Echocardiographic Particle Image Velocimetry: A Novel Technique for Quantification of Left Ventricular Blood Vorticity Pattern

Heart failure in children and adolescents: an update on diagnostic approaches and management

Cardiac failure is a clinical syndrome that may develop in children owing to cardiac dysfunction or underlying structural heart diseases. Considering the differences in diagnostic and therapeutic approaches for pediatric heart failure (PHF) and adult heart failure, we have reviewed the current literature on PHF. Relevant studies were extracted from MEDLINE/PubMed, Google Scholar, and Clinical Trial Registries using the terms "pediatric heart failure" or "heart failure in children" and "management" or "decongestive therapy." Recent advances in diagnostic approaches, such as cardiac magnetic resonance, speckle-tracking echocardiography, tissue Doppler imaging, and molecular diagnostic techniques, have increased our under -standing of PHF. It is imperative that clinicians evaluate the interrelated factors responsible for the develop ment of PHF, including myocardial function, pulmonary and systemic blood flow, heart rhythm, valve function, and nutritional status. Although recent advances have demon strated the efficacy of many new drugs in adult heart failure trials, it cannot be concluded that these drugs will show similar efficacy in children, considering the heterogeneous nature of the underlying mechanisms and variable pharmacody-namics and pharmacokinetics. Therefore, the underlying pathophysiology of PHF and the mechanisms of action of different drugs should be considered when selecting appropriate therapies. Further trials are needed to establi sh the efficacy and safety of these drugs, and a combined mul-ti disciplinary strategy will help enhance PHF outcomes.

Artificial intelligence-based speckle featurization and localization for ultrasound speckle tracking velocimetry

Deep learning-based super-resolution ultrasound (DL-SRU) framework has been successful in improving spatial resolution and measuring the velocity field information of a blood flows by localizing and tracking speckle signals of red blood cells (RBCs) without using any contrast agents. However, DL-SRU can localize only a small part of the speckle signals of blood flow owing to ambiguity problems encountered in the classification of blood flow signals from ultrasound B-mode images and the building up of suitable datasets required for training artificial neural networks, as well as the structural limitations of the neural network itself. An artificial intelligence-based speckle featurization and localization (AI-SFL) framework is proposed in this study. It includes a machine learning-based algorithm for classifying blood flow signals from ultrasound B-mode images, dimensionality reduction for featurizing speckle patterns of the classified blood flow signals by approximating them with quantitative values. A novel and robust neural network (ResSU-net) is trained using the online data generation (ODG) method and the extracted speckle features. The super-resolution performance of the proposed AI-SFL and ODG method is evaluated and compared with the results of previous U-net and conventional data augmentation methods under in silico conditions. The predicted locations of RBCs by the AI-SFL and DL-SRU for speckle patterns of blood flow are applied to a PTV algorithm to measure quantitative velocity fields of the flow. Finally, the feasibility of the proposed AI-SFL framework for measuring real blood flows is verified under in vivo conditions.

An Anatomically Shaped Mitral Valve for Hemodynamic Testing

In vitro modeling of the left heart relies on accurately replicating the physiological conditions of the native heart. The targeted physiological conditions include the complex fluid dynamics coming along with the opening and closing of the aortic and mitral valves. As the mitral valve possess a highly sophisticated apparatus, thence, accurately modeling it remained a missing piece in the perfect heart duplicator puzzle. In this study, we explore using a hydrogel-based mitral valve that offers a full representation of the mitral valve apparatus. The valve is tested using a custom-made mock circulatory loop to replicate the left heart. The flow analysis includes performing particle image velocimetry measurements in both left atrium and ventricle. The results showed the ability of the new mitral valve to replicate the real interventricular and atrial flow patterns during the whole cardiac cycle. Moreover, the investigated valve has a ventricular vortex formation time of 5.2, while the peak e- and a-wave ventricular velocities was 0.9 m/s and 0.4 m/s respectively.

A clinician's guide to understanding aortic 4D flow MRI

Four-dimensional flow magnetic resonance imaging is an emerging technique which may play a role in diagnosis and risk-stratification of aortic disease. Some knowledge of flow dynamics and related parameters is necessary to understand and apply this technique in clinical workflows. The purpose of the current review is to provide a guide for clinicians to the basics of flow imaging, frequently used flow-related parameters, and their relevance in the context of aortic disease.Clinical relevance statement Understanding normal and abnormal aortic flow could improve clinical care in patients with aortic disease.

Effects of MitraClip Therapy on Mitral Flow Patterns and Vortex Formation: An In Vitro Study

MitraClip transcatheter edge-to-edge repair is used to treat mitral regurgitation (MR). While MR is reduced, diastolic left ventricular flows are altered. An in vitro left heart simulator was used to assess a porcine mitral valve in the native, MR, and MR plus MitraClip cases. Velocity, vorticity, and Reynolds shear stress (RSS) were quantified by particle image velocimetry. Peak velocity increased from 1.20 m/s for native to 1.30 m/s with MR. With MitraClip, two divergent jets of 1.18 and 0.61 m/s emerged. Higher vorticity was observed with MR than native and lessened with MitraClip. MitraClip resulted in shear layer formation and downstream vortex formation. Native RSS decreased from 33 Pa in acceleration to 29 Pa at peak flow, then increased to 31 Pa with deceleration. MR RSS increased from 27 Pa in acceleration to 40 Pa at peak flow to 59 Pa during deceleration. MitraClip RSS increased from 79 Pa in acceleration to 162 Pa during peak flow, then decreased to 45 Pa during deceleration. After MitraClip, two divergent jets of reduced velocity emerged, accompanied by shear layers and recirculation. Chaotic flow developed, resulting in elevated RSS magnitude and coverage. Findings help understand consequences of MitraClip on left ventricular flow dynamics.

Simultaneous visualization of flow fields and oxygen concentrations to unravel transport and metabolic processes in biological systems

From individual cells to whole organisms, O2 transport unfolds across micrometer- to millimeter-length scales and can change within milliseconds in response to fluid flows and organismal behavior. The spatiotemporal complexity of these processes makes the accurate assessment of O2 dynamics via currently available methods difficult or unreliable. Here, we present "sensPIV," a method to simultaneously measure O2 concentrations and flow fields. By tracking O2-sensitive microparticles in flow using imaging technologies that allow for instantaneous referencing, we measured O2 transport within (1) microfluidic devices, (2) sinking model aggregates, and (3) complex colony-forming corals. Through the use of sensPIV, we find that corals use ciliary movement to link zones of photosynthetic O2 production to zones of O2 consumption. SensPIV can potentially be extendable to study flow-organism interactions across many life-science and engineering applications.

