Ultrasound Segmentation of Rat Hearts Using Convolution Neural Networks

Ultrasound is widely used for diagnosing cardiovascular diseases. However, estimates such as left ventricle volume currently require manual segmentation, which can be time consuming. In addition, cardiac ultrasound is often complicated by imaging artifacts such as shadowing and mirror images, making it difficult for simple intensity-based automated segmentation methods. In this work, we use convolutional neural networks (CNNs) to segment ultrasound images of rat hearts embedded in agar phantoms into four classes: background, myocardium, left ventricle cavity, and right ventricle cavity. We also explore how the inclusion of a single diseased heart changes the results in a small dataset. We found an average overall segmentation accuracy of 70.0% ± 7.3% when combining the healthy and diseased data, compared to 72.4% ± 6.6% for just the healthy hearts. This work suggests that including diseased hearts with healthy hearts in training data could improve segmentation results, while testing a diseased heart with a model trained on healthy hearts can produce accurate segmentation results for some classes but not others. More data are needed in order to improve the accuracy of the CNN based segmentation.

Abstract TMP106: Humanized Sickle Mice Are Sensitive to Hypoxia-Ischemia-Induced Stroke, but Respond to Tissue Plasminogen Activator Treatment

Introduction: Stroke, a devastating complication in children with Sickle Cell Anemia (SCA), consists of silent cerebral infarct (SCI) and large overt stroke. The current management relies on blood transfusion without the use of thrombolytic agents. However, a recent study showed that co-existent SCA does not impact the safety of tissue plasminogen activator (tPA) treatment. This finding calls for systemic analysis of the effects of thrombolysis in experimental stroke.

Hypothesis: We hypothesize that sickle mice are highly vulnerable to hypoxia/ischemia-induced stroke, but respond to tPA-thrombolytic therapy.

Methods: Townes sickle mice (knock-in/out mice that express the human α, γ, and sickle-β hemoglobin genes) were subjected to Doppler measurement of the carotid artery and evaluated for their responses to repetitive-mild hypoxia-ischemia (rmHI) and transient hypoxia-ischemia (tHI)-induced stroke at 3 and 6 months of age, respectively. The effects of tPA treatment after tHI in sickle mice were also examined.

Results: First, 3-month-old sickle mice of SS genotype with a higher resistive index (RI) in common carotid artery were also prone to rmHI-induced cerebral infarct and mortality. Second, 6-month-old SS mice developed elevated flow velocity and greater RI without stenosis of the carotid artery akin to those previously implicated in large overt stroke in SCA. Finally, 6-month-old SS mice endured 20-min, but manifested enhanced leukocyte and platelet adherence to cerebral blood vessel, as well as, extensive vascular perfusion deficits and fibrin deposition at 4 h post-injury, followed by greatly increased mortality than AA and AS mice at 24 h recovery (p<0.0001, n>8 for each group). Importantly, intravenous tPA treatment at 0.5 h post-tHI markedly improved vascular reperfusion, mitigated fibrin deposition, and cut the mortality of SS mice by nearly 60%.

Conclusions: Humanized sickle mice develop hyper-coagulation and hypersensitivity to HI-induced stroke without large-vessel obstructive vasculopathy at up to 6 months of age. Elevated RI may be an early ultrasonic marker for sickle cell vasculopathy and the risk of SCI in SCA. Future studies are warranted to confirm the therapeutic benefits of thrombolytic stroke therapy in SCA.

Sickle Mice Are Sensitive to Hypoxia/Ischemia-Induced Stroke but Respond to Tissue-Type Plasminogen Activator Treatment

BACKGROUND AND PURPOSE

The effects of lytic stroke therapy in patients with sickle cell anemia are unknown, although a recent study suggested that coexistent sickle cell anemia does not increase the risk of cerebral hemorrhage. This finding calls for systemic analysis of the effects of thrombolytic stroke therapy, first in humanized sickle mice, and then in patients. There is also a need for additional predictive markers of sickle cell anemia-associated vasculopathy.

METHODS

We used Doppler ultrasound to examine the carotid artery of Townes sickle mice tested their responses to repetitive mild hypoxia-ischemia- and transient hypoxia-ischemia-induced stroke at 3 or 6 months of age, respectively. We also examined the effects of tPA (tissue-type plasminogen activator) treatment in transient hypoxia-ischemia-injured sickle mice.

RESULTS

Three-month-old sickle cell (SS) mice showed elevated resistive index in the carotid artery and higher sensitivity to repetitive mild hypoxia-ischemia-induced cerebral infarct. Six-month-old SS mice showed greater resistive index and increased flow velocity without obstructive vasculopathy in the carotid artery. Instead, the cerebral vascular wall in SS mice showed ectopic expression of PAI-1 (plasminogen activator inhibitor-1) and P-selectin, suggesting a proadhesive and prothrombotic propensity. Indeed, SS mice showed enhanced leukocyte and platelet adherence to the cerebral vascular wall, broader fibrin deposition, and higher mortality after transient hypoxia-ischemia. Yet, post-transient hypoxia-ischemia treatment with tPA reduced thrombosis and mortality in SS mice.

CONCLUSIONS

Sickle mice are sensitive to hypoxia/ischemia-induced cerebral infarct but benefit from thrombolytic treatment. An increased resistive index in carotid arteries may be an early marker of sickle cell vasculopathy.

Estimating cardiac fiber orientations in pig hearts using registered ultrasound and MR image volumes

Heart fiber mechanics can be important predictors in current and future cardiac function. Accurate knowledge of these mechanics could enable cardiologists to provide a diagnosis before conditions progress. Magnetic resonance diffusion tensor imaging (MR-DTI) has been used to determine cardiac fiber orientations. Ultrasound is capable of providing anatomical information in real time, enabling a physician to quickly adjust parameters to optimize image scans. If known fiber orientations from a template heart measured using DTI can be accurately deformed onto a cardiac ultrasound volume, fiber orientations could be estimated for the patient without the need for a costly MR scan while still providing cardiologists valuable information about the heart mechanics. In this study, we apply the method to pig hearts, which are a close representation of human heart anatomy. Experiments from pig hearts show that the registration method achieved an average Dice similarity coefficient (DSC) of 0.819 ± 0.050 between the ultrasound and deformed MR volumes and that the proposed ultrasound-based method is able to estimate the cardiac fiber orientation in pig hearts.

A new method to quantify fiber orientation similarity in registered volumes

Differences in fiber orientations between registered image volumes can be difficult to quantify. Angular errors between diffusion tensor imaging (DTI) volumes are often a combination of image registration errors and fluctuations of diffusion values that are used to determine the fiber orientations. In order to properly quantify the similarity between two images containing fiber orientation information, both displacement and angular fluctuation should be considered. We present a method to quantify fiber orientation similarity between registered images by allowing small pixel displacements in conjunction with minor angle differences. Adjustments to the allowed pixel displacement and degree of angle difference can help identify the major factor contributing to the error of fiber angles. The proposed method can provide a new metric for the evaluation of the fiber orientation difference.

Doxazosin Stimulates Galectin-3 Expression and Collagen Synthesis in HL-1 Cardiomyocytes Independent of Protein Kinase C Pathway

Doxazosin, a drug commonly prescribed for hypertension and prostate disease, increases heart failure risk. However, the underlying mechanism remains unclear. Galectin-3 is an important mediator that plays a pathogenic role in cardiac hypertrophy and heart failure. In the present study, we investigated whether doxazosin could stimulate galectin-3 expression and collagen synthesis in cultured HL-1 cardiomyocytes. We found that doxazosin dose-dependently induced galectin-3 protein expression, with a statistically significant increase in expression with a dose as low as 0.01 μM. Doxazosin upregulated collagen I and α-smooth muscle actin (α-SMA) protein levels and also induced apoptotic protein caspase-3 in HL-1 cardiomyocytes. Although we previously reported that activation of protein kinase C (PKC) stimulates galectin-3 expression, blocking the PKC pathway with the PKC inhibitor chelerythrine did not prevent doxazosin-induced galectin-3 and collagen expression. Consistently, doxazosin treatment did not alter total and phosphorylated PKC. These results suggest that doxazosin-stimulated galectin-3 is independent of PKC pathway. To determine if the α1-adrenergic pathway is involved, we pretreated the cells with the irreversible α-adrenergic receptor blocker phenoxybenzamine and found that doxazosin-stimulated galectin-3 and collagen expression was similar to controls, suggesting that doxazosin acts independently of α1-adrenergic receptor blockade. Collectively, we show a novel effect of doxazosin on cardiomycytes by stimulating heart fibrosis factor galectin-3 expression. The mechanism of action of doxazosin is not mediated through either activation of the PKC pathway or antagonism of α1-adrenergic receptors.

