each of the three parameters. Increasing heart rate and stroke volume were found to significantly decrease flow energy efficiency, but the effect of chamber size was inconsistent. Strong complex interplay was observed between the three parameters, necessitating the use of non-dimensional parameterization to characterize flow energy efficiency. The ratio of Reynolds to Strouhal number, which is a form of Womersley number, was found to be the most effective non-dimensional parameter to represent energy efficiency of flow in the heart. We believe that this non-dimensional number can be computed for clinical cases via ultrasound and hypothesize that it can serve as a biomarker for clinical evaluations.

Characterization of left ventricle energy loss in healthy adults using vector flow mapping: Preliminary results

BACKGROUND

Energy loss (EL) is a new quantitative hemodynamic index based on vector flow mapping (VFM). This study aimed to characterize EL of the left ventricle (LV) in healthy adults.

METHODS

Fifty-one healthy adults were enrolled in this study. EL of LV was analyzed frame by frame using color Doppler images of a standard apical three-chamber dynamic view on an offline VFM workstation. The average EL of systole and diastole was calculated, and the results were averaged over three cardiac cycles.

RESULTS

The average EL for systole and diastole was 11.07±5.82J/m/s and 11.58±5.54 J/m/s, respectively. Multivariate regression analysis showed that the aortic velocity time integral (AOVTI), A-wave peak velocity, and isovolumetric contraction time (IVCT) were independently associated with the average systolic EL. E-wave peak velocity, height, and IVCT were independently associated with the average diastolic EL. For females, the average systolic and diastolic EL was 12.66±7.06J/m/s and 13.90±5.37J/m/s, respectively. For males, the systolic and diastolic EL was 9.29±3.33J/m/s and 8.97±4.55J/m/s, respectively.

CONCLUSIONS

Energy loss in LV changes regularly during the cardiac cycle. The average systolic EL has a high positive correlation with AOVTI, whereas the average diastolic EL has with E-wave peak velocity. Women have higher average EL than men in both systole and diastole. By recognizing the EL characterization of healthy adults, the variation in EL may reflect cardiac dysfunction. These were preliminary results, and thus, the clinical implications of EL warrant further investigation.

Creating hemodynamic atlases of cardiac 4D flow MRI

Purpose

Hemodynamic atlases can add to the pathophysiological understanding of cardiac diseases. This study proposes a method to create hemodynamic atlases using 4D Flow magnetic resonance imaging (MRI). The method is demonstrated for kinetic energy (KE) and helicity density (H_d).

Materials and Methods

Thirteen healthy subjects underwent 4D Flow MRI at 3T. Phase‐contrast magnetic resonance cardioangiographies (PC‐MRCAs) and an average heart were created and segmented. The PC‐MRCAs, KE, and H_d were nonrigidly registered to the average heart to create atlases. The method was compared with 1) rigid, 2) affine registration of the PC‐MRCAs, and 3) affine registration of segmentations. The peak and mean KE and H_d before and after registration were calculated to evaluate interpolation error due to nonrigid registration.

Results

The segmentations deformed using nonrigid registration overlapped (median: 92.3%) more than rigid (23.1%, P < 0.001), and affine registration of PC‐MRCAs (38.5%, P < 0.001) and affine registration of segmentations (61.5%, P < 0.001). The peak KE was 4.9 mJ using the proposed method and affine registration of segmentations (P = 0.91), 3.5 mJ using rigid registration (P < 0.001), and 4.2 mJ using affine registration of the PC‐MRCAs (P < 0.001). The mean KE was 1.1 mJ using the proposed method, 0.8 mJ using rigid registration (P < 0.001), 0.9 mJ using affine registration of the PC‐MRCAs (P < 0.001), and 1.0 mJ using affine registration of segmentations (P = 0.028). The interpolation error was 5.2 ± 2.6% at mid‐systole, 2.8 ± 3.8% at early diastole for peak KE; 9.6 ± 9.3% at mid‐systole, 4.0 ± 4.6% at early diastole, and 4.9 ± 4.6% at late diastole for peak H_d. The mean KE and H_d were not affected by interpolation.

Conclusion

Hemodynamic atlases can be obtained with minimal user interaction using nonrigid registration of 4D Flow MRI.

Level of Evidence: 2

Technical Efficacy: Stage 1

J. Magn. Reson. Imaging 2017;46:1389–1399.

Computational Analysis of Intra-Ventricular Flow Pattern Under Partial and Full Support of BJUT-II VAD

Background

Partial support, as a novel support mode, has been widely applied in clinical practice and widely studied. However, the precise mechanism of partial support of LVAD in the intra-ventricular flow pattern is unclear.

