Three-dimensional mapping of mechanical activation patterns, contractile dyssynchrony and dyscoordination by two-dimensional strain echocardiography: Rationale and design of a novel software toolbox

<p>Abstract</p> <p>Background</p> <p>Dyssynchrony of myocardial deformation is usually described in terms of variability only (e.g. standard deviations SD's). A description in terms of the spatio-temporal distribution pattern (vector-analysis) of dyssynchrony or by indices estimating its impact by expressing dyscoordination of shortening in relation to the global ventricular shortening may be preferential. Strain echocardiography by speckle tracking is a new non-invasive, albeit 2-D imaging modality to study myocardial deformation.</p> <p>Methods</p> <p>A post-processing toolbox was designed to incorporate local, speckle tracking-derived deformation data into a 36 segment 3-D model of the left ventricle. Global left ventricular shortening, standard deviations and vectors of timing of shortening were calculated. The impact of dyssynchrony was estimated by comparing the end-systolic values with either early peak values only (early shortening reserve ESR) or with all peak values (virtual shortening reserve VSR), and by the internal strain fraction (ISF) expressing dyscoordination as the fraction of deformation lost internally due to simultaneous shortening and stretching. These dyssynchrony parameters were compared in 8 volunteers (NL), 8 patients with Wolff-Parkinson-White syndrome (WPW), and 7 patients before (LBBB) and after cardiac resynchronization therapy (CRT).</p> <p>Results</p> <p>Dyssynchrony indices merely based on variability failed to detect differences between WPW and NL and failed to demonstrate the effect of CRT. Only the 3-D vector of onset of shortening could distinguish WPW from NL, while at peak shortening and by VSR, ESR and ISF no differences were found. All tested dyssynchrony parameters yielded higher values in LBBB compared to both NL and WPW. CRT reduced the spatial divergence of shortening (both vector magnitude and direction), and improved global ventricular shortening along with reductions in ESR and dyscoordination of shortening expressed by ISF.</p> <p>Conclusion</p> <p>Incorporation of local 2-D echocardiographic deformation data into a 3-D model by dedicated software allows a comprehensive analysis of spatio-temporal distribution patterns of myocardial dyssynchrony, of the global left ventricular deformation and of newer indices that may better reflect myocardial dyscoordination and/or impaired ventricular contractile efficiency. The potential value of such an analysis is highlighted in two dyssynchronous pathologies that impose particular challenges to deformation imaging.</p

Use of advanced echocardiography imaging techniques in the critically ill

Background: Critical care echocardiography has become standard of care in the ICU. New technologies have been developed and have shown potential clinical utility to elucidate myocardial dysfunction not seen with conventional imaging. We sought to determine the feasibility and potential clinical benefit of these techniques in common situations seen in the ICU. Hypothesis: Advanced echo techniques would be feasible in the majority of critically ill patients and have prognostic significance, clinical utility and diagnose cardiac abnormalities, potentially in a more sensitive manner than conventional techniques. Results: (a) Speckle tracking echocardiography (STE) Left ventricle and RV analysis with STE was feasibly in ~80% of patients. More dysfunction was found using STE vs conventional analysis. RV dysfunction assessed by STE held significant prognostic relevance in those with septic shock and highlighted subtle dysfunction induced by mechanical ventilation, both in animal and human studies. (b) 3D transthoracic echocardiography (3D TTE) Despite finding 3D TTE feasible in mechanically ventilated ICU patients (LV 72% and RV 55%), it lacked necessary low variability and high precision vs standard measures. (c) Myocardial contrast perfusion echocardiography (MCPE) Assessing acute coronary artery occlusion in the ICU patient is challenging. Troponin elevation, acute ECG changes, regional wall motion analysis on echo and overall clinical acumen often lack diagnostic capabilities. MCPE was found to be feasible in the critically ill and had better association predicting acute coronary artery occlusion vs clinical acumen alone. Conclusions: STE, 3D TTE and MCPE are feasible in the majority of ICU patients. STE may show dysfunction not recognised by conventional imaging. 3D TTE for volumetric analysis is likely not suitable for clinical use at this stage. MCPE may help guide interventions in acute coronary artery occlusion

Hierarchical template matching for 3D myocardial tracking and cardiac strain estimation