Myocardial dysfunction occurs prior to changes in ventricular geometry in mice with chronic kidney disease (CKD)

Uremic cardiomyopathy is responsible for high morbidity and mortality rates among patients with chronic kidney disease (CKD), but the underlying mechanisms contributing to this complex phenotype are incompletely understood. Myocardial deformation analyses (ventricular strain) of patients with mild CKD have recently been reported to predict adverse clinical outcome. We aimed to determine if early myocardial dysfunction in a mouse model of CKD could be detected using ventricular strain analyses. CKD was induced in 5-week-old male 129X1/SvJ mice through partial nephrectomy (5/6Nx) with age-matched mice undergoing bilateral sham surgeries serving as controls. Serial transthoracic echocardiography was performed over 16 weeks following induction of CKD. Invasive hemodynamic measurements were performed at 8 weeks. Gene expression and histology was performed on hearts at 8 and 16 weeks. CKD mice developed decreased longitudinal strain (-25 ± 4.2% vs. -29 ± 2.3%; P = 0.01) and diastolic dysfunction (E/A ratio 1.2 ± 0.15 vs. 1.9 ± 0.18; P < 0.001) compared to controls as early as 2 weeks following 5/6Nx. In contrast, ventricular hypertrophy was not apparent until 4 weeks. Hearts from CKD mice developed progressive fibrosis at 8 and 16 weeks with gene signatures suggestive of evolving heart failure with elevated expression of natriuretic peptides. Uremic cardiomyopathy in this model is characterized by early myocardial dysfunction which preceded observable changes in ventricular geometry. The model ultimately resulted in myocardial fibrosis and increased expression of natriuretic peptides suggestive of progressive heart failure.

A human pluripotent stem cell model of catecholaminergic polymorphic ventricular tachycardia recapitulates patient-specific drug responses

Although β-blockers can be used to eliminate stress-induced ventricular arrhythmias in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT), this treatment is unsuccessful in ∼25% of cases. Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) generated from these patients have potential for use in investigating the phenomenon, but it remains unknown whether they can recapitulate patient-specific drug responses to β-blockers. This study assessed whether the inadequacy of β-blocker therapy in an individual can be observed in vitro using patient-derived CPVT iPSC-CMs. An individual with CPVT harboring a novel mutation in the type 2 cardiac ryanodine receptor (RyR2) was identified whose persistent ventricular arrhythmias during β-blockade with nadolol were abolished during flecainide treatment. iPSC-CMs generated from this patient and two control individuals expressed comparable levels of excitation-contraction genes, but assessment of the sarcoplasmic reticulum Ca(2+) leak and load relationship revealed intracellular Ca(2+) homeostasis was altered in the CPVT iPSC-CMs. β-adrenergic stimulation potentiated spontaneous Ca(2+) waves and unduly frequent, large and prolonged Ca(2+) sparks in CPVT compared with control iPSC-CMs, validating the disease phenotype. Pursuant to the patient's in vivo responses, nadolol treatment during β-adrenergic stimulation achieved negligible reduction of Ca(2+) wave frequency and failed to rescue Ca(2+) spark defects in CPVT iPSC-CMs. In contrast, flecainide reduced both frequency and amplitude of Ca(2+) waves and restored the frequency, width and duration of Ca(2+) sparks to baseline levels. By recapitulating the improved response of an individual with CPVT to flecainide compared with β-blocker therapy in vitro, these data provide new evidence that iPSC-CMs can capture basic components of patient-specific drug responses.

Simulated Microgravity and 3D Culture Enhance Induction, Viability, Proliferation and Differentiation of Cardiac Progenitors from Human Pluripotent Stem Cells

Efficient generation of cardiomyocytes from human pluripotent stem cells is critical for their regenerative applications. Microgravity and 3D culture can profoundly modulate cell proliferation and survival. Here, we engineered microscale progenitor cardiac spheres from human pluripotent stem cells and exposed the spheres to simulated microgravity using a random positioning machine for 3 days during their differentiation to cardiomyocytes. This process resulted in the production of highly enriched cardiomyocytes (99% purity) with high viability (90%) and expected functional properties, with a 1.5 to 4-fold higher yield of cardiomyocytes from each undifferentiated stem cell as compared with 3D-standard gravity culture. Increased induction, proliferation and viability of cardiac progenitors as well as up-regulation of genes associated with proliferation and survival at the early stage of differentiation were observed in the 3D culture under simulated microgravity. Therefore, a combination of 3D culture and simulated microgravity can be used to efficiently generate highly enriched cardiomyocytes.

Abstract 207: Electrically-induced Calcium Handling in Human Cardiac Progenitor Cells

The discovery of a resident population of cardiac stem cells known as cardiac progenitor cells (CPCs) has raised the question of the mechanisms involved in regenerative properties of this niche of cells. The physiology of human CPCs is not well understood, and a thorough understanding of the Ca 2+ handling ability of these cells is crucial in order to fully realize their regenerative potential. Therefore, to characterize the mechanism of electrically-induced Ca 2+ handling in human CPCs, we have used cells loaded with fluo-4 calcium dye and imaged using confocal microscopy to determine the spatial and temporal profile of cytosolic Ca 2+ upon electrical stimulation. Upon activation of electrical stimulation, a large increase in cytosolic Ca 2+ was observed followed by oscillations of the cytosolic Ca 2+ . The electrically-induced Ca 2+ oscillations were found to be dependent on the activity of L-type Ca 2+ channels (LTCC) and the presence of extracellular Ca 2+ . Furthermore, these oscillations could be abolished by pre-treatment of the cells with the inositol 1,4,5-trisphosphate receptor (IP 3 R) antagonist 2-APB. High-speed confocal imaging of the electrically-induced Ca 2+ oscillations in hCPCs revealed that these cells oscillate in a Ca 2+ wave-like fashion with activity originating in isolated regions of the cell and propagating throughout the cytosol and nucleus. In conclusion, we propose that Ca 2+ -dependent regulatory mechanisms can be exploited to influence their differentiation potential leading to improved function in cardiac regenerative medicine.

Hypertension and Afro-descendant ethnicity: a bad interaction for lupus nephritis treated with cyclophosphamide?

Hypertension and ethnicity are important prognostic factors in evolution of lupus nephritis. A cohort of 75 patients with lupus nephritis treated with cyclophosphamide was conducted to investigate the evolution of creatinine levels between Caucasians and Afro-descendants. A multiple linear model was used to evaluate the combined effects of ethnicity and hypertension over delta creatinine controlling confounders. Sample characteristics were: 85% females; mean (±SD) age of 33.6 ± 12.0 years; 77% Caucasians; 40% hypertensive at renal biopsy; 91% WHO class IV; mean basal creatinine: 1.5 ± 1.3 mg/dL; mean final creatinine: 2.1 ± 2.5 mg/dL; 40% anaemia; proteinuria: 5.4 ± 4.8 g/day. Comparing Caucasians and Afro-descendants, it was found: 28.1% versus 72.2% for hypertension ( P = 0.002); 31.6% versus 66.7% for anaemia ( P = 0.018); 5.9 ± 5.0 versus 3.8 ± 4.0. g/day ( P = 0.02) for proteinuria. Other comparisons including basal creatinine did not reach statistical significance. Comparing outcomes between Caucasians and Afro-descendants, it was found: 10.5% versus 22.2% for doubling of creatinine ( P = 0.24); 0.41 ± 2.03 versus 1.05 ± 2.41 for delta creatinine ( P = 0.29); 8.8% versus 22.2% for haemodialysis ( P = 0.21) and 3.5% versus 5.6% for death ( P = 0.99). Analysing delta creatinine with multiple linear regression showed that hypertension had a significant overall effect ( b = 0.80; SE = 0.32; P = 0.015), ethnicity alone was not significant ( b = 0.35; SE = 0.29; P = 0.228); however, the effect of hypertension on delta creatinine was more intense among Afro-descendants than among Caucasians (interaction term b = — 0.83; SE = 0.37; P = 0.027). Afro-descendants lupus patients experience worst prognosis of renal function probably due to the effect of hypertension and not ethnicity per se. Lupus (2007) 16, 724—730.

Simulating cardiac ultrasound image based on MR diffusion tensor imaging

PURPOSE

Cardiac ultrasound simulation can have important applications in the design of ultrasound systems, understanding the interaction effect between ultrasound and tissue and setting the ground truth for validating quantification methods. Current ultrasound simulation methods fail to simulate the myocardial intensity anisotropies. New simulation methods are needed in order to simulate realistic ultrasound images of the heart.

