Effect of simulated microgravity by head-down bed rest on T wave alternans

Reports of ventricular arrhythmias during spaceflights raise the question of whether microgravity increases sudden cardiac death risk. Our aim in this work was to study changes in T-wave alternans (TWA) during VO₂ max stress tests before and after five days of -6° head-down bed rest (HDBR) simulating exposure to microgravity. Two HDBR campaigns were organized by the European Space Agency in MEDES (Toulouse, France) and DLR (Koln, Germany). High-resolution ECG signal was recorded in 19 male volunteers during VO₂ max tests by bicycle exercise stress, the day before the beginning of HDBR (pre) and within 26 hours after the end of HDBR (post). ECG was analyzed for multilead TWA detection. In the MEDES campaign, 4 subjects at pre while 6 at post-HDBR presented TWA. In the DLR campaign, TWA was detected in all subjects both in pre and post-HDBR. Various TWA features were compared, but only the heart rate at the onset of TWA episodes from the beginning of the VO₂ max test resulted in significant differences between pre and post, being always higher than 110 beats/min.