Abnormal early diastolic intraventricular flow 'kinetic energy index' assessed by vector flow mapping in patients with elevated filling pressure

Blood Flow Quantification in Peripheral Arterial Disease: Emerging Diagnostic Techniques in Vascular Surgery

The assessment of local blood flow patterns in patients with peripheral arterial disease is clinically relevant, since these patterns are related to atherosclerotic disease progression and loss of patency in stents placed in peripheral arteries, through mechanisms such as recirculating flow and low wall shear stress (WSS). However, imaging of vascular flow in these patients is technically challenging due to the often complex flow patterns that occur near atherosclerotic lesions. While several flow quantification techniques have been developed that could improve the outcomes of vascular interventions, accurate 2D or 3D blood flow quantification is not yet used in clinical practice. This article provides an overview of several important topics that concern the quantification of blood flow in patients with peripheral arterial disease. The hemodynamic mechanisms involved in the development of atherosclerosis and the current clinical practice in the diagnosis of this disease are discussed, showing the unmet need for improved and validated flow quantification techniques in daily clinical practice. This discussion is followed by a showcase of state-of-the-art blood flow quantification techniques and how these could be used before, during and after treatment of stenotic lesions to improve clinical outcomes. These techniques include novel ultrasound-based methods, Phase-Contrast Magnetic Resonance Imaging (PC-MRI) and Computational Fluid Dynamics (CFD). The last section discusses future perspectives, with advanced (hybrid) imaging techniques and artificial intelligence, including the implementation of these techniques in clinical practice.

Blood Flow Quantification in Peripheral Arterial Disease: Emerging Diagnostic Techniques in Vascular Surgery

The assessment of local blood flow patterns in patients with peripheral arterial disease is clinically relevant, since these patterns are related to atherosclerotic disease progression and loss of patency in stents placed in peripheral arteries, through mechanisms such as recirculating flow and low wall shear stress (WSS). However, imaging of vascular flow in these patients is technically challenging due to the often complex flow patterns that occur near atherosclerotic lesions. While several flow quantification techniques have been developed that could improve the outcomes of vascular interventions, accurate 2D or 3D blood flow quantification is not yet used in clinical practice. This article provides an overview of several important topics that concern the quantification of blood flow in patients with peripheral arterial disease. The hemodynamic mechanisms involved in the development of atherosclerosis and the current clinical practice in the diagnosis of this disease are discussed, showing the unmet need for improved and validated flow quantification techniques in daily clinical practice. This discussion is followed by a showcase of state-of-the-art blood flow quantification techniques and how these could be used before, during and after treatment of stenotic lesions to improve clinical outcomes. These techniques include novel ultrasound-based methods, Phase-Contrast Magnetic Resonance Imaging (PC-MRI) and Computational Fluid Dynamics (CFD). The last section discusses future perspectives, with advanced (hybrid) imaging techniques and artificial intelligence, including the implementation of these techniques in clinical practice.

Colour-Doppler echocardiography flow field velocity reconstruction using a streamfunction-vorticity formulation

We introduce a new method (Doppler Velocity Reconstruction or DoVeR), for reconstructing two-component velocity fields from colour Doppler scans. DoVeR employs the streamfunction-vorticity equation, which satisfies mass conservation while accurately approximating the flow rate of rotation. We validated DoVeR using artificial colour Doppler images generated from computational fluid dynamics models of left ventricle (LV) flow. We compare DoVeR against the conventional intraventricular vector flow mapping (iVFM1D) and reformulated iVFM (iVFM2D). LV model error analysis showed that DoVeR is more robust to noise and probe placement, with noise RMS errors (nRMSE) between 3.81% and 6.67%, while the iVFM methods delivered 4.16-24.17% for iVFM1D and 4.06-400.21% for iVFM2D. We test the DoVeR and iVFM methods using in vivo mouse LV ultrasound scans. DoVeR yielded more haemodynamically accurate reconstructions, suggesting that it can provide a more reliable approach for robust quantification of cardiac flow.

