T-wave alternans and autonomic nervous system activity during orthostatic stress after 5 days of head-down bed-rest

Reports of ventricular arrhythmias during spaceflights raise the question of whether microgravity increases sudden cardiac death risk. We aimed at studying changes in T-wave alternans (TWA) together with Autonomic Nervous System activity during tilt-table (TT) testing before and after five days of -6° head-down bed-rest (HDBR), simulating exposure to microgravity. ECG signals were obtained in 22 males during TT, before and immediately after the end of HDBR, analyzed for multilead TWA detection and spectral analysis of heart rate variability. No differences in TWA indices before and after HDBR were found. However, subjects with lower orthostatic tolerance time after HDBR presented higher TWA values and unbalanced sympato-vagal response to TT already before HDBR.