Assessment of methodologies to calculate intraventricular pressure differences in computational models and patients

Assessment of Early Diastolic Intraventricular Pressure Difference in Children by Blood Speckle-Tracking Echocardiography

BACKGROUND

The lack of reliable echocardiographic techniques to assess diastolic function in children is a major clinical limitation. Our aim was to develop and validate the intraventricular pressure difference (IVPD) calculation using blood speckle-tracking (BST) and investigate the method's potential role in the assessment of diastolic function in children.

METHODS

Blood speckle-tracking allows two-dimensional angle-independent blood flow velocity estimation. Blood speckle-tracking images of left ventricular (LV) inflow from the apical 4-chamber view in 138 controls, 10 patients with dilated cardiomyopathies (DCMs), and 21 patients with hypertrophic cardiomyopathies (HCMs) <18 years of age were analyzed to study LV IVPD during early diastole. Reproducibility of the IVPD analysis was assessed, IVPD estimates from BST and color M mode were compared, and the validity of the BST-based IVPD calculations was tested in a computer flow model.

RESULTS

Mean IVPD was significantly higher in controls (-2.28 ± 0.62 mm Hg) compared with in DCM (-1.21 ± 0.39 mm Hg, P < .001) and HCM (-1.57 ± 0.47 mm Hg, P < .001) patients. Feasibility was 88.3% in controls, 80% in DCM patients, and 90.4% in HCM patients. The peak relative negative pressure occurred earlier at the apex than at the base and preceded the peak E-wave LV filling velocity, indicating that it represents diastolic suction. Intraclass correlation coefficients for intra- and interobserver variability were 0.908 and 0.702, respectively. There was a nonsignificant mean difference of 0.15 mm Hg between IVPD from BST and color M mode. Estimation from two-dimensional velocities revealed a difference in peak IVPD of 0.12 mm Hg (6.6%) when simulated in a three-dimensional fluid mechanics model.

CONCLUSIONS

Intraventricular pressure difference calculation from BST is highly feasible and provides information on diastolic suction and early filling in children with heart disease. Intraventricular pressure difference was significantly reduced in children with DCM and HCM compared with controls, indicating reduced early diastolic suction in these patient groups.

Divergence-Free Constrained Phase Unwrapping and Denoising for 4D Flow MRI Using Weighted Least-Squares

A novel divergence-free constrained phase unwrapping method was proposed and evaluated for 4D flow MRI. The unwrapped phase field was obtained by integrating the phase variations estimated from the wrapped phase data using weighted least-squares. The divergence-free constraint for incompressible blood flow was incorporated to regulate and denoise the resulting phase field. The proposed method was tested on synthetic phase data of left ventricular flow and in vitro 4D flow measurement of Poiseuille flow. The method was additionally applied to in vivo 4D flow measurements in the thoracic aorta from 30 human subjects. The performance of the proposed method was compared to the state-of-the-art 4D single-step Laplacian algorithm. The synthetic phase data were completely unwrapped by the proposed method for all the cases with velocity encoding (venc) as low as 20% of the maximum velocity and signal-to-noise ratio as low as 5. The in vitro Poiseuille flow data were completely unwrapped with a 60% increase in the velocity-to-noise ratio. For the in-vivo aortic datasets with venc ratio less than 0.4, the proposed method significantly improved the success rate by as much as 40% and reduced the velocity error levels by a factor of 10 compared to the state-of-the-art method. The divergence-free constrained method exhibits reliability and robustness on phase unwrapping and shows improved accuracy of velocity and hemodynamic quantities by unwrapping the low-venc 4D flow MRI data.

Left ventricular diastolic pressure gradient and outcome in advanced chronic kidney disease patients with preserved ejection fraction

Assessment of left ventricular (LV) diastolic dysfunction is important in patients with chronic kidney disease (CKD). The early diastolic peak intraventricular pressure gradient (IVPG) has a vital role in diastolic function. Relative pressure imaging (RPI) is a new echocardiographic method to quantify IVPG. The purpose of this study was to analyze RPI-derived IVPG in advanced CKD patients with preserved LV ejection fraction. The study population consisted of 51 advanced CKD patients and 39 healthy controls. Patients were stratified by the evidence of heart failure with preserved ejection fraction (HFpEF) into HFpEF group (32 patients) and non-HFpEF group (19 patients). RPI analysis was used to determine the early diastolic LV relative pressure and pressure distribution. The total IVPG and segmental IVPGs corresponding to basal, mid, and apical part of the LV were calculated. Total IVPG, along with apical and mid IVPGs were all significantly reduced in HFpEF Group compared with non-HFpEF Group and controls (all P < 0.05). But no significant difference of total or segmental IVPGs was found between non-HFpEF Group and the controls. Additionally, apical IVPG < 0.02 mmHg/cm (Hazard ratio 9.82, 95 % confidence interval 2.01-48.01, P = 0.005) was the independent risk factor for the composite outcome (mortality and cardiovascular hospitalization) during a median follow-up of 24 months. Advanced CKD patients with HFpEF exhibited decreased apical and mid IVPG of the LV, and the severity of apical IVPG reduction correlated with poor outcome.