Full-volume three-component intraventricular vector flow mapping by triplane color Doppler

Objective. Intraventricular vector flow mapping (iVFM) is a velocimetric technique for retrieving two-dimensional velocity vector fields of blood flow in the left ventricular cavity. This method is based on conventional color Doppler imaging, which makes iVFM compatible with the clinical setting. We have generalized the iVFM for a three-dimensional reconstruction (3D-iVFM). Approach. 3D-iVFM is able to recover three-component velocity vector fields in a full intraventricular volume by using a clinical echocardiographic triplane mode. The 3D-iVFM problem was written in the spherical (radial, polar, azimuthal) coordinate system associated to the six half-planes produced by the triplane mode. As with the 2D version, the method is based on the mass conservation, and free-slip boundary conditions on the endocardial wall. These mechanical constraints were imposed in a least-squares minimization problem that was solved through the method of Lagrange multipliers. We validated 3D-iVFM in silico in a patient-specific CFD (computational fluid dynamics) model of cardiac flow and tested its clinical feasibility in vivo in patients and in one volunteer. Main results. The radial and polar components of the velocity were recovered satisfactorily in the CFD setup (correlation coefficients, r  = 0.99 and 0.78). The azimuthal components were estimated with larger errors ( r  = 0.57) as only six samples were available in this direction. In both in silico and in vivo investigations, the dynamics of the intraventricular vortex that forms during diastole was deciphered by 3D-iVFM. In particular, the CFD results showed that the mean vorticity can be estimated accurately by 3D-iVFM. Significance. Our results tend to indicate that 3D-iVFM could provide full-volume echocardiographic information on left intraventricular hemodynamics from the clinical modality of triplane color Doppler.

Left ventricular high frame rate echo-particle image velocimetry: clinical application and comparison with conventional imaging

Background

Echo-Particle Image Velocimetry (echoPIV) tracks speckle patterns from ultrasound contrast agent(UCA), being less angle-sensitive than colour Doppler. High frame rate (HFR) echoPIV enables tracking of high velocity flow in the left ventricle (LV). We aimed to demonstrate the potential clinical use of HFR echoPIV and investigate the feasibility and accuracy in patients.

Methods

Nineteen patients admitted for heart failure were included. HFR contrast images were acquired from an apical long axis view (ALAX), using a fully-programmable ultrasound system. A clinical UCA was continuously infused with a dedicated pump. Additionally, echocardiographic images were obtained using a clinical system, including LV contrast-enhanced images and pulsed-wave (PW) Doppler of the LV inflow and outflow in ALAX. 11 patients underwent CMR and 4 cardiac CT as clinically indicated. These CMR and CT images were used as reference. In 10 patients with good echoPIV tracking and reference imaging, the intracavitary flow was compared between echoPIV, conventional and UCA echocardiography.

Results

EchoPIV tracking quality was good in 12/19 (63%), moderate in 2/19 (10%) and poor in 5/19 (26%) subjects. EchoPIV could determine inflow velocity in 17/19 (89%), and outflow in 14/19 (74%) patients. The correlation of echoPIV and PW Doppler was good for the inflow (R² = 0.77 to PW peak; R² = 0.80 PW mean velocity) and moderate for the outflow (R² = 0.54 to PW peak; R² = 0.44 to PW mean velocity), with a tendency for echoPIV to underestimate PW velocities. In selected patients, echoPIV was able in a single acquisition to demonstrate flow patterns which required multiple interrogations with classical echocardiography. Those flow patterns could also be linked to anatomical abnormalities as seen in CMR or CT.

Conclusion

HFR echoPIV tracks multidirectional and complex flow patterns which are unapparent with conventional echocardiography, while having comparable feasibility. EchoPIV tends to underestimate flow velocities as compared to PW Doppler. It has the potential to provide in one acquisition all the functional information obtained by conventional imaging, overcoming the angle dependency of Doppler and low frame rate of classical contrast imaging.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12947-022-00283-4.

Noninvasive Evaluation of Intraventricular Flow Dynamics by the HyperDoppler Technique: First Application to Normal Subjects, Athletes, and Patients with Heart Failure

Background: HyperDoppler is a new echocardiographic color Doppler-based technique that can assess intracardiac flow dynamics. The aim of this study was to verify the feasibility and reproducibility of this technique in unselected patients and its capability to differentiate measures of vortex flow within the left ventricle (LV) in normal sedentary subjects, athletes, and patients with heart failure. Methods: Two hundred unselected, consecutive patients presenting at the echocardiographic laboratory, 50 normal subjects, 30 athletes, and 50 patients with chronic heart failure and LV ejection fraction <50% were enrolled. Images were acquired using a MyLab X8 echo-scanner. Area, intensity, depth, length, and kinetic energy dissipation (KED) of vortex flow were measured. Results: The HyperDoppler technique feasibility was 94.5%. According to the intraclass correlation coefficient evaluations, repeatability and reproducibility of vortex flow measures were good for vortex area (0.82, 0.85), length (0.83, 0.82), and depth (0.87, 0.84) and excellent for intensity (0.92, 0.90) and KED (0.98, 0.98). Combining different vortex flow measures, the LV flow profile of healthy sedentary individuals, athletes, and heart failure patients could be differentiated. Conclusions: HyperDoppler is a feasible, reliable, and practical technique for the assessment of LV flow dynamics and may distinguish normal subjects and patients with heart failure.

Preoperative Left Ventricular Energy Loss in the Operating Theater Reflects Subjective Symptoms in Chronic Aortic Regurgitation

Background

There is currently no subjective, definitive evaluation method for therapeutic indication other than symptoms in aortic regurgitation. Energy loss, a novel parameter of cardiac workload, can be visualized and quantified using echocardiography vector flow mapping. The purpose of the present study was to evaluate whether energy loss in patients with chronic aortic regurgitation can quantify their subjective symptoms more clearly than other conventional metrics.

Methods

We studied 15 patients undergoing elective aortic valve surgery for aortic regurgitation. We divided the patients into symptomatic and asymptomatic groups using their admission records. We analyzed the mean energy loss in one cardiac cycle using transesophageal echocardiography during the preoperative period. The relationships between symptoms, energy loss, and other conventional metrics were statistically analyzed.

Results

There were seven and eight patients in the symptomatic and asymptomatic groups, respectively. The mean energy loss of one cardiac cycle was higher in the symptomatic group (121 mW/m [96–184]) than in the asymptomatic group (87 mW/m [80–103]) (p = 0.040), whereas the diastolic diameter was higher in the asymptomatic group (65 mm [59–78]) than in the symptomatic group (57 mm [51–57]) (p = 0.040). There was no significant difference between the symptomatic and asymptomatic groups in terms of other conventional metrics.

