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  • Title: Hysteresis of electrocardiographic depolarization-repolarization intervals during dynamic physical exercise and subsequent recovery.
    Author: Lewis MJ, Short AL.
    Journal: Physiol Meas; 2006 Feb; 27(2):191-201. PubMed ID: 16400205.
    Abstract:
    The post-exercise electrocardiographic QT interval is shortened relative to that at similar heart rates during exercise or pre-exercise rest. This lag in QT adaptation to the recovering heart rate is described as "hysteresis". No previous studies have quantified the influence of ECG electrode placement on hysteresis following physical exercise. Six males and six females of similar age, mass and aerobic fitness undertook progressive sub-maximal bicycle exercise. A three-channel ECG was recorded continuously during pre-exercise, exercise and recovery. Beat-to-beat NN (cardiac interval) and QT(a) interval (Q wave onset to T wave apex) data were measured for each sinus heart beat. QT(a)-NN hysteresis was calculated as the difference in QT(a) magnitude at identical heart rates during the rest/exercise and post-exercise recovery periods. There were some significant (p < 0.05) between-channel and between-gender differences in calculated hysteresis values. Hysteresis was generally greatest during the second or third minute post-exercise; ranges of means for all channels were 10.9 +/- 11.7 ms to 25.5 +/- 16.8 ms (males) and 19.1 +/- 10.3 ms to 28.4 +/- 3.0 ms (females). For males only, hysteresis values calculated using channel 1 between 1 and 3 min post-exercise were generally significantly (p < 0.05) different to those between 4 and 10 min. Similar trends were observed in females. QT(a)-NN hysteresis is significantly affected by the locations of the ECG electrodes used to record the surface ECG. These results emphasize the need for standardization of ECG electrode placement in future investigations.
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