Regional ejection fraction and regional area strain for left ventricular function assessment in male patients after first-time myocardial infarction

Reduced graphene oxide facilitates biocompatibility of alginate for cardiac repair

The benefits of combined cell/material therapy appear promising for myocardial infarction treatment. The safety of alginate, along with its excellent biocompatibility and biodegradability, has been extensively investigated for cardiac tissue engineering. Among graphene-based nanomaterials, reduced graphene oxide has been considered as a promising candidate for cardiac treatment due to its unique physicochemical properties. In this study, the reduced graphene oxide incorporation effect within alginate hydrogels was investigated for cardiac repair application. Reduced graphene oxide reinforced alginate properties, resulting in an increase in gel stiffness. The cytocompatibility of the hydrogels prepared with human bone marrow–derived mesenchymal stem cells was assessed by the 3-(4,5dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide) assay. Following reduced graphene oxide addition, alginate-reduced graphene oxide retained significantly higher cell viability compared to that of alginate and cells cultured on tissue culture plates. Acridine orange/propidium iodide staining was also used to identify both viable and necrotic human bone marrow–derived mesenchymal stem cells within the prepared hydrogels. After a 72-h culture, the percentage of viable cells was twice as much as those cultured on either alginate or tissue culture plate, reaching approximately 80%. Quantitative reverse transcription polymerase chain reaction analysis was performed to assess gene expression of neonatal rat cardiac cells encapsulated on hydrogels for TrpT-2, Conx43, and Actn4 after 7 days. The expression of all genes in alginate-reduced graphene oxide increased significantly compared to that in alginate or tissue culture plate. The results obtained confirmed that the presence of reduced graphene oxide, as an electro-active moiety within alginate, could tune the physicochemical properties of this material, providing a desirable electroactive hydrogel for stem cell therapy in patients with ischemic heart disease.

Reference Ranges for Left Ventricular Curvedness and Curvedness-Based Functional Indices Using Cardiovascular Magnetic Resonance in Healthy Asian Subjects

Curvature-based three-dimensional cardiovascular magnetic resonance (CMR) allows regional function characterization without an external spatial frame of reference. However, introduction of this modality into clinical practice is hampered by lack of reference values. We aim to establish normal ranges for 3D left ventricular (LV) regional parameters in relation to age and gender for 171 healthy subjects. LV geometrical reconstruction and automatic calculation of regional parameters were implemented by in-house software (CardioWerkz) using stacks of short-axis cine slices. Parameter normal ranges were stratified by gender and age categories (≤44, 45-64, 65-74 and 75-84 years). Our software had excellent intra- and inter-observer agreement. Ageing was significantly associated with increases in end-systolic (ES) curvedness (C_ES) and area strain (AS) with higher rates of increase in males, end-diastolic (ED) and ES wall thickness (WT_ED, WT_ES) with higher rates of increase in females, and reductions in ED and ES wall stress indices (σ_i,ED) with higher rates of increase in females. Females exhibited greater ED curvedness, C_ES, σ_i,ED and AS than males, but smaller WT_ED and WT_ES. Age × gender interaction was not observed for any parameter. This study establishes age and gender specific reference values for 3D LV regional parameters using CMR without additional image acquisition.

Efficacy of intramyocardial injection of Algisyl-LVR for the treatment of ischemic heart failure in swine

BACKGROUND

Progressive thinning and dilation of the LV due to ischemic heart failure (IHF) increases wall stress and myocardial oxygen consumption. Injectable biopolymers implanted in the myocardial wall have been used to increase wall thickness to reduce chamber volume, decrease wall stress, and improve cardiac function. We sought to evaluate the efficacy of a biopolymer (Algisyl-LVR) to prevent left ventricular (LV) remodeling in a swine model of IHF.

METHODS

IHF was induced in 11 swine by occluding the marginal obtuse branches of the left circumflex artery. Eight weeks later, Algisyl-LVR was injected into the LV myocardial free wall in five of the 11 animals. Echocardiographic examinations were done every 2weeks for 16weeks.

