Changes in ventricular repolarization and cardiac function induced by head-down bed rest

Reports of ventricular arrhythmias during spaceflights raise the question of whether microgravity increases sudden cardiac death risk. To test if changes in cardiac structure and neurohumoral environment during space flight could alter electrical conduction, we studied both changes in ventricular repolarization (VR) and cardiac echocardiographic parameters in 12 males before and after five days of head-down (-6°) sedentary bed-rest (HDBR), simulating exposure to microgravity. Increased heterogeneity in VR was found, but not related to cardiac atrophy. In fact, changes in LV morphology were restored 3 days after HDBR. Longer HDBR studies are needed to better elucidate the phenomenon.