Introduction

Leadless pacemakers like the Abbott Aveir VR have revolutionized cardiac care. However, some patients experience intermittent capture failure during sleep. Understanding the physiological factors behind this can help prevent unnecessary reprogramming or replacements.

1. Elevated Vagal Tone During Sleep

At night, the parasympathetic nervous system becomes dominant, increasing vagal tone. This can lead to sinus slowing and elevated pacing thresholds, especially in patients with bradycardia or conduction disease.

2. Postural Effects on Threshold Capture

Sleeping in the right lateral decubitus position may reduce contact between the pacemaker electrode and myocardium. Studies show variations in capture efficacy based on body position.

3. Intermittent Fibrosis Formation

Over time, fibrotic tissue may form around the electrode, increasing impedance and capture thresholds. This is especially true in patients with high pacing output settings.

4. Nighttime Hypothermia & Autonomic Fluctuations

Core body temperature drops during deep sleep, which can influence myocardial excitability and voltage requirements. The combination of low HR and temperature may challenge pacemaker sensing.

5. Device Programming Limitations

Some leadless pacemakers are programmed with minimal safety margins to preserve battery life. A base rate of 50 bpm with 3.0V @ 0.4 ms might be insufficient in certain nocturnal conditions.

What Can Be Done?

• Discuss reprogramming options (e.g., base rate increase, voltage adjustment) with your cardiologist.
• Track symptoms and correlate with heart rate data using a wearable monitor.
• Consider remote interrogation using Abbott’s Merlin system if available.

Frequently Asked Questions

Sources

• Circulation Journal
• Abbott Medical Devices
• ClinicalTrials.gov - Aveir CSP Trial