{"metabolics" ["research/metabolics/Brent_1.jpg" "research/metabolics/Brent_3.jpg" "research/metabolics/Brent_2.jpg"], "model-building" ["research/model-building/Fijoy_pipeIllustrWithFibersNew.jpg"], "electrophysiology" ["research/electrophysiology/alex_fig2.jpg" "research/electrophysiology/Kelly_F4.jpg" "research/electrophysiology/JB_Figure_atrial2.jpg" "research/electrophysiology/JB_Figure_atrial1.jpg" "research/electrophysiology/kathleen_fig1.png" "research/electrophysiology/alex_fig3.jpg" "research/electrophysiology/alex_fig1.jpg" "research/electrophysiology/kathleen_fig3.jpg" "research/electrophysiology/Lukas_Figure.jpg" "research/electrophysiology/arevalo_fig1.jpg" "research/electrophysiology/kathleen_fig4.png" "research/electrophysiology/JB_Figure_fiber.jpg" "research/electrophysiology/kathleen_fig4.jpg" "research/electrophysiology/kathleen_fig2.png"], "electromechanics" ["research/electromechanics/JC_Fig2.png" "research/electromechanics/Yuxuan_paperSAC_4.jpg" "research/electromechanics/JC_Fig1.jpg"]}

{"research/model-building/Fijoy_pipeIllustrWithFibersNew.jpg" "This figure demonstrates our fiber orientation estimation methodology with an example patient heart image. (A) The epicardial (red) and endocardial (green and magenta) splines, and corresponding landmarks (yellow) overlaid on a slice of the patient heart image. (B) Patient ventricles in 3D. (C) Superimposition of ventricles of atlas (magenta) and patient. (D) Patient ventricles and the affine transformed atlas ventricles. (E) Patient ventricles and non-linearly transformed atlas ventricles. (F) Estimated patient ventricular fiber orientations.", "research/electrophysiology/JB_Figure_fiber.jpg" "We developed a novel rule-based algorithm for incorporating fiber orientation in computational heart models as an inexpensive alternative to image-based fiber orientation from DTI. Our algorithm is particularly useful in cases when DTI data is not available or is too noisy to use. The algorithm we developed offers several advantages over existing rule-based algorithms, in that it is much faster, more efficient, easier to implement and user-friendly, as well as, works for model's with very convoluted geometry. Briefly, the algorithm works as such for mammalian ventricles; i.) compute solutions to Laplace's equation with Dirichlet boundary conditions applied to the surfaces of the ventricles in order to construct an orthonormal axis system aligned with the transmural and apical-basal directions of the heart, ii.) assign fiber orientation angles derived from histology and DTI studies to the axis system constructed in the previous step, and iii.) use bi-directional spherical linear interpolation to interpolate fiber orientation throughout the entire myocardium to guarantee continuous fiber orientation with the LV, RV and septum. Lastly, in a recent study we showed that activation patterns in canine ventricles with our rule-based fiber orientation versus DTI fiber orientation had mean differences in activation time of <3.2 msec and Pearson moment correlation coefficients >0.98 for various pacing protocols. These results provide strong evidence that our new algorithm is a robust alternative to DTI for assigning fiber orientation to computational heart models.", "research/electrophysiology/arevalo_fig1.jpg" "A. Experimentally successful ablation site is correctly predicted in computer model by targeting phase singularities (orange dots). B. Failed ablation in experiment is due to ablation of tissue away from PIZ where phase singularities are located. Simulations with experimental ablation site resulted in VT inducibility, as well. The predicted optimal ablation site targets the phase singularities in the PIZ.", "research/electrophysiology/Kelly_F4.jpg" "Electrical impulse propagation is an essential function in cardiac, skeletal muscle, and nervous tissue. Abnormalities in cardiac impulse propagation underlie lethal reentrant arrhythmias, including ventricular fibrillation. Temporary propagation block throughout the ventricular myocardium could possibly terminate these arrhythmias. Electrical stimulation has been applied to nervous tissue to cause reversible conduction block, but has not been explored sufficiently in cardiac tissue. We show that reversible propagation block can be achieved in cardiac tissue by