page_title: Cardiac rhythm problems during space flight
section_title: Left ventricular mass
hierarchical_section_title: Cardiac rhythm problems during space flight / Contributing factors / Left ventricular mass
caption_attribution_description: English: Figure 4. Left ventricular mass before and after short-duration space flight [based on(8), n=38]. * = P ≤ 0.05.
context_page_description: Heart rhythm disturbances have been seen among astronauts. Most of these have been related to cardiovascular disease, but it is not clear whether this was due to pre-existing conditions or effects of space flight. It is hoped that advanced screening for coronary disease has greatly mitigated this risk. Other heart rhythm problems, such as atrial fibrillation, can develop over time, necessitating periodic screening of crewmembers’ heart rhythms. Beyond these terrestrial heart risks, some concern exists that prolonged exposure to microgravity may lead to heart rhythm disturbances. Although this has not been observed to date, further surveillance is warranted.
  The incidence and clinical significance of cardiac arrhythmias during long-term exposure to microgravity experienced on the International Space Station or during a prolonged sojourn to Mars or on the Moon are a concern for the National Aeronautics and Space Administration. At present, there are only anecdotal reports of cardiac arrhythmias in space, including one documented episode of non-sustained ventricular tachycardia.
context_section_description: Recent evidence suggests that the development of apoptosis, or “programmed cell death” in response to pathological, physiologic, and/or genetic signals, may be a key developmental factor in causing cardiac arrhythmias. For example, apoptosis associated with atrophy and fibrofatty replacement of right ventricular tissue has been identified as the likely mechanism forarrhythmia development in arrhythmogenic right ventricular dysplasia, a condition that may lead to sudden death in otherwise healthy young individuals.
  Two publications have reported decreases in left ventricular mass after short-duration space flight. In one of these publications,  cardiac MRI was used and showed a reduction in left ventricular mass on landing day; however, extended recovery data were not obtained (Figure 3). In the other publication,  echocardiography was used and showed a similar decrease in mass on landing day with full recovery 3 days after landing.
  Unpublished data (also measured with ultrasound) show decreases in left ventricular mass after 6-month missions aboard the ISS. These decreases are double those observed after short flights and do not fully recover by the third day after landing (Figure 5).
  There is some disagreement over the mechanism of the decrease in mass, especially after short-duration missions. While there is evidence to support the idea that tissue dehydration contributes to the loss in mass after short-duration space flights, there are data from bed rest studies showing that the decrease in mass can be prevented with exercise and/or nutritional countermeasures. However, there is agreement that the greater loss of mass with long-duration flight is most likely due to atrophy.
caption: Figure 4. Left ventricular mass before and after short-duration space flight [based on(8), n=38]. * = P ≤ 0.05.
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