METHODS

The proposed cardiac ultrasound image simulation method is based on diffusion tensor imaging (DTI) data of the heart. The method utilizes both the cardiac geometry and the fiber orientation information to simulate the anisotropic intensities in B-mode ultrasound images. Before the simulation procedure, the geometry and fiber orientations of the heart are obtained from high-resolution structural MRI and DTI data, respectively. The simulation includes two important steps. First, the backscatter coefficients of the point scatterers inside the myocardium are processed according to the fiber orientations using an anisotropic model. Second, the cardiac ultrasound images are simulated with anisotropic myocardial intensities. The proposed method was also compared with two other nonanisotropic intensity methods using 50 B-mode ultrasound image volumes of five different rat hearts. The simulated images were also compared with the ultrasound images of a diseased rat heart in vivo. A new segmental evaluation method is proposed to validate the simulation results. The average relative errors (AREs) of five parameters, i.e., mean intensity, Rayleigh distribution parameter σ, and first, second, and third quartiles, were utilized as the evaluation metrics. The simulated images were quantitatively compared with real ultrasound images in both ex vivo and in vivo experiments.

RESULTS

The proposed ultrasound image simulation method can realistically simulate cardiac ultrasound images of the heart using high-resolution MR-DTI data. The AREs of their proposed method are 19% for the mean intensity, 17.7% for the scale parameter of Rayleigh distribution, 36.8% for the first quartile of the image intensities, 25.2% for the second quartile, and 19.9% for the third quartile. In contrast, the errors of the other two methods are generally five times more than those of their proposed method.

CONCLUSIONS

The proposed simulation method uses MR-DTI data and realistically generates cardiac ultrasound images with anisotropic intensities inside the myocardium. The ultrasound simulation method could provide a tool for many potential research and clinical applications in cardiac ultrasound imaging.

Age-Dependent Effect of Pediatric Cardiac Progenitor Cells After Juvenile Heart Failure

To investigate the role of age of human pediatric cardiac progenitor cells (hCPCs) on ventricular remodeling, the authors injected neonate, infant, or child hCPCs into rats with right ventricular heart failure. Mechanisms including migration and proliferation assays, as suggested by computational modeling, showed improved chemotactic and proliferative capacity of neonatal hCPCs compared with infant or child hCPCs. Thus, the reparative potential of hCPCs is age-dependent.

Children with congenital heart diseases have increased morbidity and mortality, despite various surgical treatments, therefore warranting better treatment strategies. Here we investigate the role of age of human pediatric cardiac progenitor cells (hCPCs) on ventricular remodeling in a model of juvenile heart failure. hCPCs isolated from children undergoing reconstructive surgeries were divided into 3 groups based on age: neonate (1 day to 1 month), infant (1 month to 1 year), and child (1 to 5 years). Adolescent athymic rats were subjected to sham or pulmonary artery banding surgery to generate a model of right ventricular (RV) heart failure. Two weeks after surgery, hCPCs were injected in RV musculature noninvasively. Analysis of cardiac function 4 weeks post-transplantation demonstrated significantly increased tricuspid annular plane systolic excursion and RV ejection fraction and significantly decreased wall thickness and fibrosis in rats transplanted with neonatal hCPCs compared with saline-injected rats. Computational modeling and systems biology analysis were performed on arrays and gave insights into potential mechanisms at the microRNA and gene level. Mechanisms including migration and proliferation assays, as suggested by computational modeling, showed improved chemotactic and proliferative capacity of neonatal hCPCs compared with infant/child hCPCs. In vivo immunostaining further suggested increased recruitment of stem cell antigen 1-positive cells in the right ventricle. This is the first study to assess the role of hCPC age in juvenile RV heart failure. Interestingly, the reparative potential of hCPCs is age-dependent, with neonatal hCPCs exerting the maximum beneficial effect compared with infant and child hCPCs.

Significance

Stem cell therapy for children with congenital heart defects is moving forward, with several completed and ongoing clinical trials. Although there are studies showing how children differ from adults, few focus on the differences among children. This study using human cardiac progenitor cells shows age-related changes in the reparative ability of cells in a model of pediatric heart failure and uses computational and systems biology to elucidate potential mechanisms.

Cell alignment induced by anisotropic electrospun fibrous scaffolds alone has limited effect on cardiomyocyte maturation

Enhancing the maturation of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) will facilitate their applications in disease modeling and drug discovery. Previous studies suggest that cell alignment could enhance hPSC-CM maturation; however, the robustness of this approach has not been well investigated. To this end, we examined if the anisotropic orientation of hPSC-CMs imposed by the underlying aligned fibers within a 3D microenvironment could improve the maturation of hPSC-CMs. Enriched hPSC-CMs were cultured for two weeks on Matrigel-coated anisotropic (aligned) and isotropic (random) polycaprolactone (PCL) fibrous scaffolds, as well as tissue culture polystyrenes (TCPs) as a control. As expected, hPSC-CMs grown on the two types of fibrous scaffolds exhibited anisotropic and isotropic orientations, respectively. Similar to cells on TCPs, hPSC-CMs cultured on these scaffolds expressed CM-associated proteins and were pharmacologically responsive to adrenergic receptor agonists, a muscarinic agonist, and a gap junction uncoupler in a dose-dependent manner. Although hPSC-CMs grown on anisotropic fibrous scaffolds displayed the highest expression of genes encoding a number of sarcomere proteins, calcium handling proteins and ion channels, their calcium transient kinetics were slower than cells grown on TCPs. These results suggest that electrospun anisotropic fibrous scaffolds, as a single method, have limited effect on improving the maturation of hPSC-CMs.

Cell alignment induced by anisotropic electrospun fibrous scaffolds alone has limited effect on cardiomyocyte maturation

Enhancing the maturation of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) will facilitate their applications in disease modeling and drug discovery. Previous studies suggest that cell alignment could enhance hPSC-CM maturation; however, the robustness of this approach has not been well investigated. To this end, we examined if the anisotropic orientation of hPSC-CMs imposed by the underlying aligned fibers within a 3D microenvironment could improve the maturation of hPSC-CMs. Enriched hPSC-CMs were cultured for two weeks on Matrigel-coated anisotropic (aligned) and isotropic (random) polycaprolactone (PCL) fibrous scaffolds, as well as tissue culture polystyrenes (TCPs) as a control. As expected, hPSC-CMs grown on the two types of fibrous scaffolds exhibited anisotropic and isotropic orientations, respectively. Similar to cells on TCPs, hPSC-CMs cultured on these scaffolds expressed CM-associated proteins and were pharmacologically responsive to adrenergic receptor agonists, a muscarinic agonist, and a gap junction uncoupler in a dose-dependent manner. Although hPSC-CMs grown on anisotropic fibrous scaffolds displayed the highest expression of genes encoding a number of sarcomere proteins, calcium handling proteins and ion channels, their calcium transient kinetics were slower than cells grown on TCPs. These results suggest that electrospun anisotropic fibrous scaffolds, as a single method, have limited effect on improving the maturation of hPSC-CMs.

Determining Cardiac Fiber Orientation Using FSL and Registered Ultrasound/DTI volumes

Accurate extraction of cardiac fiber orientation from diffusion tensor imaging is important for determining heart structure and function. However, the acquisition of magnetic resonance (MR) diffusion tensor images is costly and time consuming. By comparison, cardiac ultrasound imaging is rapid and relatively inexpensive, but it lacks the capability to directly measure fiber orientations. In order to create a detailed heart model from ultrasound data, a three-dimensional (3D) diffusion tensor imaging (DTI) with known fiber orientations can be registered to an ultrasound volume through a geometric mask. After registration, the cardiac orientations from the template DTI can be mapped to the heart using a deformable transformation field. This process depends heavily on accurate fiber orientation extraction from the DTI. In this study, we use the FMRIB Software Library (FSL) to determine cardiac fiber orientations in diffusion weighted images. For the registration between ultrasound and MRI volumes, we achieved an average Dice similarity coefficient (DSC) of 81.6±2.1%. For the estimation of fiber orientations from the proposed method, we achieved an acute angle error (AAE) of 22.7±3.1° as compared to the direct measurements from DTI. This work provides a new approach to generate cardiac fiber orientation that may be used for many cardiac applications.

Bioactive nanoparticles improve calcium handling in failing cardiac myocytes

AIMS

To evaluate the ability of N-acetylglucosamine (GlcNAc) decorated nanoparticles and their cargo to modulate calcium handling in failing cardiac myocytes (CMs).

MATERIALS & METHODS

Primary CMs isolated from normal and failing hearts were treated with GlcNAc nanoparticles in order to assess the ability of the nanoparticles and their cargo to correct dysfunctional calcium handling in failing myocytes.