Vorticity in lower urinary tract can be assessed and associates with urinary tract morphology in men

OBJECTIVES

The aim of this study is to develop a method to evaluate the fluid dynamics of urine flow in the lower urinary tract (LUT), especially that of vorticity.

MATERIALS AND METHODS

This investigation included three sub-studies to demonstrate urine flow in the entire LUT. First, we attempted to observe vorticity generation in the urinary bladder during spontaneous voiding using transabdominal color Doppler ultrasonography (CDUS). Second, we performed transrectal CDUS to evaluate the vorticity of urine flow in the prostatic urethra. Patients with prostate cancer were enrolled before robotic surgery and divided into the vorticity and non-vorticity groups based on CDUS findings for comparisons of longitudinal urethral diameter and prostatic urethral angle. Third, the vorticity of the voided urine stream was observed using a high-speed video-camera. Micturition was done in a standing position while synchronously monitored for urine flow using uroflowmetry.

RESULTS

Vorticity formation could be dynamically demonstrated in the urinary bladder and prostatic urethra using CDUS. The prostatic urethral angle of the vorticity group was more than that of the non-vorticity group. High-speed video recording could clearly capture vorticity and spiral shape generation in voided urine. The distance from the external urethral orifice to the first twist changed in accordance with urine flow rate.

CONCLUSIONS

In a series of sub-studies, this investigation proved vorticity generation in the LUT and voided urine. Vorticity was detectable in the LUT and in voided urine using CDUS and a high-speed video-camera. Vorticity generation might be associated with urethral morphology.

Ultrasonic Vascular Vector Flow Mapping for 2-D Flow Estimation

A vascular vector flow mapping (VFM) method visualizes 2-D cardiac flow dynamics by estimating the radial component of flow from the Doppler velocities and wall motion velocities using the mass conservation equation. Although VFM provides 2-D flow, the algorithm is applicable only to bounded regions. Here, a modified VFM algorithm, vascular VFM, is proposed so that the velocities are estimated regardless of the flow geometry. To validate the algorithm, a phantom mimicking a carotid artery was fabricated and VFM velocities were compared with optical particle image velocimetry (PIV) data acquired in the same imaged plane. The validation results indicate that given optimal beam angle condition, VFM velocitiy is fairly accurate, where the correlation coefficient R between VFM and PIV velocities is 0.95. The standard deviation of the total VFM error, normalized by the maximum velocity, ranged from 8.1% to 16.3%, whereas the standard deviation of the measured input errors ranged from 8.9% to 12.7% for color flow mapping and from 4.5% to 5.9% for subbeam calculation. These results indicate that vascular VFM is reliable as its accuracy is comparable to that of conventional Doppler-flow images.

Impact of myocardial infarction on intraventricular vortex and flow energetics assessed using computational simulations

Flow energetics have been proposed as early indicators of progressive left ventricular (LV) functional impairment in patients with myocardial infarction (MI), but its correlation with individual MI parameters has not been fully explored. Using electro-fluid-structure interaction LV models, this study investigated the correlation between four MI parameters: infarct size, infarct multiplicity, regional enhancement of contractility at the viable myocardium area (RECVM), and LV mechanical dyssynchrony (LVMD) with intraventricular vortex and flow energetics. In LV with small infarcts, our results showed that infarct appearance amplified the energy dissipation index (DI), where substantial viscous energy loss was observed in areas with high flow velocity and near the infarct-vortex interface. The LV with small multiple infarcts and RECVM showed remarkable DI increment during systole and diastole. In correlation analysis, the systolic kinetic energy fluctuation index (E') was positively related to ejection fraction (EF) (R²  = 0.982) but negatively correlated with diastolic E' (R²  = 0.970). Diastolic E' was inversely correlated with vortex kinetic energy (R²  = 0.960) and vortex depth (R²  = 0.876). We showed an excessive systolic DI could differentiate infarcted LV with normal EF from healthy LV. Strong flow acceleration, LVMD, and vortex-infarct interactions were predominant factors that induced excessive DI in infarcted LVs. Instead of causing undesired flow turbulence, high systolic E' suggested the existence of energetic flow acceleration, while high diastolic E' implied an inefficient diastolic filling. Thus, systolic E' is not a suitable early indicator for progressive LV dysfunction in MI patients, while diastolic E' may be a useful index to indicate diastolic impairment in these patients.