holding myocardial cells in a refractory state for a designated period of time by applying a sustained sinusoidal high-frequency alternating current (HFAC); in doing so, reentrant arrhythmias are terminated. We demonstrate proof of concept using several models, including optically mapped monolayers of neonatal rat ventricular cardiomyocytes, Langendorff-perfused guinea pig and rabbit hearts, intact anesthetized adult rabbits, and computer simulations of whole-heart impulse propagation. HFAC may be an effective and potentially safer alternative to direct current application, currently used to treat ventricular fibrillation.", "research/electrophysiology/kathleen_fig3.jpg" "APD maps in the models (A) and those when ionic current remodeling in the PZ is removed (B). 0% (top row) or 80% (bottom row) Mfbs in the scar region. 0% (left column), 10% (middle column), or 30% (right column) Mfbs in the PZ. The average APD and its standard devia- tion are listed below each preparation. Boxplots represent distribution of APD in the PZ (C) and healthy tissue (D) for both sets of models.", "research/electrophysiology/kathleen_fig4.jpg" "VREST and APD as a function of distance along the vertical line between points A (in the outer edge of the PZ) and B (10 mm removed from the outer edge of the PZ) in the Scar80PZ30 model.", "research/electromechanics/JC_Fig1.jpg" "Stylized model of rabbit electromechanics was employed here to demonstrate that the distribution of the electromechanical delay, the time interval between myocyte depolarization and onset of myofiber shortening, is heterogeneous and is dependent on the loading conditions. Electrical activation times (A), mechanical activation times (B), and EMD (C) during SR and EP. Each panel presents LV lateral view of epicardium (left) and endocardium (right). (Lines) Fiber direction.", "research/electrophysiology/kathleen_fig1.png" "Model generation. Representative MRI slice of the rabbit heart, segmentation of the slice, and whole heart mode.", "research/electrophysiology/JB_Figure_atrial2.jpg" "In electrophysiology studies of patients with persistent atrial fibrillation (AF), beta-adrenergic stimulation increases the slope of action potential duration restitution (APDR) to > 1 and promotes fibrillation. However, the mechanism by which beta-adrenergic stimulation steepens APDR is unclear. Using computational modeling, we set out to determine if beta-adrenergic stimulation directly steepens APDR by altering ion channel currents or decreasing activation latency (AL).", "research/electrophysiology/kathleen_fig2.png" "(A) VREST maps in the models. 0% (top row) or 80% (bottom row) Mfbs in the scar region. 0% (left column), 10% (middle column), or 30% (right column) Mfbs in the PZ. Average PZ VREST values and standard deviations are listed below the respective preparations (B). Boxplots of VREST in PZ of each substrate. Whiskers represent minimum and maximum of all values in a given preparation.", "research/electromechanics/Yuxuan_paperSAC_4.jpg" "The goal of this study is to use a sophisticated, strongly-coupled MRI-based model of human electromechanics that incorporates a circulatory system and a biophysically detailed representation of cardiac myofilament to elucidate the effect of MEF on arrhythmia patterns, specifically the effect of MEF on spiral wave stability.", "research/electromechanics/JC_Fig2.png" "Image-based electromechanical models of the normal canine and failing canine heart are used to demonstrate that the electromechanical delay is prolonged in dyssynchronous heart failure (DHF). Shown here are the electrical activation (left), mechanical activation (middle), and electromechanical delay distribution (right) maps.", "research/electrophysiology/alex_fig1.jpg" "The result of Kaplan-Meier analysis of arrhythmia risk stratification using QTII.", "research/electrophysiology/alex_fig2.jpg" "QTI instability, measured as the number of minute-long ECG episode with unstable QT interval dynamics (Nus), was increased before the onset of ventricular tachycardia, compared against the value of Nus 1-hour before the onset.", "research/electrophysiology/alex_fig3.jpg" "The development of unstable QT interval dynamics, measured as the number of patients with unstable QT interval dynamics (N), towards the onset of ventricular fibrillation."}