Foreword
Foreword
University of Lausanne
CHUV-CardioMet
Switzerland
Medtronic Europe
Tolochenaz
Switzerland
University of Lausanne
Department of Cardiology
Switzerland
This issue of Europace presents the proceedings of the Fifth International Workshop on Computer Simulation and Experimental Assessment of Cardiac Electrical Function, which was organized by the Lausanne Heart group and held in Lausanne on 11–12 December 2006. The objective of these biennial workshops is to provide a firm link between researchers from many diverse fields involved in computer modelling and to ensure an appropriate transition of major findings to the clinical field.
The title of this fifth workshop was ‘From Anatomy to Electrograms’ and its objective was to cover all steps involved in computer modelling, in particular the extraction of relevant information about the anatomy and morphology of the human heart. This included the impact of morphology on observable cellular and major electrophysiological properties, the creation of whole organ models, and the expression of these electrophysiological properties in the potentials observed on the body surface. In addition to the modelling of healthy tissue, it is important to develop accurate models of cardiac diseases. This allows the simulation of several pathologies and, in some cases, the simulation of therapeutical options in an interaction with the different levels of modelling.
The first article by Anderson et al. is a review describing the anatomy of the atrial chambers. This anatomically accurate information is of great help for the modelling of atrial structure and computing the associate electrical signals. This information about atrial anatomy is complemented by detailed information about interatrial conduction in the review article by Platonov.
The next article by Rudy deals with the computer modelling of cellular mechanisms. It offers a summary of the computational biology of the repolarization properties of the ventricular myocytes. The article by Hubbard et al. describes how such models of single myocytes can be connected via gap junctions to form two-dimensional structures. They show the impact of different gap junction properties on electrical impulse propagation.
The two subsequent articles discuss the effects of fibrosis on impulse propagation in cardiac tissue. Jacquemet et al. propose a method for computer modelling the coupling of myocytes and fibroblasts and study this effect (which is due to aging and various other cardiac diseases) on conduction velocity and action potentials. In their article, Ten Tusscher et al. study the impact of fibrosis on the arrhythmogenic properties of a model human ventricular fibrotic tissue.
Arrhythmogenesis is an important aspect of computer modeling. The article by Tice et al. describes the mechanisms of arrhythmias in a two-dimensional slice of ventricle with regional ischemia following coronary occlusion. Zemlin et al. show that, due to coupling heterogeneities, reentrant cardiac arrhythmias can be initiated spontaneously in two-dimensional ventricular tissue.
Whole organ computer models are the logical extension of the two-dimensional tissue models in the papers mentioned above. Such models allow a comparison of the results of clinical experiments with simulations of electrophysiology and virtual therapeutic interventions. The article by Haissaguerre et al. compares the atrial fibrillatory cycle length obtained during a progressive ablation of focal fibrillatory sources and compares the results to clinical data. Ruchat et al. show how clinical ablation of atrial fibrillation can be simulated in a computer model and compare the results with clinical data.
Another link to clinical data can be made through observation of signals such as action potentials. The article by Wilson et al. provides a review on alternans of the cellular action potential and more specifically discusses the possible mechanisms for discordant alternans, which is linked to a mechanism of arrhythmogenesis. In the article by Pruvot et al. that follows, an experimental chronic sheep model is proposed for studying repolarization alternans and the susceptibility to re-entrant arrhythmias. The fact that monophasic action potentials can be used more effectively than bipolar electrograms in assessing the presence of fractionated electrograms during atrial fibrillation is shown in the article by Narayan et al. All the clinical phenomena mentioned were found to be accurately simulated in and, supported by, dedicated computer models.
In the last group of articles, computer models of whole organs are discussed in their link with body surface potentials. The article by Weiss et al. proposes a computer model of human ventricles, based on magnetic resonance imaging, in which detailed data on fibre orientation is included. A possible extension of this model would include a complete torso model for studying the impact of fibre orientation as far as it is observable on the body surface ECG. Similar computer models have previously been developed for the human atria. On the clinical side, the article by Thilén et al. describes how in human signal-average ECG analysis, delayed atrial conduction can lead to prolonged P-wave duration. On the modelling side, the article by Lemay et al. shows how information about electrical activity of the atria can be extracted from simulated vector cardiograms based on a three-dimensional model of atria and a volume conductor model of the thorax. Finally, the article by van Dam et al. indicates that it is possible not only to compute an ECG from a three-dimensional model of human atria, but also to simulate the subcutaneous bipolar electrograms as recorded by an implantable loop recorder positioned just below the subcutaneous fat.
The papers included in this issue offer a wide spectrum illustration of model-based approaches to various clinical problems. It is our sincere hope that they will work towards promoting a closer collaboration between clinicians, physiologists, mathematicians, and engineers, and facilitate the much-needed interaction between basic science and clinical medicine.
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