Material/Methods

In this study, a patient-specific left ventricular geometric model was reconstructed based on CT data. The intra-ventricular flow pattern under 3 simulated conditions – “heart failure”, “partial support”, and “full support” – were simulated by using fluid-structure interaction (FSI). The blood flow pattern, wall shear stress (WSS), time-average wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT) were calculated to evaluate the hemodynamic effects.

Results

The results demonstrate that the intra-ventricular flow pattern is significantly changed by the support level of BJUT-II VAD. The intra-ventricular vortex was enhanced under partial support and was eliminated under full support, and the high OSI and RRT regions changed from the septum wall to the cardiac apex.

Conclusions

In brief, the support level of the BJUT-II VAD has significant effects on the intra-ventricular flow pattern. The partial support mode of BJUT-II VAD can enhance the intra-ventricular vortex, while the distribution of high OSI and RRT moved from the septum wall to the cardiac apex. Hence, the partial support mode of BJUT-II VAD can provide more benefit for intra-ventricular flow pattern.

A posteriori accuracy estimation of ultrasonic vector-flow mapping (VFM)

Abstract

A novel method, called a posteriori “VFM accuracy estimation” (VAE), for resolving an intrinsic VFM problem is proposed. The problem is that VFM uncertainty can easily vary according to blood flows through an echocardiographic imaged plane (i.e., “through-plane” flows), and it is unknown. Knowing the VFM uncertainty for each patient will make it possible to refine the quality of VFM-based diagnosis. In the present study, VAE was derived on the basis of an error-propagation analysis and a statistical analysis. The accuracy of VAE with a pulsatile left-ventricle phantom was experimentally investigated for realistic cases with through-plane flows. VAE was validated by comparing VFM uncertainty (S.D.) estimated by VAE with VFM uncertainty measured by particle-image velocimetry (PIV) for different imaged planes. VAE accurately estimated the S.D. of VFM uncertainty measured by PIV for all cases with different image planes (R > 0.6 and p < 0.001). These findings on VFM accuracy will provide the basis for widespread clinical application of VFM-based diagnosis.

Graphical Abstract

Clinical assessment of intraventricular blood transport in patients undergoing cardiac resynchronization therapy

In the healthy heart, left ventricular (LV) filling generates different flow patterns which have been proposed to optimize blood transport by coupling diastole and systole. This work presents a novel image-based method to assess how different flow patterns influence LV blood transport in patients undergoing cardiac resynchronization therapy (CRT). Our approach is based on solving the advection equation for a passive scalar field from time-resolved blood velocity fields. Imposing time-varying inflow boundary conditions for the scalar field provides a straightforward method to distinctly track the transport of blood entering the LV in the different filling waves of a given cardiac cycle, as well as the transport barriers which couple filling and ejection. We applied this method to analyze flow transport in a group of patients with implanted CRT devices and a group of healthy volunteers. Velocity fields were obtained using echocardiographic color Doppler velocimetry, which provides two-dimensional time-resolved flow maps in the apical long axis three-chamber view of the LV. In the patients under CRT, the device programming was varied to analyze flow transport under different values of the atrioventricular conduction delay, and to model tachycardia (100 bpm). Using this method, we show how CRT influences the transit of blood inside the left ventricle, contributes to conserving kinetic energy, and favors the generation of hemodynamic forces that accelerate blood in the direction of the LV outflow tract. These novel aspects of ventricular function are clinically accessible by quantitative analysis of color-Doppler echocardiograms.

Fluid mechanics of human fetal right ventricles from image-based computational fluid dynamics using 4D clinical ultrasound scans

There are 0.6–1.9% of US children who were born with congenital heart malformations. Clinical and animal studies suggest that abnormal blood flow forces might play a role in causing these malformation, highlighting the importance of understanding the fetal cardiovascular fluid mechanics. We performed computational fluid dynamics simulations of the right ventricles, based on four-dimensional ultrasound scans of three 20-wk-old normal human fetuses, to characterize their flow and energy dynamics. Peak intraventricular pressure gradients were found to be 0.2–0.9 mmHg during systole, and 0.1–0.2 mmHg during diastole. Diastolic wall shear stresses were found to be around 1 Pa, which could elevate to 2–4 Pa during systole in the outflow tract. Fetal right ventricles have complex flow patterns featuring two interacting diastolic vortex rings, formed during diastolic E wave and A wave. These rings persisted through the end of systole and elevated wall shear stresses in their proximity. They were observed to conserve ∼25.0% of peak diastolic kinetic energy to be carried over into the subsequent systole. However, this carried-over kinetic energy did not significantly alter the work done by the heart for ejection. Thus, while diastolic vortexes played a significant role in determining spatial patterns and magnitudes of diastolic wall shear stresses, they did not have significant influence on systolic ejection. Our results can serve as a baseline for future comparison with diseased hearts.

