The Pixel Variation Score: An Echocardiographic Index to Assess Temporal Variation of Mitral Regurgitant Flow.

BACKGROUND: In mitral regurgitation (MR), temporal variation of MR flow has been considered an important reason for inaccurate MR grading. Current echocardiographic methods for assessing temporal MR flow variation are complex, and their clinical relevance has not been investigated. In this study, we investigated whether assessing MR flow variation using a dimensionless index with echocardiography is feasible, clinically meaningful, and related to patient outcomes. METHODS: Consecutive patients with mitral valve prolapse (MVP, n = 244) and functional MR (FMR, n = 396) underwent comprehensive echocardiography. Mitral regurgitation severity was assessed using an integrated approach advocated by current guidelines. The MR continuous-wave Doppler envelope was divided into 3 segments of equal duration. Each segment's pixel intensity was assessed to calculate the pixel variation score (PVS). RESULTS: The PVS was lower in FMR patients than in MVP patients. Lower PVS was associated with worse MR, larger left atrial and left ventricular dimensions, lower ejection fraction, and higher pulmonary artery pressures. In MVP, PVS was significantly associated with postoperative left ventricular reverse remodeling and was able to reclassify most patients in whom single-frame measures overestimated MR severity. Finally, PVS had incremental prognostic value on top of clinical and echocardiographic predictors of outcome. CONCLUSIONS: Temporal variation in MR flow can reliably be assessed with echocardiography through analysis of the continuous-wave Doppler signal. A high PVS value may alert the echocardiographer to defer from single-frame MR grading and also suggests that the MR is probably not severe.

4D Flow Patterns and Relative Pressure Distribution in a Left Ventricle Model by Shake-the-Box and Proper Orthogonal Decomposition Analysis.

PURPOSE: Intraventricular blood flow dynamics are associated with cardiac function. Accurate, noninvasive, and easy assessments of hemodynamic quantities (such as velocity, vortex, and pressure) could be an important addition to the clinical diagnosis and treatment of heart diseases. However, the complex time-varying flow brings many challenges to the existing noninvasive image-based hemodynamic assessments. The development of reliable techniques and analysis tools is essential for the application of hemodynamic biomarkers in clinical practice. METHODS: In this study, a time-resolved particle tracking method, Shake-the-Box, was applied to reconstruct the flow in a realistic left ventricle (LV) silicone model with biological valves. Based on the obtained velocity, 4D pressure field was calculated using a Poisson equation-based pressure solver. Furthermore, flow analysis by proper orthogonal decomposition (POD) of the 4D velocity field has been performed. RESULTS: As a result of the Shake-the-Box algorithm, we have extracted: (i) particle positions, (ii) particle tracks, and finally, (iii) 4D velocity fields. From the latter, the temporal evolution of the 3D pressure field during the full cardiac cycle was obtained. The obtained maximal pressure difference extracted along the base-to-apex was about 2.7 mmHg, which is in good agreement with those reported in vivo. The POD analysis results showed a clear picture of different scale of vortices in the pulsatile LV flow, together with their time-varying information and corresponding kinetic energy content. To reconstruct 95% of the kinetic energy of the LV flow, only the first six POD modes would be required, leading to significant data reduction. CONCLUSIONS: This work demonstrated Shake-the-Box is a promising technique to accurately reconstruct the left ventricle flow field in vitro. The good spatial and temporal resolutions of the velocity measurements enabled a 4D reconstruction of the pressure field in the left ventricle. The application of POD analysis showed its potential in reducing the complexity of the high-resolution left ventricle flow measurements. For future work, image analysis, multi-modality flow assessments, and the development of new flow-derived biomarkers can benefit from fast and data-reducing POD analysis.

Echo planar imaging-induced errors in intracardiac 4D flow MRI quantification.

