| Sumario: | Background: Optimization of atrioventricular (AV) intervals for cardiac resynchronization therapy (CRT) programming is typically performed in supine patients at rest, which may not reflect AV timing in other conditions. Objective: To evaluate the effects of posture, exercise, and atrial pacing on intrinsic AV intervals in patients with CRT devices. Methods: Rate‐dependent A‐V delay by exercise was a multicenter, prospective trial of patients in sinus rhythm following CRT implantation. Intracardiac electrograms were recorded to analyze atrial to right ventricular (ARV), atrial to left ventricular (ALV), and RV to LV (VV) time intervals. Heart rate was increased with incremental atrial pacing in different postures, followed by an exercise treadmill test. Results: This study included 36 patients. At rest, AV intervals changed minimally with posture. With atrial pacing, AV interval immediately increased compared with sinus rhythm, with ARV slopes being 8.1 ± 7.7, 8.8 ± 13.4, and 6.8 ± 6.5 milliseconds per beat per minute (ms/bpm) and ALV slopes being 8.2 ± 7.7, 9.1 ± 12.8, and 7.0 ± 6.5 ms/bpm for supine, standing and sitting positions, respectively. As the paced heart rate increased, ARV and ALV intervals increased more gradually with similar trends. Interventricular conduction times changed less than 0.2 ms/bpm with atrial pacing. During exercise, the direction of change of intrinsic ARV intervals, as heart rate increased, was variable between patients with relatively small overall group changes (0.1 ± 1.4 and 0.2 ± 1.2 ms/bpm for ARV and ALV, respectively). Conclusion: Posture and exercise have a smaller effect on AV timing compared with atrial pacing. However, individualized optimization and dynamic rate related changes may be needed to maintain optimal fusion with left ventricular (LV) stimulation.
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