Conclusions

An energy loss can quantify patients' subjective symptoms more clearly than other conventional metrics. The small sample size is the primary limitation of our study, further studies assessing larger cohort of patients are warranted to validate our findings.

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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12947-021-00269-8.

Ultrasonic biomechanics method for vortex and wall motion of left ventricle: a phantom and in vivo study

Background

The non-invasive quantitative evaluation of left ventricle (LV) function plays a critical role in clinical cardiology. This study proposes a novel ultrasonic biomechanics method by integrating both LV vortex and wall motion to fully assess and understand the LV structure and function. The purpose of this study was to validate the ultrasonic biomechanics method as a quantifiable approach to evaluate LV function.

Methods

Firstly, B-mode ultrasound images were acquired and processed, which were utilized to implement parameters for quantifying the LV vortex and wall motion respectively. Next, the parameters were compared in polyvinyl alcohol cryogen (PVA) phantoms with different degree of stiffness corresponding to different freezing and thawing cycles in vitro. Finally, the parameters were computed in vivo during one cardiac cycle to assess the LV function in normal and abnormal subjects in vivo.

Results

In vitro study, the velocity field of PVA phantom differed with stiffness (varied elasticity modulus). The peak of strain for wall motion decreases with the increase of elasticity modulus, and periodically changed values. Statistical analysis for parameters of vortex dynamics (energy dissipation index, DI; kinetic energy fluctuations, KEF; relative strength, RS; and vorticity, W) based on different elasticity (E) of phantom depicted the good viability of this algorithm. In vivo study, the results confirmed that subjects with LV dysfunction had lower vorticity and strain (S) compared to the normal group.

Conclusion

Ultrasonic biomechanics method can obtain the vortex and wall motion of left ventricle. The method may have potential clinical value in evaluation of LV dysfunction.

Novel Imaging and Genetic Risk Markers in Takotsubo Syndrome

Takotsubo syndrome (TTS) is an increasingly recognized condition burdened by significant acute and long-term adverse events. The availability of novel techniques expanded the knowledge on TTS and allowed a more accurate risk-stratification, potentially guiding clinical management. The present review aims to summarize the recent advances in TTS prognostic evaluation with a specific focus on novel imaging and genetic markers. Parametric deformation analysis by speckle-tracking echocardiography, as well as tissue characterization by cardiac magnetic resonance imaging T1 and T2 mapping techniques, currently appear the most clinically valuable applications. Notwithstanding, computed tomography and nuclear imaging studies provided limited but promising data. A genetic predisposition to TTS has been hypothesized, though available evidence is still not sufficient. Although a genetic predisposition appears likely, further studies are needed to fully characterize the genetic background of TTS, in order to identify genetic markers that could assist in predicting disease recurrences and help in familial screening.

Alterations in Intracardiac Flow Patterns Affect Mitral Leaflets Dynamics in a Model of Ischemic Mitral Regurgitation

PURPOSE

This study was to evaluate the effects of ischemic mitral regurgitation (IMR) on vortex formation and leaflet dynamics using an established porcine infarct model of IMR.

METHODS

Using direct coronary ligation, five animals were subjected to a posterolateral myocardial infarction (MI) followed by an MRI at 12-weeks post MI. MR imaging consisted of 4D time-resolved left ventricular (LV) flow, full coverage 2D LV cine, and high resolution 2D cine of mitral valve dynamics. Five additional naïve animals underwent identical imaging protocols to serve as controls. Image analysis was performed to obtain mitral transvalvular flows as well as LV volumes throughout the cardiac cycle. In addition, anterior to posterior mid-leaflet tip distances were measured throughout the cardiac cycle for determination of temporal leaflet dynamics.

RESULTS

It was found IMR caused asymmetric vortex ring formation with the anterior vortex having a lower vorticity relative to its posterior counterpart. In contrast, normal ventricles create symmetric and tightly curled vortices in the basal chamber just underneath the mitral leaflets which conserve kinetic energy and aid in effective ejection. IMR animals were also evaluated for leaflet separation and were found to have a greater leaflet opening and achieved peak vorticity and peak leaflet opening later than control animals.

CONCLUSION

In conclusion, this study shows the effects that altered vortex formation, due to IMR, can have on ventricular filling and leaflet dynamics. These findings have important implications for understanding blood flow through the dilated heart and how ring annuloplasty and volume reduction interventions may influence mitral valve dynamics.

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.

Optimization of Microbubble Concentration and Acoustic Pressure for Left Ventricular High-Frame-Rate EchoPIV in Patients

High-frame-rate (HFR) echo-particle image velocimetry (echoPIV) is a promising tool for measuring intracardiac blood flow dynamics. In this study, we investigate the optimal ultrasound contrast agent (UCA: SonoVue) infusion rate and acoustic output to use for HFR echoPIV (PRF = 4900 Hz) in the left ventricle (LV) of patients. Three infusion rates (0.3, 0.6, and 1.2 ml/min) and five acoustic output amplitudes (by varying transmit voltage: 5, 10, 15, 20, and 30 V-corresponding to mechanical indices of 0.01, 0.02, 0.03, 0.04, and 0.06 at 60-mm depth) were tested in 20 patients admitted for symptoms of heart failure. We assess the accuracy of HFR echoPIV against pulsed-wave Doppler acquisitions obtained for mitral inflow and aortic outflow. In terms of image quality, the 1.2-ml/min infusion rate provided the highest contrast-to-background ratio (CBR) (3-dB improvement over 0.3 ml/min). The highest acoustic output tested resulted in the lowest CBR. Increased acoustic output also resulted in increased microbubble disruption. For the echoPIV results, the 1.2-ml/min infusion rate provided the best vector quality and accuracy; mid-range acoustic outputs (corresponding to 15-20-V transmit voltages) provided the best agreement with the pulsed-wave Doppler. Overall, the highest infusion rate (1.2 ml/min) and mid-range acoustic output amplitudes provided the best image quality and echoPIV results.

