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

Left Ventricular Vortex Characteristics in Fetuses With Coarctation of the Aorta by Blood Speckle-Tracking Echocardiography

OBJECTIVES

The aims of this study were to assess the vortex characteristics of left ventricle (LV) in fetuses with coarctation of the aorta (CoA) using high-frame rate ultrasound with blood speckle-tracking (BST) and explore its relationships with cardiac function and morphology parameters.

METHODS

Thirty fetuses with CoA and 30 gestational-age matched normal fetuses were included in this cross-sectional study. The area, length, width, and position of the vortex in the LV were recorded and quantitatively analyzed by BST echocardiography. The associations of vortex properties with ventricular function and morphology were also determined.

RESULTS

Based on BST imaging, the LV vortex can be observed in 93% of the fetuses. The fetuses with CoA exhibited significantly larger and wider vortex than the controls (P < .05). Linear regression analysis indicated that vortex area was positively related to sphericity index of LV as well as isovolumic relaxation time (r = .52, P = .003 and r = .42, P = .021). There was a negative correlation between vortex area and mitral valve size (r = -.443, P = .014). No significant association was found between vortex area and myocardial performance index and aortic isthmus size.

CONCLUSIONS

It is feasible to quantitatively evaluate the left ventricular vortex in fetuses by BST. The fetuses with CoA exhibited greater vortex area and width, and the altered vortex property is associated with geometry of LV. This will facilitate our comprehension of the unique flow patterns and early cardiac remodeling in fetuses with CoA.

Amount of dissipative energy loss when assessing left ventricular dysfunction in female patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is associated with an increased risk of cardiovascular disease. The purpose of the current study was to explore the amount of energy loss (EL) using vector flow mapping (VFM) in the detection of early stage left ventricular (LV) dysfunction among patients with SLE. Eighty-nine patients with SLE and fifty-six healthy controls were enrolled. SLE patients were further divided into inactive (SLEDAI ≤ 4, n = 43) and active (SLEDAI ≥ 5, n = 46) subgroups. A prosound F75 echocardiography machine was used for echocardiographic examination. Intra-cardiac flow images were analysed by a VFM workstation. Compared with the healthy group, the inactive SLE group had increased diastolic EL values (38.05 mW/m vs. 33.02 mW/m, p = 0.010). However, the systolic EL values were comparable between the inactive SLE group and the control group (26.07mW/m vs 23.15 mW/m, p = 0.105). The active SLE group exhibited significantly higher diastolic (104.13 mW/m vs 33.02 mW/m, p < 0.001) and systolic (48.83 mW/m vs 23.15 mW/m, p < 0.001) EL values than the control group. The most notable correlation was observed between the values of the diastolic EL and SLEDAI in the inactive SLE group (r = 0.633, p < 0.001) and in the active SLE group (r = 0.824, p < 0.001). LV-dissipative EL assessed by using VFM is useful and feasible for estimating lesions of LV systolic and diastolic function in active SLE patients with preserved left ventricular ejection fraction. Increased disease activity may lead to increased risk of LV dysfunction.

Intraventricular Vector Flow Imaging with Blood Speckle Tracking in Adults: Feasibility, Normal Physiology and Mechanisms in Healthy Volunteers

This study examines the feasibility of blood speckle tracking for vector flow imaging in healthy adults and describes the physiologic flow pattern and vortex formation in relation to the wall motion in the left ventricle. The study included 21 healthy volunteers and quantified and visualized flow patterns with high temporal resolution down to a depth of 10-12 cm without the use of contrast agents. Intraventricular flow seems to originate during the isovolumetric relaxation with a propagation of blood from base to apex. With the E-wave, rapid inflow and vortex formation occurred on both sides of the valve basally. During diastasis the flow gathers in a large vortex before the pattern from the E-wave repeats during the A-wave. In isovolumetric contraction, the flow again gathers in a large vortex that seems to facilitate the flow out in the aorta during systole. No signs of a persistent systolic vortex were visualized. The geometry of the left ventricle and the movement of the AV-plane is important in creating vortices that are favorable for the blood flow and facilitate outflow. The quantitative measurements are in concordance with these findings, but the clinical interpretation must be evaluated in future clinical studies.