Myocardial tracking and strain estimation can non-invasively assess cardiac functioning using subject-specific MRI. As the left-ventricle does not have a uniform shape and functioning from base to apex, the development of 3D MRI has provided opportunities for simultaneous 3D tracking, and 3D strain estimation. We have extended a Local Weighted Mean (LWM) transformation function for 3D, and incorporated in a Hierarchical Template Matching model to solve 3D myocardial tracking and strain estimation problem. The LWM does not need to solve a large system of equations, provides smooth displacement of myocardial points, and adapt local geometric differences in images. Hence, 3D myocardial tracking can be performed with 1.49 mm median error, and without large error outliers. The maximum error of tracking is up to 24% reduced compared to benchmark methods. Moreover, the estimated strain can be insightful to improve 3D imaging protocols, and the computer code of LWM could also be useful for geo-spatial and manufacturing image analysis researchers

An optimisation-based iterative approach for speckle tracking echocardiography

Speckle tracking is the most prominent technique used to estimate the regional movement of the heart based on echocardiograms. In this study, we propose an optimised-based block matching algorithm to perform speckle tracking iteratively. The proposed technique was evaluated using a publicly available synthetic echocardiographic dataset with known ground-truth from several major vendors and for healthy/ischaemic cases. The results were compared with the results from the classic (standard) two-dimensional block matching. The proposed method presented an average displacement error of 0.57 pixels, while classic block matching provided an average error of 1.15 pixels. When estimating the segmental/regional longitudinal strain in healthy cases, the proposed method, with an average of 0.32 ± 0.53, outperformed the classic counterpart, with an average of 3.43 ± 2.84. A similar superior performance was observed in ischaemic cases. This method does not require any additional ad hoc filtering process. Therefore, it can potentially help to reduce the variability in the strain measurements caused by various post-processing techniques applied by different implementations of the speckle tracking

Left ventricular remodeling and function in ischemic heart disease and aortic valve disease

Background: Cardiac remodeling is a broad term that refers to structural and functional alterations of the heart in response to chronic changes in loading conditions or left ventricular (LV) contractile performance. Different loading conditions will affect the heart in different ways, some leading to impaired heart function, symptoms of heart failure, or even death. However, the process of remodeling may not be permanent. If the heart is relieved of the underlying cause of the remodeling, the heart function and structure may normalize in a process referred to as reverse remodeling. The complex interplay of factors that determine the process of reverse remodeling is not fully elucidated. Cardiac remodeling can be evaluated by many different diagnostic modalities, but the most widely used diagnostic tool is two-dimensional echocardiography (2DE). In recent years, three-dimensional echocardiography (3DE) has emerged with possible advantages in the assessment of LV volume and function. The thesis aimed to evaluate 3DE in the assessment of LV function and remodeling, and to study different aspects of remodeling in response to pressure and volume overload in patients with aortic stenosis (AS) and aortic regurgitation (AR), respectively. Methods: Studies I and II investigated patients with ischemic heart disease (n = 15 and n = 32, respectively). In Study I, the assessments of LV volume and ejection fraction (EF) were compared using 3DE, cardiac magnetic resonance (CMR), and single-photon emission computer tomography (SPECT). Study II compared the performance of 2DE, contrast-enhanced 2DE, 3DE, and contrast-enhanced 3DE in the assessment LV volumes and EF, using CMR as a reference standard. In Studies III and IV, 65 patients with severe AR and 120 patients with severe AS, respectively, were examined using 2DE and 3DE before and at one year after aortic valve replacement (AVR). In Study III, LV volumes, systolic and diastolic LV function, and left atrial strain (LAS) were analyzed to identify predictors of impaired LV reverse remodeling in AR. Study IV assessed LV functional indices, including 2D global longitudinal strain (GLS) and 3D strain, to assess predictors of incomplete reverse remodeling in AS. Results and conclusions: There were significant differences among 3DE, SPECT and CMR regarding the measurement of LV volumes. However, the estimation of EF showed good agreement. 3DE was more accurate and showed more favorable reproducibility than 2DE for the assessment of EF and LV volumes. Contrast enhancement improved accuracy and reproducibility for both 2DE and 3DE. One-third of patients with AR had signs of impaired LV diastolic function. After AVR, diastolic LV functional indices improved, LV and left atrial (LA) volumes decreased, and indices of LA function increased. LA conduit strain had an incremental prognostic value for the prediction of impaired LV functional and structural recovery. In patients with AS, AVR was associated with a decrease in LV mass, an improvement in 2D GLS, and a decrease in LV twist. 2D GLS and left ventricular mass index were predictive of incomplete reverse remodeling during the follow-up period. 3D GLS did not add discriminatory or predictive information over 2D GLS