Spatial phenotyping of the endocardial endothelium as a function of intracardiac hemodynamic shear stress

Despite substantial evidence for the central role of hemodynamic shear stress in the functional integrity of vascular endothelial cells, hemodynamic and molecular regulation of the endocardial endothelium lining the heart chambers remains understudied. We propose that regional differences in intracardiac hemodynamics influence differential endocardial gene expression leading to phenotypic heterogeneity of this cell layer. Measurement of intracardiac hemodynamics was performed using 4-dimensional flow MRI in healthy humans (n=8) and pigs (n=5). Local wall shear stress (WSS) and oscillatory shear indices (OSI) were calculated in three distinct regions of the LV - base, mid-ventricle (midV), and apex. In both the humans and pigs, WSS values were significantly lower in the apex and midV relative to the base. Additionally, both the apex and midV had greater oscillatory shear indices (OSI) than the base. To investigate regional phenotype, endocardial endothelial cells (EEC) were isolated from an additional 8 pigs and RNA sequencing was performed. A false discovery rate of 0.10 identified 1051 differentially expressed genes between the base and apex, and 321 between base and midV. Pathway analyses revealed apical upregulation of genes associated with translation initiation. Furthermore, tissue factor pathway inhibitor (TFPI; mean 50-fold) and prostacyclin synthase (PTGIS; 5-fold), genes prominently associated with antithrombotic protection, were consistently upregulated in LV apex. These spatio-temporal WSS values in defined regions of the left ventricle link local hemodynamics to regional heterogeneity in endocardial gene expression.

Patient-specific CFD models for intraventricular flow analysis from 3D ultrasound imaging: Comparison of three clinical cases

BACKGROUND

As the intracardiac flow field is affected by changes in shape and motility of the heart, intraventricular flow features can provide diagnostic indications. Ventricular flow patterns differ depending on the cardiac condition and the exploration of different clinical cases can provide insights into how flow fields alter in different pathologies.

METHODS

In this study, we applied a patient-specific computational fluid dynamics model of the left ventricle and mitral valve, with prescribed moving boundaries based on transesophageal ultrasound images for three cardiac pathologies, to verify the abnormal flow patterns in impaired hearts. One case (P1) had normal ejection fraction but low stroke volume and cardiac output, P2 showed low stroke volume and reduced ejection fraction, P3 had a dilated ventricle and reduced ejection fraction.

RESULTS

The shape of the ventricle and mitral valve, together with the pathology influence the flow field in the left ventricle, leading to distinct flow features. Of particular interest is the pattern of the vortex formation and evolution, influenced by the valvular orifice and the ventricular shape. The base-to-apex pressure difference of maximum 2mmHg is consistent with reported data.

CONCLUSION

We used a CFD model with prescribed boundary motion to describe the intraventricular flow field in three patients with impaired diastolic function. The calculated intraventricular flow dynamics are consistent with the diagnostic patient records and highlight the differences between the different cases. The integration of clinical images and computational techniques, therefore, allows for a deeper investigation intraventricular hemodynamics in patho-physiology.

Role of Mitral Annulus Diastolic Geometry on Intraventricular Filling Dynamics

The mitral valve (MV) is a bileaflet valve positioned between the left atrium and ventricle of the heart. The annulus of the MV has been observed to undergo geometric changes during the cardiac cycle, transforming from a saddle D-shape during systole to a flat (and less eccentric) D-shape during diastole. Prosthetic MV devices, including heart valves and annuloplasty rings, are designed based on these two configurations, with the circular design of some prosthetic heart valves (PHVs) being an approximation of the less eccentric, flat D-shape. Characterizing the effects of these geometrical variations on the filling efficiency of the left ventricle (LV) is required to understand why the flat D-shaped annulus is observed in the native MV during diastole in addition to optimizing the design of prosthetic devices. We hypothesize that the D-shaped annulus reduces energy loss during ventricular filling. An experimental left heart simulator (LHS) consisting of a flexible-walled LV physical model was used to characterize the filling efficiency of the two mitral annular geometries. The strength of the dominant vortical structure formed and the energy dissipation rate (EDR) of the measured fields, during the diastolic period of the cardiac cycle, were used as metrics to quantify the filling efficiency. Our results indicated that the O-shaped annulus generates a stronger (25% relative to the D-shaped annulus) vortical structure than that of the D-shaped annulus. It was also found that the O-shaped annulus resulted in higher EDR values throughout the diastolic period of the cardiac cycle. The results support the hypothesis that a D-shaped mitral annulus reduces dissipative energy losses in ventricular filling during diastole and in turn suggests that a symmetric stent design does not provide lower filling efficiency than an equivalent asymmetric design.

