How do cardiac repolarization properties (QT, QTp, Tp-Te intervals) change during and after a standardized exercise test in healthy subjects?
During exercise, the rate-associated shortening of the QT interval occurs primarily in the QTp interval rather than the Tp-Te interval, with a delayed return to resting state post-exercise.
Changes in QT, QT peak (QTp) and terminal T-wave, Tp-Te (QT-QTp) were studied in 11 apparently healthy subjects during and after a standardized exercise test. ECG was recorded at scalar lead positions. Averaged complexes were later analysed by computer for the different time intervals. QT and QTp decreased in parallel with increasing heart rate with a ratio QTp/QT of 0.80 +/- 0.02 at rest and 0.74 +/- 0.02 at maximal heart rate around 170. After exercise QT and QTp prolonged disproportionately slower than heart rate, reaching the relation observed during exercise only 9.5 min post exercise. Tp-Te was 75 +/- 10 ms at rest and 65 +/- 8 ms at maximal heart rate. The decrease was significant (P less than 0.001). The main part of the rate-associated shortening of the QT interval occurred in the QTp interval where it was about six to seven times larger than in the Tp-Te interval. In conclusion, QT and QTp decreased similarly with heart rate during exercise. Post exercise there was an initial slower return of these intervals to the resting state than for heart rate. Tp-Te changes were minimal.
Sundqvist et al. (1989) studied this question.