Cardiac repolarization properties during standardized exercise test as studied by QT,QT peak and terminated T-wave intervals

Summary. Changes in QT, QT peak (QT_p) and terminal T-wave, T_p–T_e (QT–QT_p) 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 QT_p decreased in parallel with increasing heart rate with a ratio QT_p/QT of 0·80 ± 0.02 at rest and 0·74 ± 0·02 at maximal heart rate around 170. After exercise QT and QT_p prolonged disproportionately slower than heart rate, reaching the relation observed during exercise only 9·5 min post exercise. T_p–T_e was 75 ± 10 ms at rest and 65 ± 8 ms at maximal heart rate. The decrease was significant (P<0·001). The main part of the rate-associated shortening of the QT interval occurred in the QT_p interval where it was about six to seven times larger than in the T_p–T_e interval. In conclusion, QT and QT_p 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. T_p–T_e changes were minimal.