Myocardial segment-specific model generation for simulating the electrical action of the heart

<p>Abstract</p> <p>Background</p> <p>Computer models of the electrical and mechanical actions of the heart, solved on geometrically realistic domains, are becoming an increasingly useful scientific tool. Construction of these models requires detailed measurement of the microstructural features which impact on the function of the heart. Currently a few generic cardiac models are in use for a wide range of simulation problems, and contributions to publicly accessible databases of cardiac structures, on which models can be solved, remain rare. This paper presents to-date the largest database of porcine left ventricular segment microstructural architecture, for use in both electrical and mechanical simulation.</p> <p>Methods</p> <p>Cryosectioning techniques were used to reconstruct the myofibre and myosheet orientations in tissue blocks of size ~15 × 15 × 15 mm, taken from the mid-anterior left ventricular freewall, of seven hearts. Tissue sections were gathered on orthogonal planes, and the angles of intersection of myofibres and myosheets with these planes determined automatically with a gradient intensity based algorithm. These angles were then combined to provide a description of myofibre and myosheet variation throughout the tissue, in a form able to be input to biophysically based computational models of the heart.</p> <p>Results</p> <p>Several microstructural features were common across all hearts. Myofibres rotated through 141 ± 18° (mean ± SD) from epicardium to endocardium, in near linear fashion. In the outer two-thirds of the wall sheet angles were predominantly negative, however, in the inner one-third an abrupt change in sheet angle, with reversal in sign, was seen in six of the seven hearts. Two distinct populations of sheets with orthogonal orientations often co-existed, usually with one population dominating. The utility of the tissue structures was demonstrated by simulating the passive and active electrical responses of two of the tissue blocks to current injection. Distinct patterns of electrical response were obtained in the two tissue blocks, illustrating the importance of testing model based predictions on a variety of tissue architectures.</p> <p>Conclusion</p> <p>This study significantly expands the set of geometries on which models of cardiac function can be solved.</p

Educational archaeology and the practice of utopian pedagogy

This paper explores the idea, and some elements of the (potential) practice, of utopian pedagogy. It begins by outlining the general aims of ‘utopian pedagogy’ and notes the shift within contemporary writings away from the metaphor of the architect (armed with a utopian ‘blueprint’) towards that of the archaeologist. The ontological underpinnings of educational archaeology are discussed before attention turns to a critical examination of the pedagogical process of excavation. The key questions here are (to labour the metaphor) where to dig and how to identify a utopian find. The paper argues that, without a substantive normative vision to serve as a guide, utopian archaeology is conceptually flawed and practically ineffectual, romanticising an endlessly open process of exploration. The final section suggests that the fears associated with utopian architecture (authoritarian imposition, totalising closure) are misplaced and that drawing up a ‘blueprint’ should be the aim and responsibility of utopian pedagogy

Atrial Fibrillation Mechanisms and Implications for Catheter Ablation

AF is a heterogeneous rhythm disorder that is related to a wide spectrum of etiologies and has broad clinical presentations. Mechanisms underlying AF are complex and remain incompletely understood despite extensive research. They associate interactions between triggers, substrate and modulators including ionic and anatomic remodeling, genetic predisposition and neuro-humoral contributors. The pulmonary veins play a key role in the pathogenesis of AF and their isolation is associated to high rates of AF freedom in patients with paroxysmal AF. However, ablation of persistent AF remains less effective, mainly limited by the difficulty to identify the sources sustaining AF. Many theories were advanced to explain the perpetuation of this form of AF, ranging from a single localized focal and reentrant source to diffuse bi-atrial multiple wavelets. Translating these mechanisms to the clinical practice remains challenging and limited by the spatio-temporal resolution of the mapping techniques. AF is driven by focal or reentrant activities that are initially clustered in a relatively limited atrial surface then disseminate everywhere in both atria. Evidence for structural remodeling, mainly represented by atrial fibrosis suggests that reentrant activities using anatomical substrate are the key mechanism sustaining AF. These reentries can be endocardial, epicardial, and intramural which makes them less accessible for mapping and for ablation. Subsequently, early interventions before irreversible remodeling are of major importance. Circumferential pulmonary vein isolation remains the cornerstone of the treatment of AF, regardless of the AF form and of the AF duration. No ablation strategy consistently demonstrated superiority to pulmonary vein isolation in preventing long term recurrences of atrial arrhythmias. Further research that allows accurate identification of the mechanisms underlying AF and efficient ablation should improve the results of PsAF ablation