PURPOSE: To assess errors associated with EPI-accelerated intracardiac 4D flow MRI (4DEPI) with EPI factor 5, compared with non-EPI gradient echo (4DGRE). METHODS: Three 3T MRI experiments were performed comparing 4DEPI to 4DGRE: steady flow through straight tubes, pulsatile flow in a left-ventricle phantom, and intracardiac flow in 10 healthy volunteers. For each experiment, 4DEPI was repeated with readout and blip phase-encoding gradient in different orientations, parallel or perpendicular to the flow direction. In vitro flow rates were compared with timed volumetric collection. In the left-ventricle phantom and in vivo, voxel-based speed and spatio-temporal median speed were compared between sequences, as well as mitral and aortic transvalvular net forward volume. RESULTS: In steady-flow phantoms, the flow rate error was largest (12%) for high velocity (>2 m/s) with 4DEPI readout gradient parallel to the flow. Voxel-based speed and median speed in the left-ventricle phantom were ≤5.5% different between sequences. In vivo, mean net forward volume inconsistency was largest (6.4 ± 8.5%) for 4DEPI with nonblip phase-encoding gradient parallel to the main flow. The difference in median speed for 4DEPI versus 4DGRE was largest (9%) when the 4DEPI readout gradient was parallel to the flow. CONCLUSIONS: Velocity and flow rate are inaccurate for 4DEPI with EPI factor 5 when flow is parallel to the readout or blip phase-encoding gradient. However, mean differences in flow rate, voxel-based speed, and spatio-temporal median speed were acceptable (≤10%) when comparing 4DEPI to 4DGRE for intracardiac flow in healthy volunteers.

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.

Tomographic PIV in a model of the left ventricle: 3D flow past biological and mechanical heart valves.

Left ventricular flow is intrinsically complex, three-dimensional and unsteady. Its features are susceptible to cardiovascular pathology and treatment, in particular to surgical interventions involving the valves (mitral valve replacement). To improve our understanding of intraventricular fluid mechanics and the impact of various types of prosthetic valves thereon, we have developed a custom-designed versatile left ventricular phantom with anatomically realistic moving left ventricular membrane. A biological, a tilting disc and a bileaflet valve (in two different orientations) were mounted in the mitral position and tested under the same settings. To investigate 3D flow within the phantom, a four-view tomographic particle image velocimetry setup has been implemented. The results compare side-by-side the evolution of the 3D flow topology, vortical structures and kinetic energy in the left ventricle domain during the cardiac cycle. Except for the tilting disc valve, all tested prosthetic valves induced a crossed flow path, where the outflow crosses the inflow path, passing under the mitral valve. The biological valve shows a strong jet with a peak velocity about twice as high compared to all mechanical heart valves, which makes it easier to penetrate deeply into the cavity. Accordingly, the peak kinetic energy in the left ventricle in case of the biological valve is about four times higher than the mechanical heart valves. We conclude that the tomographic particle imaging velocimetry setup provides a useful ground truth measurement of flow features and allows a comparison of the effects of different valve types on left ventricular flow patterns.

The effect of trochlear dysplasia on patellofemoral biomechanics: a cadaveric study with simulated trochlear deformities.

BACKGROUND: Trochlear dysplasia appears in different geometrical variations. The Dejour classification is widely used to grade the severity of trochlear dysplasia and to decide on treatment. PURPOSE: To investigate the effect of trochlear dysplasia on patellofemoral biomechanics and to determine if different types of trochlear dysplasia have different effects on patellofemoral biomechanics. STUDY DESIGN: Controlled laboratory study. METHODS: Trochlear dysplasia was simulated in 4 cadaveric knees by replacing the native cadaveric trochlea with different types of custom-made trochlear implants, manufactured with 3-dimensional printing. For each knee, 5 trochlear implants were designed: 1 implant simulated the native trochlea (control condition), and 4 implants simulated 4 types of trochlear dysplasia. The knees were subjected to 3 biomechanical tests: a squat simulation, an open chain extension simulation, and a patellar stability test. The patellofemoral kinematics, contact area, contact pressure, and stability were compared between the control condition (replica implants) and the trochlear dysplastic condition and among the subgroups of trochlear dysplasia. RESULTS: The patellofemoral joint in the trochlear dysplastic group showed increased internal rotation, lateral tilt, and lateral translation; increased contact pressures; decreased contact areas; and decreased stability when compared with the control group. Within the trochlear dysplastic group, the implants graded as Dejour type D showed the largest deviations for the kinematical parameters, and the implants graded as Dejour types B and D showed the largest deviations for the patellofemoral contact areas and pressures. CONCLUSION: Patellofemoral kinematics, contact area, contact pressure, and stability are significantly affected by trochlear dysplasia. Of all types of trochlear dysplasia, the models characterized with a pronounced trochlear bump showed the largest deviations in patellofemoral biomechanics. CLINICAL RELEVANCE: Investigating the relationship between the shape of the trochlea and patellofemoral biomechanics can provide insight into the short-term effects (maltracking, increased pressures, and instability) and long-term effects (osteoarthritis) of different types of trochlear dysplasia. Furthermore, this investigation provides an empirical explanation for better treatment outcomes of trochleoplasty for Dejour types B and D dysplasia.