Age-Related Changes in Left Ventricular Vortex Formation and Flow Energetics

Analysis of the cardiac vortex has been used for a deeper understanding of the pathophysiology in heart diseases. However, physiological changes of the cardiac vortex with normal aging are incompletely defined. Vector flow mapping (VFM) is a novel echocardiographic technique based on Doppler and speckle tracking for analysis of the cardiac vortex. Transthoracic echocardiography and VFM analysis were performed in 100 healthy adults (33 men; age = 18–67 years). The intracardiac flow was assessed throughout the cardiac cycle. The size (cross-sectional area) and circulation (equivalent to the integral of normal component of vorticity) of the largest vortices in systole (S-vortex), early diastole (E-vortex), and late diastole (A-vortex) were measured. Peak energy loss (EL) was calculated from information of the velocity vector of intracardiac flow in systole and diastole. With normal aging, the circulation (p = 0.049) of the E-vortex decreased, while that of the A-vortex increased (both p < 0.001). E-vortex circulation correlated directly to e’ (p = 0.003), A-vortex circulation correlated directly to A and a’ (both p < 0.001), and S-vortex circulation correlated directly to s’ (p = 0.032). Despite changes in vortex patterns, energy loss was not significantly different in older individuals. Normal aging is associated with altered intracardiac vortex patterns throughout the cardiac cycle, with the late-diastolic A-vortex becoming physiologically more dominant. Maintained energy efficiency accompanies changes in vortex patterns in aging hearts.

Vector flow mapping: A review from theory to practice

BACKGROUND

The interest in intra-cardiac blood flow analysis is rapidly growing, and it has encouraged the development of different non-invasive imaging techniques. Among these, Vector Flow Mapping (VFM), combing Color-Doppler imaging and speckle tracking data, seems to be a promising approach, feasible in adult and children population.

AIM OF THE REVIEW

The aim of this review is to give a historical perspective on the development of VFM method and a summary of the current algorithms and parameters potentially evaluable. Then, we will present the current state-of-the-art of VFM with an overview of clinical studies and applications of this technique.

Energy loss associated with in-vitro modeling of mitral annular calcification

Introduction

Study aims were to compare hemodynamics and viscous energy dissipation (VED) in 3D printed mitral valves–one replicating a normal valve and the other a valve with severe mitral annular calcification (MAC). Patients with severe MAC develop transmitral gradients, without the commissural fusion typifying rheumatic mitral stenosis (MS), and may have symptoms similar to classical MS. A proposed mechanism relates to VED due to disturbed blood flow through the diseased valve into the ventricle.

Methods

A silicone model of a normal mitral valve (MV) was created using a transesophageal echocardiography dataset. 3D printed calcium phantoms were incorporated into a second valve model to replicate severe MAC. The synthetic MVs were tested in a left heart duplicator under rest and exercise conditions. Fine particles were suspended in a water/glycerol blood analogue for particle image velocimetry calculation of VED.

Results

Catheter mean transmitral gradients were slightly higher in the MAC valve compared to the normal MV, both at rest (3.2 vs. 1.3 mm Hg) and with exercise (5.9 vs. 5.0 mm Hg); Doppler gradients were 2.7 vs. 2.1 mm Hg at rest and 9.9 vs 8.2 mm Hg with exercise. VED was similar between the two valves at rest. During exercise, VED increased to a greater extent for the MAC valve (240%) versus the normal valve (127%).

Conclusion

MAC MS is associated with slightly increased transmitral gradients but markedly increased VED during exercise. These energy losses may contribute to the exercise intolerance and exertional dyspnea present in MAC patients.

Energy loss by right ventricular pacing: Patients with versus without hypertrophic cardiomyopathy

BACKGROUND

Right ventricular (RV) pacing causes left ventricular (LV) dyssynchrony sometimes resulting in pacing-induced cardiomyopathy. However, RV pacing for hypertrophic obstructive cardiomyopathy is one of the treatment options. LV flow energy loss (EL) using vector flow mapping (VFM) is a novel hemodynamic index for assessing cardiac function. Our study aimed to elucidate the impact of RV pacing on EL in normal LV function and hypertrophic cardiomyopathy (HCM) patients.

METHODS

A total of 36 patients with dual-chamber pacemakers for sick sinus syndrome or implantable cardioverter defibrillators for fatal ventricular tachyarrhythmias were enrolled. All patients were divided into two groups: 16 patients with HCM (HCM group) and others (non-HCM group). The absolute changes in EL under AAI (without RV pacing) and DDD (with RV pacing) modes were assessed using VFM on color Doppler echocardiography.

