Key Points
- To assess the reliability of the evoked T-wave response in controlling paced ventricular rate and determine the functional performance of rate-responsive QT (TX) pacemakers.
- Evaluated 13 patients implanted with TX pacemakers that adjust pacing rates according to the stimulus artifact-to-T-wave (stimulus-T) interval.
- Compared treadmill exercise performance during TX pacing mode against atrial synchronized ventricular (VAT) and fixed ventricular demand (VOO/VVI at 70 beats per minute) modes.
- Monitored heart rate to stimulus-T interval relationships and programming adjustments repeatedly via serial treadmill exercise tests and Holter recordings.
- Exercise performance improved significantly during TX rate-responsive pacing compared to VVI pacing, yielding functional capacity comparable to VAT pacing.
- Satisfactory rate response was achieved in 12 of 13 patients by adjusting the response slope and sensing window, though T-wave sensing deteriorated over time in most patients and caused initial detection failures in 3 patients.
- Resting stimulus-T interval correlated inversely with paced rate according to the regression equation stimulus-T = 466 - 1.68 × paced-rate (r2 = -0.62), exhibiting wide inter- and intra-patient variability.
Structured PICO
Does TX pacing mode improve exercise performance compared to VVI and VAT pacing modes in patients requiring pacemakers?
PPopulation13 patients with pacemakers
IInterventionTX pacing mode (QT or rate responsive pacemaker adapting pacing rate to stimulus-T interval)
CComparatorAtrial synchronized ventricular (VAT) and asynchronous ventricular demand (VOO and VVI--70 beats per minute) pacing modes
OOutcomeTreadmill exercise performancesurrogate
QT-responsive (TX) pacing provides better exercise performance than fixed-rate VVI pacing and comparable performance to VAT pacing, though it requires frequent reprogramming due to sensing variations.
Limitations
- T-wave sensing deteriorated with the passage of time in most patients
- Wide inter- and intra-patient variation in chronotropic response
- Requires reprogramming based on exercise tests and Holter monitoring to adjust for changes in T-wave sensing