Left ventricular diastolic mechanics in trained athletes during submaximal exercise using speckle tracking echocardiography

A thesis submitted to the University of Bedfordshire in partial fulfilment of the requirements for the degree of Masters of Science by ResearchThis thesis investigated sport specific responses of diastolic mechanics at rest and during submaximal exercise. Two-dimensional speckle tracking echocardiography (STE) was used to assess diastolic mechanics at rest and whilst triathletes (TRI, n=9, 32 ± 7 years), long distance runners (LDR, n=7, 34 ± 3 years), resistance trained (RT, n=5, 24 ± 5 years) and untrained controls (CON, n=5, 29 ± 5 years) performed dynamic and static exercise. Cycling consisted of 5 minute stages at 30% and 60% maximum workload (Wmax), and leg extension involved 15 second contractions at 40% and 75% maximal voluntary isometric contraction (MVIC). Peak untwisting velocity (PUV), apical and basal rotation velocities did not differ between groups at rest or during exercise (p>0.05). PUV increased in TRI from rest to 30% and 60% Wmax (p<0.01), remained unchanged in LDR, RT and CON from rest to 30% (p>0.05, p0.05, respectively) and 60% Wmax (p=0.018, p>0.05, p>0.05, respectively). PUV did not change from rest to 40% (p>0.05) and 75% MVIC in TRI, LDR, CON (p>0.05) and RT (p<0.05). These findings suggest diastolic mechanics do not differ at rest or during exercise based on sport specificity, yet mixed training (TRI) athletes demonstrate augmented diastolic mechanics during dynamic exercise

Echocardiography

The book "Echocardiography - New Techniques" brings worldwide contributions from highly acclaimed clinical and imaging science investigators, and representatives from academic medical centers. Each chapter is designed and written to be accessible to those with a basic knowledge of echocardiography. Additionally, the chapters are meant to be stimulating and educational to the experts and investigators in the field of echocardiography. This book is aimed primarily at cardiology fellows on their basic echocardiography rotation, fellows in general internal medicine, radiology and emergency medicine, and experts in the arena of echocardiography. Over the last few decades, the rate of technological advancements has developed dramatically, resulting in new techniques and improved echocardiographic imaging. The authors of this book focused on presenting the most advanced techniques useful in today's research and in daily clinical practice. These advanced techniques are utilized in the detection of different cardiac pathologies in patients, in contributing to their clinical decision, as well as follow-up and outcome predictions. In addition to the advanced techniques covered, this book expounds upon several special pathologies with respect to the functions of echocardiography

Video Kinematic Evaluation: new insights on the cardiac mechanical function

The cardiac mechanical function plays a critical role in governing and regulating its performance under both normal and pathological conditions. The left ventricle has historically received more attention in both congenital and acquired heart diseases and was considered as the mainstay of normal hemodynamics. However, over the past few decades, there has been increasing recognition of the pivotal role of the right ventricle in determining functional performance status and prognosis in multiple conditions. Nonetheless, the ventricles should not be considered separately as they share the septum, are encircled with common myocardial fibers and are surrounded by the pericardium. Thus, changes in the filling of one ventricle may alter the mechanical function of its counterpart. This ventricular interdependence remains even after the removal of the pericardium because of constrictive pericarditis or during open chest surgery. Interestingly, during open chest surgery, only the right ventricle mechanical activity is visually checked by the surgeon and cardiologist due to the absence of an intraoperative imaging technique able to evaluate its complex function. Noteworthy, most of the imaging techniques available to clinicians are established for the assessment of the left ventricle, with the ejection fraction being the most used parameter. However, this value is a measure of global systolic function which comes short in identifying regional myocardial impairment and the mechanical contraction. Therefore, new approaches are needed to deeply investigate the mechanics of both ventricles and correctly assess the cardiac mechanical performance. In this thesis, I studied the mechanical function of the left ventricle through different modalities of cardiac magnetic resonance and employed an innovative imaging technique for the assessment of the right ventricle mechanical function during open chest surgery