Is a leadless AAI (atrial pacing) pacemaker suitable for sinus node dysfunction, and how would the presence of a junctional escape rhythm influence the management?

Leadless AAI Pacing for Sinus Node Dysfunction

Leadless AAI pacing is appropriate for sinus node dysfunction (SND) when AV conduction is preserved, but the presence of a junctional escape rhythm is a critical red flag that suggests underlying AV conduction disease and makes single-chamber atrial pacing potentially dangerous.

Primary Recommendation for Standard SND

For isolated SND with preserved AV conduction, single-lead atrial-based pacing is the established strategy 1. The 2018 ACC/AHA/HRS guidelines explicitly recommend this approach to limit the number of leads and preserve vascular patency, particularly important in younger patients who face lifetime risk of multiple lead revisions 1.

Recent real-world data strongly support leadless atrial pacing for this indication:

• The LEADLESS ARRIVE study (2026) demonstrated that leadless atrial pacemakers had significantly fewer 1-year complications (3.6% vs 8.5%) and reinterventions compared to dual-chamber transvenous systems 2
• Mortality was equivalent across all pacing modalities 2

The Junctional Escape Rhythm Problem

A junctional escape rhythm fundamentally changes the clinical picture and contraindications for AAI pacing. Here's why this matters:

What the Junctional Rhythm Tells You

A junctional escape rhythm in the setting of SND indicates:

• The sinus node is failing to pace the atrium adequately
• The AV node has assumed pacemaker function, which only occurs when atrial impulses are absent or failing to conduct
• This suggests potential AV conduction system disease beyond isolated sinus node pathology 3

The Critical Risk

If you implant an AAI leadless pacemaker and the patient subsequently develops AV block:

• The atrial pacemaker will continue firing
• No ventricular pacing backup exists
• The patient faces complete heart block with potential syncope or sudden death
• You cannot upgrade a leadless atrial pacemaker - it requires explantation and new device implantation

Historical Context on AV Block Progression

While older AAI(R) pacemaker data showed low rates of AV block progression 4, the presence of a junctional escape rhythm was not the baseline in those studies. A junctional rhythm specifically indicates the AV junction is already actively participating as a pacemaker, suggesting the conduction system is more broadly diseased 5.

Clinical Decision Algorithm

If junctional escape rhythm is present:

1. Perform comprehensive AV conduction assessment:

   • Baseline PR interval and QRS duration
   • Exercise testing to assess AV conduction during increased atrial rates
   • Consider electrophysiology study to measure AH and HV intervals
   • Assess for any degree of AV block (even first-degree) 1

2. If ANY evidence of AV conduction impairment exists:

   • Choose dual-chamber pacing (either transvenous or dual leadless system when available)
   • Do NOT proceed with AAI-only pacing

3. If AV conduction is definitively normal despite junctional rhythm:

   • The junctional rhythm may represent enhanced automaticity rather than conduction disease
   • Leadless AAI could be considered, but maintain very low threshold for dual-chamber system
   • Close follow-up is mandatory

Common Pitfalls to Avoid

• Do not assume isolated SND based on surface ECG alone when junctional rhythm is present - this may mask underlying AV nodal disease 3
• Do not rely solely on resting ECG - assess AV conduction during physiologic stress
• Do not underestimate the significance of subsidiary pacemaker activation, which indicates more extensive conduction system involvement 5

Special Circumstances

In post-cardiac transplant patients with biatrial technique, junctional rhythms may represent atrial parasystole rather than true AV disease 6. Even in these cases, leadless atrial pacing has been successfully used, but only after confirming preserved AV conduction through electrophysiology study 6.

In acute MI settings with rhythm-mediated shock, leadless atrial pacing has been used successfully despite adverse electrical parameters, but this represents salvage therapy in extremis 7.

The bottom line: A junctional escape rhythm in SND is not isolated sinus node disease until proven otherwise through rigorous AV conduction testing. When in doubt, choose dual-chamber capability.