Abstract 18904: Cardiac Arrhythmias During Long Duration Spaceflight

Abstract

PURPOSE: Whether cardiac arrhythmias are increased during spaceflight has been a long standing question for the human space program. Few data are available from long duration flight. To evaluate the incidence of in-flight arrhythmias we studied 12 astronauts during 4-6 months on the International Space Station with high-fidelity Holter monitoring. We hypothesized that spaceflight does not increase the incidence of cardiac arrhythmias, and when arrhythmias are observed they represent a benign substrate. METHODS: Twelve astronauts (3 women) wore 48hr Holter monitors: two preflight; in-Flight Day (FD)-14, 30, 75, 135; 15 days prior to return; and immediately upon landing. Individuals recorded symptoms in a diary. Arrhythmia frequency was assessed blindly by an experienced electrophysiologist. RESULTS: Baseline data showed 125±359 (range 1-1262) supraventricular ectopic beats (SEB) per 48hr period, while in-flight recordings showed 320±1137 SEB (range 0-5405); ventricular ectopy (VEB) at baseline was 286±944 beats (range 0-3282) and 305±775 beats (range 0-3439) in-flight confirming the substantial inter-individual variability. SEB and VEB at baseline were 0.06±0.16% and 0.13 ± 0.42% of all beats respectively, while the 48hr Holter with the largest number of ectopic beats for each astronaut was 0.25±0.74% (p=0.284) and 0.24±0.51% (p=0.177) respectively, demonstrating no significant change in ambient ectopy. There were no sustained arrhythmias in flight; short runs of NSVT (all <5 beats) were observed both pre and in-flight in some astronauts. Filtered QRS duration (baseline: 84.5±8.2; in-flight maximum: 90.5±12.1 msec, p<0.001), and low amplitude signal duration (baseline: 23.2±6.4; in-flight maximum: 27.1±6.4 msec, p<0.01) increased subtly, but remained within normal limits; root mean square voltage of the terminal 40 ms did not change (baseline: 62.5±34.3; in-flight maximum: 73.0±29.4 microV, p=0.19). T wave alternans was not present at any time. Analysis of QT variability and T wave morphology in the first 6 astronauts did not change. CONCLUSIONS: Baseline arrhythmias are quite variable between astronauts; data suggest that long duration spaceflight is not associated with changes in arrhythmia frequency or arrhythmic substrate.