Mass production of shaped particles through vortex ring freezing

A vortex ring is a torus-shaped fluidic vortex. During its formation, the fluid experiences a rich variety of intriguing geometrical intermediates from spherical to toroidal. Here we show that these constantly changing intermediates can be 'frozen' at controlled time points into particles with various unusual and unprecedented shapes. These novel vortex ring-derived particles, are mass-produced by employing a simple and inexpensive electrospraying technique, with their sizes well controlled from hundreds of microns to millimetres. Guided further by theoretical analyses and a laminar multiphase fluid flow simulation, we show that this freezing approach is applicable to a broad range of materials from organic polysaccharides to inorganic nanoparticles. We demonstrate the unique advantages of these vortex ring-derived particles in several applications including cell encapsulation, three-dimensional cell culture, and cell-free protein production. Moreover, compartmentalization and ordered-structures composed of these novel particles are all achieved, creating opportunities to engineer more sophisticated hierarchical materials.

Moderate Aortic Valvular Insufficiency Invalidates Vortex Formation Time as an Index of Left Ventricular Filling Efficiency in Patients With Severe Degenerative Calcific Aortic Stenosis Undergoing Aortic Valve Replacement

OBJECTIVE

Transmitral blood flow produces a vortex ring (quantified using vortex formation time [VFT]) that enhances the efficiency of left ventricular (LV) filling. VFT is attenuated in LV hypertrophy resulting from aortic valve stenosis (AS) versus normal LV geometry. Many patients with AS also have aortic insufficiency (AI). The authors tested the hypothesis that moderate AI falsely elevates VFT by partially inhibiting mitral leaflet opening in patients with AS.

DESIGN

Observational study.

SETTING

Veterans Affairs medical center.

PARTICIPANTS

Patients with AS in the presence or absence of moderate AI (n = 8 per group) undergoing aortic valve replacement (AVR) were studied after institutional review board approval.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Under general anesthesia, peak early LV filling (E) and atrial systole (A) blood flow velocities and their corresponding velocity-time integrals were obtained using pulse-wave Doppler transesophageal echocardiography (TEE) to determine E/A and atrial filling fraction (beta). Mitral valve diameter (D) was calculated as the average of major and minor axis lengths obtained in the midesophageal bicommissural (transcommissural anterior-lateral-posterior medial) and LV long-axis (anterior-posterior) TEE imaging planes, respectively. VFT was calculated as 4·(1-beta)·SV/πD(3), where SV = stroke volume measured using thermodilution. Hemodynamics, diastolic function, and VFT were determined during steady-state conditions before cardiopulmonary bypass. The severity of AS (mean and peak pressure gradients, peak transvalvular jet velocity, aortic valve area) and diastolic function (E/A, beta) were similar between groups. Moderate centrally directed AI was present in 8 patients with AS (ratio of regurgitant jet width to LV outflow tract diameter of 36±6%). Pulse pressure and mean pulmonary artery pressure were elevated in patients with versus without AI, but no other differences in hemodynamics were observed. Mitral valve minor and major axis lengths, diameter, and area were reduced in the presence versus the absence of AI. VFT was increased significantly (5.7±1.7 v 3.2±0.6; p = 0.00108) in patients with AS and AI compared with AS alone.

CONCLUSION

Moderate AI falsely elevates VFT in patients with severe AS undergoing AVR by partially inhibiting mitral valve opening. VFT may be an unreliable index of LV filling efficiency with competitive diastolic flow into the LV.

A D-Shaped Bileaflet Bioprosthesis which Replicates Physiological Left Ventricular Flow Patterns

Prior studies have shown that in a healthy heart, there exist a large asymmetric vortex structure that aids in establishing a steady flow field in the left ventricle. However, the implantation of existing artificial heart valves at the mitral position is found to have a negative effect on this physiological flow pattern. In light of this, a novel D-shaped bileaflet porcine bioprosthesis (GD valve) has been designed based on the native geometry mitral valve, with the hypothesis that biomimicry in valve design can restore physiological left ventricle flow patterns after valve implantation. An in-vitro experiment using two dimensional particle velocimetry imaging was carried out to determine the hemodynamic performance of the new bileaflet design and then compared to that of the well-established St. Jude Epic valve which functioned as a control in the experiment. Although both valves were found to have similar Reynolds shear stress and Turbulent Kinetic Energy levels, the novel D-shape valve was found to have lower turbulence intensity and greater mean kinetic energy conservation.