Left ventricular energy loss and wall shear stress assessed by vector flow mapping in patients with hypertrophic cardiomyopathy

The aim of this study was to assess left ventricular (LV) summation of energy loss (EL-SUM), average energy loss (EL-AVE) and wall shear stress (WSS) using vector flow mapping (VFM) in patients with hypertrophic cardiomyopathy (HCM). Forty HCM patients, and 40 controls were evaluated by transthoracic echocardiography. Conventional echocardiographic parameters, summation and average of energy loss (EL-total, EL-base, EL-mid and EL-apex), and WSS in each segment were calculated at different phases. Compared with controls, conventional diastolic measurements were impaired in HCM patients. HCM patients also showed increased EL-SUM-total and EL-AVE-total at the peak of LV rapid ejection period as well as decreased EL-SUM-total and EL-AVE-total at the end of early diastole. In controls, EL-SUM and EL-AVE showed a gradual decrease from the basal segment to the apex, this regularity was not observed in HCM patients. Compared with controls, HCM patients showed increased WSS at the peak of the LV rapid ejection period and the atrial contraction period as well as decreased WSS at the end of early diastole (all p < 0.05). WSS was increased slightly at the peak of the LV rapid filling period in HCM patients (p = 0.055). EL and WSS values derived from VFM are novel flow dynamic parameters that can effectively evaluate systolic and diastolic hemodynamic function in HCM patients.

Flow Energy Loss as a Predictive Parameter for Right Ventricular Deterioration Caused by Pulmonary Regurgitation After Tetralogy of Fallot Repair

The optimal timing for pulmonary valve replacement after Tetralogy of Fallot (TOF) repair remains controversial. In this study, we estimated the feasibility of using flow energy loss (FEL) to predict right ventricular (RV) deterioration due to pulmonary regurgitation after TOF repair. We examined RV outflow tract (RVOT) flow in nine patients who underwent TOF or double-outlet right ventricle repair in the intervention group (Group I) and compared them with three healthy children in the control group (Group C). We evaluated flow across the RVOT and pulmonary valve by vector flow mapping (VFM) on echocardiography and by phase contrast-magnetic resonance imaging (PC-MRI). Next, we calculated FEL and analyzed the relationship between FEL and clinical parameters of RV function. The mean FEL was significantly greater in Group I than in Group C (p = 0.002). Flow pattern and FEL were comparable by VFM and PC-MRI at the same phase 14.6 years after TOF repair. There was a significant positive correlation for the cardiothoracic ratio with both the mean FEL [correlation coefficient (r) = 0.78; p = 0.012] and the diastolic peak FEL (r = 0.75; p = 0.021) in Group I. There was also a significant positive correlation between the serial change in QRS duration with both the mean FEL (r = 0.82; p = 0.014) and the diastolic FEL (r = 0.70; p = 0.052) in Group I. FEL by VFM is an effective tool for evaluating ventricular deterioration caused by RV workload.

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.

New imaging tools in cardiovascular medicine: computational fluid dynamics and 4D flow MRI

Blood flow imaging is a novel technology in cardiovascular medicine and surgery. Today, two types of blood flow imaging tools are available: measurement-based flow visualization including 4D flow MRI (or 3D cine phase-contrast magnetic resonance imaging), or echocardiography flow visualization software, and computer flow simulation modeling based on computational fluid dynamics (CFD). MRI and echocardiography flow visualization provide measured blood flow but have limitations in temporal and spatial resolution, whereas CFD flow calculates the flow according to assumptions instead of flow measurement, and it has sufficiently fine resolution up to the computer memory limit, and it enables even virtual surgery when combined with computer graphics. Blood flow imaging provides profound insight into the pathophysiology of cardiovascular diseases, because it quantifies and visualizes mechanical stress on the vessel walls or heart ventricle. Wall shear stress (WSS) is a stress on the endothelial wall caused by the near wall blood flow, and it is thought to be a predictor of atherosclerosis progression in coronary or aortic diseases. Flow energy loss (EL) is the loss of blood flow energy caused by viscous friction of turbulent diseased flow, and it is expected to be a predictor of ventricular workload on various heart diseases including heart valve disease, cardiomyopathy, and congenital heart diseases. Blood flow imaging can provide useful information for developing predictive medicine in cardiovascular diseases, and may lead to breakthroughs in cardiovascular surgery, especially in the decision-making process.