A Wavelet Approach to the Estimation of Left Ventricular Early Filling Wave Propagation Velocity from Color M-Mode Echocardiograms

A new approach to calculating left ventricular (LV) early filling propagation velocity (VP) from color M-mode echocardiograms using wavelet analysis is described. Current methods for measuring VP do not account for the spatiotemporal variation in VP. They are confined by empirical assumptions and user inputs that hinder the accuracy of VP, limiting its clinical utility. We evaluated three methods for measuring LV early filling: conventional VP, the strength of propagation (VS) and wavelet propagation velocity (VW) determined from the most energetically significant wave (peak VW). Group A comprised 125 patients (n = 50 normal filling, n = 25 impaired relaxation, n = 25 pseudonormal filling and n = 25 restrictive filling), and group B comprised 69 patients (n = 32 normal, n = 15 dilated and n = 22 hypertrophic). Peak VW most accurately distinguished normal from diseased patients. For group A, the area under the receiver operating characteristic curve was 0.92 for peak VW versus 0.62 for VP, 0.63 for VS and 0.58 for intraventricular pressure difference. These correspond to a 50%-70% improvement in classification ability. Similar improvements were measured in group B. Peak VW may provide a more accurate evaluation of diastolic function than standard methods and enable better diagnostic classification of patients with diastolic dysfunction.

Progression of left ventricular diastolic function in the neonate and early childhood from transmitral color M-mode filling analysis

BACKGROUND

We implemented sophisticated color M-mode analysis to assess age-dependent progression of left ventricular (LV) diastolic function.

METHODS

Normal infants were prospectively enrolled for serial echocardiograms at 1 week, 1 month, 6 months, 1 year, and 2 years. From color M-mode scans, propagation velocity (V_P), strength of filling (V_S), and intraventricular pressure difference (IVPD) in 3 segments along apex-to-mitral valve scan line were measured.

RESULTS

Age-wise comparisons of diastolic filling from 121 echocardiograms in 31 infants showed V_P (cm/s), V_S (cm²/s), and E-wave IVPD (mmHg) at 1 week to be 66.2 ± 11.9, 75.3 ± 19.9, and 1.5 ± 0.4, respectively, while V_P, V_S, and E-wave IVPD at 1 month were 80.3 ± 14.4, 101.2 ± 28.3, and 2.42 ± 1.1, respectively. There were significant differences in V_P and segmental IVPD between first week and first month (p < 0.005) and IVPD between the age groups (p < 0.001).

CONCLUSIONS

Comprehensive analysis of transmitral color M-mode data is feasible in infants, enabling calculation of pressure drop between the LV base and apex and strength of propagation from two distinct slopes. Profound changes very early followed by relatively constant filling mechanics in later infancy indicate significant LV maturation occurring during the first month of life.

IMPACT

We implemented sophisticated analytic methods for color M-mode echocardiography in infants to assess age- and dimension-dependent changes in left ventricular diastolic function. Comprehensive characterization of transmitral color M-mode flow was feasible, enabling calculation of pressure drop between left ventricular base and apex and strength of propagation. Left ventricular diastolic filling function has predictable maturational progression, with significant differences in the intraventricular pressure between infants from birth to 2 years. This study forms the basis for future studies to examine alteration of early diastolic filling in congenital heart disease.

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 (iVFM_1D) and reformulated iVFM (iVFM_2D). 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 iVFM_1D and 4.06-400.21% for iVFM_2D. 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.

Non-invasive intraventricular pressure differences estimated with cardiac MRI in subjects without heart failure and with heart failure with reduced and preserved ejection fraction

Objective

Non-invasive assessment of left ventricular (LV) diastolic and systolic function is important to better understand physiological abnormalities in heart failure (HF). The spatiotemporal pattern of LV blood flow velocities during systole and diastole can be used to estimate intraventricular pressure differences (IVPDs). We aimed to demonstrate the feasibility of an MRI-based method to calculate systolic and diastolic IVPDs in subjects without heart failure (No-HF), and with HF with reduced ejection fraction (HFrEF) and HF with preserved ejection fraction (HFpEF).

Methods

We studied 159 subjects without HF, 47 subjects with HFrEF and 32 subjects with HFpEF. Diastolic and systolic intraventricular flow was measured using two-dimensional in-plane phase-contrast MRI. The Euler equation was solved to compute IVPDs in diastole (mitral base to apex) and systole (apex to LV outflow tract).

Results

Subjects with HFpEF demonstrated a higher magnitude of the early diastolic reversal of IVPDs (−1.30 mm Hg) compared with the No-HF group (−0.78 mm Hg) and the HFrEF group (−0.75 mm Hg; analysis of variance p=0.01). These differences persisted after adjustment for clinical variables, Doppler-echocardiographic parameters of diastolic filling and measures of LV structure (No-HF=−0.72; HFrEF=−0.87; HFpEF=−1.52 mm Hg; p=0.006). No significant differences in systolic IVPDs were found in adjusted models. IVPD parameters demonstrated only weak correlations with standard Doppler-echocardiographic parameters.

Conclusions

Our findings suggest distinct patterns of systolic and diastolic IVPDs in HFpEF and HFrEF, implying differences in the nature of diastolic dysfunction between the HF subtypes.