Lagrangian-averaged vorticity deviation of spiraling blood flow in the heart during isovolumic contraction and ejection phases

The formation of vortex rings in the left ventricular (LV) blood flow is a mechanism for optimized blood transport from the mitral valve inlet to aortic valve outlet, and the vorticity is an important measure of a well-functioning LV. However, due to lack of quantitative methods, the process of defining the boundary of a vortex in the LV and identifying the dominant vortex components has not been studied previously. The Lagrangian-averaged vorticity deviation (LAVD) can enable us to compute the trajectory integral of the normed difference of the vorticity from its spatial mean. Therefore, in this work, we have employed LAVD to identify the Lagrangian vortices and Eulerian vortices for measuring the vortex volume and vorticity in the LV blood flow. We found that during the LV ejection period, the positive (counterclockwise) and negative (clockwise) vorticity of patients are consistently stronger than those of the healthy groups, and the counterclockwise vortex volume of healthy groups (0.84+0.26 ml) is greater than that of patients (0.55+0.28 ml) during the pre-ejection period. Then, during the middle ejection phase, the counterclockwise vortex ring volume of patients (1.89+0.36 ml) exceeds that of healthy groups (1.38+0.43 ml). Finally, during the end-ejection period, the counterclockwise vortex ring volume of healthy subjects (0.61+0.17 ml) is the same as that of patients (0.60+0.19 ml). The results presented in this paper can provide new insights into the blood flow patterns within the LV. It can accurately indicate the role of vortices and vorticity values in intra-LV flow, and portray how cardiomyopathy (and its distorted contractile mechanism) can affect intra-LV flow patterns and mitigate adequate LV outflow.

Left Ventricular Deformation and Vortex Analysis in Heart Failure: From Ultrasound Technique to Current Clinical Application

Heart failure (HF) is a leading cause of cardiovascular morbidity and mortality. However, its symptoms and signs are not specific or can be absent. In this context, transthoracic echocardiography plays a key role in diagnosing the various forms of HF, guiding therapeutic decision making and monitoring response to therapy. Over the last few decades, new ultrasound modalities have been introduced in the field of echocardiography, aiming at better understanding the morpho-functional abnormalities occurring in cardiovascular diseases. However, they are still struggling to enter daily and routine use. In our review article, we turn the spotlight on some of the newest ultrasound technologies; in particular, analysis of myocardial deformation by speckle tracking echocardiography, and intracardiac flow dynamics by color Doppler flow mapping, highlighting their promising applications to HF diagnosis and management. We also focus on the importance of these imaging modalities in the selection of responses to cardiac resynchronization therapy.

Vortex dynamics and transport phenomena in stenotic aortic models using Echo-PIV

Atherosclerosis is the most fatal cardiovascular disease. As disease progresses, stenoses grow inside the arteries blocking their lumen and altering blood flow. Analysing flow dynamics can provide a deeper insight on the stenosis evolution. In this work we combined Eulerian and Lagrangian descriptors to analyze blood flow dynamics and fluid transport in stenotic aortic models with morphology, mechanical and optical properties close to those of real arteries. To this end, vorticity, particle residence time (PRT), particle's final position (FP) and finite time Lyapunov's exponents (FTLE) were computed from the experimental fluid velocity fields acquired using ultrasonic particle imaging velocimetry (Echo-PIV). For the experiments, CT-images were used to create morphological realistic models of the descending aorta with 0%, 35% and 50% occlusion degree with same mechanical properties as real arteries. Each model was connected to a circuit with a pulsatile programmable pump which mimics physiological flow and pressure conditions. The pulsatile frequency was set to ≈0.9 Hz (55 bpm) and the upstream peak Reynolds number (Re) was changed from 1100 to 2000. Flow in the post-stenotic region was composed of two main structures: a high velocity jet over the stenosis throat and a recirculation region behind the stenosis where vortex form and shed. We characterized vortex kinematics showing that vortex propagation velocity increases withRe. Moreover, from the FTLE field we identified Lagrangian coherent structures (i.e. material barriers) that dictate transport behind the stenosis. The size and strength of those barriers increased withReand the occlusion degree. Finally, from the PRT and FP maps, we showed that independently ofRe, the same amount of fluid remains on the stenosis over more than a pulsatile period.

In vitro performance of echoPIV for assessment of laminar flow profiles in a carotid artery stent

Purpose: Detailed blood flow studies may contribute to improvements in carotid artery stenting. High-frame-rate contrast-enhanced ultrasound followed by particle image velocimetry (PIV), also called echoPIV, is a technique to study blood flow patterns in detail. The performance of echoPIV in presence of a stent has not yet been studied extensively. We compared the performance of echoPIV in stented and nonstented regions in an in vitro flow setup.

Approach: A carotid artery stent was deployed in a vessel-mimicking phantom. High-frame-rate contrast-enhanced ultrasound images were acquired with various settings. Signal intensities of the contrast agent, velocity values, and flow profiles were calculated.

Results: The results showed decreased signal intensities and correlation coefficients inside the stent, however, PIV analysis in the stent still resulted in plausible flow vectors.

Conclusions: Velocity values and laminar flow profiles can be measured in vitro in stented arteries using echoPIV.

Blood flow patterns estimation in the left ventricle with low-rate 2D and 3D dynamic contrast-enhanced ultrasound

BACKGROUND AND OBJECTIVE

Left ventricle (LV) dysfunction always occurs at early heart-failure stages, producing variations in the LV flow patterns. Cardiac diagnostics may therefore benefit from flow-pattern analysis. Several visualization tools have been proposed that require ultrafast ultrasound acquisitions. However, ultrafast ultrasound is not standard in clinical scanners. Meanwhile techniques that can handle low frame rates are still lacking. As a result, the clinical translation of these techniques remains limited, especially for 3D acquisitions where the volume rates are intrinsically low.

METHODS

To overcome these limitations, we propose a novel technique for the estimation of LV blood velocity and relative-pressure fields from dynamic contrast-enhanced ultrasound (DCE-US) at low frame rates. Different from other methods, our method is based on the time-delays between time-intensity curves measured at neighbor pixels in the DCE-US loops. Using Navier-Stokes equation, we regularize the obtained velocity fields and derive relative-pressure estimates. Blood flow patterns were characterized with regard to their vorticity, relative-pressure changes (dp/dt) in the LV outflow tract, and viscous energy loss, as these reflect the ejection efficiency.

RESULTS

We evaluated the proposed method on 18 patients (9 responders and 9 non-responders) who underwent cardiac resynchronization therapy (CRT). After CRT, the responder group evidenced a significant (p<0.05) increase in vorticity and peak dp/dt, and a non-significant decrease in viscous energy loss. No significant difference was found in the non-responder group. Relative feature variation before and after CRT evidenced a significant difference (p<0.05) between responders and non-responders for vorticity and peak dp/dt. Finally, the method feasibility is also shown with 3D DCE-US.

CONCLUSIONS

Using the proposed method, adequate visualization and quantification of blood flow patterns are successfully enabled based on low-rate DCE-US of the LV, facilitating the clinical adoption of the method using standard ultrasound scanners. The clinical value of the method in the context of CRT is also shown.