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.

Mitral valve coaptation and its relationship to late diastolic flow: A color Doppler and vector flow map echocardiographic study in normal subjects

BACKGROUND

Three competing theories about the mechanism of mitral coaptation in normal subjects were evaluated by color Doppler and vector flow mapping (VFM): (1) beginning of ventricular (LV) ejection, (2) "breaking of the jet" of diastolic LV inflow, and (3) returning diastolic vortices impacting the leaflets on their LV surfaces.

METHODS AND RESULTS

We analyzed 80 color Doppler frames and 320 VFM measurements. In all 20 normal subjects, coaptation occurred before LV ejection, 78±16 ms before onset. On color Doppler frames the larger anterior, and smaller posterior vortices circle back and, in all cases, strike the ventricular surfaces of the leaflets. On the first closing-begins frame, for the first time, vortex velocity normal to the ventricular surface of the anterior leaflet (AML) is greater than that in the mitral orifice, and the angle of attack of LV vortical flow onto the AML is twice as high as the angle of flow onto the valve in orifice. Thus, at the moment coaptation begins, vortical flow strikes the mitral leaflet with higher velocity, and higher angle of attack than orifice flow, and thus with greater force. According to the "breaking of the jet" theory, one would expect to see de novo LV flow perpendicular to the leaflets beginning after transmitral flow terminates. Instead, the returning continuous LV vortical flow that impacts the valve builds continuously after the P-wave.

CONCLUSIONS

Late diastolic vortices strike the ventricular surfaces of the mitral leaflets and contribute to valve coaptation, permitted by concomitant decline in transmitral flow.

Vector flow mapping analysis of left ventricular energetic performance in healthy adult volunteers

BACKGROUND

Vector flow mapping, a novel flow visualization echocardiographic technology, is increasing in popularity. Energy loss reference values for children have been established using vector flow mapping, but those for adults have not yet been provided. We aimed to establish reference values in healthy adults for energy loss, kinetic energy in the left ventricular outflow tract, and the energetic performance index (defined as the ratio of kinetic energy to energy loss over one cardiac cycle).

METHODS

Transthoracic echocardiography was performed in fifty healthy volunteers, and the stored images were analyzed to calculate energy loss, kinetic energy, and energetic performance index and obtain ranges of reference values for these.

RESULTS

Mean energy loss over one cardiac cycle ranged from 10.1 to 59.1 mW/m (mean ± SD, 27.53 ± 13.46 mW/m), with a reference range of 10.32 ~ 58.63 mW/m. Mean systolic energy loss ranged from 8.5 to 80.1 (23.52 ± 14.53) mW/m, with a reference range of 8.86 ~ 77.30 mW/m. Mean diastolic energy loss ranged from 7.9 to 86 (30.41 ± 16.93) mW/m, with a reference range of 8.31 ~ 80.36 mW/m. Mean kinetic energy in the left ventricular outflow tract over one cardiac cycle ranged from 200 to 851.6 (449.74 ± 177.51) mW/m with a reference range of 203.16 ~ 833.15 mW/m. The energetic performance index ranged from 5.3 to 37.6 (18.48 ± 7.74), with a reference range of 5.80 ~ 36.67.

CONCLUSIONS

Energy loss, kinetic energy, and energetic performance index reference values were defined using vector flow mapping. These reference values enable the assessment of various cardiac conditions in any clinical situation.

Ultrasound Vector Flow Imaging-Part I: Sequential Systems

This paper gives a review of the most important methods for blood velocity vector flow imaging (VFI) for conventional sequential data acquisition. This includes multibeam methods, speckle tracking, transverse oscillation, color flow mapping derived VFI, directional beamforming, and variants of these. The review covers both 2-D and 3-D velocity estimation and gives a historical perspective on the development along with a summary of various vector flow visualization algorithms. The current state of the art is explained along with an overview of clinical studies conducted and methods for presenting and using VFI. A number of examples of VFI images are presented, and the current limitations and potential solutions are discussed.

