Aim: The aim of this study was to evaluate the circadian variation of atrial pacing threshold in young patients.
Methods and results: Atrial Capture Management (ACM) algorithm is a Medtronic EnPulse pacemaker (PM) feature that uses two algorithms: atrioventricular conduction (AVC) (atrial pacing and spontaneous AVC) and atrial chamber reset (ACR) [intrinsic atrial activity with atrioventricular block (AVB)]. For this prospective, non-randomized study, ACM automatically measured and recorded thresholds every 4 h. Data are reported as median (range) or mean +/- SD. In 2004-05, 14 consecutive patients (11 males, 79%), aged 12 years (1 day-24 years) received an EnPulse DDD/R PM for AVB (eight patients, 57%) or sinus node dysfunction. A new pacing system was implanted in eight patients (57%) and a replaced PM in six patients. Epicardial leads were implanted in 10 patients (71%). The follow-up duration is 11 (1-18) months: 9742 threshold measurements were attempted (6328 AVC, 3414 ACR), of which 3797 (39%) were successful (1807 AVC, 29%, 1990 ACR, 58%) in 11 (79%) patients. Three infants had no successful measurements. Measurement success was 42 +/- 34% (AVC 27 +/- 39%, ACR 41 +/- 29%). Higher thresholds were found between 00.00 and 12.00 a.m. and lower between 12.00 and 20.00.
Conclusion: Young patients show a circadian variability of atrial threshold with higher thresholds between 00.00 and 12.00.