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 30,000 ft. 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).


CONCLUSIONS
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.
Oztürk
Cengiz
C
Department of Cardiology, Military Hospital, Eskişehir, Turkey. cisozt@yahoo.com
Sen
Ahmet
A
Açikel
Cengiz Han
CH
Ilgenli
Tevfik Fikret
TF
Onem
Yalçin
Y
Oztürk
Ahmet
A
Akin
Ahmet
A
D000328:Adult; D000531:Altitude; D001145:Arrhythmias, Cardiac / Q000453:epidemiology* / Q000209:etiology; D001273:Atmosphere Exposure Chambers; D001274:Atmospheric Pressure; D016000:Cluster Analysis; D015716:Electrocardiography, Ambulatory / Q000379:methods*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000150:complications / Q000503:physiopathology*; D008133:Long QT Syndrome / Q000209:etiology*; D008137:Longitudinal Studies; D008297:Male; D011237:Predictive Value of Tests; D012307:Risk Factors; D055815:Young Adult