Abstract
The aim of the study was to develop a three-dimensional (3D) anatomically-detailed model of the rabbit right atrium containing the sinoatrial and atrioventricular nodes to study the electrophysiology of the nodes. A model was generated based on 3D images of a rabbit heart (atria and part of ventricles), obtained using high-resolution magnetic resonance imaging. Segmentation was carried out semi-manually. A 3D right atrium array model (∼3.16 million elements), including eighteen objects, was constructed. For description of cellular electrophysiology, the Rogers-modified FitzHugh-Nagumo model was further modified to allow control of the major characteristics of the action potential with relatively low computational resource requirements. Model parameters were chosen to simulate the action potentials in the sinoatrial node, atrial muscle, inferior nodal extension and penetrating bundle. The block zone was simulated as passive tissue. The sinoatrial node, crista terminalis, main branch and roof bundle were considered as anisotropic. We have simulated normal and abnormal electrophysiology of the two nodes. In accordance with experimental findings: (i) during sinus rhythm, conduction occurs down the interatrial septum and into the atrioventricular node via the fast pathway (conduction down the crista terminalis and into the atrioventricular node via the slow pathway is slower); (ii) during atrial fibrillation, the sinoatrial node is protected from overdrive by its long refractory period; and (iii) during atrial fibrillation, the atrioventricular node reduces the frequency of action potentials reaching the ventricles. The model is able to simulate ventricular echo beats. In summary, a 3D anatomical model of the right atrium containing the cardiac conduction system is able to simulate a wide range of classical nodal behaviours.
Highlights
Accurate simulation of the generation and propagation of cardiac electrical activity requires detailed anatomical and electrophysiological models
The action potential reached the rest of the right atrium in,50 ms (Figure 5A, B)
In the simulation of sinus rhythm, the action potential from the sinoatrial node (SAN) had to propagate around the block zone to reach the interatrial septum at,35 ms (Figure 5A, B)
Summary
Accurate simulation of the generation and propagation of cardiac electrical activity requires detailed anatomical and electrophysiological models. Vetter and McCulloch [10] developed a 3D finite element model of rabbit ventricular geometry with fibre orientation. None of these models includes both the sinoatrial and atrioventricular (AVN) nodes. We have generated a 3D anatomically-detailed model of the rabbit heart, including the conduction system, using micro-CT [13], at present the model is unsuitable for electrophysiological simulation. A 3D anatomically-detailed model of the right atrium of the rabbit heart, including the SAN and AVN and suitable for electrophysiological simulations, was generated based on magnetic resonance (MR) imaging
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