QTp Interval Behavior during Treadmill Exercise in Airlines Pilots

ABSTRACT

BACKGROUND AND OBJECTIVES: QT interval on ECG strongly depends on heart rate. Prolonged early phase of repolarization may be responsible for mechanisms of arrhythmogenesis. Investigation of physiologic behavior of QT interval and their relation to cardiac cycle length may explain mechanisms of arrhythmogenesis. The aim of this study is to investigate the physiologic behavior of the QT intervals during various stages of treadmill exercise test in healthy airlines pilots. METHOD: A retrospective analysis of treadmill exercise test ws done in 60 healthy men. Each underwent 10 ECG recordings, which were performed in resting, 1 minute, 2 minute and 3 minute of exercise stage 1, 2 and 3 of Bruce protocol respectively. The QT interval was measured as the time interval from the earliest Q onset to the peak T wave (QTp) in precordial lead V2. RESULTS: The mean heart rate before exercise was 72 +/-5 beats/minute, and at 1, 2 and 3 minute of exercise stage 1, 2 and 3 were 96 +/-8, 97 +/-7, 99 +/-9, 112 +/-9, 117 +/-9, 120 +/-10, 137 +/-12, 145 +/-12 and 152 +/-10, respectively. The d-QTp/d-RR at 1, 2 and 3 minute of exercise stage 1, 2 and 3 were 10.4 +/-5.9, 14.1 +/-5.8, 15.1 +/-6.2, 14.8 +/-4.2, 16.1 +/-3.7, 16.3 +/-3.5, 16.8 +/-2.9, 17.1 +/-3.0%, respectively. The QTp interval respond slowly for rapid changes in cycle length. The change of QTp interval showed a linear correlation with the change of the RR interval (y=0.189x-10.864, r=0.83, P<0.0001). CONCLUSION: The changes in QT interval lagged behind the rapid and sustained changes in the heart rate elicited by treadmill exercise test. It is concluded that the d-QTp/d-RR showed hysteresis in the changes in the RR interval may be useful in assessing in the dynamic regulation of the ventricular repolariza-tion process.