The use of rapid prototyped implants to simulate knee joint abnormalities for in vitro testing: a validation study with replica implants of the native trochlea.

To investigate the biomechanical effect of skeletal knee joint abnormalities, the authors propose to implant pathologically shaped rapid prototyped implants in cadaver knee specimens. This new method was validated by replacing the native trochlea by a replica implant on four cadaver knees with the aid of cadaver-specific guiding instruments. The accuracy of the guiding instruments was assessed by measuring the rotational errors of the cutting planes (on average 3.01° in extension and 1.18° in external/internal rotation). During a squat and open chain simulation, the patella showed small differences in its articulation with the native trochlea and the replica trochlea, which could partially be explained by the rotational errors of the implants. This study concludes that this method is valid to investigate the effect of knee joint abnormalities with a replica implant as a control condition to account for the influence of material properties and rotational errors of the implant.

Effective arterial elastance is insensitive to pulsatile arterial load.

Effective arterial elastance (E(A)) was proposed as a lumped parameter that incorporates pulsatile and resistive afterload and is increasingly being used in clinical studies. Theoretical modeling studies suggest that E(A) is minimally affected by pulsatile load, but little human data are available. We assessed the relationship between E(A) and arterial load determined noninvasively from central pressure-flow analyses among middle-aged adults in the general population (n=2367) and a diverse clinical population of older adults (n=193). In a separate study, we investigated the sensitivity of E(A) to changes in pulsatile load induced by isometric exercise (n=73). The combination of systemic vascular resistance and heart rate predicted 95.6% and 97.8% of the variability in E(A) among middle-aged and older adults, respectively. E(A) demonstrated a quasi-perfect linear relationship with the ratio of systemic vascular resistance/heart period (middle-aged adults, R=0.972; older adults, R=0.99; P<0.0001). Aortic characteristic impedance, total arterial compliance, reflection magnitude, and timing accounted together for <1% of the variability in E(A) in either middle-aged or older adults. Despite pronounced changes in pulsatile load induced by isometric exercise, changes in E(A) were not independently associated with changes pulsatile load but were rather a nearly perfect linear function of the ratio of systemic vascular resistance/heart period (R=0.99; P<0.0001). Our findings demonstrate that E(A) is simply a function of systemic vascular resistance and heart rate and is negligibly influenced by (and insensitive to) changes in pulsatile afterload in humans. Its current interpretation as a lumped parameter of pulsatile and resistive afterload should thus be reassessed.

Semi-automated landmark-based 3D analysis reveals new morphometric characteristics in the trochlear dysplastic femur.

PURPOSE: The authors hypothesise that the trochlear dysplastic distal femur is not only characterised by morphological changes to the trochlea. The purpose of this study is to describe the morphological characteristics of the trochlear dysplastic femur in and outside the trochlear region with a landmark-based 3D analysis. METHODS: Arthro-CT scans of 20 trochlear dysplastic and 20 normal knees were used to generate 3D models including the cartilage. To rule out size differences, a set of landmarks were defined on the distal femur to isotropically scale the 3D models to a standard size. A predefined series of landmark-based reference planes were applied on the distal femur. With these landmarks and reference planes, a series of previously described characteristics associated with trochlear dysplasia as well as a series of morphometric characteristics were measured. RESULTS: For the previously described characteristics, the analysis replicated highly significant differences between trochlear dysplastic and normal knees. Furthermore, the analysis showed that, when knee size is taken into account, the cut-off values of the trochlear bump and depth would be 1 mm larger in the largest knees compared to the smallest knees. For the morphometric characteristics, the analysis revealed that the trochlear dysplastic femur is also characterised by a 10% smaller intercondylar notch, 6-8% larger posterior condyles (lateral-medial) in the anteroposterior direction and a 6% larger medial condyle in the proximodistal direction compared to a normal femur. CONCLUSIONS: This study shows that knee size is important in the application of absolute metric cut-off values and that the posterior femur also shows a significantly different morphology.

