Olivier Blanc

Study of unipolar electrogram morphology in a computer model of atrial fibrillation.

Introduction: Electrograms exhibit a wide variety of morphologies during atrial fibrillation (AF). The basis of these time courses, however, is not completely understood. In this study, data from computer models were studied to relate features of the signals to the underlying dynamics and tissue substrate.

Study of atrial arrhythmias in a computer model based on magnetic resonance images of human atria.

The maintenance of multiple wavelets appears to be a consistent feature of atrial fibrillation (AF). In this paper, we investigate possible mechanisms of initiation and perpetuation of multiple wavelets in a computer model of AF. We developed a simplified model of human atria that uses an ionic-based membrane model and whose geometry is derived from a segmented magnetic resonance imaging data set. The three-dimensional surface has a realistic size and includes obstacles corresponding to the location of major vessels and valves, but it does not take into account anisotropy. The main advantage of this approach is its ability to simulate long duration arrhythmias (up to 40 s). Clinically relevant initiation protocols, such as single-site burst pacing, were used. The dynamics of simulated AF were investigated in models with different action potential durations and restitution properties, controlled by the conductance of the slow inward current in a modified Luo-Rudy model. The simulation studies show that (1) single-site burst pacing protocol can be used to induce wave breaks even in tissue with uniform membrane properties, (2) the restitution-based wave breaks in an atrial model with realistic size and conduction velocities are transient, and (3) a significant reduction in action potential duration (even with apparently flat restitution) increases the duration of AF. (c) 2002 American Institute of Physics.

A numerical scheme for modeling wavefront propagation on a monolayer of arbitrary geometry

The majority of models of wavefront propagation in cardiac tissue have assumed relatively simple geometries. Extensions to complicated three-dimensional (3-D) representations are computationally challenging due to issues related both to problem size and to the correct implementation of flux conservation. In this paper, we present a generalized finite difference scheme (GDFS) to simulate the reaction-diffusion system on a 3-D monolayer of arbitrary shape. GDFS is a vertex-centered variant of the finite-volume method that ensures local flux conservation. Owing to an effectively lower dimensionality, the overall computation time is reduced compared to full 3-D models at the same spatial resolution. We present the theoretical background to compute both the wavefront conduction and local electrograms using a matrix formulation. The same matrix is used for both these quantities. We then give some results of simulation for simple monolayers and complex monolayers resembling a human atria.

Evaluation of ablation patterns by means of a computer model of human atria

Atrial fibrillation is the most common form of arrhythmia. Consequences for patients are discomfort, blood clot formation and a high risk of embolic stroke. The choice of therapy is patient-dependent and is usually based on the degree of disability and the associated symptoms. Surgical/catheter ablation is a therapeutical procedure, which consists in creating lines of conduction block to interrupt maintenance of atrial fibrillation. The purpose of this paper is to evaluate different ablation patterns by means of a computer model of human atria. The importance of ablation lines in the right or left atrium is studied and compared to Maze-type procedures, which represent the standard in ablation therapy.

Comparison between propagation in a numerical and in a real microscopic cardiac tissue

Today, computer models of the heart can simulate electrical propagation in complex and realistic anatomical structures. Nevertheless, the direct comparison of the results with real cardiac phenomena remains difficult. The objective of this work is to provide a validation of a numerical model of cardiac tissue using published results obtained in a real microscopic structure (neonatal rat cardiac cell cultures). The authors have therefore organized their virtual numerical tissue in order to allow a direct comparison with experimental results. The simulations were in good agreement with results from cell cultures, showing that the virtual tissue has a realistic behavior.

Virtual RF ablation in a 3D computer model of atrial arrhythmias

A realistic 3D anatomical computer model of human atria has been designed, which simulates the cellular and tissue electrophysiology of atria. After having initiated sustained atrial flutter, the authors have tested some antiarrhythmic interventions, like pharmacological treatment and RF ablation. The virtual RF ablation simulations have a behavior similar to that reported in biological experiments. Therefore this anatomical model constitutes a new tool to study the impact of ablation for atrial arrhythmias.

Simulated atrial fibrillation in a computer model of human atria

Atrial arrhythmias are the most frequent rhythm disorder in humans and often lead to severe complications such as heart failure and stroke. While different mapping techniques have provided significant information on the electro-physiological processes associated with atrial fibrillation (AF), the mechanisms underlying its initiation and maintenance remain unclear. To assist the study of the complex, spatio-temporal dynamics of AF, we developed a simplified homogeneous, isotropic, but realistic-size computer model of human atria that uses an ionic-based membrane model and whose geometry is derived from segmented MRI dataset. By representing the domain as a three-dimensional monolayer, the computational load is sufficiently reduced to enable the simulation of long duration arrhythmia. With this model, simulated atrial fibrillation (SAF), i.e. multiple reentrant wavelets, can be induced using a single-site burst pacing protocol. The model outputs both transmembrane potential maps and electrograms at any location in the atria, facilitating comparisons between simulation results and experimental or clinical data. It is shown here that our SAF model presents the same characteristics of spatio-temporal organization as real AF in terms of the correlation coefficient proposed by Botteron et al. (1995).