Peggy C. Stanley

Bio: Peggy C. Stanley is an academic researcher from Duke University. The author has contributed to research in topics: Torso & Skeletal muscle. The author has an hindex of 3, co-authored 4 publications receiving 172 citations.

The Effects of Thoracic Inhomogeneities on the Relationship Between Epicardial and Torso Potentials

Abstract: This study examines the effects of the lungs, spine, sternum, and the anisotropic skeletal muscle layer on the relationship between torso and epicardial potentials. Boundary integral equations representing potentials on the epicardial surface, the torso surface, and the internal conductivity interfaces were solved yielding a set of transfer coefficients valid for any source inside the epicardium and for any conductivity configuration outside the epicardial surface. These transfer coefficients relate potentials on the torso to potentials on the epicardial surface. Calculated torso potentials are generated via the transfer coefficients and measured epicardial potentials for comparison to measured torso potentials. This comparison indicates whether including the thoracic inhomogeneities improves attainable accuracy in calculations relating torso potentials to epicardial potentials.

A Comparison of Finite Element and Integral Equation Formulations for the Calculation of Electrocardiographic Potentials-II

Abstract: This paper is a comparison of the major methodologies utilized in computer simulations of electrocardiographic potential calculations. Two integral equation methods (Green's theorem and the equivalent single layer) and finite element methods are compared for forward and inverse solutions. The results suggest that the differences in accuracy between the two integral equation formulations are small. However, the use of a basic finite element formulation improves the accuracy over that obtainable with integral equations, and the improvement in accuracy is particularly notable for inverse estimation.

An assessment of variable thickness and fiber orientation of the skeletal muscle layer on electrocardiographic calculations

Abstract: A realistic model of a canine torso which includes extensive detail about skeletal muscle layer thickness and fiber orientation is compared with two other uniformly anisotropic models. A transfer coefficient is developed which relates torso potentials to epicardial potentials for a given anisotropic skeletal muscle layer thickness and muscle fiber orientation. The transfer coefficient is valid for any set of measured epicardial potentials and is independent of the conductivity of the heart. Transfer coefficients calculated for different thicknesses and muscle fiber orientations of the skeletal muscle layer are used to compute torso potentials directly from measured epicardial potentials. A comparison of the measured torso potentials with the potentials calculated from the different transfer coefficients indicates the effectiveness of including variations in fiber orientation and in thickness of the skeletal muscle layer in the model. >

Electrocardiographic Modeling Of The Fiber Orientation Of The Skeletal Muscle Layer

Abstract: The effectiveness of including variable thickness and fiber orientation characteristics of the skeletal muscle layer in calculations relating epicardial and torso potentials was examined in this study. The comparison of calculated and measured torso potentials indicates that a simple model consisting of a uniformly anisotropic skeletal muscle layer of 1.0 to 1.5 cm constant thickness significantly improves the model. However, when more detailed data about the variation in skeletal muscle thickness or fiber orientation is introduced into the model, the agreement between calculated and measured torso potentials decreased, although a finite element mesh of over 5000 nodes was used to describe the skeletal muscle in the more detailed model.

Electrical imaging of the heart

Abstract: We give an overview of "cardiac electrical imaging", which is a generalization of the ECG in which more information is acquired by using a larger array of electrodes to record a sequence of "electrical images". These image sequences can be measured noninvasively on the body surface or invasively on or in the heart muscle itself. Here we briefly discuss the motivation for cardiac electrical imaging, we describe some relevant background electrophysiology to indicate how cardiac electrical imaging can provide information about the heart' s health, and then we give an overview of the technical challenges that arise in displaying, representing, and analyzing these image sequences.