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.

Intra-left ventricular flow dynamics in patients with preserved and impaired left ventricular function: Analysis with 3D cine phase contrast MRI (4D-Flow)

PURPOSE

To examine how left ventricular (LV) volume and function affect flow dynamics by analyzing 3D intra-LV vortex features using 4D-Flow.

MATERIALS AND METHODS

Twenty-one patients with preserved (LVEF > 60%) and 14 with impaired LV function (LVEF < 40%) underwent 4D-Flow (at 3T).

RESULTS

In patients with preserved LV function, the intra-LV vortices developed in both the early and late diastolic phases. The shift of inflow vectors at the basal LV toward the posterior-lateral side of the LV and the mid-ventricular turn of inflow vectors toward the LV outflow could explain clearer vortex formation in the late diastolic phase. In patients with impaired LV function, the intra-LV vortices during the diastolic phase located at the more apical LV were larger and more spherically shaped. Both the distance to the vortex core and the vortex area correlated significantly with LV end-diastolic volume (r = 0.66 and 0.73), LVEF (r = -0.74 and -0.68), LV sphericity index (r = -0.60 and -0.65), and peak filling rate (r = -0.61 and -0.64), respectively (P < 0.01). The intra-LV vortices developed during the systolic phase in 10 cases. In those, some of the particles at the apical LV rotated within the LV, whereas in patients with preserved LV function, all of the particles were directed straight to the ascending aorta with accelerated flow velocity (256.8 ± 120.2 cm/s vs. 414.3 ± 88.2 cm/s, P < 0.01).

CONCLUSION

Vortex formation during the diastolic phase may be critical for both LV filling and ejection. 4D-Flow showed the 3D alterations of intra-LV flow dynamics by LV dilatation and dysfunction in a noninvasive and comprehensive manner. J. Magn. Reson. Imaging 2016;44:1493-1503.

Intervendor Variabilities of Left and Right Ventricular Myocardial Velocities among Three Tissue Doppler Echocardiography Systems

BACKGROUND

Whether an intervendor discordance of myocardial velocities determined by tissue Doppler echocardiography (TDE) can be generalized remains unclear. We compared intervendor variabilities of left ventricular (LV) and right ventricular (RV) myocardial velocities among three TDE systems.

METHODS

Examinations with TDE were performed in 41 healthy subjects and 11 patients with cardiovascular risk factors (CVR) using α-7 (V1, Hitachi Aloka Medical), Artida (V2, Toshiba Medical Systems), and Vivid E9 (V3, GE Healthcare) on the same day. Peak systolic (s'), early diastolic (e'), and late diastolic (a') myocardial velocities at medial and lateral sites of the mitral annulus and lateral site of the tricuspid annulus were measured using both pulsed-wave TDE and color TDE. Intra-observer and inter-observer variabilities were determined in 10 subjects and test-retest variability in 14 subjects.

RESULTS

As for test-retest variability, reproducibilities of LV and RV myocardial velocities determined by pulsed-wave TDE and color TDE were relatively low but comparable between V1, V2, and V3. Myocardial velocities in healthy subjects determined by both pulsed-wave TDE and color TDE were significantly different among the three TDE systems. Myocardial velocities by pulsed-wave TDE in V3 were 2-12% lower (P < 0.05) than those by V2 and 5-14% lower (P < 0.05) than those by V1. Similar differences in myocardial velocities determined by both pulsed-wave TDE and color TDE were found in patients with CVR.

CONCLUSIONS

LV and RV myocardial velocities determined by both pulsed-wave TDE and color TDE are vendor dependent, and reproducibility of the myocardial velocities determined by both TDE systems is relatively low.