Pilot validation study on a quasi-static weight-bearing knee rig.

This article presents a pilot study on a quasi-static knee rig designed to investigate the influence of pathologies and surgical interventions on the patellofemoral kinetics of cadaveric knees. The knee rig allows cadaveric knees to flex and extend under a simulated body weight by transmitting a force to the quadriceps tendon. During the squat simulation, the ground reaction force stays within physiological values. Before using this device to answer clinical questions, two knee specimens were tested to assess the repeatability of the rig. Four repeated flexion-extension cycles were performed under a simulated body weight of 700 N, with an isolated force on the quadriceps tendon up to 2700 N and with a ground reaction force close to 350 N. The resulting patellofemoral contact area shifted from distal to proximal during knee flexion. From 20 degrees to 60 degrees of knee flexion, the mean contact area and pressure increased from 80.2 +/- 3.3 to 349.5 +/- 10.1 mm2 and from 0.9 +/- 0.2 to 5.9 +/- 0.7 MPa, respectively. The transmitted force on the quadriceps tendon, the ground reaction force and the patellofemoral contact area and pressure were continuously measured and showed a relative variability of 1.6%, 2.4%, 2.8% and 3.2%, respectively. The presented knee rig shows a good repeatability that allows us to use this knee rig to quantify the influence of anatomical changes on the patellofemoral contact area and pressures during a squat simulation.

Early and late systolic wall stress differentially relate to myocardial contraction and relaxation in middle-aged adults: the Asklepios study.

Experimental studies implicate late systolic load as a determinant of impaired left-ventricular relaxation. We aimed to assess the relationship between the myocardial loading sequence and left-ventricular contraction and relaxation. Time-resolved central pressure and time-resolved left-ventricular geometry were measured with carotid tonometry and speckle-tracking echocardiography, respectively, for computation of time-resolved ejection-phase myocardial wall stress (EP-MWS) among 1214 middle-aged adults without manifest cardiovascular disease from the general population. Early diastolic annular velocity and systolic annular velocities were measured with tissue Doppler imaging, and segment-averaged longitudinal strain was measured with speckle-tracking echocardiography. After adjustment for age, sex, and potential confounders, late EP-MWS was negatively associated with early diastolic mitral annular velocity (standardized ß=-0.25; P<0.0001) and mitral inflow propagation velocity (standardized ß=-0.13; P=0.02). In contrast, early EP-MWS was positively associated with early diastolic mitral annular velocity (standardized ß=0.18; P<0.0001) and mitral inflow propagation velocity (standardized ß=0.22; P<0.0001). A higher late EP-MWS predicted a lower systolic mitral annular velocity (standardized ß=-0.31; P<0.0001) and lesser myocardial longitudinal strain (standardized ß=0.32; P<0.0001), whereas a higher early EP-MWS was associated with a higher systolic mitral annular velocity (standardized ß=0.16; P=0.002) and greater longitudinal strain (standardized ß=-0.24; P=0.002). The loading sequence remained independently associated with early diastolic mitral annular velocity after adjustment for systolic mitral annular velocity or systolic longitudinal strain. In the context of available experimental data, our findings support the role of the myocardial loading sequence as a determinant of left-ventricular systolic and diastolic function. A loading sequence characterized by prominent late systolic wall stress was associated with lower longitudinal systolic function and diastolic relaxation.

Assessment of variables affecting late left ventricular flow propagation velocity.