Contrast-Enhanced High-Frame-Rate Ultrasound Imaging of Flow Patterns in Cardiac Chambers and Deep Vessels

Cardiac function and vascular function are closely related to the flow of blood within. The flow velocities in these larger cavities easily reach 1 m/s, and generally complex spatiotemporal flow patterns are involved, especially in a non-physiologic state. Visualization of such flow patterns using ultrasound can be greatly enhanced by administration of contrast agents. Tracking the high-velocity complex flows is challenging with current clinical echographic tools, mostly because of limitations in signal-to-noise ratio; estimation of lateral velocities; and/or frame rate of the contrast-enhanced imaging mode. This review addresses the state of the art in 2-D high-frame-rate contrast-enhanced echography of ventricular and deep-vessel flow, from both technological and clinical perspectives. It concludes that current advanced ultrasound equipment is technologically ready for use in human contrast-enhanced studies, thus potentially leading to identification of the most clinically relevant flow parameters for quantifying cardiac and vascular function.

A Systematic Review for the Design of In Vitro Flow Studies of the Carotid Artery Bifurcation

PURPOSE

In vitro blood flow studies in carotid artery bifurcation models may contribute to understanding the influence of hemodynamics on carotid artery disease. However, the design of in vitro blood flow studies involves many steps and selection of imaging techniques, model materials, model design, and flow visualization parameters. Therefore, an overview of the possibilities and guidance for the design process is beneficial for researchers with less experience in flow studies.

METHODS

A systematic search to in vitro flow studies in carotid artery bifurcation models aiming at quantification and detailed flow visualization of blood flow dynamics results in inclusion of 42 articles.

RESULTS

Four categories of imaging techniques are distinguished: MRI, optical particle image velocimetry (PIV), ultrasound and miscellaneous techniques. Parameters for flow visualization are categorized into velocity, flow, shear-related, turbulent/disordered flow and other parameters. Model materials and design characteristics vary between study type.

CONCLUSIONS

A simplified three-step design process is proposed for better fitting and adequate match with the pertinent research question at hand and as guidance for less experienced flow study researchers. The three consecutive selection steps are: flow parameters, image modality, and model materials and designs. Model materials depend on the chosen imaging technique, whereas choice of flow parameters is independent from imaging technique and is therefore only determined by the goal of the study.

The Effect of Inflow Cannula Angle on the Intraventricular Flow Field of the Left Ventricular Assist Device-Assisted Heart: An In Vitro Flow Visualization Study

Previous studies have identified left ventricular assist device (LVAD) inflow cannula (IC) malposition as a significant risk for pump thrombosis. Thrombus development is a consequence of altered flow dynamics, which can produce areas of flow stasis or high shear that promote coagulation. The goal of this study was to measure the effect of IC orientation on the left ventricle (LV) flow field using a mock circulatory loop, and identify flow-based indices that are sensitive measures of cannula malposition. Experimental studies were performed with a customized silicone model of the dilated LV and the EVAHEART Centrifugal LVAS (Evaheart, Inc.; Houston TX). The velocity field of the LV midplane was measured for a transparent IC oriented parallel to and rotated 15° toward the septum under matched hemodynamic conditions. Vortex structures were analyzed and localized stasis calculated within the IC and combined with a map of normalized pulsatile velocity. The velocity fields revealed increased apical stasis and lower pulsatility with a small angulation of the IC. A significant change in vortex dynamics with the angled IC was observed, doubling the size of the counterclockwise (CCW) vortex while reducing the kinetic energy provided by LVAD support. A significant decrease in average and systolic velocities within the IC was found with cannula angulation, suggesting an increased resistance that affects primarily systolic flow and is worsened with increased LVAD support. These common echocardiographic indices offer the opportunity for immediate clinical application during ramp study assessment. Optimized IC positioning may be determined preoperatively using imaging techniques to develop patient-specific surgical recommendations.

Determining Haemodynamic Wall Shear Stress in the Rabbit Aorta In Vivo Using Contrast-Enhanced Ultrasound Image Velocimetry

Abnormal blood flow and wall shear stress (WSS) can cause and be caused by cardiovascular disease. To date, however, no standard method has been established for mapping WSS in vivo. Here we demonstrate wide-field assessment of WSS in the rabbit abdominal aorta using contrast-enhanced ultrasound image velocimetry (UIV). Flow and WSS measurements were made independent of beam angle, curvature or branching. Measurements were validated in an in silico model of the rabbit thoracic aorta with moving walls and pulsatile flow. Mean errors over a cardiac cycle for velocity and WSS were 0.34 and 1.69%, respectively. In vivo time average WSS in a straight segment of the suprarenal aorta correlated highly with simulations (PC = 0.99) with a mean deviation of 0.29 Pa or 5.16%. To assess fundamental plausibility of the measurement, UIV WSS was compared to an analytic approximation derived from the Poiseuille equation; the discrepancy was 17%. Mapping of WSS was also demonstrated in regions of arterial branching. High time average WSS (TAWSS_xz = 3.4 Pa) and oscillatory flow (OSI_xz = 0.3) were observed near the origin of conduit arteries. In conclusion, we have demonstrated that contrast-enhanced UIV is capable of measuring spatiotemporal variation in flow velocity, arterial wall location and hence WSS in vivo with high accuracy over a large field of view.

4-D Echo-Particle Image Velocimetry in a Left Ventricular Phantom

Left ventricular (LV) blood flow is an inherently complex time-varying 3-D phenomenon, where 2-D quantification often ignores the effect of out-of-plane motion. In this study, we describe high frame rate 4-D echocardiographic particle image velocimetry (echo-PIV) using a prototype matrix transesophageal transducer and a dynamic LV phantom for testing the accuracy of echo-PIV in the presence of complex flow patterns. Optical time-resolved tomographic PIV (tomo-PIV) was used as a reference standard for comparison. Echo-PIV and tomo-PIV agreed on the general profile of the LV flow patterns, but echo-PIV smoothed out the smaller flow structures. Echo-PIV also underestimated the flow rates at greater imaging depths, where the PIV kernel size and transducer point spread function were large relative to the velocity gradients. We demonstrate that 4-D echo-PIV could be performed in just four heart cycles, which would require only a short breath-hold, providing promising results. However, methods for resolving high velocity gradients in regions of poor spatial resolution are required before clinical translation.

Quantitative Analysis of Left Ventricular Flow Dynamics in Latent Obstructive Hypertrophic Cardiomyopathy Using Vector Flow Mapping

OBJECTIVES

This study aimed to assess left ventricular (LV) energy loss (EL), circulation and vortex area using vector flow mapping (VFM) in patients with latent obstructive hyper-trophic cardiomyopathy (LOHCM) and nonobstructive hypertrophic cardiomyopathy (NOHCM).

