Abstract
The heart rhythm of a person following heart transplantation (HTX) is assumed to display an intrinsic cardiac rhythm because it is significantly less influenced by the autonomic nervous system—the main source of heart rate variability in healthy people. Therefore, such a rhythm provides evidence for arrhythmogenic processes developing, usually silently, in the cardiac tissue. A model is proposed to simulate alterations in the cardiac tissue and to observe the effects of these changes on the resulting heart rhythm. The hybrid automata framework used makes it possible to represent reliably and simulate efficiently both the electrophysiology of a cardiac cell and the tissue organization. The curve fitting method used in the design of the hybrid automaton cycle follows the well-recognized physiological phases of the atrial myocyte membrane excitation. Moreover, knowledge of the complex architecture of the right atrium, the ability of the almost free design of intercellular connections makes the automata approach the only one possible. Two particular aspects are investigated: impairment of the impulse transmission between cells and structural changes in intercellular connections. The first aspect models the observed fatigue of cells due to specific cardiac tissue diseases. The second aspect simulates the increase in collagen deposition with aging. Finally, heart rhythms arising from the model are validated with the sinus heart rhythms recorded in HTX patients. The modulation in the impairment of the impulse transmission between cells reveals qualitatively the abnormally high heart rate variability observed in patients living long after HTX.
Highlights
Biological functionality of an organism is maintained by both the dynamics of individual elements and the network of couplings that arise from the spatial distribution of these elements (Müller et al, 2016)
The rule ST2 of the cell definition given in section 3.1.2, which allows any cell with probability prefuse to refuse for the excitation, can be interpreted as the mean ability of the atrial tissue to respond to stimulation
Progress in our understanding of multi-component, multilayered and spatially complex composite systems has created an excellent foundation for exploring and evaluating the structural and dynamic characteristics of real systems based on experimental data (Bashan et al, 2012; Havlin et al, 2012; Müller et al, 2016)
Summary
Biological functionality of an organism is maintained by both the dynamics of individual elements and the network of couplings that arise from the spatial distribution of these elements (Müller et al, 2016). In the following, assuming that the cardiac tissue other than the right atrium works properly, we investigate relations between degradation in right atrial tissue modeled by hybrid. Heart Rhythm by Timed Automata automata and the resultant rhythm of heartbeats. From these relations, we expect to find hints about the sources of the unusual heart rate variability (HRV). We want to learn whether early stages of tissue impairment can be discerned from an analysis of heart rate variability. To this end, we compare rhythms obtained from the model with the rhythms recorded on patients after heart transplantation
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