page_title: Cardiac rhythm problems during space flight
section_title: Spaceflight evidence
hierarchical_section_title: Cardiac rhythm problems during space flight / Spaceflight evidence
caption_attribution_description: Figure 2. Number of premature ventricular and atrial contractions seen before, during and after space flight. Other information Page 8
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: There have been no systematic studies of the arrhythmogenic potential of long-duration space flight, and only two studies of short-duration space flight. There have been, however, a number of published reports detailing in-flight arrhythmias. Table 1 includes a summary of some of these reports.
  Leguay and Seigneuric also compiled some of the reports from the pre-Shuttle era of crewed space flight. Several of these reports are briefly described below.
  One crewmember during Apollo 15 experienced a 22-beat nodal bigeminal rhythm, which was followed by premature atrial beats. This crewmember reported extreme fatigue during the incident, but only when questioned about it by crew surgeons; thus, it was not severe enough to impact the mission. Twenty-one months later the crew member suffered from coronary artery disease and a cardiac infarction without suggestive ECG changes.
  In the Skylab missions, several instances of ventricular PVCs, supraventricular PVCs, and nodal arrhythmia were recorded. The arrhythmias occurred during effort tests, extravehicular activities (EVAs), lower body negative pressure sessions, and throughout the entire mission. These included two consecutive PVCs in one astronaut during exercise and an episode of atrioventricular dissociation preceded by sinus bradycardia in two astronauts.
  In addition, an isolated incident of a non-sustained 14-beat ventricular tachycardia (Figure 1), with a maximum heart rate of 215 beats per minute, was recorded using in-flight Holter monitoring aboard the Mir. Although not part of a systematic scientific study, this case provides additional evidence of arrhythmias during long-duration space flight.
  Systematic studies of cardiac rhythm disturbances have been performed during short-duration space flight. These studies were conducted in response to medical reports of arrhythmias occurring in 9 to 14 Space Shuttle EVA astronauts between 1983 and 1985.  Rossum et al. used 24-hour Holter recordings acquired during and after high altitude chamber activity, 30 days before launch, during and after each extravehicular activity performed, and on return to Earth. The investigators observed no change in the number of premature ventricular contractions of premature atrial contractions per hour during flight compared to preflight or postflight (Figure 2).  Likewise, arrhythmias were not observed by Fritsch-Yelle et al. in 12 astronauts studied before, during and after 6 Space Shuttle missions. Given the fact that these data disagreed with previous reports, the investigators suggested that further study was required.
  It is unknown whether long-duration exposure to microgravity itself may precipitate cardiac arrhythmias. Based on observations and clinical judgement, medical operations personnel have suggested that some of these incidents have been related to pre-existing, undiagnosed coronary artery disease. Additional pre-selection crew screening tests, including calcium scoring, have been added to reduce such occurrences in the future.
caption: Figure 2. Number of premature ventricular and atrial contractions seen before, during and after space flight.[3]
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