UNLABELLED: Early colour M-mode flow propagation velocity (Vpe) in the left ventricle is a well-known non-invasive index for assessing left ventricular relaxation. However, the utility and determinants of late colour M-mode flow propagation (Vpa) have received little attention to date. Vpa as a representation of the left ventricular vortex travelling velocity during late filling could have a distinct role in differentiating potential subgroups in diastolic failure. The aim of the present study was to establish the normal values of late flow propagation in a healthy population of various ages (18-79 years), and to examine the general and echocardiographic variables that affect Vpa. METHODS: We studied 75 apparently healthy subjects (age range, 18-79 years; 38 women, 37 men) as part of an outpatient clinic check-up screening. General parameters were recorded, including age, gender, height, weight, blood pressure, and heart rate. In addition, conventional grey-scale M-mode, 2D, as well as colour M-mode, 2D, and pulsed wave (tissue) Doppler echocardiographic parameters were obtained in a single centre and using a single operator setting. Backward linear regression analysis (dependent variable: Vpa) was performed to find the optimal model, taking into account multicollinearity and maximum coefficient of determination (R2). Due to the heteroscedasticity of the collected data, a logarithmic transformation was used. In addition, separate linear backward regression analysis was performed for the male and female subgroups. RESULTS: Vpa values were 26-179 cm/s. The optimal regression model after elimination included the following variables: age (beta = 0.684, P < 0.001), height (beta = 0.521, P < 0.001), gender (beta = 0.343, P < 0.05), left ventricular Vpe (beta = 0.299, P < 0.01), left ventricular posterior systolic (M-mode) wall thickness (beta = 0.288, P < 0.01), interventricular septum thickness diastole (beta = 0.346, P < 0.005), transmitral Doppler E-wave deceleration time apical 4-chamber (beta = -0.297, P < 0.05), and tissue Doppler peak E-wave mitral annulus (beta = 0.459, P < 0.005). The total coefficient of determination (R2) for this model was 0.540 (P < 0.001); 0.673 (P < 0.001) for men and 0.645 (P < 0.001) for women. CONCLUSION: Vpa, representing left ventricular vortex travelling velocity during late filling, shows a large range of values in normal healthy subjects. It is mainly depending on age, gender and left ventricular mass. Moreover, substantially different determinants are found between men and women. Further study is required to explore these findings.

A fast strong coupling algorithm for the partitioned fluid-structure interaction simulation of BMHVs.

The numerical simulation of Bileaflet Mechanical Heart Valves (BMHVs) has gained strong interest in the last years, as a design and optimisation tool. In this paper, a strong coupling algorithm for the partitioned fluid-structure interaction simulation of a BMHV is presented. The convergence of the coupling iterations between the flow solver and the leaflet motion solver is accelerated by using the Jacobian with the derivatives of the pressure and viscous moments acting on the leaflets with respect to the leaflet accelerations. This Jacobian is numerically calculated from the coupling iterations. An error analysis is done to derive a criterion for the selection of useable coupling iterations. The algorithm is successfully tested for two 3D cases of a BMHV and a comparison is made with existing coupling schemes. It is observed that the developed coupling scheme outperforms these existing schemes in needed coupling iterations per time step and CPU time.

The upstream boundary condition influences the leaflet opening dynamics in the numerical FSI simulation of an aortic BMHV.

In this paper, the influence of the upstream boundary condition in the numerical simulation of an aortic bileaflet mechanical heart valve (BMHV) is studied. Three three-dimensional cases with different upstream boundary conditions are compared. The first case consists of a rigid straight tube with a velocity profile at its inlet. In the second case, the upstream geometry is a contracting left ventricle (LV), positioned symmetrically with respect to the valve. In the last case, the LV is positioned asymmetrical with respect to the valve. The cases are used to simulate the same three-dimensional BMHV. The change in time of the LV volume is calculated such that the flow rate through the valve is identical in each case. The opening dynamics of the BMHV are modelled using fluid-structure interaction. The simulations show that differences occur in the leaflet movement of the three cases. In particular, with the asymmetric LV, one of the leaflets impacts the blocking mechanism at its open position with a 34% higher velocity than when using the velocity profile, and with an 88% higher velocity than in the symmetric LV case. Therefore, when simulating such an impact, the upstream boundary condition needs to be chosen carefully.

Histogram analysis: a novel method to detect and differentiate fractionated electrograms during atrial fibrillation.