RESULTS & CONCLUSION

GlcNAc particles reduced aberrant calcium release in failing CMs and restored sarcomere function. Additionally, encapsulation of a small calcium-modulating protein, S100A1, in GlcNAc nanoparticles also showed improved calcium regulation. Thus, the development of our bioactive nanoparticle allows for a 'two-hit' treatment, by which the cargo and also the nanoparticle itself can modulate intracellular protein activity.

Register cardiac fiber orientations from 3D DTI volume to 2D ultrasound image of rat hearts

Two-dimensional (2D) ultrasound or echocardiography is one of the most widely used examinations for the diagnosis of cardiac diseases. However, it only supplies the geometric and structural information of the myocardium. In order to supply more detailed microstructure information of the myocardium, this paper proposes a registration method to map cardiac fiber orientations from three-dimensional (3D) magnetic resonance diffusion tensor imaging (MR-DTI) volume to the 2D ultrasound image. It utilizes a 2D/3D intensity based registration procedure including rigid, log-demons, and affine transformations to search the best similar slice from the template volume. After registration, the cardiac fiber orientations are mapped to the 2D ultrasound image via fiber relocations and reorientations. This method was validated by six images of rat hearts ex vivo. The evaluation results indicated that the final Dice similarity coefficient (DSC) achieved more than 90% after geometric registrations; and the inclination angle errors (IAE) between the mapped fiber orientations and the gold standards were less than 15 degree. This method may provide a practical tool for cardiologists to examine cardiac fiber orientations on ultrasound images and have the potential to supply additional information for diagnosis of cardiac diseases.

3D in vivo imaging of rat hearts by high frequency ultrasound and its application in myofiber orientation wrapping

Cardiac ultrasound plays an important role in the imaging of hearts in basic cardiovascular research and clinical examinations. 3D ultrasound imaging can provide the geometry or motion information of the heart. Especially, the wrapping of cardiac fiber orientations to the ultrasound volume could supply useful information on the stress distributions and electric action spreading. However, how to acquire 3D ultrasound volumes of the heart of small animals in vivo for cardiac fiber wrapping is still a challenging problem. In this study, we provide an approach to acquire 3D ultrasound volumes of the rat hearts in vivo. The comparison between both in vivo and ex vivo geometries indicated 90.1% Dice similarity. In this preliminary study, the evaluations of the cardiac fiber orientation wrapping errors were 24.7° for the acute angle error and were 22.4° for the inclination angle error. This 3D ultrasound imaging and fiber orientation estimation technique have potential applications in cardiac imaging.

A proliferative burst during preadolescence establishes the final cardiomyocyte number

It is widely believed that perinatal cardiomyocyte terminal differentiation blocks cytokinesis, thereby causing binucleation and limiting regenerative repair after injury. This suggests that heart growth should occur entirely by cardiomyocyte hypertrophy during preadolescence when, in mice, cardiac mass increases many-fold over a few weeks. Here, we show that a thyroid hormone surge activates the IGF-1/IGF-1-R/Akt pathway on postnatal day 15 and initiates a brief but intense proliferative burst of predominantly binuclear cardiomyocytes. This proliferation increases cardiomyocyte numbers by ~40%, causing a major disparity between heart and cardiomyocyte growth. Also, the response to cardiac injury at postnatal day 15 is intermediate between that observed at postnatal days 2 and 21, further suggesting persistence of cardiomyocyte proliferative capacity beyond the perinatal period. If replicated in humans, this may allow novel regenerative therapies for heart diseases.

Microscale generation of cardiospheres promotes robust enrichment of cardiomyocytes derived from human pluripotent stem cells

Cardiomyocytes derived from human pluripotent stem cells (hPSCs) are a promising cell source for regenerative medicine, disease modeling, and drug discovery, all of which require enriched cardiomyocytes, ideally ones with mature phenotypes. However, current methods are typically performed in 2D environments that produce immature cardiomyocytes within heterogeneous populations. Here, we generated 3D aggregates of cardiomyocytes (cardiospheres) from 2D differentiation cultures of hPSCs using microscale technology and rotary orbital suspension culture. Nearly 100% of the cardiospheres showed spontaneous contractility and synchronous intracellular calcium transients. Strikingly, from starting heterogeneous populations containing ∼10%-40% cardiomyocytes, the cell population within the generated cardiospheres featured ∼80%-100% cardiomyocytes, corresponding to an enrichment factor of up to 7-fold. Furthermore, cardiomyocytes from cardiospheres exhibited enhanced structural maturation in comparison with those from a parallel 2D culture. Thus, generation of cardiospheres represents a simple and robust method for enrichment of cardiomyocytes in microtissues that have the potential use in regenerative medicine as well as other applications.

Eruption stage of permanent molars and occlusal caries activity/arrest

This study assessed the association between the eruption stage of permanent second molars and occlusal caries activity among 12-year-old schoolchildren from South Brazil. A cross-sectional study was performed in Porto Alegre using a multistage probability sampling strategy to select a representative sample. Clinical examination was conducted to assess the eruption stage of permanent molars, Gingival Bleeding Index, and, after tooth cleaning and drying, caries experience (noncavitated and cavitated lesions, including caries activity assessment). Data were collected on sex, socioeconomic status, mother's education, brushing frequency, and consumption of soft drinks. Generalized estimating equations were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Overall, 983 schoolchildren with 3,071 second molars were available for analysis. Whereas active caries was observed in 6.6% of fully erupted permanent second molars, caries affected 26.2%, 29.6%, and 18.2% of erupting molars classified as stages 1, 2, and 3, respectively: stage 1, partially erupted occlusal surface; stage 2, fully erupted occlusal surface, <1/2 crown exposed; and stage 3, fully erupted occlusal surface, >1/2 crown exposed. After adjusting for socioeconomic and behavioral variables, partially erupted molars were significantly more likely to present active caries lesions than molars in full occlusion: stage 1, OR = 4.99 (95% CI = 3.38, 7.38); stage 2, OR = 5.18 (95% CI = 3.14, 8.53); stage 3, OR = 3.20 (95% CI = 2.21, 4.64). Similar results were found when clinical variables were included in the adjusted model. In conclusion, most occlusal caries lesions tend to arrest/revert when teeth reach the occlusal plan; however, an important proportion of these lesions remains active and in need of proper management. Children at risk should be targeted with preventive and minimally invasive strategies.

Dysregulation of catalase activity in newborn myocytes during hypoxia is mediated by c-Abl tyrosine kinase

In the adult heart, catalase (CAT) activity increases appropriately with increasing levels of hydrogen peroxide, conferring cardioprotection. This mechanism is absent in the newborn for unknown reasons. In the present study, we examined how the posttranslational modification of CAT contributes to its activation during hypoxia/ischemia and the role of c-Abl tyrosine kinase in this process. Hypoxia studies were carried out using primary cardiomyocytes from adult (>8 weeks) and newborn rats. Following hypoxia, the ratio of phosphorylated to total CAT and c-Abl in isolated newborn rat myocytes did not increase and were significantly lower (1.3- and 4.2-fold, respectively; P < .05) than their adult counterparts. Similarly, there was a significant association (P < .0005) between c-Abl and CAT in adult cells following hypoxia (30.9 ± 8.2 to 70.7 ± 13.1 au) that was absent in newborn myocytes. Although ubiquitination of CAT was higher in newborns compared to adults following hypoxia, inhibition of this did not improve CAT activity. When a c-Abl activator (5-(1,3-diaryl-1H-pyrazol-4-yl)hydantoin [DPH], 200 µmol/L) was administered prior to hypoxia, not only CAT activity was significantly increased (P < .05) but also phosphorylation levels were also significantly improved (P < .01) in these newborn myocytes. Additionally, ischemia-reperfusion (IR) studies were performed using newborn (4-5 days) rabbit hearts perfused in a Langendorff method. The DPH given as an intracardiac injection into the right ventricle of newborn rabbit resulted in a significant improvement (P < .002) in the recovery of developed pressure after IR, a key indicator of cardiac function (from 74.6% ± 6.6% to 118.7% ± 10.9%). In addition, CAT activity was increased 3.92-fold (P < .02) in the same DPH-treated hearts. Addition of DPH to adult rabbits in contrast had no significant effect (from 71.3% ± 10.7% to 59.4% ± 12.1%). Therefore, in the newborn, decreased phosphorylation of CAT by c-Abl potentially mediates IR-induced dysfunction, and activation of c-Abl may be a strategy to prevent ischemic injury associated with surgical procedures.