Myocardial segment-specific model generation for simulating the electrical action of the heart-1

<p><b>Copyright information:</b></p><p>Taken from "Myocardial segment-specific model generation for simulating the electrical action of the heart"</p><p>http://www.biomedical-engineering-online.com/content/6/1/21</p><p>BioMedical Engineering OnLine 2007;6():21-21.</p><p>Published online 5 Jun 2007</p><p>PMCID:PMC1896167.</p><p></p> () generated by focal current application at the tissue centres are shown in the . Activation time () fields derived from wavefront propagation from the site of current injection are shown in the . The epi (epicardium) to endo (endocardium) distance is ~17 mm for both models

Myocardial segment-specific model generation for simulating the electrical action of the heart-2

<p><b>Copyright information:</b></p><p>Taken from "Myocardial segment-specific model generation for simulating the electrical action of the heart"</p><p>http://www.biomedical-engineering-online.com/content/6/1/21</p><p>BioMedical Engineering OnLine 2007;6():21-21.</p><p>Published online 5 Jun 2007</p><p>PMCID:PMC1896167.</p><p></p>o endocardium (right), plotted between -90° to +90° (upper and lower horizontal dashed lines respectively). The transmural depth of each tissue block is recorded in at the bottom right of each graph

Myocardial segment-specific model generation for simulating the electrical action of the heart-0

<p><b>Copyright information:</b></p><p>Taken from "Myocardial segment-specific model generation for simulating the electrical action of the heart"</p><p>http://www.biomedical-engineering-online.com/content/6/1/21</p><p>BioMedical Engineering OnLine 2007;6():21-21.</p><p>Published online 5 Jun 2007</p><p>PMCID:PMC1896167.</p><p></p>o endocardium (right), plotted between -90° to +90° (upper and lower horizontal dashed lines respectively). The transmural depth of each tissue block is recorded in at the bottom right of each graph

Myocardial segment-specific model generation for simulating the electrical action of the heart-4

<p><b>Copyright information:</b></p><p>Taken from "Myocardial segment-specific model generation for simulating the electrical action of the heart"</p><p>http://www.biomedical-engineering-online.com/content/6/1/21</p><p>BioMedical Engineering OnLine 2007;6():21-21.</p><p>Published online 5 Jun 2007</p><p>PMCID:PMC1896167.</p><p></p>r wall. : Circumferential plane (X-X) sections taken at three Xlocations through the wall. : Epicardial (X-X) plane sections taken at five Xlocations, revealing the gradual change in myofibre orientation from epicardium to endocardium. : Inset from the base-apex section showing zoomed-in section of tissue with overlayed structural angles automatically determined by the gradient-intensity algorithm

Myocardial segment-specific model generation for simulating the electrical action of the heart-5

<p><b>Copyright information:</b></p><p>Taken from "Myocardial segment-specific model generation for simulating the electrical action of the heart"</p><p>http://www.biomedical-engineering-online.com/content/6/1/21</p><p>BioMedical Engineering OnLine 2007;6():21-21.</p><p>Published online 5 Jun 2007</p><p>PMCID:PMC1896167.</p><p></p>0 grid. : Cleavage plane angles (β") computed from serial circumferential plane (X-X) sections, mapped to the same base-apex plane as in . Each row of angles is derived from a single circumferential plane tissue section, along its edge that abuts the base-apex plane section. Grayed boxes in the grids of both β' and β" panels represent areas of indeterminate cleavage plane angle. : Graph of the full model description including the transmural dependence of myofibre angle (line), from epicardium (epi) to endocardium (endo), and transmural distribution of sheet angles (β; dots) as derived from the β' and β" fields. The transmural thickness of the tissue block (20.55 mm) is shown at the bottom-right corner of the graph

First Simultaneous Endocardial and Epicardial Mapping of a Ventricular Tachycardia in an ARVD/C Patient

International audienc