A coupled chemo-fluidic computational model for thrombogenesis in infarcted left ventricles

A coupled chemo-fluidic computational model for investigating flow-mediated thrombogenesis in infarcted left ventricles (LVs) is proposed. LV thrombus (LVT) formation after the acute myocardial infarction (AMI) may lead to thromboembolic events that are associated with high mortality and morbidity, and reliable stratification of LVT risk is the key to managing the treatment of AMI patients. There have been several studies emphasizing the importance of LV blood flow patterns on thrombus formation; however, given the complex interplay between ventricular flow dynamics and biochemistry of thrombogenesis, current understanding is mostly empirical. In the present model, blood flow in the LV is obtained by solving the incompressible Navier-Stokes equations, and this is coupled to the biochemical modeling of the coagulation cascade, platelet activation, and fibrinogen polymerization. The coupled model is used to examine the effect of ventricular flow patterns on thrombogenesis in modeled ventricles. It is expected that the method developed here will enable in-depth studies of thrombogenesis in patient-derived infarcted LV models.

Integrated Regional Cardiac Hemodynamic Imaging and RNA Sequencing Reveal Corresponding Heterogeneity of Ventricular Wall Shear Stress and Endocardial Transcriptome

Background

Unlike arteries, in which regionally distinct hemodynamics are associated with phenotypic heterogeneity, the relationships between endocardial endothelial cell phenotype and intraventricular flow remain largely unexplored. We investigated regional differences in left ventricular wall shear stress and their association with endocardial endothelial cell gene expression.

Methods and Results

Local wall shear stress was calculated from 4‐dimensional flow magnetic resonance imaging in 3 distinct regions of human (n=8) and pig (n=5) left ventricle: base, adjacent to the outflow tract; midventricle; and apex. In both species, wall shear stress values were significantly lower in the apex and midventricle relative to the base; oscillatory shear index was elevated in the apex. RNA sequencing of the endocardial endothelial cell transcriptome in pig left ventricle (n=8) at a false discovery rate ≤10% identified 1051 genes differentially expressed between the base and the apex and 327 between the base and the midventricle; no differentially expressed genes were detected at this false discovery rate between the apex and the midventricle. Enrichment analyses identified apical upregulation of genes associated with translation initiation including mammalian target of rapamycin, and eukaryotic initiation factor 2 signaling. Genes of mitochondrial dysfunction and oxidative phosphorylation were also consistently upregulated in the left ventricular apex, as were tissue factor pathway inhibitor (mean 50‐fold) and prostacyclin synthase (5‐fold)—genes prominently associated with antithrombotic protection.

Conclusions

We report the first spatiotemporal measurements of wall shear stress within the left ventricle and linked regional hemodynamics to heterogeneity in ventricular endothelial gene expression, most notably to translation initiation and anticoagulation properties in the left ventricular apex, in which oscillatory shear index is increased and wall shear stress is decreased.

The numerical analysis of non-Newtonian blood flow in human patient-specific left ventricle

Recently, various non-invasive tools such as the magnetic resonance image (MRI), ultrasound imaging (USI), computed tomography (CT), and the computational fluid dynamics (CFD) have been widely utilized to enhance our current understanding of the physiological parameters that affect the initiation and the progression of the cardiovascular diseases (CVDs) associated with heart failure (HF). In particular, the hemodynamics of left ventricle (LV) has attracted the attention of the researchers due to its significant role in the heart functionality. In this study, CFD owing its capability of predicting detailed flow field was adopted to model the blood flow in images-based patient-specific LV over cardiac cycle. In most published studies, the blood is modeled as Newtonian that is not entirely accurate as the blood viscosity varies with the shear rate in non-linear manner. In this paper, we studied the effect of Newtonian assumption on the degree of accuracy of intraventricular hemodynamics. In doing so, various non-Newtonian models and Newtonian model are used in the analysis of the intraventricular flow and the viscosity of the blood. Initially, we used the cardiac MRI images to reconstruct the time-resolved geometry of the patient-specific LV. After the unstructured mesh generation, the simulations were conducted in the CFD commercial solver FLUENT to analyze the intraventricular hemodynamic parameters. The findings indicate that the Newtonian assumption cannot adequately simulate the flow dynamic within the LV over the cardiac cycle, which can be attributed to the pulsatile and recirculation nature of the flow and the low blood shear rate.