INTRODUCTION: Complex fractionated atrial electrograms (CFAEs) might identify the critical substrate maintaining AF. We developed a method based upon histogram analysis of interpeak intervals (IPIs) to automatically quantify fractionation and differentiate between subtypes of CFAEs. METHODS: Two experts classified 1,681 fibrillatory electrograms recorded in 13 patients with persistent AF into 3 categories (gold standard): normal electrograms, discontinuous CFAEs, or continuous CFAEs. Histogram analysis of IPI was performed to calculate the P5, P50, P95, and the mean of IPIs, in addition to the total number of IPI (N(Total)), and the number of IPI within predetermined ranges: 10-60 (N(Short)), 60-120 (N(Intermediate)), and >120 ms (N(Long)). RESULTS: P50 and N(Long) were higher in the normal electrograms compared to the other 2 categories (P < 0.001). N(Intermediate) was higher in the discontinuous CFAE category compared to the other 2 categories. P95, mean IPI, N(Total), and N(Short) were all significantly different among the 3 categories (P < 0.001) and correlated with the degree of fractionation (r =-0.52, -0.55, 0.68, and 0.67, respectively). Receiver operating characteristic (ROC) curves showed good diagnostic accuracy (area under curve, AUC > 0.8) of P50 and N(Long) to detect normal electrograms. An algorithm using N(Intermediate) showed good diagnostic accuracy (AUC > 0.7) to detect discontinuous CFAEs, whereas P95, mean, N(Total), and N(Short) all revealed high diagnostic accuracy (AUC > 0.85) to detect continuous CFAEs. This was confirmed in a prospective data set. CONCLUSIONS: Histogram analysis of IPI can differentiate between normal electrograms, discontinuous and continuous fractionated electrograms. This method might be used to standardize and optimize ablation strategies in AF.

Anatomical and functional changes in the upper airways of sleep apnea patients due to mandibular repositioning: a large scale study.

The obstructive sleep apnea-hypopnea syndrome (OSAHS) is a sleep related breathing disorder. A popular treatment is the use of a mandibular repositioning appliance (MRA) which advances the mandibula during the sleep and decreases the collapsibility of the upper airway. The success rate of such a device is, however, limited and very variable within a population of patients. Previous studies using computational fluid dynamics have shown that there is a decrease in upper airway resistance in patients who improve clinically due to an MRA. In this article, correlations between patient-specific anatomical and functional parameters are studied to examine how MRA induced biomechanical changes will have an impact on the upper airway resistance. Low-dose computed tomography (CT) scans are made from 143 patients suffering from OSAHS. A baseline scan and a scan after mandibular repositioning (MR) are performed in order to study variations in parameters. It is found that MR using a simulation bite is able to induce resistance changes by changing the pharyngeal lumen. The change in minimal cross-sectional area is the best parameter to predict the change in upper airway resistance. Looking at baseline values, the ideal patients for MR induced resistance decrease seem to be women with short airways, high initial resistance and no baseline occlusion.

Left ventricular mass: allometric scaling, normative values, effect of obesity, and prognostic performance.

The need for left ventricular mass (LVM) normalization to body size is well recognized. Currently used allometric exponents to normalize LVM may not account for the confounding effect of sex. Because sex is a strong determinant of body size and LVM, we hypothesized that these are subject to potential bias. We analyzed data from 7528 subjects enrolled in the Asklepios Study (n=2524) and the Multiethnic Study of Atherosclerosis (limited access data set; n=5,004) to assess metric relationships between LVM and body size, generate normative data for indexed LVM, and compare the ability of normalization methods to predict cardiovascular events. The allometric exponent that adequately described the LVM-body height relationship was 1.7 in both studies and significantly different from both the unity and 2.7, whereas the LVM-body surface area relationship was approximately linear. LVM/height(2.7) consistently demonstrated important residual relationships with body height and systematically misclassified subjects regarding the presence of LVH. LVH defined by LVM/height(1.7) was more sensitive than LVM/body surface area to identify obesity-related LVH and was most consistently associated with cardiovascular events and all-cause death. In contrast to current assumptions, LVM/height(2.7) is not an adequate method to normalize LVM for body size. We provide more appropriate normalization methods, normative data by 2D echocardiography and gradient-echo cardiac MRI, and cutoffs for defining LVH, along with prognostic validation data.

