Clinical Case: Nocturnal Pacemaker Malfunction in Aveir VR Leadless Pacemaker
Clinical Question
A patient 71 years old with an Aveir VR LP starts the day at 4 AM with 60 minutes of exercise, followed by 4 hours of driving and two work meetings. The patient goes to bed at 9:30 PM after drinking 250 ml of soy milk, almond milk and water. He goes to sleep in the right lateral position. At that moment he has a heart rate of 50 bpm, SpO2 of 98% and a perfusion index of 4.5.
After 5 hours of deep sleep (2:30 AM) the patient wakes up with a heart rate of 27 beats per minute, SpO2 of 95% and perfusion index of 20. Then he goes to bathroom to urinate 50 ml when normally urinates 250 ml. From 2:30 to 3:00 AM the patient is in bed with no symptoms at all and SpO2 of 95%, heart rate of 27 beats per minute and perfusion index of 20. He drinks 100 ml of water.
Around 3:00 AM the patient falls asleep again and wakes up at 6 AM with a big discomfort, close to pain and a heart rate of 50 beats per minute, SpO2 of 97% and PI of 5. He goes to urinate, and the amount of urine is 50 ml when usually at that time of the day is 150 ml. The big discomfort remains until the patient goes to the swimming pool when he swims 30 minutes with no pain or any discomfort.
My question to you: What happens in the hours the patient was sleeping?
Clinical Analysis
This is a fascinating and clinically significant nocturnal event in a patient with an Aveir VR leadless pacemaker. Let me analyze what likely occurred during those sleep hours:
What Happened During Sleep (2:30-6:00 AM)
The Critical Event: Pacemaker Inhibition Leading to Profound Bradycardia
The heart rate drop from 50 bpm (at bedtime) to 27 bpm (at 2:30 AM) represents a concerning failure of pacing that persisted for approximately 3.5 hours. Here's what likely transpired:
Mechanism of Pacemaker Inhibition
Oversensing-Induced Pacing Suppression: The Aveir VR likely experienced inappropriate sensing that inhibited ventricular pacing. Several factors converged:
- Right Lateral Decubitus Position: This sleeping position can alter the spatial relationship between the leadless pacemaker and cardiac structures, potentially increasing susceptibility to:
- Myopotential oversensing from diaphragmatic or intercostal muscle activity
- Changes in intracardiac electrogram amplitude
- Altered sensing vector geometry
- Deep Sleep Physiology (2:30-6:00 AM): During deep sleep, particularly REM sleep which is more prevalent in early morning hours:
- Increased vagal tone further suppresses intrinsic heart rate
- The patient became completely dependent on pacing
- When pacing was inhibited, the escape rhythm was only 27 bpm
- Fluid and Positional Factors: The intake of 350 ml of fluids before bed (soy milk, almond milk, water) combined with right lateral position may have contributed to:
- Altered thoracic fluid distribution
- Changes in cardiac chamber geometry
- Potential increase in diaphragmatic proximity to the RV apex
Physiological Consequences
Hemodynamic Compromise at 27 bpm:
- Reduced Cardiac Output: At 27 bpm, even with compensatory increased stroke volume, cardiac output was severely reduced (likely 40-50% of normal)
- Oliguria: Reduced urine output (50 ml vs. normal 250 ml at 2:30 AM, and 50 ml vs. 150 ml at 6 AM) indicates:
- Decreased renal perfusion
- Activation of renin-angiotensin-aldosterone system
- Antidiuretic hormone release
- Tissue Hypoperfusion Indicators:
- Perfusion Index spike to 20 (from baseline 4.5): This paradoxical increase likely reflects peripheral vasoconstriction with centralization of blood flow. The PI measures pulse strength; the high value might indicate compensatory mechanisms or measurement artifact from poor peripheral perfusion
- SpO2 drop to 95%: Mild desaturation from baseline 98% suggests inadequate cardiac output
- "Big Discomfort, Close to Pain" at 6 AM: This symptom upon awakening represents:
- Myocardial ischemia from prolonged bradycardia
- Possible lactic acidosis from tissue hypoperfusion during 3.5 hours of severe bradycardia
- Cardiac strain from attempting to maintain output with profound bradycardia
Why the Patient Had No Symptoms from 2:30-3:00 AM
During the 30-minute wakeful period, the patient reported no symptoms despite HR of 27 bpm because:
- He was resting in bed (minimal metabolic demand)
- Cerebral perfusion was adequate in supine position
- Compensatory mechanisms were maintaining vital organ perfusion
- Sympathetic activation from waking may have improved cardiac function slightly
Resolution at 6 AM and Beyond
Why HR returned to 50 bpm at 6 AM:
- Change in body position (getting up to urinate)
- Transition from deep sleep to wakefulness
- Altered sensing conditions allowed the pacemaker to resume functioning
- Increased sympathetic tone upon awakening
Complete Resolution with Swimming:
The fact that discomfort completely resolved with 30 minutes of swimming and the patient could exercise without symptoms indicates:
- The pacemaker was functioning properly during exercise
- The bradycardic episode caused reversible myocardial stunning or metabolic disturbance
- No permanent myocardial damage occurred
- Rate response was appropriate during activity
Clinical Implications and Recommendations
This patient experienced nocturnal pacemaker malfunction requiring urgent evaluation:
- Device Interrogation: Immediate download of stored electrograms to identify the cause of pacing inhibition
- Sensitivity Reprogramming: Consider decreasing sensing sensitivity if oversensing is confirmed
- Lower Rate Limit: May need to increase the lower rate limit from current setting
- Sleep Position Counseling: Advise avoiding prolonged right lateral decubitus position
- Holter Monitoring: Document any recurrent nocturnal events
- Consider Alternative Pacing: If recurrent, may require transition to a dual-chamber system or alternative single-chamber device
The combination of prolonged severe bradycardia, oliguria, elevated PI, and morning discomfort suggests this was a clinically significant event that, if recurrent, could lead to syncope, falls, or more serious consequences.