Key result
Supine bicycle exercise with a 90% slope resulted in maximal QT shortening occurring significantly earlier after exercise termination compared to an 80% slope (29.2 sec vs 69.5 sec; P<0.05).
Why the study?
Does the slope of exercise affect the timing of QT shortening in patients with QT pacemakers?
Observational (n=10)
Does the slope of exercise affect the timing of QT shortening in patients with QT pacemakers?
Absolute Event Rate: 29.2% vs 69.5%
p-value: p=<0.05
In patients with QT pacemakers, the earliest rate response is limited by QT shortening, which typically occurs only after the first minute of exercise.
Exercise slope influences post-exercise QT shortening timing in QT pacemakers; hypothesis-generating for sensor optimization and does not yet change practice.
The present study was undertaken to examine the temporal relationship between exercise and QT interval shortening as one of the principal determinants for the functioning of QT pacemakers. Ten patients (mean age of 72.6 years) with implanted QT pacemakers were subjected to supine bicycle exercise with two different slopes, 90% and 80%. The QT interval as seen by the pacemaker was monitored by telemetry and stored on magnetic tape. After the beginning of exercise QT prolongation of a few msec occurred up to 40 sec in most patients. The earliest QT shortening of 4 msec was noted after 63.4 sec with 90% slope and 75.7 sec with 80% slope. The difference was not significant. The further time course was dependent on slope and pacemaker algorithm. Maximal QT shortening was 65.9 msec with 90% and 69.8 msec with 80% slope. It was seen 29.2 sec after termination of exercise with 90% slope and 69.5 sec with 80% slope (P less than 0.05). There was no correlation of the measured delays with age. Earliest rate response in QT driven pacemakers is determined by earliest QT shortening on one hand and by the slope setting of the pacemaker on the other, where the limiting parameter appears to be QT shortening, which occurs after the first minute of exercise.
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Horstmann et al. (1989) conducted an observational in Implanted QT pacemakers (n=10). Supine bicycle exercise with 90% slope vs. Supine bicycle exercise with 80% slope was evaluated on Time to maximal QT shortening after termination of exercise (sec) (p=<0.05). Supine bicycle exercise with a 90% slope resulted in maximal QT shortening occurring significantly earlier after exercise termination compared to an 80% slope (29.2 sec vs 69.5 sec; P<0.05).
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