A 66-year-old woman with a history of hypertension was examined for recurrent chest discomfort and palpitations at our hospital. A dual-chamber pacemaker (Abbott/SJM) was implanted due to sick sinus syndrome 1 year ago. The Holter monitor test recorded recurrent episodes of a sudden change in pacing rate, starting with an intrinsic P wave (Figure 1a). In total, 25 episodes were recorded, of which, the longest episode lasted for 3 min.Most episodes corresponded to the patient's symptoms of recurrent chest discomfort and palpitations. Notably, Figure 1b shows pacing pulses in two opposite directions: an upward pulse (Up), followed by a positive P wave, and a downward pulse (Dp), followed by a negative P wave.The patient offered following information about the last interrogation: DDD mode, base rate 60 bpm, auto-mode switch base rate (AMSBR) 80 bpm, PAV/SAV interval 300/250 ms, and activity sensor off.What accounts for the sudden change in pacing rate?
| COMMENTARYThe following reasons may be attributed for the sudden change in pacing rate: an auto-mode switch (AMS) (Sharma et al., 2016), atrial overdrive pacing function (Hohnloser et al., 2012), and sensor rate.Every episode started with an intrinsic P wave, which is consistent with the startup characteristics of AMS in the SJM (Barold, 2017). However, no atrial tachycardia was observed before any episode. This suggested that the AMS might be due to atrial oversensing. In contrast, the atrial pacing rate (105 bpm, AP-AP interval 570 ms) did not correspond with AMSBR (80 bpm). The atrial pacing rate to