Atrial systole enhances intraventricular filling flow propagation during increasing heart rate

Diastolic fluid dynamics in the left ventricle (LV) has been examined in multiple clinical studies for understanding cardiac function in healthy humans and developing diagnostic measures in disease conditions. The question of how intraventricular filling vortex flow pattern is affected by increasing heart rate (HR) is still unanswered. Previous studies on healthy subjects have shown a correlation between increasing HR and diminished E/A ratio of transmitral peak velocities during early filling (E-wave) to atrial systole (A-wave). We hypothesize that with increasing HR under constant E/A ratio, E-wave contribution to intraventricular vortex propagation is diminished. A physiologic in vitro flow phantom consisting of a LV physical model was used for this study. HR was varied across 70, 100 and 120 beats per minute (bpm) with E/A of 1.1-1.2. Intraventricular flow patterns were characterized using 2D particle image velocimetry measured across three parallel longitudinal (apical-basal) planes in the LV. A pair of counter-rotating vortices was observed during E-wave across all HRs. With increasing HR, diminished vortex propagation occurred during E-wave and atrial systole was found to amplify secondary vorticity production. The diastolic time point where peak vortex circulation occurred was delayed with increasing HR, with peak circulation for 120bpm occurring as late as 90% into diastole near the end of A-wave. The role of atrial systole is elevated for higher HR due to the limited time available for filling. Our baseline findings and analysis approach can be applied to studies of clinical conditions where impaired exercise tolerance is observed.

Assessment of viscous energy loss and the association with three-dimensional vortex ring formation in left ventricular inflow: In vivo evaluation using four-dimensional flow MRI

PURPOSE

To evaluate viscous energy loss and the association with three-dimensional (3D) vortex ring formation in left ventricular (LV) blood flow during diastolic filling.

THEORY AND METHODS

Thirty healthy volunteers were compared with 32 patients with corrected atrioventricular septal defect as unnatural mitral valve morphology and inflow are common in these patients. 4DFlow MRI was acquired from which 3D vortex ring formation was identified in LV blood flow at peak early (E)-filling and late (A)-filling and characterized by its presence/absence, orientation, and position from the lateral wall. Viscous energy loss was computed over E-filling, A-filling, and complete diastole using the Navier-Stokes energy equations.

RESULTS

Compared with healthy volunteers, viscous energy loss was significantly elevated in patients with disturbed vortex ring formation as characterized by a significantly inclined orientation and/or position closer to the lateral wall. Highest viscous energy loss was found in patients without a ring-shaped vortex during E-filling (on average more than double compared with patients with ring-shape vortex, P < 0.003). Altered A-filling vortex ring formation was associated with significant increase in total viscous energy loss over diastole even in the presence of normal E-filling vortex ring.

CONCLUSION

Altered vortex ring formation during LV filling is associated with increased viscous energy loss. Magn Reson Med 77:794-805, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Vortex ring behavior provides the epigenetic blueprint for the human heart

The laws of fluid dynamics govern vortex ring formation and precede cardiac development by billions of years, suggesting that diastolic vortex ring formation is instrumental in defining the shape of the heart. Using novel and validated magnetic resonance imaging measurements, we show that the healthy left ventricle moves in tandem with the expanding vortex ring, indicating that cardiac form and function is epigenetically optimized to accommodate vortex ring formation for volume pumping. Healthy hearts demonstrate a strong coupling between vortex and cardiac volumes (R² = 0.83), but this optimized phenotype is lost in heart failure, suggesting restoration of normal vortex ring dynamics as a new, and possibly important consideration for individualized heart failure treatment. Vortex ring volume was unrelated to early rapid filling (E-wave) velocity in patients and controls. Characteristics of vortex-wall interaction provide unique physiologic and mechanistic information about cardiac diastolic function that may be applied to guide the design and implantation of prosthetic valves, and have potential clinical utility as therapeutic targets for tailored medicine or measures of cardiac health.

Changes in electrical activation modify the orientation of left ventricular flow momentum: novel observations using echocardiographic particle image velocimetry

AIMS

Changes in electrical activation sequence are known to affect the timing of cardiac mechanical events. We aim to demonstrate that these also modify global properties of the intraventricular blood flow pattern. We also explore whether such global changes present a relationship with clinical outcome.

METHODS AND RESULTS

We investigated 30 heart failure patients followed up after cardiac resynchronization therapy (CRT). All subjects underwent echocardiography before implant and at follow-up after 6+ months. Left ventricular mechanics was investigated at follow-up during active CRT and was repeated after a temporary interruption <5 min later. Strain analysis, performed by speckle tracking, was used to assess the entity of contraction (global longitudinal strain) and its synchronicity (standard deviation of time to peak of radial strain). Intraventricular fluid dynamics, by echographic particle image velocimetry, was used to evaluate the directional distribution of global momentum associated with blood motion. The discontinuation of CRT pacing reflects into a reduction of deformation synchrony and into the deviation of blood flow momentum from the base-apex orientation with the development of transversal flow-mediated haemodynamic forces. The deviation of flow momentum presents a significant correlation with the degree of volumetric reduction after CRT.

