A Hybrid Tissue-Level Model of the Left Ventricle: Application to the Analysis of the Regional Cardiac Function in Heart Failure

International audienceThis work contributes to the systemic interpretation of clinical data for the analysis of the regional cardiac function in the context of heart failure. A two-step patient-specific approach, combining a realistic geometry and a hybrid, tissue-level electromechanical model of the left ventricle is proposed. For the first step, a fast framework to extract a realistic geometry of the left ventricle from MSCT data is proposed. This geometry is then applied to a tissue-level model of the left ventricle, coupling a discrete electrical model, a mechanical model integrating a visco-elastic law, solved by a finite element method and a hydraulic model. A set of simulations carried out with the model are shown and preliminary results of the parameter identification approach, based on real patient data, are presented and discussed

A tissue-level model of the left ventricle for the analysis of regional myocardial function.

International audienceThis paper presents a model-based method for the analysis of regional myocardial strain, based on echocardiography and Tissue Doppler Imaging (TDI). A multi-formalism, tissue-level electromechanical model of the left ventricle is proposed. The parameters of the model are identified in order to reproduce regional strain signal morphologies obtained from a healthy subject and a patient presenting a dilated cardiomyopathy. The parameters identified for the DCM patient allow the localization of the failing myocardial segments and may be useful for a better design of cardiac resynchronization therapy on heart failure patients

QUANTIFICATION OF MYOCARDIAL MECHANICS IN LEFT VENTRICLES UNDER INOTROPIC STIMULATION AND IN HEALTHY RIGHT VENTRICLES USING 3D DENSE CMR

Statistical data from clinical studies indicate that the death rate caused by heart disease has decreased due to an increased use of evidence-based medical therapies. This includes the use of magnetic resonance imaging (MRI), which is one of the most common non-invasive approaches in evidence-based health care research. In the current work, I present 3D Lagrangian strains and torsion in the left ventricle of healthy and isoproterenol-stimulated rats, which were investigated using Displacement ENcoding with Stimulated Echoes (DENSE) cardiac magnetic resonance (CMR) imaging. With the implementation of the 12-segment model, a detailed profile of regional cardiac mechanics was reconstructed for each subject. Statistical analysis revealed that isoproterenol induced a significant change in the strains and torsion in certain regions at the mid-ventricle level. In addition, I investigated right ventricular cardiac mechanics with the methodologies developed for the left ventricle. This included a comparison of different regions within the basal and mid-ventricular regions. Despite no regional variation found in the peak circumferential strain, the peak longitudinal strain exhibited regional variation at the anterior side of the RV due to the differences in biventricular torsion, mechanism of RV free wall contraction, and fiber architecture at RV insertions. Future applications of the experimental work presented here include the construction and validation of biventricular finite element models. Specifically, the strains predicted by the models will be statistically compared with experimental strains. In addition, the results of the present study provide an essential reference of RV baseline evaluated with DENSE MRI, a highly objective technique

Combined flow-based imaging assessment of optimal cardiac resynchronization therapy pacing vector: A case report

Background: There are still many pendent issues about the effective evaluation of cardiac resynchronization therapy impact on functional mitral regurgitation. In order to reduce the intrinsic difficulties of quantification of functional mitral regurgitation itself, an automatic quantification of real-time three-dimensional full-volume color Doppler transthoracic echocardiography was proposed as a new, rapid, and accurate method for the assessment of functional mitral regurgitation severity. Recent studies suggested that images of left ventricle flow by echo-particle imaging velocimetry could be a useful marker of synchrony. Echo-particle imaging velocimetry has shown that regional anomalies of synchrony/synergy of the left ventricle are related to the alteration, reduction, or suppression of the physiological intracavitary pressure gradients. Case summary: We describe a case in which the two technologies are used in combination during acute echocardiographic optimization of left pacing vector in a 63-year-old man, Caucasian, who showed worsening heart failure symptoms a few days after an implant, and the effect of the device\u2019s optimization at 6-month follow-up. Discussion: The degree of realignment of hemodynamic forces, with quantitative analysis of the orientation of blood flow momentum (\u3c6), can represent improvement of fluid dynamics synchrony of the left ventricle, and explain, with a new deterministic parameter, the effects of cardiac resynchronization therapy on functional mitral regurgitation. Realtime three-dimensional color flow Doppler quantification is feasible and accurate for measurement of mitral inflow, left ventricular outflow stroke volumes, and functional mitral regurgitation severity. Conclusion: This clinical case offers an innovative and accurate approach for acute echocardiographic optimization of left pacing vector. It shows clinical utility of combined three-dimensional full-volume color Doppler transthoracic echocardiography/echo-particle imaging velocimetry assessment to increase response to cardiac resynchronization therapy, in terms of reduction of functional mitral regurgitation, improving fluid dynamics synchrony of the left ventricle