RESULTS

Within eight weeks of treatment, the ejection fraction increased from 30.5%±7.7% to 42.4%±3.5% (treated group) vs. 37.3%±3.8% to 34.3%±2.9% (control), p<0.01. Stroke volume increased from 18.5±9.3mL to 41.3±13.3mL (treated group) vs. 25.4±2.3mL to 31.4±5.3mL (control), p<0.05. Wall thickness in end-diastole of the infarcted region changed from 0.69±0.06cm to 0.81±0.13cm (treated group) vs. 0.73±0.09cm to 0.68±0.11cm (control), p<0.05. Sphericity index remained almost unchanged after treatment, although differences were found at the end of the study between both groups (p<0.001). Average myofiber stress changed from 16.3±5.8kPa to 10.2±4.0kPa (treated group) vs. 15.2±4.8kPa to 17.9±5.6kPa (control), p<0.05.

CONCLUSIONS

Algisyl-LVR is an effective strategy that serves as a micro-LV assist device to reduce stress and hence prevent or reverse maladaptive cardiac remodeling caused by IHF in swine.

Left Ventricular Wall Stress Is Sensitive Marker of Hypertrophic Cardiomyopathy With Preserved Ejection Fraction

Hypertrophic cardiomyopathy (HCM) patients present altered myocardial mechanics due to the hypertrophied ventricular wall and are typically diagnosed by the increase in myocardium wall thickness. This study aimed to quantify regional left ventricular (LV) shape, wall stress and deformation from cardiac magnetic resonance (MR) images in HCM patients and controls, in order to establish superior measures to differentiate HCM from controls. A total of 19 HCM patients and 19 controls underwent cardiac MR scans. The acquired MR images were used to reconstruct 3D LV geometrical models and compute the regional parameters (i.e., wall thickness, curvedness, wall stress, area strain and ejection fraction) based on the standard 16 segment model using our in-house software. HCM patients were further classified into four quartiles based on wall thickness at end diastole (ED) to assess the impact of wall thickness on these regional parameters. There was a significant difference between the HCM patients and controls for all regional parameters (P < 0.001). Wall thickness was greater in HCM patients at the end-diastolic and end-systolic phases, and thickness was most pronounced in segments at the septal regions. A multivariate stepwise selection algorithm identified wall stress index at ED (σ_i,ED) as the single best independent predictor of HCM (AUC = 0.947). At the cutoff value σ_i,ED < 1.64, both sensitivity and specificity were 94.7%. This suggests that the end-diastolic wall stress index incorporating regional wall curvature—an index based on mechanical principle—is a sensitive biomarker for HCM diagnosis with potential utility in diagnostic and therapeutic assessment.

Analysis of three-dimensional endocardial and epicardial strains from cardiac magnetic resonance in healthy subjects and patients with hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a genetic disease that leads to left ventricle (LV) hypertrophy with or without the presence of LV outflow tract obstruction. The aim of this study was to find an easy and useful indicator based on cardiac magnetic resonance (CMR) images for control subjects and patients with and without obstruction. CMR scans were performed for 19 control subjects and 19 HCM patients. Endocardial strain was defined as [Formula: see text], with [Formula: see text] being the length of endocardium at end-diastole (end-systole); similarly for epicardial strain ([Formula: see text]). The strains were evaluated in cine CMR two-, three- and four-chamber views. Six atrioventricular junction (AVJ) points from three CMR views were semi-automatically tracked. The peak systolic velocity (Sm1), peak early diastolic velocity and late diastolic velocity (Em, Am) were extracted and analysed. Compared with control subjects, HCM patients had significantly smaller three-dimensional strains and AVJ motion incorporating measurements from three long-axis views (all P < 0.05). Moreover, ROC analysis found that three-dimensional global epicardial strain <17.2% had the best sensitivity 94.4% and specificity 94.7% to differentiate HCM from control (AUC = 0.97). Therefore, three-dimensional endocardial and epicardial strains provide an easy and effective approach to manage and triage hypertrophic cardiomyopathy patients.

Correcting motion in multiplanar cardiac magnetic resonance images

BACKGROUND

Misalignment in cardiac magnetic resonance (CMR) images can adversely affect three-dimensional left ventricle modelling and downstream quantitative analysis. Currently, there are two types of approaches for dealing with realignment and motion distortion problems, one image based and the other geometry based. Image-based approaches are limited by the inherent non-homogeneity and anisotropy of CMR images. Geometry-based approaches rely on idealized models and over-simplified assumptions. This study was motivated by the need for a robust and effective approach for correcting motion related distortions due to misalignment in CMR images.