CONCLUSION

Changes in electrical activation alter the orientation of blood flow momentum. The long-term CRT outcome correlates with the degree of re-alignment of haemodynamic forces. These preliminary results suggest that flow orientation could be used for optimizing the biventricular pacing setting. However, larger prospective studies are needed to confirm this hypothesis.

Age-related changes in intraventricular kinetic energy: a physiological or pathological adaptation?

Measuring intracardiac kinetic energy using four-dimensionl flow cardiac magnetic resonance provides important information on the decline in the early diastolic kinetic energy of blood with aging. The decline is comparable with that seen in those with heart failure and may be a marker of cardiac function.

Aging has important deleterious effects on the cardiovascular system. We sought to compare intraventricular kinetic energy (KE) in healthy subjects of varying ages with subjects with ventricular dysfunction to understand if changes in energetic momentum may predispose individuals to heart failure. Four-dimensional flow MRI was acquired in 35 healthy subjects (age: 1–67 yr) and 10 patients with left ventricular (LV) dysfunction (age: 28–79 yr). Healthy subjects were divided into age quartiles (1st quartile: <16 yr, 2nd quartile: 17–32 yr, 3rd quartile: 33–48 yr, and 4th quartile: 49–64 yr). KE was measured in the LV throughout the cardiac cycle and indexed to ventricular volume. In healthy subjects, two large peaks corresponding to systole and early diastole occurred during the cardiac cycle. A third smaller peak was seen during late diastole in eight adults. Systolic KE (P = 0.182) and ejection fraction (P = 0.921) were preserved through all age groups. Older adults showed a lower early peak diastolic KE compared with children (P < 0.0001) and young adults (P = 0.025). Subjects with LV dysfunction had reduced ejection fraction (P < 0.001) and compared with older healthy adults exhibited a similar early peak diastolic KE (P = 0.142) but with the addition of an elevated KE in diastasis (P = 0.029). In healthy individuals, peak diastolic KE progressively decreases with age, whereas systolic peaks remain constant. Peak diastolic KE in the oldest subjects is comparable to those with LV dysfunction. Unique age-related changes in ventricular diastolic energetics might be physiological or herald subclinical pathology.

Assessment of intracardiac flow and vorticity in the right heart of patients after repair of tetralogy of Fallot by flow-sensitive 4D MRI

OBJECTIVES

To comprehensively and quantitatively analyse flow and vorticity in the right heart of patients after repair of tetralogy of Fallot (rTOF) compared with healthy volunteers.

METHODS

Time-resolved flow-sensitive 4D MRI was acquired in 24 rTOF patients and 12 volunteers. Qualitative flow evaluation was based on consensus reading of two observers. Quantitative analysis included segmentation of the right atrium (RA) and ventricle (RV) in a four-chamber view to extract volumes and regional haemodynamic information for computation of regional mean and peak vorticity.

RESULTS

Right heart intra-atrial, intraventricular and outflow tract flow patterns differed considerably between rTOF patients and volunteers. Peak RA and mean RV vorticity was significantly higher in patients (p = 0.02/0.05). Significant negative correlations were found between patients' maximum and mean RV and RA vorticity and ventricular volumes (p < 0.05). The main pulmonary artery (MPA) regurgitant flow was associated with higher RA and RV vorticity, which was significant for RA maximum and RV mean vorticity (p = 0.01/0.03).

CONCLUSION

The calculation of vorticity based on 4D flow data is an alternative approach to assess intracardiac flow changes in rTOF patients compared with qualitative flow visualization. Alterations in intracardiac vorticity could be relevant with regard to the development of RV dilation and impaired function.

KEY POINTS

• 4D flow MRI with vorticity calculation enables a novel approach to assess intracardiac flow. • Significantly higher intracardiac vorticity occurred in patients after repair of tetralogy of Fallot. • Regurgitant flow in the main pulmonary artery is associated with higher right heart vorticity.

Determinants of kinetic energy of blood flow in the four-chambered heart in athletes and sedentary controls