RESULTS

In the non-HCM group, the mean systolic EL significantly increased from the AAI to DDD modes (14.0 ± 7.7 to 17.0 ± 8.6 mW/m, P = .003), whereas the mean diastolic EL did not change (19.0 ± 12.3 to 17.0 ± 14.8 mW/m, P = .231). In the HCM group, the mean systolic EL significantly decreased from the AAI to DDD modes (26.7 ± 14.2 to 21.6 ± 11.9 mW/m, P < .001), whereas the mean diastolic EL did not change (28.7 ± 16.4 to 23.9 ± 19.7 mW/m, P = .130).

CONCLUSIONS

RV pacing increased the mean systolic EL in patients without HCM. Conversely, RV pacing decreased the mean systolic EL in patients with HCM.

Characterization of left ventricular cavity flow, wall stress and energy loss by color doppler vector flow mapping in children and adolescents with cardiomyopathy

Background

Vector flow mapping is an emerging echocardiographic method allowing for investigation of intracardiac blood flow mechanics, wall shear stress (WSS), and energy loss (EL). We hypothesized that alterations in EL and WSS will differ among subjects with hypertrophic (HCM), dilated (DCM) cardiomyopathy, and normal controls.

Methods

Echocardiograms were prospectively performed with the ProSound F75CV (Hitachi HealthCare., Tokyo, Japan) on all subjects. 2D color Doppler cine loop images were obtained from apical 5 and the apical long axis views and stored digitally. Measurements were averaged over three cardiac cycles using VFM software to derive flow patterns, WSS, and EL. Standard left ventricular (LV) systolic and diastolic functional parameters were also obtained.

Results

A total of 85 subjects, 22 with HCM (age 18 ± 9 yrs.), 18 DCM (age 18 ± 9 yrs.), and 45 age and gender matched controls were included in the study. Diastolic wall shear stress was found significantly different in HCM (0.004 ± 0.185 N/m²) compared with DCM (0.397 ± 0.301 N/m², P < 0.001), and controls (0.175 ± 0.255 N/m², P = 0.027). Furthermore, indexed systolic EL was found to be significantly elevated in HCM (13.91 ± 13.17 mW/m²/m³) compared with DCM (8.17 ± 9.77 mW/m²/m³, P < 0.001), but not controls (6.45 ± 7.47 mW/m²/m³).

Conclusion

Differences in abnormal ventricular mechanics observed in HCM and DCM are reflected in both EL and WSS, and are suggestive that changes in energetic parameters may represent novel indices of ventricular dysfunction.

Assessment of left ventricular energy loss using vector flow mapping in patients with stages 1-3 chronic kidney disease

BACKGROUND

Patients with chronic kidney disease (CKD) experience abnormality of intracardiac blood flow status during early-stages of disease. Left ventricular energy loss (EL) derived from vector flow mapping (VFM) represents fluid energy lost as heat in left ventricle and had been used to detect intracardiac blood flow efficiency. We aimed to evaluate the left ventricular EL in stage 1-3 CKD patients, and explored whether hypertension, a main cardiovascular risk, deteriorate the abnormality of intracardiac blood flow status.

METHODS

Transthoracic echocardiography was performed in 41 controls and 48 patients with stages 1-3 CKD. CKD patients consisted a subgroup with no hypertension, a subgroup with well-controlled hypertension and a subgroup with poorly controlled hypertension. The EL were calculated in the left ventricle using VFM analysis from the apical 3-chamber view. Furthermore, the correlation and stepwise multiple regression analysis were used to explore the potential independent predictors of left ventricular EL.

RESULTS

Compared with controls, stage 1-3 CKD patients showed increased left ventricular EL during total diastole, late diastole, total systole, isovolumic contraction and ejection. CKD patients with poorly controlled hypertension had higher left ventricular EL compared to the other CKD subgroups. Additionally, the ratio of mitral early filling wave peak velocity and early mitral annular peak velocity on septal side, mitral early filling wave peak velocity, and left ventricular mass index were independent predictors of the diastolic EL; whereas systolic blood pressure and left ventricular mass index were independent predictors of the systolic EL.

CONCLUSIONS

Left ventricular EL was a useful echocardiographic parameter to evaluate the impaired intracardiac blood flow efficiency in patients with stages 1-3 CKD. Hypertension was a crucial contributor for intracardiac blood flow abnormality. This study might provide valuable clinical data to discern cardiac dysfunction and reduce the cardiovascular risk in early-stage CKD.

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.

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.