Microgravity and Cardiac Electrophysiology: Autonomic Remodeling, Arrhythmogenesis, and Implications for Long-Duration Spaceflight

BACKGROUND: In microgravity, the human heart undergoes significant geometric and functional remodeling due to the removal of gravity-dependent hydrostatic gradients. These adaptations include a transition from an elliptical to a more spherical shape configuration. Furthermore, cephalad fluid shifts trigger an early spaceflight diuresis, inducing a stable reduction in circulating plasma volume. OBJECTIVE: To describe resulting electrophysiologic alterations and arrhythmia promotion. METHOD: While most spaceflight arrhythmias are transient and non-lethal, they remain a concern for long-duration missions. Frequently reported irregularities include isolated premature atrial and ventricular complexes. Other events, including non-sustained ventricular tachycardia during spaceflight, the possibility of early-onset atrial fibrillation, and atherosclerosis in former astronauts following exposure to high-energy ionizing radiation have been documented, though the association is still being evaluated. The underlying arrhythmogenic substrate is driven by autonomic resetting, spatiotemporal heterogeneity, and QTc interval prolongation. RESULTS: The National Aeronautics and Space Administration utilizes a multi-faceted approach to maintain electrical stability, incorporating high-intensity interval training and electrolyte monitoring and supplementation. Real-time monitoring of wearable technology enables continuous telemetry of the heart. Recently, automated chest compression devices have been shown to significantly outperform manual cardiopulmonary resuscitation in microgravity environments. CONCLUSION: Although structural changes typically revert to baseline upon return to Earth gravity, deep-space missions present some risks. Astronauts exposed to ionizing radiation beyond Earth's magnetic field may face risk of long-term cardiovascular disease. Design of personalized nutrition to mitigate electrolyte loss and development of advanced screening tools for cardiac risk assessment are essential to improve the safety of future planetary missions.