Development of the pacing threshold after the implantation of an atrial leadless device

Introduction

Since 2024, the first atrial Leadless Pacemaker has been approved in Germany and allows the use as a first fully functional dual-chamber leadless pacing system. Initial real-world data have become available following successful implantations. Two major factors are crucial for achieving optimal device longevity: minimizing energy consumption through low pacing thresholds and ensuring effective inter-device communication. During implantation, both the distance between the device capsules and the choice of optimal implantation sites play an essential role. However, due to the limited size of the atrial chamber, options for positional optimization remain restricted.

Despite fluoroscopically optimal positioning of the atrial device and, consequently, an ideal electrode placement, initially elevated atrial pacing thresholds are observed.

Hypothesis

Despite initially high pacing thresholds of the atrial leadless pacemaker even with optimal positioning confirmed by fluoroscopy and electroanatomical mapping, implantation can be performed, as a significant decrease in thresholds is consistently observed during follow-up.

Study Design

We retrospectively included all patients who underwent atrial leadless implantation between August 2024 and October 2025 (n = 14). Epidemiological and general patient data were collected, along with measurements of pacing threshold, sensing, and impedance at implantation (t), and at t + 1 day, t + 30 days, t + 90 days, and t + 180 days. For comparison, a control group of 50 randomly selected patients who received a ventricular leadless device-provided by the same company with the same fixation mechanism during the same period was analyzed. Electrophysiological, demographic, and epidemiological data were documented identically.

Results

No statistically significant differences were observed between the Atrial and Ventricular groups regarding epidemiological characteristics, comorbidities, or echocardiographic parameters. Regardless of individual patient factors, such as right or left atrial dimensions and comorbidities, the atrial pacing threshold at implantation was significantly higher compared to the ventricular device. During follow-up, the atrial threshold showed a marked and statistically significant decrease, stabilizing at low levels over time. In contrast, the ventricular threshold exhibited a slight, non-significant decline and remained largely stable.

Conclusion

When implanted under fluoroscopic guidance with appropriate sensing and impedance parameters and an appropriate injury potential, the atrial device demonstrates a significant post-implantation reduction in pacing threshold, achieving stable values during follow-up. This effect may be attributed to a relatively larger local edema and electrode–tissue interface in the smaller atrial cavity compared with the ventricle. Further studies are warranted to elucidate the underlying mechanisms of this phenomenon.