Bradycardia-Dependent Loss of Atrial Capture After Single-Chamber Leadless Atrial Pacemaker Implantation.

BACKGROUND: Bradycardia-dependent pacing threshold elevation is a rarely reported cause of early postimplant loss of capture, with only 1 prior case reported in an atrial leadless pacemaker. CASE SUMMARY: 88-year-old woman with sinus pauses underwent Aveir AR implantation. On postoperative day 1, intermittent loss of atrial capture occurred at the programmed lower rate limit. Interrogation revealed stable impedance, current of injury, and sensing. Threshold testing revealed marked rate-dependence: 2.75 V/0.4 milliseconds at 60 beats/min vs 0.75 V/0.4 milliseconds at 90 beats/min. Fluoroscopy confirmed device stability, and output was increased conservatively. DISCUSSION: Proposed mechanisms of this phenomenon include rate-dependent variation in the electrode-tissue interface and phase 4 block from diastolic depolarization in injured myocardium. When early intermittent capture loss occurs with stable device parameters, threshold testing across pacing rates should be performed to assess for bradycardia-dependent threshold elevation. TAKE-HOME MESSAGE: Bradycardia-dependent capture threshold elevation is a possible etiology of early postimplant loss of atrial capture after Aveir AR implantation.