QT dispersion during hypobaric hypoxia

Objective: Hypoxia is one of the major concerns in aviation. Clinical hypoxia has been shown to increase QT dispersion (QTd). We aimed to examine QTd during hypobaric chamber training to observe the effect of hypobaric hypoxia on QT dispersion.
Methods: A total of 38 healthy male aviators volunteered to take part in this longitudinal study. Subjects' electrocardiograms were recorded by 12-lead digital Holter device before, during, and after hypobaric exposure at simulated altitude of 30,000ft. Data from 23 of the subjects, aged 27.91±6.02 years (range 22–39) was used. QT intervals were measured manually. QT dispersion and heart rate adjusted QTd (QTcd) were calculated for each subject. Statistical significance of changes in parameters was analyzed using the Friedman test. Comparison of pre-post exposure clusters was made using Dunn’s test.
Results: QT dispersion values were as following: prehypoxic 64.09±8.39 ms, hypoxic 50.35±11.06 ms and posthypoxic 59.83±9.06 ms (Median: 64, 50, 60; Mean rank: 2.65, 1.28, 2.07) (p=0.0001 for prehypoxic–hypoxic, p=0.046-prehypoxic-posthypoxic, and p=0.002 for posthypoxic-hypoxic). Heart rate values were as following: prehypoxic 74.09±6.43 beats/min, hypoxic 127.1±17.39 beats/min, and posthypoxic 95.17±11.35 beats/min (Median: 75, 122, 92; Mean rank: 1, 3, 2) (p=0.0001 for prehypoxic–hypoxic, prehypoxic–posthypoxic, and posthypoxic–hypoxic). The change in QTd and HR during hypobaric chamber exposure was statistically significant but, the change in QTcd was not (p<0.001, p<0.001, p>0.1, respectively).
Conclusion: From the findings of present study, it is not possible to directly comment on the validity of QTd in revealing arrhythmogenic predisposition of healthy subjects exposed to hypobaric hypoxia. The relationship between QT dispersion and hypobaric hypoxic exposure is not clear, particularly when QTd is corrected for the increased heart rate. QT dispersion measurement has not been proven a reliable and practical method to show arrhythmia predisposition during a hypobaric hypoxic exposure in healthy individuals.