Mapping Cardiac Fiber Orientations from High-Resolution DTI to High-Frequency 3D Ultrasound

The orientation of cardiac fibers affects the anatomical, mechanical, and electrophysiological properties of the heart. Although echocardiography is the most common imaging modality in clinical cardiac examination, it can only provide the cardiac geometry or motion information without cardiac fiber orientations. If the patient's cardiac fiber orientations can be mapped to his/her echocardiography images in clinical examinations, it may provide quantitative measures for diagnosis, personalized modeling, and image-guided cardiac therapies. Therefore, this project addresses the feasibility of mapping personalized cardiac fiber orientations to three-dimensional (3D) ultrasound image volumes. First, the geometry of the heart extracted from the MRI is translated to 3D ultrasound by rigid and deformable registration. Deformation fields between both geometries from MRI and ultrasound are obtained after registration. Three different deformable registration methods were utilized for the MRI-ultrasound registration. Finally, the cardiac fiber orientations imaged by DTI are mapped to ultrasound volumes based on the extracted deformation fields. Moreover, this study also demonstrated the ability to simulate electricity activations during the cardiac resynchronization therapy (CRT) process. The proposed method has been validated in two rat hearts and three canine hearts. After MRI/ultrasound image registration, the Dice similarity scores were more than 90% and the corresponding target errors were less than 0.25 mm. This proposed approach can provide cardiac fiber orientations to ultrasound images and can have a variety of potential applications in cardiac imaging.

Abstract 337: cAbl Tyrosine Kinase Increases Catalase Activity in the Catalase-Dysregulated Newborn Rabbit Heart

Introduction: Pediatric patients undergoing corrective cardiothoracic surgery numbered in the tens of thousands annually and therefore it is necessary that pre- and post-operative strategies be employed to limit ischemia-reperfusion (IR) injury. We have found differences in the way the newborn (versus the adult) heart responds to IR injury. In the adult, catalase activity increases appropriately with increasing levels of hydrogen peroxide (H2O2), conferring cardioprotection. This effect however does not occur in the newborn.

Materials and Methods: Hypoxia studies were carried out using primary cardiomyocytes from adult (>8 weeks) and newborn rats. Ischemia-reperfusion (IR) studies were performed using newborn (4-5 days) rabbits. Isolated rat cardiomyocytes were exposed to 1 hour of hypoxia (95%N2,5%CO2). Immunoprecipitation and western blot analysis were done for phosphorylated and total catalase and c-Abl. In addition, catalase activity was determined spectrophotometrically by measuring the decomposition of H2O2. Newborn rabbit hearts were perfused using Langendorff method with ischemia and reperfusion periods lasting 30 and 60 minutes, respectively. DPH (200µM), a cAbl activator was injected directly into the newborn right ventricle (RV) two minutes before the reperfusion period.

Results: Following hypoxia, the ratio of phosphorylated to total catalase and c-Abl in isolated newborn rat myocytes did not increase and were significantly lower (1.92- and 6.21-fold, respectively; p<0.05) than their adult counterparts. Interestingly, when DPH was administered one hour prior to hypoxia, not only was catalase activity significantly increased 6.28-fold (p<0.01) but phosphorylation levels were also altered. Finally, direct injection of DPH into the RV of Langendorff-perfused newborn rabbit hearts caused a significant improvement in percent recovery of developed pressure (from 49.53±5.42% to 125.5±15.5%) after IR, a key indicator of cardiac function. Catalase activity in these same hearts increased 2.92-fold.

Conclusion: In the newborn, decreased phosphorylation of catalase by c-Abl potentially mediates IR-induced dysfunction. Activation of c-Abl may be a strategy to prevent ischemic injury associated with surgical procedures.

Extracting Cardiac Myofiber Orientations from High Frequency Ultrasound Images

Cardiac myofiber plays an important role in stress mechanism during heart beating periods. The orientation of myofibers decides the effects of the stress distribution and the whole heart deformation. It is important to image and quantitatively extract these orientations for understanding the cardiac physiological and pathological mechanism and for diagnosis of chronic diseases. Ultrasound has been wildly used in cardiac diagnosis because of its ability of performing dynamic and noninvasive imaging and because of its low cost. An extraction method is proposed to automatically detect the cardiac myofiber orientations from high frequency ultrasound images. First, heart walls containing myofibers are imaged by B-mode high frequency (>20 MHz) ultrasound imaging. Second, myofiber orientations are extracted from ultrasound images using the proposed method that combines a nonlinear anisotropic diffusion filter, Canny edge detector, Hough transform, and K-means clustering. This method is validated by the results of ultrasound data from phantoms and pig hearts.

Mitochondrial calcium and reactive oxygen species regulate agonist-initiated platelet phosphatidylserine exposure

OBJECTIVE

To study the interactions of cytoplasmic calcium elevation, mitochondrial permeability transition pore (mPTP) formation, and reactive oxygen species formation in the regulation of phosphatidylserine (PS) exposure in platelets.

METHODS AND RESULTS

mPTP formation, but not the degree of cytoplasmic calcium elevation, was associated with PS exposure in wild-type, cyclophilin D-null, ionomycin-treated, and reactive oxygen species-treated platelets. In the absence of the mPTP regulator cyclophilin D, agonist-initiated mPTP formation and high-level PS exposure were markedly blunted, but cytoplasmic calcium transients were unchanged. Mitochondrial calcium (Ca(2+)(mit)) transients and reactive oxygen species, key regulators of mPTP formation, were examined in strongly stimulated platelets. Increased reactive oxygen species production occurred in strongly stimulated platelets and was dependent on extracellular calcium entry, but not the presence of cyclophilin D. Ca(2+)(mit) increased significantly in strongly stimulated platelets. Abrogation of Ca(2+)(mit) entry, either by inhibition of the Ca(2+)(mit) uniporter or mitochondrial depolarization, prevented mPTP formation and exposure but not platelet aggregation or granule release.

CONCLUSIONS

Sustained cytoplasmic calcium levels are necessary, but not sufficient, for high-level PS exposure in response to agonists. Increased Ca(2+)(mit) levels are a key signal initiating mPTP formation and PS exposure. Blockade of Ca(2+)(mit) entry allows the specific inhibition of platelet procoagulant activity.

Abstract 69: Diminished T-Tubule Density in Newborn Human Ventricular Cells Is Associated with Heterogeneity of Calcium Transients

For children with congenital heart disease (CHD), therapies developed for adults may have different effects on immature myocardium. Thus, it is critical to understand calcium handling in the young human ventricle.

Methods: Human ventricular cells were isolated from tissue removed as part of the surgical repair for CHDs from two age groups: newborns (<1 week old) and infants (2-12 months old). Developmental changes in t-tubules were examined in live cells with Di-8 ANEPPS which highlights the cell membrane. We measured the T-index (percent of cell interior occupied by t-tubules), averaged for at least 3 confocal z-sections per cell. Changes in calcium transients were measured by confocal line scans in cells loaded with Fluo-4 and field stimulated (37°C).

Results: Newborn human myocytes have very few t-tubules whereas infant myocytes have a range of t-tubule densities. The T-index in newborn myocytes was significantly less than in infant myocytes (4.4±0.2%, n=8 cells, 3 newborns vs. 9.1±0.9%, n=55 cells, 7 infants). Furthermore, there was sizable heterogeneity in the T-index for each patient in the infant group, in which some cells had few t-tubules and others had many t-tubules. We calculated the coefficient of variation (CV=SD/mean*100) for each patient and compared CV values for newborns vs. infants. CV was significantly greater in infants compared to newborns (46.5±7.4%, n=7, vs. 9.4±1.9%, n=3, p<0.02). In addition, calcium transients from newborn cells had a ‘U’ shaped wavefront with calcium first increasing at the outer edge of the cell then propagating toward the center. In contrast, infant cells had a homogenous calcium wavefront. The delay of peak calcium from the edge to center was significantly longer in newborns compared to infants (61.7±8.9 ms, n=8 cells, 3 newborns vs. 10.6±1.6 ms, n=6 cells, 4 infants, p<0.001).

Conclusions: There are heterogeneous calcium transients in newborn human myocytes that correspond to a lack of t-tubules. Furthermore, t-tubule development occurs in a heterogeneous manner throughout the first year of life with cells from the same patient exhibiting different degrees of t-tubule development. This is the first study to examine t-tubule development and calcium transients in the very young human ventricular myocardium.

