Mary N. Morrow

Bio: Mary N. Morrow is an academic researcher from Duke University. The author has contributed to research in topics: Torso & Skeletal muscle. The author has an hindex of 7, co-authored 10 publications receiving 629 citations.

Left Heart Volume Estimation in Infancy and Childhood Reevaluation of Methodology and Normal Values

Abstract: Left ventricular (LV) volume determinations by the area-length method were reevaluated in postmortem studies of left ventricles ranging from 0.5 to 90 cm3 absolute volume. The regression equation relating known and calculated volumes for calculated volumes 15 cm3 (V' = 0.974V - 3.1). From these equations, normal values for cinecardiographic LV end-diastolic volume (LVEDV), LV ejection fraction (LVEF), LV systolic output (LVSO), LV mass (LVM), and left atrial maximal volume (LAMax) were derived from 56 children (19 < 2 years) with normal left ventricles who underwent cardiac catheterization. Values for LVEDV/BSA were significantly less for infants (< 2 years) than for older children (42 ± 10 versus 73 ± 11 cm3/m2, P <0.001). Values for LAMax/BSA were also less for infants than for older children (26 ± 5 versus 38 ± 8 cm3/ m2, P <0.001), and LVEF was significantly increasel for infants (0.68 ± 0.05 versus 0.63 ± ...

Electrical Potential Distribution Surrounding the Atria during Depolarization and Repolarization in the Dog

Abstract: The potential distribution at the atrial surface during depolarization and repolarization was studied in intact dogs. A preparation was developed by implanting 30 to 40 miniature electrodes permanently on each atrium to record unipolar electrograms in the intact animal. Heart block was created to dissociate atrial and ventricular activity. The electrograms were recorded on magnetic tape and atrial isopotential heart maps produced with the use of a digital computer. The changing potential distribution during excitation indicated the early presence of multiple wave fronts which were related primarily to the crista terminalis, Bachmann's bundle, and a special bundle to the base of the right appendage. The interatrial septum provided a conducting bridge which had an important influence of global atrial excitation, depending on the site of impulse formation. Colliding excitation wave fronts were quite prominent. During terminal atrial excitation, repolarization maxima were present simultaneously with depolarization maxima. Repolarization was characterized by a changing potential distribution which followed the same general pattern as excitation spread; and, furthermore, the earliest areas of excitation were associated with a repolarization maximum and terminal areas of excitation were associated with repolarization minima.

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.

Statistically Constrained Inverse Electrocardiography

Abstract: This paper examines the feasibility of utilizing statistical constraints on the inverse potential model to determine the potential distribution over a 4 cm sphere surrounding the heart from perturbed torso potentials. These perturbed torso potentials reflect instrumentation, quadrature, electrode placement, and heart position uncertainties. This work is an extension of the authors' previous work which concluded that it is not feasible to determine this same potential distribution using unconstrained solutions. However, the results of the present work indicate that with the use of approximate signal and noise covariance matrices, it is possible to achieve estimates of this potential distribution with an average sum squared error of twenty-five percent. Further, the estimation of the signal and noise covariance matrices can be accomplished with a knowledge of heart geometry, torso geometry, The approximate measurement error, and a rough estimate of the time an average section of myocardium is depolarized, but without an a priori specification of the activation sequence.

Recommendations for quantification methods during the performance of a pediatric echocardiogram: a report from the Pediatric Measurements Writing Group of the American Society of Echocardiography Pediatric and Congenital Heart Disease Council.