On the theory of the electrocardiogram

Abstract: The biophysical basis for understanding the electrocardiogram is set forth. Bioelectric sources arise from electrical activity in the heart at the cellular level. The relation of these sources, which can be formally represented as impressed currents, to potentials involves solution of the volume conductor problem. This solution is based on Green's theorem. Sources are related to the transmembrane action potential through a bidomain model of heart muscle. Microscopic and macroscopic aspects of the bidomain model are developed. Various transformations of the source are considered, including multipoles, multiple dipoles, and replacement of the volume distribution with distributions on the heart surface. Time integrals of the waveform are related to excitation time and action potential duration. The theoretical results form the basis of a computer model of the electrocardiogram that relates skin potentials to the spatial and temporal distribution of action potentials in the heart. >

Geometric modeling of the human torso using cubic hermite elements

Abstract: We discuss the advantages and problems associated with fitting geometric data of the human torso obtained from magnetic resonance imaging, with high-order (bicubic Hermite) surface elements. These elements preserve derivative (C 1) continuity across element boundaries and permit smooth anatomically accurate surfaces to be obtained with relatively few elements. These elements are fitted to the data with a new nonlinear fitting procedure that minimizes the error in the fit while maintainingC 1 continuity with nonlinear constraints. Nonlinear Sobelov smoothing is also incorporated into this fitting scheme. The structures fitted along with their corresponding root meansquared error, number of elements used, and number of degrees of freedom (df) per variable are: epicardium (0.91 mm, 40 elements, 142 df), left lung (1.66 mm, 80 elements, 309 df), right lung (1.69 mm, 80 elements, 309 df), skeletal muscle surface (1.67 mm, 264 elements, 1,010 df), fat layer (1.79 mm, 264 elements, 1,010 df), and the skin layer (1.43 mm, 264 elements, 1,010 df). The fitted surfaces are assembled into a combined finite element/boundary element model of the torso in which the exterior surfaces of the heart and lungs are modeled with two-dimensional boundary elements and the layers of the skeletal muscle, fat, and skin are modeled with finite elements. The skeletal muscle and fat layers are modeled with bicubic Hermite linear elements and are obtained by joining the adjacent surface elements for each layer. Applications for the torso model include the forward and inverse problems of electrocardiography, defibrillation studies, radiation dosage studies, and heat transfer studies.

The potential gradient field created by epicardial defibrillation electrodes in dogs.

Abstract: Knowledge of the potential gradient field created by defibrillation electrodes is important for the understanding and improvement of defibrillation. To obtain this knowledge by direct measurements, potentials were recorded from 60 epicardial, eight septal, and 36 right ventricular transmural electrodes in six open-chest dogs while 1 to 2 V shocks were given through defibrillation electrodes on the right atrium and left ventricular apex (RA. V) and on the right and left ventricles (RV .LV). The potential gradient field across the ventricles was calculated for these low voltages. Ventricular fibrillation was electrically induced, and ventricular activation patterns were recorded after delivering high-voltage shocks just below the defibrillation threshold. With the low-voltage shocks, the potential gradient field was very uneven, with the highest gradient near the epicardial defibrillation electrodes and the weakest gradient distant from the defibrillation electrodes for both RA. V and RV .LV combinations. The mean ratio of the highest to the lowest measured gradient over the entire ventricular epicardium was 19.4 +/- 8.1 SD for the RA. V combination and 14.4 +/- 3.4 for the RV .LV combination. For both defibrillation electrode combinations, the earliest sites of activation after unsuccessful shocks just below the defibrillation threshold were located in areas where the potential gradient was weak for the low-voltage shocks. We conclude that there is a markedly uneven distribution of potential gradients for epicardial defibrillation electrodes with most of the voltage drop occurring near the electrodes, the potential gradient field is significant because it determines where shocks fail to halt fibrillation, and determination of the potential gradient field should lead to the development of improved electrode locations for defibrillation.

Recent progress in inverse problems in electrocardiology

Abstract: The considerable progress achieved in the inverse problem of electrocardiography over the last decade has provided grounds for optimism about the possibility of approaching significant clinically relevant applications in the next decade. However, there are a number of basic questions that still remain. In addressing these questions, the authors feel it is important to seek solutions that emphasize physiological rather than mathematical significance. This approach leads to twin requirements for useful inverse solutions: accuracy, defined in a physiologically meaningful (and not just averaged and mathematical) sense, and reliability, not only to measurement noise but also to geometric modeling errors and other uncertainties that are inescapable in practical application. Studies using analytically tractable models may still be relevant, but it seems more important to find solutions to practical inverse problems, which will move the field toward wider acceptance and credibility.