Cardioprotection from oxidative stress in the newborn heart by activation of PPARγ is mediated by catalase

Regulation of catalase (CAT) by peroxisome proliferator-activated receptor-γ (PPARγ) was investigated to determine if PPARγ activation provides cardioprotection from oxidative stress caused by hydrogen peroxide (H(2)O(2)) in an age-dependent manner. Left ventricular developed pressure (LVDP) was measured in Langendorff perfused newborn or adult rabbit hearts, exposed to 200μM H(2)O(2), with perfusion of rosiglitazone (RGZ) or pioglitazone (PGZ), PPARγ agonists. We found: (1) H(2)O(2) significantly decreased sarcomere shortening in newborn ventricular cells but not in adult cells. Lactate dehydrogenase (LDH) release occurred earlier in newborn than in adult heart, which may be due, in part, to the lower expression of CAT in newborn heart. (2) RGZ increased CAT mRNA and protein as well as activity in newborn but not in adult heart. GW9662 (PPARγ blocker) eliminated the increased CAT mRNA by RGZ. (3) In newborn heart, RGZ and PGZ treatment inhibited release of LDH in response to H(2)O(2) compared to H(2)O(2) alone. GW9662 decreased this inhibition. (4) LVDP was significantly higher in both RGZ+H(2)O(2) and PGZ+H(2)O(2) groups than in the H(2)O(2) group. Block of PPARγ abolished this effect. In contrast, there was no effect of RGZ in adult. (5) The cardioprotective effects of RGZ were abolished by inhibition of CAT. In conclusion, PPARγ activation is cardioprotective to H(2)O(2)-induced stress in the newborn heart by upregulation of catalase. These data suggest that PPARγ activation may be an effective therapy for the young cardiac patient.

Abstract P322: Chamber-Specific Differences in Oxidative Stress in Newborn Versus Adult Rabbit Hearts Following Ischemia-Reperfusion

Each year, tens of thousands of children undergo cardiopulmonary bypass (CPB) to correct congenital heart defects. While necessary for surgery, CPB involves stopping the heart and exposing it to ischemic conditions. While much is known about adult injury, little is known about the effects of global ischemia on newborn ventricles. The purpose of this study was to determine age- and chamber-specific differences in oxidative stress following global ischemia-reperfusion injury. We studied newborn (2–4 days) and adult (>8 weeks) rabbit hearts subjected to Langendorff ischemia-reperfusion (30 minutes ischemia, 60 minutes reperfusion). Catalase and superoxide dismutase (SOD) activities were measured, as well as real-time hydrogen peroxide (H 2 O 2 ) and superoxide (O 2 − ) generation using confocal microscopy in isolated left and right ventricular (LV and RV) myocytes exposed to hypoxia. Our data demonstrate chamber and age-specific changes in oxidative stress. During ischemia, H 2 O 2 increased significantly in the RV while remaining constant in the LV of newborn rat rabbit myocytes. In contrast, there was a smaller, nonsignificant increase in H 2 O 2 in both both RV and LV myocytes of adults. The increase seen in the RV of newborns was several fold higher than that of adults (4.3-fold vs. 2.2 fold; p<0.05). In whole heart tissue, catalase activity was significantly increased following ischemia in both adult ventricles, while no increase was seen in newborn hearts compared to sham hearts. Additionally, levels in newborns were several fold lower (p<0.05), indicating less scavenging potential. SOD activity was increased from sham vs. ischemia in the LV of both adult and newborn hearts, but only in the RV of the newborn heart (0.80±0.09 to 3.0±0.43 U/mg; p<0.001). Intra-cardiac injection of an H 2 O 2 scavenger, Ebselen, loaded in nanoparticles, improved recovery of developed pressure (49.53±16.25 to 80.0±11.31) in the RV of the newborn (p<0.05), suggesting the local delivery of an exogenous antioxidant is cardioprotective in newborn RVs. Our data demonstrate there are ventricle-specific differences in oxidative stress between newborn and adult rabbit hearts. Local therapy is able to address some of these differences and may limit damage during bypass surgery.

Impact of a Low-Cost and Simple Intervention in Enhancing Treatment Adherence in a Brazilian Asthma Sample

The aim of this study was to evaluate adherence to treatment in persistent asthma in Brazil to determine the factors associated with non-adherence and to measure the efficacy of telephone calls in enhancing adherence. In a prospective, multicenter, interventional clinical trial with parallel groups, asthmatics were randomized into an intervention group or a control group. Asthmatics included in the intervention group received an initial telephone call to record demographic information and asthma characterization. After that, biweekly telephone calls were made to promote treatment adherence. Asthmatics included in the control group received only the initial and final telephone calls. Both groups received three packages of salmeterol/fluticasone for 3 months. The main outcome measure was the percentage of participants who took the prescribed doses of the drug. A total of 271 patients were included. The overall adherence rate was 51.9% for the control group and 74.3% for the intervention group. This meant a reduction of relative risk (RRR) of 47% (p < 0.001). The number needed to treat (NNT) was 4.5. The only variable associated with better adherence was severe persistent asthma. A low-cost easily implemented intervention, tailored to each individual, enhanced the adherence rate among Brazilian asthmatic patients.

Force frequency relationship of the human ventricle increases during early postnatal development

Understanding developmental changes in contractility is critical to improving therapies for young cardiac patients. Isometric developed force was measured in human ventricular muscle strips from two age groups: newborns (<2 wk) and infants (3-14 mo) undergoing repair for congenital heart defects. Muscle strips were paced at several cycle lengths (CLs) to determine the force frequency response (FFR). Changes in Na/Ca exchanger (NCX), sarcoplasmic reticulum Ca-ATPase (SERCA), and phospholamban (PLB) were characterized. At CL 2000 ms, developed force was similar in the two groups. Decreasing CL increased developed force in the infant group to 131 +/- 8% (CL 1000 ms) and 157 +/- 18% (CL 500 ms) demonstrating a positive FFR. The FFR in the newborn group was flat. NCX mRNA and protein levels were significantly larger in the newborn than infant group whereas SERCA levels were unchanged. PLB mRNA levels and PLB/SERCA ratio increased with age. Immunostaining for NCX in isolated newborn cells showed peripheral staining. In infant cells, NCX was also found in T-tubules. SERCA staining was regular and striated in both groups. This study shows for the first time that the newborn human ventricle has a flat FFR, which increases with age and may be caused by developmental changes in calcium handling.

Stretch-activated channel activation promotes early afterdepolarizations in rat ventricular myocytes under oxidative stress

Mechanical stretch and oxidative stress have been shown to prolong action potential duration (APD) and produce early afterdepolarizations (EADs). Here, we developed a simulation model to study the role of stretch-activated channel (SAC) currents in triggering EADs in ventricular myocytes under oxidative stress. We adapted our coupling clamp circuit so that a model ionic current representing the actual SAC current was injected into ventricular myocytes and added as a real-time current. This current was calculated as I(SAC) = G(SAC) * (V(m) - E(SAC)), where G(SAC) is the stretch-activated conductance, V(m) is the membrane potential, and E(SAC) is the reversal potential. In rat ventricular myocytes, application of G(SAC) did not produce sustained automaticity or EADs, although turn-on of G(SAC) did produce some transient automaticity at high levels of G(SAC). Exposure of myocytes to 100 microM H(2)O(2) induced significant APD prolongation and increase in intracellular Ca(2+) load and transient, but no EAD or sustained automaticity was generated in the absence of G(SAC). However, the combination of G(SAC) and H(2)O(2) consistently produced EADs at lower levels of G(SAC) (2.6 +/- 0.4 nS, n = 14, P < 0.05). Pacing myocytes at a faster rate further prolonged APD and promoted the development of EADs. SAC activation plays an important role in facilitating the development of EADs in ventricular myocytes under acute oxidative stress. This mechanism may contribute to the increased propensity to lethal ventricular arrhythmias seen in cardiomyopathies, where the myocardium stretch and oxidative stress generally coexist.

Dopamine increases L-type calcium current more in newborn than adult rabbit cardiomyocytes via D1 and β2 receptors

Dopamine is used to treat heart failure, particularly after cardiac surgery in infants, but the mechanisms of action are unclear. We investigated differences in the effect of dopamine on L-type calcium current ( ICa) between newborn (NB, 1–4 days) and adult (AD, 3–4 mo) rabbit ventricular myocytes. Myocytes were enzymatically dissociated from NB and AD rabbit hearts. ICa was recorded by using the whole cell patch-clamp technique. mRNA levels of cardiac dopamine receptor type 1 (D1), type 2 (D2), and β-adrenergic receptors (β-ARs) were measured by real-time RT-PCR. Dopamine (100 μM) increased ICa more in NB (Emax 87 ± 10%) than in AD ventricular cells (Emax 21 ± 3%). Further investigation of this difference showed that mRNA levels of the D1 receptor were significantly higher in NB, and, with β-AR blockade, dopamine increased ICa more in NB than AD cells. Additionally, SKF-38393 (selective D1 receptor agonist) significantly increased ICa by 55 ± 4% in NB ( P < 0.05, n = 4) and by 11 ± 1% in AD ( P < 0.05, n = 6). Dopamine in the presence of SCH-23390 (D1 receptor antagonist) increased ICa in NB cells by 67 ± 5% and by 22 ± 2% in AD cells, suggesting a role for β-AR stimulation. Selective blockade of β1- or β2-receptors (with block of D1 receptors) showed that the β-AR action of dopamine in the NB was largely mediated via β2-AR activation. Dopamine produces a larger increase in ICa in NB cardiomyocytes compared with ADs. The mechanism of action is not only through β2-ARs but also due to higher expression of cardiac D1 receptor in NB.

