44Signal-to-Noise Ratio During Haemodynamic Optimisation of AV Delay is Improved more by Atrial Pacing than by Increasing Heart Rate

BackgroundHaemodynamic optimisation of atrioventricular delay has higher information content under fast atrial pacing. This study tests whether it is the presence of atrial pacing or the elevation of heart rate that is important.Methods43 patients with CRT underwent haemodynamic optimisation of AV delay using non-invasive beat-to-beat systolic blood pressure in three states: rest (A-sensing, 66 plus or minus 11 bpm), slow atrial pacing (73 plus or minus 11 bpm), and fast atrial pacing (92 plus or minus 11 bpm). A 20-patient subset underwent a fourth optimisation, during exercise (80 plus or minus 11 bpm).ResultsIntraclass correlation coefficient (ICC, quantifying information content) was 0.30 plus or minus 0.07 for resting sensed optimisation, 0.73 plus or minus 0.04 for slow atrial pacing (p < 0.0001 versus rest-sensed), and 0.82 plus or minus 0.02 for fast atrial pacing (p = 0.03 versus slow-paced). 83% of the increase in ICC, from sinus rhythm to fast atrial pacing, is achieved by simply atrially pacing just above sinus rate.Atrial pacing increased signal (blood pressure difference between best and worst AV delay) from 6.5 plus or minus 0.6 mmHg at rest to 13.3 plus or minus 1.1 mmHg during slow atrial pacing (p < 0.0001) and 17.2 plus or minus 1.3 mmHg during fast atrial pacing (p < 0.001 versus slow atrial pacing) (Figure 1).[Figure]Atrial pacing reduced noise (average SEM of systolic blood pressure measurements) from 1.6 plus or minus 0.1 mmHg at rest to 1.4 plus or minus 0.1 mmHg during slow atrial pacing (p = 0.02). At faster atrial pacing the noise was 1.5 plus or minus 0.1 mmHg (p = 0.2 versus slow-paced, p = 0.3 versus resting sensed).In the exercise subgroup ICC was 0.23 plus or minus 0.19 (p = 1 versus rest-sensed).ConclusionsAtrial pacing, rather than the increase in heart rate, contributes to 80% of the observed information content improvement from sinus rhythm to fast atrial pacing. This is predominantly through increase in measured signal.