Long-term follow-up of single-chamber atrial pacing - system upgrade and wenckebach block point behavior: potential implications for leadless AAI pacing?

Until recently leadless pacemakers (PM) did not support atrial pacing. A novel dual chamber leadless PM system now provides treatment option for a wide range of indications. Single-chamber atrial stimulation (AAI) for the treatment of symptomatic sick sinus syndrome (SSS) is scarcely used due to concerns about the potential development of atrioventricular block (AVB) and development of paroxysmal atrial fibrillation (AF). Long-term follow-up data of AAI-PM is however scarce. Little is known about the role of serial Wenckebach block point (WBP) measurements in AAI-PM patients for risk stratification.

To assess the incidence of dual chamber upgrade of patients treated with AAI-PM for SSS during long-term follow-up and to investigate the role of serial WBP measurements for risk stratification.

Prospectively enrolled patients undergoing implantation of an AAI-PM between October 2002 and December 2023. WBP was measured at implantation and serially during follow up.

We included a total of 178 patients, of which 58% were female and the median age at implantation was 78 [IQR 71 – 83] years. The median follow-up duration was 6.5 [IQR 2.0 – 9.7] years. 24 patients (13.5%) received a system upgrade to DDD including 3 patients (1.7%) with a mode change to ventricular pacing only (VVI). Adjusted for years of follow-up the upgrade rate was 2.1% per year. Median time to system upgrade was 5.2 [IQR 1.6 – 8.7] years. Reasons for system upgrade were high-degree AVB (38%), low WBP (17%), atrial arrhythmias (33%), unclear syncope (8%) and infection (4%). Median WBP at implantation was 130 [120 – 140] bpm, showing a significant decline over time in the upgrade-group with 105 [95 – 130] bpm compared to the rest of the cohort with 130 [120-130] bpm (p = 0.009). A decline in WBP >20 bpm was found in 17.9% patients and a decline of 10-20 bpm in 33.7% of patients. New-onset atrial arrythmias were found in 36 patients (20%), 29% in the upgrade group and 19% in the rest of the cohort (p = 0.3). Neither age at implantation, sex, WBP at implantation, nor atrial arrhythmia prior to implantation were predictive for the need of a future system upgrade.

In this cohort of patients undergoing AAI-PM implantation for SSS, a system upgrade was required in 2% per year. The WBP remained stable in 48% of patients. Therefore, AAI-PM due to SSS emerges as a judicious and secure therapeutic modality, warranting increased consideration in the light of new treatment options for leadless pacing.