Design of an artificial left ventricular muscle: an innovative way to actuate blood pumps?

Blood pumps assist or take over the pump function of a failing heart. They are essentially activated by a pusher plate, a pneumatic compression of collapsible sacs, or they are driven by centrifugal pumps. Blood pumps relying upon one of these actuator mechanisms do not account for realistic wall deformation. In this study, we propose an innovative design of a blood pump actuator device which should be able to mimic fairly well global left ventricular (LV) wall deformation patterns in terms of circumferential and longitudinal contraction, as well as torsion. In order to reproduce these basic wall deformation patterns in our actuator device, we designed a novel kind of artificial LV "muscle" composed of multiple actively contracting cells. Its contraction is based on a mechanism by which pressurized air, inside such a cell, causes contraction in one direction and expansion perpendicular to this direction. The organization and geometry of the contractile cells within one artificial LV muscle, the applied pressure in the cells, and the governing LV loading conditions (preload and afterload) together determine the global deformation of the LV wall. Starting from a simple plastic bag, an experimental model based on the above mentioned principle was built and connected to a lumped hydraulic model of the vascular system (including compliance and resistance). The wall deformation pattern of this device was validated visually and its pump performance was studied in terms of LV volume and pressure and heart rate. Our experimental results revealed (i) a global LV motion resembling a real LV, and (ii) a close correlation between our model and a real LV in terms of end-systolic volume and pressure, end-diastolic volume and pressure, stroke volume, ejection fraction and pressure-volume relationship. Our proposed model appears promising and it can be considered as a step forward when compared to currently applied actuator mechanisms, as it will likely result in more physiological intracavity blood flow patterns.

Blood pressure waveform analysis by means of wavelet transform.

The assessment of cardiovascular function by means of arterial pulse wave analysis (PWA) is well established in clinical practice. PWA is applied to study risk stratification in hypertension, with emphasis on the measurement of the augmentation index as a measure of aortic pressure wave reflections. Despite the fact that the prognostic power of PWA, in its current form, still remains to be demonstrated in the general population, there is general agreement that analysis and interpretation of the waveform might provide a deeper insight in cardiovascular pathophysiology. We propose here the use of wavelet analysis (WA) as a tool to quantify arterial pressure waveform features, with a twofold aim. First, we discuss a specific use of wavelet transform in the study of pressure waveform morphology, and its potential role in ascertaining the dynamics of temporal properties of arterial pressure waveforms. Second, we apply WA to evaluate a database of carotid artery pressure waveforms of healthy middle-aged women and men. Wavelet analysis has the potential to extract specific features (wavelet details), related to wave reflection and aortic valve closure, from a measured waveform. Analysis showed that the fifth detail, one of the waveform features extracted applying the wavelet decomposition, appeared to be the most appropriate for the analysis of carotid artery pressure waveforms. What remains to be assessed is how the information embedded in this detail can be further processed and transformed into quantitative data, and how it can be rendered useful for automated waveform classification and arterial function parameters with potential clinical applications.

Flow visualization through two types of aortic prosthetic heart valves using stereoscopic high-speed particle image velocimetry.

The number of candidates waiting for a heart valve replacement rises yearly. Even though there is a trend toward implantation of biological valves or reconstruction, the prosthetic heart valves (PHVs) are still commonly used for implantation or as a part of cardiac assist devices in many countries worldwide. However, the hemodynamic consequences of these valves are still not completely understood. Unfortunately, these devices currently do not perform sufficiently on a long-term basis and may lead to several complications, many of them are related to fluid mechanical aspects. A novel method, stereoscopic high-speed particle image velocimetry, was applied to quantify all three velocity components behind a PHV in detailed time domain. In this study, we compared clinically used bileaflet aortic prosthetic (ATS) valve and monoleaflet prototype of tilting disk PHV. The absolute velocities calculated out of two and three velocity components were compared to each other to estimate the overall difference in the desired region of interest. The most significant discrepancies between the two- and three-component absolute velocities were found at the regions of Valsalva sinuses and in a major jet stream of monoleaflet PHV.