METHODS

Fourteen LOHCM patients, 10 NOHCM patients, and 11 healthy individuals were evaluated by transthoracic echocardiography. An offline VFM workstation was used to analyze the LV blood flow patterns and fluid dynamics. The hemodynamic parameters, EL, circulation, and vortex area in 7 cardiac phases were calculated and analyzed.

RESULTS

Compared with controls and NOHCM patients, EL was significantly higher in -LOHCM patients during the rapid ejection phase, slow ejection (SE) phase, and isovolumetric relaxation phase (p < 0.05). LOHCM patients also showed increased circulation during SE compared to the other two groups (p < 0.05). The ability to discriminate between NOHCM and LOHCM was assessed by the area under the receiver-operating characteristic curve (AUC), and EL during SE was found to have the largest AUC (0.964); the best cutoff value was 6.34 J/m3/s, with a sensitivity of 100% and specificity of 80%.

CONCLUSIONS

The VFM technique can detect abnormal changes of LV EL and vortex characteristics in hypertrophic cardiomyopathy patients. Compared with controls and NOHCM patients, the LOHCM patients have worse systolic and diastolic functions.

Left Ventricular Vortices in Myocardial Infarction Observed with Echodynamography

Echodynamography (EDG) is a computational method to deduce two-dimensional (2D) blood flow vector from conventional color Doppler ultrasound image by considering that the blood flow is divided into vortex and base flow components. Left ventricular (LV) vortices indicate cardiac flow status influenced by LV wall motion. Thus, quantitative assessment of LV vortices may become new and sensitive parameters for cardiac function. In the present study, quantitative parameters of LV vortices such as vortex index, vortex size, and Reynolds number were calculated and relation between each parameter was assessed. Six healthy volunteers and three patients with myocardial infarction (MI) who underwent color Doppler echocardiography (CDE) were involved in the study. Serial CDE images in apical three-chamber view were recorded and 2D blood flow vector was superimposed on the CDE image. Vortex index, vortex size, and Reynolds number were compared between the normal volunteers and the MI patients. The results showed that vortex index (3.09±2.06 vs. 3.34±2.33, p<; 0.05), vortex size (1.76 0.69 vs. 2.01 ±0.68, p<; 0.05), Reynolds number (1020±603 vs.±1312 1046, p<; ±0.05) were significantly greater in the MI patients than in the healthy volunteers. Vortex equivalent diameter in LV showed significant positive correlation with Reynolds number (R² = 0.799, y = 0.001x + 0.7098, p <; 0.05) in healthy volunteers and (R² = 0.6404, y = 0.0005x+1.3185, p<; 0.05) in MI patients. Vortex index showed positive correlation with Reynolds number (R² = 0.9351, y = 0.002x+0.1397, p<; 0.05) in healthy volunteers and (R² = 0.758, y = 0.0019x+0.7957, p<; 0.05) in MI patients. In conclusion, EDG provides information on LV hemodynamics by quantitative LV vortices parameters both in healthy volunteers and MI patients.

Validation of Echodynamography in Comparison with Particle-image Velocimetry

Echodynamography (EDG) is a computational method to estimate and visualize two-dimensional flow velocity vectors by applying dynamic flow theories to color Doppler echocardiography. The EDG method must be validated if applied to human cardiac flow function. However, a few studies of flow estimated have compared by EDG to the flow data were acquired by other methods. In this study, EDG was validated by comparing the analysis of estimating and visualizing flow velocity vectors obtained by original particle image velocimetry (PIV) based on a left ventricular (LV) phantom hydrogel (in vitro studies) and by EDG based on the virtual Doppler velocity. Velocity measured by PIV method and velocity estimated by EDG method in the perpendicular direction and the radial direction were compared. Regression analysis for the velocity estimated in the radial direction revealed an excellent correlation (R2=0.99, slope = 0.96) and moderate correlation in the perpendicular direction (R2=0.44, slope = 0.46). As revealed by the Bland-Altman plot, however, overestimations and higher relative error were observed in the perpendicular direction (0.51 ± 2.75 mm/s) and in the radial direction (-2.15 ± 21.13 mm/s). The percentage error of the norm-wise relative error of the velocity discrepancy is less than 10%, and velocity magnitude followed the same trends and are of comparable magnitude. These findings indicate that good estimates of velocity can be obtained by the EDG method. Therefore, the EDG method was appropriate for estimating and visualizing velocity vectors in clinical studies for higher measurement accuracy and reliability. The clinical in vivo application showed that the EDG method has the ability to visualize blood flow velocity vectors and differentiate the clinical information of vortex parameters both in normal and abnormal LV subjects. In conclusion, the EDG method has potentially greater clinical acceptance as a tool assessment of LV during the cardiac cycle.

Prediction of Cardiac Resynchronization Therapy Response in Dilated Cardiomyopathy Using Vortex Flow Mapping on Cine Magnetic Resonance Imaging

Background: We investigated the association between left ventricle ejection fraction (LVEF) and vortex flow (VF), and whether cardiac resynchronization therapy (CRT) response can be predicted using VF mapping (VFM) in patients with dilated cardiomyopathy (DCM).

Methods and Results: Cardiac magnetic resonance imaging data for 20 patients with heart failure (HF) with LVEF ≥40% and 25 patients with DCM with LVEF <40%, scheduled for CRT, were retrospectively analyzed. The maximum VF (MVF) on short-axis, long-axis and 4-chamber LV cine imaging were calculated using VFM. Summed MVF was used as a representative value for each case and was significantly greater for patients with DCM than for patients with HF with LVEF ≥40% (25.2±19.2% vs. 12.1±15.4%, P<0.005). Summed MVF was significantly greater for CRT responders (n=12, 35.8±22.7%) than for non-responders (n=13, 15.8±8.7%, P=0.04) during the mean follow-up period of 38.4 months after CRT. Patients with summed MVF ≥31.3% had a significantly higher major adverse cardiac event-free rate than those with MVF <31.3% (log-rank=4.51, P<0.05).

Conclusions: On VFM analysis, LV VF interrupted efficient ejection in HF. Summed MVF can predict CRT response in DCM.

Intraventricular flow patterns during right ventricular apical pacing

Objectives

To assess differences in blood flow momentum (BFM) and kinetic energy (KE) dissipation in a model of cardiac dyssynchrony induced by electrical right ventricular apical (RVA) stimulation compared with spontaneous sinus rhythm.