Characteristics of intra-left atrial flow dynamics and factors affecting formation of the vortex flow – analysis with phase-resolved 3-dimensional cine phase contrast magnetic resonance imaging

BACKGROUND

The intra-left atrial (LA) blood flow from pulmonary veins (PVs) to the left ventricle (LV) changes under various conditions and might affect global cardiac function. By using phase-resolved 3-dimensional cine phase contrast magnetic resonance imaging (4D-Flow), the intra-LA vortex formation was visualized and the factors affecting the intra-LA flow dynamics were examined.

METHODS AND RESULTS

Thirty-two patients with or without organic heart diseases underwent 4D-Flow and transthoracic echocardiography. The intra-LA velocity vectors from each PV were post-processed to delineate streamline and pathline images. The vector images revealed intra-LA vortex formation in 20 of 32 patients. All the vortices developed during the late systolic and early diastolic phases and were directed counter-clockwise when viewed from the subjects' cranial side. The flow vectors from the right PVs lengthened predominantly toward the mitral valves and partly toward the LA appendage, whereas those from the left PVs directed rightward along the posterior wall and joined the vortex. Patients with vortex had less organic heart diseases, smaller LV and LA volume, and greater peak flow velocity and volume mainly in the left PVs, although the flow directions from each PV or PV areas did not differ.

CONCLUSIONS

4D-Flow can clearly visualize the intra-LA vortex formation and analyze its characteristic features. The vortex formation might depend on LV and LA volume and on flow velocity and volume from PVs.

Vector flow mapping in obstructive hypertrophic cardiomyopathy to assess the relationship of early systolic left ventricular flow and the mitral valve

BACKGROUND

The hydrodynamic cause of systolic anterior motion of the mitral valve (SAM) is unresolved.

OBJECTIVES

This study hypothesized that echocardiographic vector flow mapping, a new echocardiographic technique, would provide insights into the cause of early SAM in obstructive hypertrophic cardiomyopathy (HCM).

METHODS

We analyzed the spatial relationship of left ventricular (LV) flow and the mitral valve leaflets (MVL) on 3-chamber vector flow mapping frames, and performed mitral valve measurements on 2-dimensional frames in patients with obstructive and nonobstructive HCM and in normal patients.

RESULTS

We compared 82 patients (22 obstructive HCM, 23 nonobstructive HCM, and 37 normal) by measuring 164 LV pre- and post-SAM velocity vector flow maps, 82 maximum isovolumic vortices, and 328 2-dimensional frames. We observed color flow and velocity vector flow posterior to the MVL impacting them in the early systolic frames of 95% of obstructive HCM, 22% of nonobstructive HCM, and 11% of normal patients (p < 0.001). In both pre- and post-SAM frames, we measured a high angle of attack >60° of local vector flow onto the posterior surface of the leaflets whether the flow was ejection (59%) or the early systolic isovolumic vortex (41%). Ricochet of vector flow, rebounding off the leaflet into the cul-de-sac, was noted in 82% of the obstructed HCM, 9% of nonobstructive HCM, and none (0%) of the control patients (p < 0.001). Flow velocities in the LV outflow tract on the pre-SAM frame 1 and 2 mm from the tip of the anterior leaflet were low: 39 and 43 cm/s, respectively.

CONCLUSIONS

Early systolic flow impacts the posterior surfaces of protruding MVL initiating SAM in obstructive HCM.

Intraventricular vortex properties in nonischemic dilated cardiomyopathy

Vortices may have a role in optimizing the mechanical efficiency and blood mixing of the left ventricle (LV). We aimed to characterize the size, position, circulation, and kinetic energy (KE) of LV main vortex cores in patients with nonischemic dilated cardiomyopathy (NIDCM) and analyze their physiological correlates. We used digital processing of color-Doppler images to study flow evolution in 61 patients with NIDCM and 61 age-matched control subjects. Vortex features showed a characteristic biphasic temporal course during diastole. Because late filling contributed significantly to flow entrainment, vortex KE reached its maximum at the time of the peak A wave, storing 26 ± 20% of total KE delivered by inflow (range: 1-74%). Patients with NIDCM showed larger and stronger vortices than control subjects (circulation: 0.008 ± 0.007 vs. 0.006 ± 0.005 m(2)/s, respectively, P = 0.02; KE: 7 ± 8 vs. 5 ± 5 mJ/m, P = 0.04), even when corrected for LV size. This helped confining the filling jet in the dilated ventricle. The vortex Reynolds number was also higher in the NIDCM group. By multivariate analysis, vortex KE was related to the KE generated by inflow and to chamber short-axis diameter. In 21 patients studied head to head, Doppler measurements of circulation and KE closely correlated with phase-contract magnetic resonance values (intraclass correlation coefficient = 0.82 and 0.76, respectively). Thus, the biphasic nature of filling determines normal vortex physiology. Vortex formation is exaggerated in patients with NIDCM due to chamber remodeling, and enlarged vortices are helpful for ameliorating convective pressure losses and facilitating transport. These findings can be accurately studied using ultrasound.

