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Microgravity during spaceflight may cause cardiac arrhythmias. Experimental studies mimicking microgravity condition have shown some changes in cardiac tissue properties. However, it is unclear how such changes in the cardiac tissue are pro-arrhythmic. The aim of this study was to evaluate the functional impact of microgravity on cardiac electrical excitation by a simulation approach. Experimentally observed decrease in L-type Ca2+ channel current (ICaL), increases in Na+-K+ pump current (INaK) and the intercellular electrical coupling from rat with 4-weeks tail suspension were incorporated into computer models of rat ventricular myocytes and one— dimensional (1D) ventricular transmural strand. At the cellular level, it was shown that the changes in cellular membrane ion channels abbreviated the duration of action potentials (APDs) of cells, resulting in a reduced transmural dispersion in APD. At the 1D tissue level, these changes resulted in a mild increase in the conduction velocity of excitation waves, but a shortened QT interval in ECG with a depressed ST phase and flattened T-wave, which are consistent with experimental observations. They also caused a reduced tissue vulnerability to the genesis of unidirectional conduction block in response to a premature stimulus. Further analysis showed that among the microgravity-induced cellular changes, a reduced ICaL played a more important role in producing sick functional changes. In conclusion, this study provides new insights into understanding of impaired cardiac functions in microgravity condition during spaceflight.

Computer Modelling and Analysis of the Effects of Microgravity on Rat Ventriclular Excitation