Methods

We cross-sectionally enrolled 12 consecutive patients (mean age 74±8 years, 60% male, mean left ventricular ejection fraction 58%±6 %), within 48 hours from pacemaker (PMK) implantation. Inclusion criteria were: age>18 years, no PMK-dependency, sinus rhythm with a spontaneous narrow QRS at the ECG, preserved ejection fraction (>50%) and a low percentage of PMK-stimulation (<20%). All the participants underwent a complete echocardiographic evaluation, including left ventricular strain analysis and particle image velocimetry.

Results

Compared with sinus rhythm, BFM shifted from 27±3.3 to 34±7.6° (p=0.016), while RVA-pacing was characterised by a 35% of increment in KE dissipation, during diastole (p=0.043) and 32% during systole (p=0.016). In the same conditions, left ventricle global longitudinal strain (LV GLS) significantly decreased from 17±3.3 to 11%±2.8% (p=0.004) during RVA-stimulation. At the multivariable analysis, BFM and diastolic KE dissipation were significantly associated with LV GLS deterioration (Beta Coeff.=0.54, 95% CI 0.07 to 1.00, p=0.034 and Beta Coeff.=0.29, 95% CI 0.02 to 0.57, p=0.049, respectively).

Conclusions

In RVA-stimulation, BFM impairment and KE dissipation were found to be significantly associated with LV GLS deterioration, when controlling for potential confounders. Such changes may favour the onset of cardiac remodelling and sustain heart failure.

Left ventricular vortex formation time in elite athletes: novel predictor of myocardial performance

Background

Efficient transportation of blood through the left ventricle (LV) during diastole depends on vortex formation. Vortex formation time (VFT) can be measured by echocardiography as a dimensionless index. As elite athletes have supranormal diastolic LV function, we aim to assess resting and post-exercise VFT in these athletes and hypothesised that VFT may predict myocardial performance immediately post-exercise.

Method

Subjects were world class speedskaters training for the Winter Olympic Games. Echocardiographic measurements were obtained before and immediately after 3000 m of racing. VFT was computed as 4×(1-β)/π×α³×left ventricle ejection fraction where β is the fraction of diastolic stroke volume contributed by atrial contraction, α is the biplane end diastolic volume (EDV)^1/3 divided by mitral annular diameter during early diastole.

Results

Baseline VFT was 2.6±0.7 (n=24, age 22±3 years, 67% males). Post-exercise, heart rates increased (64±10 vs 89±12 beats/min, p<0.01); however, VFT was unchanged (2.9±1.0, p>0.05). VFT at rest correlated modestly with post-exertion early diastolic mitral in-flow velocity (E; r=0.59, p=0.01), tissue Doppler-derived early mitral annular velocity (E'; septal and lateral, both r=0.59, p=0.01) and systolic annular velocity (S'; septal: r=0.46, p=0.02 and lateral: r=0.48, p=0.02) but not late diastolic mitral in-flow velocity (A; r=0.06, p>0.05) or annular velocity (A'; septal: r=0.34, p=NS and lateral: r=0.35, p>0.05).

Conclusion

There was no significant difference between VFT at rest and immediately post-exercise. However, VFT at rest correlated with immediate post-exercise augmented systolic and early diastolic tissue Doppler indicators of myocardial performance in elite athletes.

Diagnosis and Pathophysiological Mechanisms of Group 3 Hypoxia-Induced Pulmonary Hypertension

PURPOSE OF REVIEW

Group 3 hypoxia-induced pulmonary hypertension (PH) is an important and increasingly diagnosed condition in both the pediatric and adult population. The majority of pulmonary hypertension studies to date and all three classes of drug therapies were designed to focus on group 1 PH. There is a clear unmet medical need for understanding the molecular mechanisms of group 3 PH and a need for novel non-invasive methods of assessing PH in neonates.

RECENT FINDINGS

Several growth factors are expressed in patients and in animal models of group 3 PH and are thought to contribute to the pathophysiology of this disease. Here, we review some of the findings on the roles of vascular endothelial growth factor A (VEGFA), platelet-derived growth factor B (PDGFB), transforming growth factor-beta (TGFB1), and fibroblast growth factors (FGF) in PH. Additionally, we discuss novel uses of echocardiographic parameters in assessing right ventricular form and function. FGF2, TGFB, PDGFB, and VEGFA may serve as biomarkers in group 3 PH along with echocardiographic methods to diagnose and follow right ventricle function. FGFs and VEGFs may also function in the pathophysiology of group 3 PH.

Real-Time Transthoracic Vector Flow Imaging of the Heart in Pediatric Patients

In children with congenital heart defects, Doppler ultrasound is the standard, bedside imaging modality. However, precise characterization of blood flow is challenging due to angle-dependent and one-dimensional velocity estimation. Contrast agent free Vector Flow Imaging is a new ultrasound technology that enables angle-independent visualization of the detailed flow field. Two piglets, one with normal cardiac anatomy and one with congenital heart disease comprised of valvular pulmonary stenosis, a dilated main pulmonary artery, and an incomplete atrioventricular canal defect, were imaged transthoracically and epicardially using a BK Ultrasound bk5000 with built-in vector flow imaging and a 5MHz linear probe. Subsequently, two children, one with normal cardiac anatomy and one with congenital heart disease comprised of aortic valve stenosis and coarctation of the aorta were imaged transthoracically. Transthoracic two-dimensional echocardiography and vector flow imaging were readily performed in both animals and were limited only by the geometry of the porcine thorax. In addition, transthoracic vector flow imaging was successfully performed in both children, and abnormal flow secondary to cardiac anomalies was visible. Adequate penetration was obtained to a depth of 6.5 cm. Our group has previously demonstrated for the first time that transthoracic vector flow imaging echocardiography is feasible and practicable in pediatric-sized patients, and this paper describes examples of these concepts and in-depth comparisons with traditional imaging modalities. This paper demonstrates that commercially available vector flow imaging technology can be utilized in pediatric cardiac applications as a bedside transthoracic imaging modality, providing advanced detail of blood flow patterns within the cardiac chambers, across valves, and in the great arteries.

Relationship between left ventricular vortex and preejectional flow velocity during isovolumic contraction studied by using vector flow mapping

OBJECTIVES

The purpose of this study was to investigate the relationship between the vortex in left ventricle (LV) during the isovolumic contraction (IVC) period and the preejectional flow velocity in LV outflow tract (V_LVOT ).

METHODS

Color Doppler loops were acquired for vector flow mapping in apical long-axis view in 76 patients with dilated cardiomyopathy, 61 patients with coronary artery disease and 36 healthy controls.