Developmental changes in time course of recovery from inactivation in L-type calcium currents of rabbit ventricular myocytes

The mechanisms of recovery from inactivation of the L-type calcium current ( ICa) are not well established, and recovery is affected by many experimental conditions. Little is known about developmental changes of recovery from inactivation of ICa. We studied developmental changes of recovery from inactivation in ICa using isolated adult and newborn (1–4 days) rabbit ventricular myocytes. We used broken-patch and perforated-patch techniques with physiological extracellular ionic concentrations of calcium and sodium and interpulse conditioning potentials of −80 or −50 mV. We also maximized ICa with forskolin. We found that recovery from inactivation did not differ between adult and newborn cells when either EGTA or BAPTA was used to buffer intracellular calcium. Maximizing ICa with forskolin slowed recovery from inactivation in newborn but not in adult cells. In contrast, when the intracellular buffering of the cell was left nearly intact (perforated patch), recovery from inactivation (half-time of recovery) in the newborn cells was significantly slower than for the adult cells when either a conditioning potential of −80 mV (140 ± 9 vs. 58 ± 4 ms, newborn vs. adult; P < 0.05) or −50 mV (641 ± 106 vs. 168 ± 15 ms, newborn vs. adult; P < 0.05) was used. Forskolin significantly increased half-time of recovery for both adult and newborn cells. Dialysis with no calcium buffer showed a slower recovery from inactivation in newborn cells. Intracellular dialysis with a calcium buffer masked differences in recovery from inactivation of ICa between newborn and adult rabbit ventricular cells.

Propagation of pacemaker activity

Spontaneous activity of specific regions (e.g., the Sinoatrial node, SAN) is essential for the normal activation sequence of the heart and also serve as a primary means of modulating cardiac rate by sympathetic tone and circulating catecholamines. The mechanisms of how a small SAN region can electrically drive a much larger atrium, or how a small ectopic focus can drive surrounding ventricular or atrial tissue are complex, and involve the membrane properties and electrical coupling within the SAN or focus region as well as the membrane properties, coupling conductance magnitudes and also regional distribution within the surrounding tissue. We review here studies over the past few decades in which mathematical models and experimental studies have been used to determine some of the design principles of successful propagation from a pacemaking focus. These principles can be briefly summarized as (1) central relative uncoupling to protect the spontaneously firing cells from too much electrotonic inhibition, (2) a transitional region in which the cell type and electrical coupling change from the central SAN region to the peripheral atrial region, and (3) a distributed anisotropy to facilitate focal activity.

Effects of Single-Site Versus Biventricular Epicardial Pacing on Myocardial Performance in an Immature Animal Model of Atrioventricular Block

INTRODUCTION

Single-site ventricular pacing results in dyssynchronous ventricular activation and may contribute to ventricular dysfunction. We evaluated epicardial biventricular (BiV) pacing as a means of maintaining synchronous ventricular activation in an acute piglet model of AV block with normal ventricular anatomy and function.

METHODS AND RESULTS

We used left ventricular (LV) impedance catheters and tissue Doppler imaging to assess the cardiodynamics of immature piglets (n = 6, 33-78 days, 9.35 +/- 0.85 kg). Following catheter ablation of the AV node, a pacemaker was programmed 20 beats per minute above the intrinsic atrial rate. The animals were paced at 5-minute intervals via the following AV sequential configurations: Right atrial appendage (RA)-RV apex (RVA), RA-LV apex (LVA), and RA-biventricular (RVA/LVA). RA-RVA was the experimental control. LV systolic mechanics, measured by the slope of the end-systolic pressure-volume relationship (E(es)), increased with BiV pacing (12.8 +/- 3.4 mmHg/mL, P < 0.02) or single-site LVA pacing (10.6 +/- 3.4 mmHg/mL, P < 0.05) compared with single-site RVA pacing (8.3 +/- 1.4 mmHg/mL). QRS duration lengthened compared with sinus rhythm (42 +/- 8 msec) with either RVA (56 +/- 9 msec, P < 0.02) or LVA (54 +/- 7 msec, P < 0.03), but not with BiV (48 +/- 7 msec, P = 0.08) pacing. Tissue Doppler imaging showed LV dyssynchrony with RVA (septal-to-lateral delay 46.0 +/- 51.7 msec), with return toward normal with LVA (-9.6 +/- 33.6 msec, P < 0.04) or BiV (-4.1 +/- 33.8 msec, P < 0.04) pacing.

CONCLUSIONS

In this acute immature piglet model of AV block, LV performance improved with single-site pacing from the LVA and BiV pacing (RVA/LVA), as compared with single-site pacing from the RVA. These changes correlated with tissue Doppler indices of mechanical synchrony, though not necessarily with QRS duration.

Remodeling of early-phase repolarization: a mechanism of abnormal impulse conduction in heart failure

BACKGROUND

The early phase of action potential (AP) repolarization is critical to impulse conduction in the heart because it provides current for charging electrically coupled cells. In the present study we tested the impact of heart failure-associated electrical remodeling on AP propagation.

METHODS AND RESULTS

Subepicardial, midmyocardial, and subendocardial myocytes were enzymatically dissociated from control and pressure-overload failing left ventricle (LV), and APs were recorded. A unique coupling-clamp technique was used to electrically couple 2 isolated myocytes with a controlled value of coupling conductance (Gc). In sham-operated mice, AP duration manifested a clear transmural gradient, with faster repolarization in subepicardial myocytes than in subendocardial myocytes. AP propagation from subendocardial to subepicardial myocytes required less Gc compared with conduction in the opposite direction. In failing heart, AP morphology was dramatically altered, with a significantly elevated plateau potential and prolonged AP duration. Spatially nonuniform alteration of AP duration in failing heart blunted the transmural gradient of repolarization. Furthermore, increased pacing rate prolonged AP duration exclusively in myocytes from failing heart, and the critical conductance required for successful AP propagation decreased significantly at high frequencies. Finally, in failing heart, asymmetry of transmural electrical propagation was abolished.

CONCLUSIONS

In failing heart, preferential conduction from subendocardial to subepicardial myocytes is lost, and failing myocytes manifest facilitated AP propagation at fast rates. Together, these electrical remodeling responses may promote conduction of premature impulses and heighten the risk of malignant arrhythmia, a prominent feature of heart failure.

No gender difference in effectiveness of smoking cessation treatment in a Brazilian real-life setting

BACKGROUND

The clinical effectiveness of pharmacotherapy for smoking cessation in real-life settings has yet to be evaluated.

OBJECTIVES

To assess the effectiveness of bupropion in general clinical practice for smoking cessation and to identify predictors of failure.

METHODS

In an open, non-randomised study, smokers were recruited at the Smoking Cessation Clinics, Hospital Sao Lucas, Porto Alegre, Brazil. Subjects participated in a motivational group meeting, completed a standardised questionnaire and Fagerstrom test, and had their vital signs and exhaled CO registered. All participants received a prescription of bupropion and the same cognitive behaviour therapy. They attended eight weekly individual sessions, then monthly until the sixth month and a final session at month 12. The primary outcome measure was the rate of abstinence at 12 months. The predictor factors studied were sex, age, educational level, nicotine dependence, previous attempts and comorbidities.

RESULTS

Among 253 smokers (62.5% females), abstinence rates at 6 months were 20.8% for males and 22.7% for females. The success rates dropped to 13.9% and 14.3% for males and females, respectively.

CONCLUSIONS

Cognitive therapy plus bupropion for smoking cessation in real-life clinics in Brazil were similar to the efficacy found in clinical trials. No significant gender differences in success rates were found.

Quality of life and sexuality in chronic dialysis female patients

Patients in end-stage renal disease (ESRD) present reduced quality of life (QOL) and impaired sexual function. Previous studies have mostly addressed male sexual dysfunction. This was a cross-sectional controlled study that applied a general and the World Health Organization Quality of Life-bref questionnaires to assess demographic, marital, and sexual conditions, and QOL in 86 healthy women aged 18 or more years (Group 1), and 38 female ESRD patients on dialysis for at least 2 months (Group 2). The effect of several explanatory variables upon QOL components was estimated. Quality of life was lower in Group 2 -- overall, and on physical and environment domains. To undergo dialysis and to be poorly educated negatively affected the QOL. Yet age, a stable marital relationship or being sexually active had no effect. Female patients undergoing chronic dialysis had lower QOL and were significantly more sexually dysfunctional than comparable healthy women. Decline in sexual function had no effect on the QOL.