Analysis of myocardial motion using generalized spline models and tagged magnetic resonance images

Heart wall motion abnormalities are the very sensitive indicators of common heart diseases, such as myocardial infarction and ischemia. Regional strain analysis is especially important in diagnosing local abnormalities and mechanical changes in the myocardium. In this work, we present a complete method for the analysis of cardiac motion and the evaluation of regional strain in the left ventricular wall. The method is based on the generalized spline models and tagged magnetic resonance images (MRI) of the left ventricle. The whole method combines dynamical tracking of tag deformation, simulating cardiac movement and accurately computing the regional strain distribution. More specifically, the analysis of cardiac motion is performed in three stages. Firstly, material points within the myocardium are tracked over time using a semi-automated snake-based tag tracking algorithm developed for this purpose. This procedure is repeated in three orthogonal axes so as to generate a set of one-dimensional sample measurements of the displacement field. The 3D-displacement field is then reconstructed from this sample set by using a generalized vector spline model. The spline reconstruction of the displacement field is explicitly expressed as a linear combination of a spline kernel function associated with each sample point and a polynomial term. Finally, the strain tensor (linear or nonlinear) with three direct components and three shear components is calculated by applying a differential operator directly to the displacement function. The proposed method is computationally effective and easy to perform on tagged MR images. The preliminary study has shown potential advantages of using this method for the analysis of myocardial motion and the quantification of regional strain

An analysis of the spatial arrangement of the myocardial aggregates making up the wall of the left ventricle

Objective: We used the technique of peeling of myocardial aggregates, usually described as ‘fibres', to determine the spatial arrangement of the myocytes in the left ventricular wall of a healthy autopsied human heart. Methods: We digitised the left ventricular outer and inner boundaries, as well as the pathways in space, of almost 3000 aggregates harvested from the left ventricular myocardium. During the process of gradual peeling, we sought to identify the myocardial aggregates as uniformly as possible. Despite this, interpolation was necessary to complete the pattern so as to construct a unit vector field that represented the preferred direction of the myocardial aggregates throughout the entirety of the walls of the left ventricle of this individual human heart. Results: Apart from the overall systematic arrangement of the aggregates necessary to achieve physiologic ventricular contraction, we documented substantial local heterogeneities in the orientation of the myocardial aggregates. In particular, a significant proportion of aggregates was found to intrude obliquely with respect to the ventricular boundaries, with markedly heterogeneous distribution. Moreover, the distribution of the helical angle of the aggregates relative to the ventricular base varied notably throughout the left ventricular free walls and the septum. Within the generally quite uniform and continuous structure of the ventricular mass, we were, however, unable to identify any organised tracts or functional subunits such as a ‘helical ventricular band', nor did we find radial fibrous lamellas coursing across the ventricular wall. Conclusion: We suggest that the impact of local anatomical inhomogeneities, associated with gradients in regional contractile function on global ventricular dynamics, has been systematically underestimated in the past. Our analysis confirms furthermore the continuous nature of the myocardium associated with an overall gross organisation of the fibre direction field; however, there is no evidence of substructures compartmentalising the ventricle