METHODS

A cine cardiac magnetic resonance image sequence was acquired using our routine clinical imaging protocol. The left ventricular endocardium was delineated manually with software assistance on all long and short-axis images. Long and short-axis contours were projected onto a patient-based coordinate system and then realigned using iterative registration. The realigned contour points were used to reconstruct the shape of the left ventricle for quantitative validation.

RESULTS

The method was tested on five myocardial infarction patients whose images showed substantial misalignment. Realignment time was about 16 seconds per case, using a 2.5 GHz CPU desktop with obvious elimination of the distortion in the reconstructed model. Using the long-axis contour as a reference in evaluating the reconstructed models, it was apparent that the models with realigned contours had better accuracy than the non-realigned ones.

CONCLUSION

This study presents a novel, geometry-based method for correcting motion distortions in CMR images. The method incorporates (1) manual delineation, (2) registration based on a generalized, iterative closest point algorithm, and (3) reconstruction of the shape of the left ventricle for quantitative validation. The effectiveness of our approach is corroborated both visually and by quantitative assessment. We envision the use of our method in current clinical practice as a means of improving accuracy in the evaluation of cardiac function.

Variational Reconstruction of Left Cardiac Structure from CMR Images

Cardiovascular Disease (CVD), accounting for 17% of overall deaths in the USA, is the leading cause of death over the world. Advances in medical imaging techniques make the quantitative assessment of both the anatomy and function of heart possible. The cardiac modeling is an invariable prerequisite for quantitative analysis. In this study, a novel method is proposed to reconstruct the left cardiac structure from multi-planed cardiac magnetic resonance (CMR) images and contours. Routine CMR examination was performed to acquire both long axis and short axis images. Trained technologists delineated the endocardial contours. Multiple sets of two dimensional contours were projected into the three dimensional patient-based coordinate system and registered to each other. The union of the registered point sets was applied a variational surface reconstruction algorithm based on Delaunay triangulation and graph-cuts. The resulting triangulated surfaces were further post-processed. Quantitative evaluation on our method was performed via computing the overlapping ratio between the reconstructed model and the manually delineated long axis contours, which validates our method. We envisage that this method could be used by radiographers and cardiologists to diagnose and assess cardiac function in patients with diverse heart diseases.

Automated quantitative assessment of cardiovascular magnetic resonance-derived atrioventricular junction velocities

The assessment of atrioventricular junction (AVJ) deformation plays an important role in evaluating left ventricular systolic and diastolic function in clinical practice. This study aims to demonstrate the effectiveness and consistency of cardiovascular magnetic resonance (CMR) for quantitative assessment of AVJ velocity compared with tissue Doppler echocardiography (TDE). A group of 145 human subjects comprising 21 healthy volunteers, 8 patients with heart failure, 17 patients with hypertrophic cardiomyopathy, 52 patients with myocardial infarction, and 47 patients with repaired Tetralogy of Fallot were prospectively enrolled and underwent TDE and CMR scan. Six AVJ points were tracked with three CMR views. The peak systolic velocity (Sm1), diastolic velocity during early diastolic filling (Em), and late diastolic velocity during atrial contraction (Am) were extracted and analyzed. All CMR-derived septal and lateral AVJ velocities correlated well with TDE measurements (Sm1: r = 0.736; Em: r = 0.835; Am: r = 0.701; Em/Am: r = 0.691; all p < 0.001) and demonstrated excellent reproducibility [intrastudy: r = 0.921-0.991, intraclass correlation coefficient (ICC): 0.918-0.991; interstudy: r = 0.900-0.970, ICC: 0.887-0.957; all p < 0.001]. The evaluation of three-dimensional AVJ motion incorporating measurements from all views better differentiated normal and diseased states [area under the curve (AUC) = 0.918] and provided further insights into mechanical dyssynchrony diagnosis in HF patients (AUC = 0.987). These findings suggest that the CMR-based method is feasible, accurate, and consistent in quantifying the AVJ deformation, and subsequently in diagnosing systolic and diastolic cardiac dysfunction.