The Effects Of Spirally Propagating Excitation Of Myocardial Cells On Their Functions

Arrhythmia is a common heart disease, and severe arrhythmia such as tachycardia and ventricular fibrillation (VF) are the leading causes of sudden cardiac death. The related studies have found that tachycardia is related to the spiral waves of myocardial excitation, while VF to the instability and breakup of spiral waves, thus demonstrating the mechanisms of cardiac spiral waves has crucial values in theory researches and practical applications. However, it is currently still unclear how spiral waves influence the functions of myocardial cells and what are the underlying mechanisms. Demonstration of these is the focus of this studv.The Luo-Rudy I model was used to realize modeling and simulation of a single ventricular myocyte and the fourth order Runge-Kutta method was adopted in numerical calculations. A two-dimensional single layer heart tissue was constructed based on the Luo-Rudy I model by adding couplings between cells. Spiral waves of myocardial excitation were induced using the cut wave method, and the tip trajectories of spiral waves were measured, which reflected the stability of the rotating waves.The cellular membrane potentials, sodium currents and their corresponding gate variables were analyzed at the positions of outside (A), on (B), and inside (C) the tip trajectories respectively. The main results are as follows:(1) The cell at A could generate and propagate action potentials (AP), but membrane potentials at B and C were abnormal and generation and conduction of APs failed at these two positions. Spiral waves rotated around the tip trajectory during their propagation, thus a functional block area was formed inside the tip trajectory of the cardiac spiral waves.(2) Sodium current at A could be inspired normally and the corresponding gate variables were also normally activated and inactivated; while the sodium currents of cells at B and C were smaller, and the corresponding gates activated and inactivated abnormally, demonstrating that the cells inside the functional block area were in steady depolarization state. Statistical analyses found that energy efficiencies of cells inside the functional block region almost approached zero, and those at the boundary ranged from 50% to 60%.Long-term steady depolarization and low energy consumption efficiency would probably aggravate cell damage, further deteriorate the conducting function, and thus cause more severe arrhythmia. Conduction of spiral waves in injured tissues (partial injury and complete injury) was macroscopically investigated. A rectangle or circular area was delimited in the middle of the myocardial tissue to simulate injury obstacles. The results are as follows:(1) The conduction of the spiral waves was affected by both the shape and size of the damage tissue.(2) Spiral waves conducted slowly in partially-defecting tissues of rectangular shape, but still stably. Wave tips of spiral wave did not pin to the injured part, so the damage degree would’t increase; While the damaged tissue of circular shape hindered the conduction of spiral waves and the wave tips pinned to the border of injured tissue, thus probably deteriorating injury degree.(3) For complete injured tissue, spiral waves always pinned to the obstacle boundary regardless of rectangular or circular shapes, but the one of rectangular shape was more likely to inspire new spiral waves.(4) The more severe and the larger the injured tissue was, the more stable the wave tips pinned to obstacle boundaries. The injured portion featured both preventing wave propagation, and, on the other hand, attracting wave tips pinning to its boundaries.These results may be useful in explaining the effects of cardiac spiral waves on myocardial functions and in evaluating the corresponding consequences. Also it can provide certain guiding advice for the clinical treatment of arrhythmia, such as determinations of radiofrequency ablation shape and size.