Assessment of Regional Myocardial Function using Tissue Doppler Imaging before and after PTCA of left anterior descending coronary Artery

INTRODUCTION: Regional wall motion abnormalities are frequently seen in coronary artery disease and diastolic function is impaired before systolic dysfunction in these patients. Reperfusion with percutaneous coronary intervention has been shown to improve the left ventricular systolic and diastolic function. Changes in the regional ventricular function may appear before alteration of global ventricular function in coronary artery disease. The most recent approach to analysis of regional wall motion is with Doppler tissue imaging or Speckle tissue tracking. Systolic and diastolic velocities of myocardium in cardiac cycle can be recorded quantitatively by Tissue Doppler Imaging and thereby provides a newer way of assessing left ventricular function which is more sensitive than traditional methods. Tissue Doppler imaging has a high sensitivity, high feasibility, reproducibility and ease of application in acute coronary syndrome Tissue Doppler imaging is easily available in most of the centres. Tissue Doppler parameters such as Sm (peak systolic velocity), Em (early diastolic velocity) and Am (late diastolic velocity) are powerful predictors of cardiac mortality. AIM OF THE STUDY: 1. To evaluate the Regional Myocardial Function using Tissue Doppler Imaging before and after Percutaneous Transluminal Coronary Angioplasty. 2. To assess the extent to which these tissue Doppler indices change 24 hours before Percutaneous Transluminal Coronary Angioplasty, 24 hours after Percutaneous Transluminal Coronary Angioplasty and 3 months after Percutaneous Transcutaneous Coronary Angioplasty. 3. To evaluate how this helps to know the success of Percutaneous Transluminal Coronary angioplasty. MATERIALS AND METHODS: This prospective non randomized follow up study was carried out at Rajiv Gandhi Government General Hospital, Chennai. This study was done between March 2012 to January 2013. This study was approved by our institution ethical committee. SELECTION OF STUDY SUBJECTS: INCLUSION CRITERIA: 1. All patients with Stable angina and prior Myocardial Infarction with age above 30 years and both sex. 2. Patients with prior coronary angiogram showing isolated Left anterior descending coronary artery disease suitable for elective percutaneous intervention and stenting were included. EXCLUSION CRITERIA: Patients with any of the following criteria were excluded from the study 1. Patients with Non ST Elevation Myocardial Infarction, Unstable angina, Acute ST Elevation Myocardial Infraction 2. Patients with multivessel coronary artery disease, left circumflex coronary artery disease, right coronary artery disease. 3. Patients with valvular heart disease, cardiomyopathy, atrial fibrillation, prior coronary revascularization, congenital heart disease, moderate to severe left ventricular systolic dysfunction (Ejection Fraction less than 40%). CONCLUSION: From our prospective follow up study, we showed that tissue Doppler myocardial imaging indices such as Sm, Em, Am will be helping us to decide the improvement in left ventricle function following angioplasty. Our findings are similar to previous animal and human studies. In conclusion we can use tissue Doppler imaging as an easily available technique to assess the reperfusion and change in regional ventricle function and success of angioplasty

Will the real ventricular architecture please stand up?

Ventricular twisting, essential for cardiac function, is attributed to the contraction of myocardial helical fibers. The exact relationship between ventricular anatomy and function remains to be determined, but one commonly used explanatory model is the helical ventricular myocardial band (HVMB) model of Torrent-Guasp. This model has been successful in explaining many aspects of ventricular function, (Torrent-Guasp et al. Eur. J. Cardiothorac. Surg., 25, 376, 2004; Buckberg et al. Eur. J. Cardiothorac. Surg., 47, 587, 2015; Buckberg et al. Eur. J. Cardiothorac. Surg. 47, 778, 2015) but the model ignores important aspects of ventricular anatomy and should probably be replaced. The purpose of this review is to compare the HVMB model with a different model (nested layers). A complication when interpreting experimental observations that relate anatomy to function is that, in the myocardium, shortening does not always imply activation and lengthening does not always imply inactivation