Upregulation of hypoxia inducible factor is associated with attenuation of neuronal injury in neonatal piglets undergoing deep hypothermic circulatory arrest

BACKGROUND

Prolonged deep hypothermic circulatory arrest is known to cause neurological injury. Hypoxia inducible factor, a transcription factor that mediates adaptive changes during hypoxia, is neuroprotective in models of ischemic brain injury, in part by upregulating erythropoietin. This study tested the hypothesis that upregulation of hypoxia inducible factor and erythropoietin by preconditioning with hypoxia or the hypoxia-mimetic agents deferoxamine and cobalt chloride would be neuroprotective in a piglet model of deep hypothermic circulatory arrest.

METHODS

Anesthetized neonatal piglets were randomized to 4 preconditioning groups (15 per group): hypoxia, deferoxamine, cobalt chloride, or control (NaCl vehicle). Brain hypoxia inducible factor and erythropoietin contents were assessed by means of Western blotting at 3, 8, and 24 hours after treatment (n = 3 per time point). Twenty-four hours after treatment, 6 to 7 animals per group underwent cardiopulmonary bypass and 110 minutes of deep hypothermic circulatory arrest. After recovery, serial neurobehavioral examinations were conducted for 6 days, after which histopathologic brain injury and neuronal apoptosis (cleaved caspase 3) were assessed.

RESULTS

Erythropoietin expression was not significantly increased by any of the pretreatment strategies. In contrast, there was a significant upregulation of hypoxia inducible factor by pretreatment with deferoxamine and cobalt chloride (P = .002). Neurobehavioral measures revealed no significant differences in time to recovery or extent of injury. Examination of histopathologic brain injury in the hippocampus revealed that pretreatment with deferoxamine (0.4 +/- 0.3) and cobalt chloride (0.5 +/- 0.3) were associated with significantly less neuronal loss than pretreatment with hypoxia or control (2.8 +/- 0.5, P = .004). Finally, cleaved caspase 3 (a marker of apoptotic cell death) was also shown to be diminished in the cobalt and deferoxamine groups, but the difference was not significantly different from the value in the control group.

CONCLUSIONS

In contrast to hypoxia, deferoxamine and cobalt chloride preconditioning upregulated hypoxia inducible factor and were associated with histopathologic neuroprotection after exposure to cardiopulmonary bypass and prolonged deep hypothermic circulatory arrest.

Calcium transients in infant human atrial myocytes

Isolated infant human atrial cells have a slower early repolarization than adult human atrial cells. In addition, from room temperature voltage-clamp studies, infant cells have lower basal L-type calcium currents than adult cells. We hypothesized that the slower repolarization increases the calcium transient of infant human atrial cells. Atrial myocytes were enzymatically dissociated from biopsies of human right atrial appendages of infant (3-8 mo) patients who were undergoing open-heart surgery. Intracellular calcium transients were measured with fluorescence microscopy with application of either square waves or action potential waveforms at physiologic temperature. After repetitive application (1 Hz) of 100-ms duration conditioning depolarizations to 10 mV (from -80 mV), a test pulse of varying duration (DeltaT; 2-100 ms) produced smaller transients (expressed as percentage of the last conditioning pulse) at shorter durations (33 +/- 7% for DeltaT = 2 ms, 80 +/- 4% for DeltaT = 25 ms). With repetitive application of either adult or infant prerecorded action potentials to infant cells, the cells had a decreased calcium transient with the adult action potential (F/F(0) 2.2 +/- 0.4 for infant action potential versus 1.6 +/- 0.2 for adult action potential; n = 7; p < 0.05). The delayed early repolarization of infant cells alters the Ca(2+) transient, which may compensate for the lower availability of basal calcium current in infant cells. The steep relationship that we have demonstrated between test-pulse duration and the calcium transient suggests that modulation of the early repolarization phase of the action potential may be of great significance in modulating excitation-contraction coupling.

Induced automaticity in isolated rat atrial cells by incorporation of a stretch-activated conductance

Stretch of the atrium and sympathetic activity have been implicated as substrates for atrial fibrillation. We investigate how a model of stretch in combination with sympathetic stimulation can induce automaticity in atrial cells. We adapted our coupling clamp circuit so that a model ionic current that represents stretch-activated channels (SACs) was injected into an isolated rat atrial cell in real time. This current was calculated as ISAC= GSAC (Vm-ESAC), where GSAC and ESAC are the conductance and reversal potential of SACs and Vm is the cell's membrane potential. Repetitive automaticity was induced by a sufficiently large GSAC and this critical value of GSAC was decreased by exposure to isoproterenol. The critical value of GSAC decreased from 0.63+/-0.05 nS (mean+/-SE) in control to 0.40+/-0.07 nS in isoproterenol (P<0.05). Additionally, after exposure to isoproterenol, automaticity continued after GSAC was no longer applied and was accompanied by delayed after-depolarizations. In three cells, repetitive automaticity could not be induced at any value of GSAC. Exposure to 10 nM isoproterenol converted these cells to cells with repetitive automaticity in response to GSAC. We conclude that automaticity can be induced in isolated rat atrial cells by application of a model of SACs. Exposure to isoproterenol enhances this effect.

Developmental differences in L-type calcium current of human atrial myocytes

We investigated differences in L-type Ca2+ current (ICa) between infant (INF, 1-12 mo old), young adult (YAD, 14-18 yr old), and older adult (AD) myocytes from biopsies of right atrial appendages. Basal ICa was smaller in INF myocytes (1.2 +/- 0.1 pA/pF, n = 29, 6 +/- 1 mo old, 11 patients) than in YAD (2.5 +/- 0.2 pA/pF, n = 20, 16 +/- 1 yr old, 5 patients) or AD (2.6 +/- 0.3 pA/pF, n = 19, 66 +/- 3 yr old, 9 patients) myocytes (P < 0.05). Maximal ICa produced by isoproterenol (Iso) was similar in INF, YAD, and AD cells: 8.4 +/- 1.1, 9.6 +/- 1.0, and 9.2 +/- 1.3 pA/pF, respectively. Efficacy (Emax) was larger in INF (607 +/- 50%) than for YAD (371 +/- 29%) or AD (455 +/- 12%) myocytes. Potency (EC50) was 8- to 10-fold higher in AD (0.82 +/- 0.09 nM) or YAD (0.41 +/- 0.14 nM) than in INF (7.6 +/- 3.5 nM) myocytes. Protein levels were similar for Gialpha2 but much greater for Gialpha3 in INF than in AD or YAD atrial tissue. When Gialpha3 activity was inhibited by inclusion of a Gialpha3 COOH-terminal decapeptide in the pipette, basal ICa and the response to 10 nM Iso were increased in INF, but not in YAD, cells. We propose that basal ICa and the response to low-dose beta-adrenergic stimulation are inhibited in INF (but not YAD or AD) cells as a result of constitutive inhibitory effects of Gialpha3.

Differences in transient outward current properties between neonatal and adult human atrial myocytes

Knowledge of postnatal modulation of I(to) in human atrial myocytes is quite limited. The present study investigated the differences in I(to) properties between neonatal and adult human atrial myocytes.

METHODS

Atrial myocytes were dissociated enzymatically from biopsies of human right atrial appendage. I(to) and action potentials were recorded by whole-cell patch-clamp technique. The expressed protein levels of Kv4.3 and KChIP2 in atrial tissue were detected by western blot technique.

RESULTS

I(to) was present in all atrial cells (n = 37) from 10 neonatal patients (2.5-7 months). The mean value of I(to) density in neonatal atrial cells was significantly larger than in adult atrial cells. The time constants for I(to) current decay were significantly faster for neonatal cells, compared to adult cells. I(to) recovery from inactivation at holding potential of - 80 mV was significantly slower for neonatal atrial cells than for adult atrial cells. There was no difference in the voltage dependence of I(to) activation between neonatal and adult cells. The voltage-dependent inactivation slope factor was smaller for neonatal compared to adult atrial cells. A more significant frequency-dependent suppression of I(to) peak current and a more significant lengthening of APD(30) were observed in neonatal atrial cells compared to adult atrial cells. Western blots showed both Kv4.3 and KChIP2 are expressed in neonatal atria, but with significantly higher level of Kv4.3 and lower level of KChIP2 protein compared to adult.

CONCLUSION

There are significant differences in the properties of I(to) between neonatal and adult human atrial cells, including a larger current density, faster inactivation and slower recovery from inactivation in the neonatal atrial cells. The physiological differences of I(to) are consistent with the different expression protein levels of Kv4.3 and KChIP2.