Current clinical application of intracardiac flow analysis using echocardiography

In evaluating the cardiac function, it is important to have a comprehensive assessment of structural factors, such as the myocardial or valvular function and intracardiac flow dynamics that pass the heart. Vortex flow that form during left ventricular filling have specific geometry and anatomical location that are critical determinants of directed blood flow during ejection. The formation of abnormal vortices relates to the abnormal cardiac function. Therefore, vortex flow may offer a novel index of cardiac dysfunction. Intracardiac flow visualization using ultrasound technique has definite advantages with a higher temporal resolution and availability in real time clinical setting. Vector flow mapping based on color-Doppler and contrast echocardiography using particle image velocimetry is currently being used for visualizing the intracardiac flow. The purpose of this review is to provide readers with an update on the current method for analyzing intracardiac flow using echocardiography and its clinical applications.

Assessment of left ventricular diastolic dysfunction based on the intraventricular velocity difference by vector flow mapping

OBJECTIVES

The diastolic intraventricular velocity difference represents diastolic function of the left ventricle (LV). Here we analyzed the LV diastolic intraventricular velocity difference in patients with impaired LV function based on the ventricular flow rate profile by vector flow mapping.

METHODS

Patients with LV diastolic dysfunction were divided into 2 groups: chronic heart failure with restricted filling (group 1; n = 27) and hypertension with abnormal relaxation (group 2; n = 34). Healthy participants were identified as controls (group 3; n = 22). Left ventricular inflow color Doppler findings were analyzed by the vector profile model with the vector flow mapping technology offline. The flow velocity rates at the base and apex of the LV were measured from vector profiles with the vector flow mapping technology. The diastolic intraventricular velocity difference was calculated from flow velocity rates.

RESULTS

The diastolic intraventricular velocity difference calculated from vector flow mapping was significantly lower in both groups with LV diastolic dysfunction than the control group (mean ± SD, 79.95 ± 9.88 cm/s in controls versus 40.35 ± 6.80 cm/s in group 1 and 48.50 ± 6.03 cm/s in group 2; P < .001 for both). The diastolic intraventricular velocity difference had a significant association with the ejection fraction (P = .0002) and deceleration time (P = .0306). The peak atrial contraction velocity was negatively related to the diastolic intraventricular velocity difference (P = .0003).

CONCLUSIONS

The diastolic intraventricular velocity difference derived from the LV velocity rate by the vector profile model on vector flow mapping can be potentially used for quantitative assessment of LV diastolic function. Vector flow mapping proved to be clinically practical for reflecting LV diastolic dysfunction in pathologic states.

Intracardiac flow visualization: current status and future directions

Non-invasive cardiovascular imaging initially focused on heart structures, allowing the visualization of their motion and inferring its functional status from it. Colour-Doppler and cardiac magnetic resonance (CMR) have allowed a visual approach to intracardiac flow behaviour, as well as measuring its velocity at single selected spots. Recently, the application of new technologies to medical use and, particularly, to cardiology has allowed, through different algorithms in CMR and applications of ultrasound-related techniques, the description and analysis of flow behaviour in all points and directions of the selected region, creating the opportunity to incorporate new data reflecting cardiac performance to cardiovascular imaging. The following review provides an overview of the currently available imaging techniques that enable flow visualization, as well as its present and future applications based on the available literature and on-going works.