The kinetic energy (KE) of intracardiac blood may play an important role in cardiac function. The aims of the present study were to 1) quantify and investigate the determinants of KE, 2) compare the KE expenditure of intracardiac blood between athletes and control subjects, and 3) quantify the amount of KE inside and outside the diastolic vortex. Fourteen athletes and fourteen volunteers underwent cardiac MRI, including four-dimensional phase-contrast sequences. KE was quantified in four chambers, and energy expenditure was calculated by determining the mean KE/cardiac index. Left ventricular (LV) mass was an independent predictor of diastolic LVKE ( R2= 0.66, P < 0.001), whereas right ventricular (RV) end-diastolic volume was important for diastolic RVKE ( R2= 0.76, P < 0.001). The mean KE/cardiac index did not differ between groups (control subjects: 0.53 ± 0.14 mJ·l−1·min·m2and athletes: 0.56 ± 0.21 mJ·l−1·min·m2, P = 0.98). Mean LV diastolic vortex KE made up 70 ± 1% and 73 ± 2% of total LV diastolic KE in athletes and control subjects ( P = 0.18). In conclusion, the characteristics of the LV as a pressure pump and the RV as a volume pump are demonstrated as an association between LVKE and LV mass and between RVKE and end-diastolic volume. This also suggests different filling mechanisms where the LV is dependent on diastolic suction, whereas the RV fills with a basal movement of the atrioventricular plane over “stationary” blood. Both groups had similar energy expenditure for intracardiac blood flow, indicating similar pumping efficiency, likely explained by the lower heart rate that cancels the higher KE per heart beat in athletes. The majority of LVKE is found within the LV diastolic vortex, in contrast to earlier findings.

Left ventricular fluid kinetic energy time curves in heart failure from cardiovascular magnetic resonance 4D flow data

BACKGROUND

Measurement of intracardiac kinetic energy (KE) provides new insights into cardiac hemodynamics and may improve assessment and understanding of heart failure. We therefore aimed to investigate left ventricular (LV) KE time curves in patients with heart failure and in controls.

METHODS

Patients with heart failure (n = 29, NYHA class I-IV) and controls (n = 12) underwent cardiovascular magnetic resonance (CMR) including 4D flow. The vortex-ring boundary was computed using Lagrangian coherent structures. The LV endocardium and vortex-ring were manually delineated and KE was calculated as ½mv(2) of the blood within the whole LV and the vortex ring, respectively.

RESULTS

The systolic average KE was higher in patients compared to controls (2.2 ± 1.4 mJ vs 1.6 ± 0.6 mJ, p = 0.048), but lower when indexing to EDV (6.3 ± 2.2 μJ/ml vs 8.0 ± 2.1 μJ/ml, p = 0.025). No difference was seen in diastolic average KE (3.2 ± 2.3 mJ vs 2.0 ± 0.8 mJ, p = 0.13) even when indexing to EDV (9.0 ± 4.4 μJ/ml vs 10.2 ± 3.3 μJ/ml, p = 0.41). In patients, a smaller fraction of diastolic average KE was observed inside the vortex ring compared to controls (72 ± 6% vs 54 ± 9%, p < 0.0001). Three distinctive KE time curves were seen in patients which were markedly different from findings in controls, and with a moderate agreement between KE time curve patterns and degree of diastolic dysfunction (Cohen's kappa = 0.49), but unrelated to NYHA classification (p = 0.12), or 6-minute walk test (p = 0.72).

CONCLUSION

Patients with heart failure exhibit higher systolic average KE compared to controls, suggesting altered intracardiac blood flow. The different KE time curves seen in patients may represent a conceptually new approach for heart failure classification.

Vortex-ring mixing as a measure of diastolic function of the human heart: Phantom validation and initial observations in healthy volunteers and patients with heart failure

PURPOSE

To present and validate a new method for 4D flow quantification of vortex-ring mixing during early, rapid filling of the left ventricle (LV) as a potential index of diastolic dysfunction and heart failure.

MATERIALS AND METHODS

4D flow mixing measurements were validated using planar laser-induced fluorescence (PLIF) in a phantom setup. Controls (n = 23) and heart failure patients (n = 23) were studied using 4D flow at 1.5T (26 subjects) or 3T (20 subjects) to determine vortex volume (VV) and inflowing volume (VVinflow ). The volume mixed into the vortex-ring was quantified as VVmix-in = VV-VVinflow . The mixing ratio was defined as MXR = VVmix-in /VV. Furthermore, we quantified the fraction of the end-systolic volume (ESV) mixed into the vortex-ring (VVmix-in /ESV) and the fraction of the LV volume at diastasis (DV) occupied by the vortex-ring (VV/DV).

RESULTS

PLIF validation of MXR showed fair agreement (R(2) = 0.45, mean ± SD 1 ± 6%). MXR was higher in patients compared to controls (28 ± 11% vs. 16 ± 10%, P < 0.001), while VVmix-in /ESV and VV/DV were lower in patients (10 ± 6% vs. 18 ± 12%, P < 0.01 and 25 ± 8% vs. 50 ± 6%, P < 0.0001).

CONCLUSION

Vortex-ring mixing can be quantified using 4D flow. The differences in mixing parameters observed between controls and patients motivate further investigation as indices of diastolic dysfunction. J. Magn. Reson. Imaging 2016;43:1386-1397.