The electrocardiogram (ECG) is ubiquitously employed as a diagnostic and monitoring tool for patients experiencing cardiac distress and/or disease. It is widely known that changes in heart position resulting from, for example, posture of the patient (sitting, standing, lying) and respiration significantly affect the body-surface potentials; however, few studies have quantitatively and systematically evaluated the effects of heart displacement on the ECG. The goal of this study was to evaluate the impact of positional changes of the heart on the ECG in the specific clinical setting of myocardial ischemia. To carry out the necessary comprehensive sensitivity analysis, we applied a relatively novel and highly efficient statistical approach, the generalized polynomial chaos-stochastic collocation method, to a boundary element formulation of the electrocardiographic forward problem, and we drove these simulations with measured epicardial potentials from whole-heart experiments. Results of the analysis identified regions on the body-surface where the potentials were especially sensitive to realistic heart motion. The standard deviation (STD) of ST-segment voltage changes caused by the apex of a normal heart, swinging forward and backward or side-to-side was approximately 0.2 mV. Variations were even larger, 0.3 mV, for a heart exhibiting elevated ischemic potentials. These variations could be large enough to mask or to mimic signs of ischemia in the ECG. Our results suggest possible modifications to ECG protocols that could reduce the diagnostic error related to postural changes in patients possibly suffering from myocardial ischemia.
G. Tamm, A. Schiewe, J. Krüger. ZAPP – A management framework for distributed visualization systems, In Proceedings of CGVCVIP 2011 : IADIS International Conference on Computer Graphics, Visualization, Computer Vision And Image Processing, pp. (accepted). 2011.
Though implantable cardioverter defibrillators (ICDs) are increasing in use in both adults and children, little progress has been devoted to optimizing device and electrode placement. To facilitate effective ICD placement, especially in pediatric cases, we have developed a predictive model that evaluates the efficacy of a delivered shock. We have also developed an experimental validation approach based on measurements from clinical cases. The approach involves obtaining body surface potential maps of ICD discharges during implantation surgery using a limited lead selection and body surface estimation algorithm. Comparison of the simulated and measured potentials yielded very similar patterns and a typical correlation greater than 0.93, suggesting that the predictive simulation generates realistic potential values. This validation approach provides confidence in application of the simulation pipeline and offers areas to focus future improvements.
Keywords: Electric potential, Electric shock, Electrodes;Estimation, Lead;Surface reconstruction, Torso, Algorithms, Body Surface Potential Mapping, Computer Simulation, Defibrillators, Implantable, Humans, Models, Cardiovascular, Therapy, Computer-Assisted
G.R. Vergara, S. Vijayakumar, E.G. Kholmovski, J.J. Blauer, M.A. Guttman, C. Gloschat, G. Payne, K. Vij, N.W. Akoum, M. Daccarett, C.J. McGann, R.S. Macleod, N.F. Marrouche.
Real-time magnetic resonance imaging-guided radiofrequency atrial ablation and visualization of lesion formation at 3 Tesla, In Heart Rhythm, Vol. 8, No. 2, pp. 295--303. 2011.
PubMed ID: 21034854
T.J. Badger, M. Daccarett, N.W. Akoum, Y.A. Adjei-Poku, N.S. Burgon, T.S. Haslam, S. Kalvaitis, S. Kuppahally, G. Vergara, L. McMullen, P.A. Anderson, E. Kholmovski, R.S. Macleod, N.F. Marrouche.
Evaluation of left atrial lesions after initial and repeat atrial fibrillation ablation: lessons learned from delayed-enhancement MRI in repeat ablation procedures, In Circulation. Arrhythmia and Electrophysiology, Vol. 3, No. 3, pp. 249--259. 2010.
PubMed ID: 20335558
J.J.E. Blauer, J. Cates, C.J. McGann, E.G. Kholmovski, A. Alexander, M.W. Prastawa, S. Joshi, N.F. Marrouche, R.S. MacLeod.
MRI Based Injury Characterization Immediately Following Ablation of Atrial Fibrillation, In Computing in Cardiology, Vol. 37, pp. 165--168. 2010.
We present a particle-based approach for generating adaptive triangular surface and tetrahedral volume meshes from CAD models. Input shapes are treated as a collection of smooth, parametric surface patches that can meet non-smoothly on boundaries. Our approach uses a hierarchical sampling scheme that places particles on features in order of increasing dimensionality. These particles reach a good distribution by minimizing an energy computed in 3D world space, with movements occurring in the parametric space of each surface patch.
Rather than using a pre-computed measure of feature size, our system automatically adapts to both curvature as well as a notion of topological separation. It also enforces a measure of smoothness on these constraints to construct a sizing field that acts as a proxy to piecewise-smooth feature size. We evaluate our technique with comparisons against other popular triangular meshing techniques for this domain.
In this paper, we present a sample-based approach for surface coloring, which is independent of the original surface resolution and representation. To achieve this, we introduce the Orthogonal Fragment Buffer (OFB)-an extension of the Layered Depth Cube-as a high-resolution view-independent surface representation. The OFB is a data structure that stores surface samples at a nearly uniform distribution over the surface, and it is specifically designed to support efficient random read/write access to these samples. The data access operations have a complexity that is logarithmic in the depth complexity of the surface. Thus, compared to data access operations in tree data structures like octrees, data-dependent memory access patterns are greatly reduced. Due to the particular sampling strategy that is employed to generate an OFB, it also maintains sample coherence, and thus, exhibits very good spatial access locality. Therefore, OFB-based surface coloring performs significantly faster than sample-based approaches using tree structures. In addition, since in an OFB, the surface samples are internally stored in uniform 2D grids, OFB-based surface coloring can efficiently be realized on the GPU to enable interactive coloring of high-resolution surfaces. On the OFB, we introduce novel algorithms for color painting using volumetric and surface-aligned brushes, and we present new approaches for particle-based color advection along surfaces in real time. Due to the intermediate surface representation we choose, our method can be used to color polygonal surfaces as well as any other type of surface that can be sampled.
A.N.M. Imroz Choudhury, M.D. Steffen, J.E. Guilkey, S.G. Parker. Enhanced Understanding of Particle Simulations Through Deformation-Based Visualization, In Computer Modeling in Engineering & Sciences, Vol. 63, No. 2, pp. 117--136. 2010.
T. Fogal, H. Childs, S. Shankar, J. Krüger, R.D. Bergeron, P. Hatcher. Large Data Visualization on Distributed Memory Multi-GPU Clusters, In Proceedings of High Performance Graphics 2010, pp. 57--66. 2010.
B.M. Isaacson, J.G. Stinstra, R.S. MacLeod, P.F. Pasquina, R.D. Bloebaum.
Developing a Quantitative Measurement System for Assessing Heterotopic Ossification and Monitoring the Bioelectric Metrics from Electrically Induced Osseointegration in the Residual Limb of Service Members, In Annals of Biomedical Engineering, Vol. 38, No. 9, pp. 2968-–2978. 2010.
PubMed ID: 20458630