Abstract: n Society of Echocardiography designates this educational activity for of 15 AMA PRA Category 1 Credits Physicians should only claim credit te with the extent of their participation in the activity CCI recognize the ASE’s certificates and have agreed to honor the credit their registry requirements for sonographers n Society of Echocardiography is committed to ensuring that its educan and all sponsored educational programs are not influenced by the special y corporation or individual, and itsmandate is to retain only those authors ial interests can be effectively resolved to maintain the goals and educaty of the activity Although amonetary or professional affiliationwith a cors not necessarily influence an author’s presentation, the Essential Areas and e ACCME require that any relationships that could possibly conflict with al value of the activity be resolved prior to publication and disclosed to Disclosures of faculty and commercial support relationships, if any, dicated ience: is designed for all cardiovascular physicians and cardiac sonographers with erest and knowledge base in the field of echocardiography; in addition, reschers, clinicians, intensivists, and other medical professionals with a spein cardiac ultrasound will find this activity beneficial

Theoretical and empirical derivation of cardiovascular allometric relationships in children

Abstract: Basic fluid dynamic principles were used to derive a theoretical model of optimum cardiovascular allometry, the relationship between somatic and cardiovascular growth. The validity of the predicted models was then tested against the size of 22 cardiovascular structures measured echocardiographically in 496 normal children aged 1 day to 20 yr, including valves, pulmonary arteries, aorta and aortic branches, pulmonary veins, and left ventricular volume. Body surface area (BSA) was found to be a more important determinant of the size of each of the cardiovascular structures than age, height, or weight alone. The observed vascular and valvar dimensions were in agreement with values predicted from the theoretical models. Vascular and valve diameters related linearly to the square root of BSA, whereas valve and vascular areas related to BSA. The relationship between left ventricular volume and body size fit a complex model predicted by the nonlinear decrease of heart rate with growth. Overall, the relationship between cardiac output and body size is the fundamental driving factor in cardiovascular allometry.

Relating Epicardial to Body Surface Potential Distributions by Means of Transfer Coefficients Based on Geometry Measurements

Abstract: Although it has been known throughout this century that a complex sequence of electrical events is produced on the body surface by the electrophysiological properties of the heart, the question of how well these body surface events can be explained mathematically on the basis of experimental measurements of cardiac geometry and electrical activity remains unanswered. Recent advances in experimental capabilities have made possible the near simultaneous measurement of both cardiac epicardial and corresponding body surface potential distributions from in vivo animal preparations using chronically implanted electrodes to keep the volume conductor intact. This report provides a method for finding transfer coefficients that relate the epicardial and body surface potential distributions to each other. The method is based on knowing the geometric location of each electrode, and on having enough electrodes to establish the geometric shape and the potential distribution of closed epicardial and body surfaces. However, the method does not require that either the heart or body surfaces have any special shape, such as that of a sphere, or that any electrical quantities, such as voltage gradients, be known in addition to the potentials. The use of potential distributions to represent heart electrical activity is advantageous since such distributions can be directly measured experimentally, without a transformation to any other form, such as multiple current-generating dipoles, being required. This report includes a statement of the underlying integral equations, the procedure. for finding the equations' coefficients from geometry measurements, some considerations for computer algorithms, and an example.

A computer model of normal conduction in the human atria.

Abstract: Although considerable progress has been made in understanding the process of wavefront propagation and arrhythmogenesis in human atria, technical concerns and issues of patient safety have limited experimental investigations. The present work describes a finite volume-based computer model of human atrial activation and current flow to complement these studies. Unlike previous representations, the model is three-dimensional, incorporating both the left and right atria and the major muscle bundles of the atria, including the crista terminalis, pectinate muscles, limbus of the fossa ovalis, and Bachmann's bundle. The bundles are represented as anisotropic structures with fiber directions aligned with the bundle axes. Conductivities are assigned to the model to give realistic local conduction velocities within the bundles and bulk tissue. Results from simulations demonstrate the role of the bundles in a normal sinus rhythm and also reveal the patterns of activation in the septum, where experimental mapping has been extremely challenging. To validate the model, the simulated normal activation sequence and conduction velocities at various locations are compared with experimental observations and data. The model is also used to investigate paced activation, and a mechanism of the relative lengthening of left versus right stimulation is presented. Owing to both the realistic geometry and the bundle structures, the model can be used for further analysis of the normal activation sequence and to examine abnormal conduction, including flutter. The full text of this article is available at http://www.circresaha.org.

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.