RESULTS

All normals exhibited an IVC vortex reaching the LV base. V_LVOT was significantly related to IVC vortex area flux, transmitral A velocity, mitral annular a' velocity and E/e' ratio, respectively. Transmitral A velocity was the only independent predictor of V_LVOT (R²  = 0.292, P = 0.001). In patients the IVC vortex could reach the LV base, middle, or apex. V_LVOT was significantly related to range, area and area flux of the IVC vortex, LV size, LVEF, mitral annular velocities, E/e' ratio, transmitral A velocity, and IVC time, respectively. Range and corrected area flux of the IVC vortex, LV end-systolic short diameter, and IVC time were independent predictors of V_LVOT (R²  = 0.608, P < 0.001).

CONCLUSIONS

In normals, the transmitral A velocity (momentum) is efficiently transferred from mitral orifice to LV outflow tract by a normally formed IVC vortex, and transmitral A velocity is the only independent predictor of V_LVOT . However, in patients with a wide range of LV enlargement and dysfunction, the momentum transfer is associated with not only the LV dimension and function, but also the range and volume of the IVC vortex.

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.

Usefulness of Left Ventricular Vortex Flow Analysis for Predicting Clinical Outcomes in Patients with Chronic Heart Failure: A Quantitative Vorticity Imaging Study Using Contrast Echocardiography

The goal of the study described here was to evaluate whether left ventricular vortex flow parameters, as assessed by contrast echocardiography, enhance prediction of major adverse cardiac events (MACE) in patients with chronic heart failure and systolic dysfunction. A total of 75 patients with contrast echocardiography and systolic dysfunction (ejection fraction ≤45%) were prospectively enrolled and underwent vortex flow analysis with particle image velocimetry using contrast echocardiography. Vortex flow parameters, including kinetic energy fluctuation (KEF), were evaluated. Patients were followed up for a primary endpoint of MACE that comprised hospital admission for cardiovascular causes and cardiac deaths. Across a median 277-d follow-up, 29 patients (38.7%) experienced MACE. Among these, the incidence of diabetes and the E/e' ratio were significantly higher in patients with MACE than in those without, whereas the hemoglobin level and ejection fraction were significantly lower. KEF was significantly lower in patients with MACE. In the multivariate analysis, higher KEF was associated with a lower risk of MACE (hazard ratio = 0.18, 95% confidence interval: 0.04-0.97, p = 0.046). The addition of KEF to a model with conventional parameters (e.g., age, diabetes, ejection fraction and the E/e' ratio) significantly improved the model's discrimination. Elevations in the quantitative left ventricular vortex flow parameter, KEF, as determined by contrast echocardiography, are associated with a lower risk of MACE and improved functional status among patients with chronic heart failure.

Ventricular flow dynamics with varying LVAD inflow cannula lengths: In-silico evaluation in a multiscale model

Left ventricular assist devices are associated with thromboembolic events, which are potentially caused by altered intraventricular flow. Due to patient variability, differences in apical wall thickness affects cannula insertion lengths, potentially promoting unfavourable intraventricular flow patterns which are thought to be correlated to the risk of thrombosis. This study aimed to present a 3D multiscale computational fluid dynamic model of the left ventricle (LV) developed using a commercial software, Ansys, and evaluate the risk of thrombosis with varying inflow cannula insertion lengths in a severely dilated LV. Based on a HeartWare HVAD inflow cannula, insertion lengths of 5, 19, 24 and 50 mm represented cases of apical hypertrophy, typical ranges of apical thicknesses and an experimental length, respectively. The risk of thrombosis was evaluated based on blood washout, residence time, instantaneous blood stagnation and a pulsatility index. By introducing fresh blood to displace pre-existing blood in the LV, after 5 cardiac cycles, 46.7%, 45.7%, 45.1% and 41.8% of pre-existing blood remained for insertion lengths of 5, 19, 24 and 50 mm, respectively. Compared to the 50 mm insertion, blood residence time was at least 9%, 7% and 6% higher with the 5, 19 and 24 mm insertion lengths, respectively. No instantaneous stagnation at the apex was observed directly after the E-wave. Pulsatility indices adjacent to the cannula increased with shorter insertion lengths. For the specific scenario studied, a longer insertion length, relative to LV size, may be advantageous to minimise thrombosis by increasing LV washout and reducing blood residence time.

Enhancement of measurement accuracy of X-ray PIV in comparison with the micro-PIV technique

The X-ray PIV (particle image velocimetry) technique has been used as a non-invasive measurement modality to investigate the haemodynamic features of blood flow. However, the extraction of two-dimensional velocity field data from the three-dimensional volumetric information contained in X-ray images is technically unclear. In this study, a new two-dimensional velocity field extraction technique is proposed to overcome technological limitations. To resolve the problem of finding a correction coefficient, the velocity field information obtained by X-ray PIV and micro-PIV techniques for disturbed flow in a concentric stenosis with 50% severity was quantitatively compared. Micro-PIV experiments were conducted for single-plane and summation images, which provide similar positional information of particles as X-ray images. The correction coefficient was obtained by establishing the relationship between velocity data obtained from summation images (V_S) and centre-plane images (V_C). The velocity differences between V_S and V_C along the vertical and horizontal directions were quantitatively analysed as a function of the geometric angle of the test model for applying the present two-dimensional velocity field extraction technique to a conduit of arbitrary geometry. Finally, the two-dimensional velocity field information at arbitrary positions could be successfully extracted from X-ray images by using the correction coefficient and several velocity parameters derived from V_S.

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.

Evaluation of the anatomic and hemodynamic abnormalities in tricuspid atresia before and after surgery using computational fluid dynamics

Analysis of hemodynamics inside tricuspid atresia (TA) chamber is essential to the understanding of TA for optimal treatment. In this study, we introduced a combined computational fluid dynamics (CFD) to simulate blood flow in the left ventricle (LV) to study the diastolic flow changes in TA.Real-time 3-dimentional echocardiography loops (ECHO) were acquired in normal control group, in TA patients before surgery (pre-op group) and after surgery (post-op group). ECHO loops were reconstructed and simulated by CFD, the geometric, volumetric changes, and vortices in the LV were studies and compare among 3 groups.Compared with the control group, pre-op TA patients demonstrated significant LV remodeling, manifesting with smaller LV length, larger diameter, width and spherical index, as well as lager volumes; post-op TA group showed revisions in values of both geometric and volumetric measurements. CDF also demonstrated the abnormality of vortices in the pre-op TA patients and the alteration of existence and measurements of vortex in postoperation group.Echo-based CFD modeling can show the abnormality of TA in both LV geometric, volumetric measurements and intracardiac vortices; and CFD is capable to demonstrate the alterations of LV after Fontan and Glenn surgical procedure.