ABC Farma - Artificial Intelligence Doctor

Aveir VR LP – Nocturnal Physiology and Possible Non-Capture

Patient 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 wake 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?

Answer

1. Key observations in this scenario

• Age 71, with an Aveir VR leadless ventricular pacemaker (VR LP).
• Normally very active: 60 minutes of exercise at 4 AM, 4 hours of driving, two work meetings.
• Goes to bed at 9:30 PM in right lateral position with:
  • HR ~ 50 bpm
  • SpO₂ 98%
  • Perfusion Index (PI) 4.5
• At 2:30 AM (after ~5 hours of deep sleep):
  • HR drops to 27 bpm
  • SpO₂ 95%
  • PI rises sharply to 20
  • Urinates only 50 ml (normally 250 ml at that time)
  • No subjective symptoms (no dizziness, no chest pain, no dyspnea)
• From 2:30 AM to 3:00 AM:
  • Stays in bed, still with HR ~ 27 bpm
  • SpO₂ 95%
  • PI remains 20
  • Drinks 100 ml of water
  • Still asymptomatic
• At 6:00 AM:
  • Wakes up with big discomfort, close to pain
  • HR 50 bpm
  • SpO₂ 97%
  • PI 5
  • Urinates only 50 ml (normally 150 ml at that time)
• After going to the swimming pool and swimming 30 minutes:
  • No pain or discomfort
  • Excellent exercise tolerance

The combination of very low heart rate (27 bpm), very high PI (20), and markedly reduced nocturnal urine output is the central physiologic triad.

2. How to interpret the perfusion index (PI) here

The perfusion index is an indirect measure of peripheral blood flow at the sensor site (usually the finger). A PI of 4–5 is modest. A PI of 20 is very high, meaning that:

• There is marked peripheral vasodilation.
• The vessels in the finger are very open, allowing a large pulsatile signal.

This may occur as a compensatory response when the body senses a reduction in central cardiac output: to preserve perfusion to vital organs and maintain blood pressure, the autonomic nervous system can shift vascular tone.

3. What likely happened during deep sleep

Putting all pieces together, the most coherent explanation is:

1. Deep sleep and high vagal tone
   During deep sleep, especially in the early part of the night, vagal (parasympathetic) tone increases significantly. This tends to:
   • Slow the sinus node.
   • Worsen AV conduction in susceptible hearts.
2. Pacemaker non-capture or severe bradycardia despite pacing
   You mentioned in other contexts that the patient has a high percentage of ventricular pacing (around 95%). A sudden HR of 27 bpm is not compatible with normal functioning of a VR pacemaker programmed, for example, at a lower rate limit of 50–60 bpm.
   
   This strongly suggests that, at least transiently:
   • The device may not have been capturing the ventricle (loss of capture).
   • Or the effective pacing output was insufficient for the momentary threshold.
   • Or there was a posture-related change (e.g. in right lateral position) that temporarily increased capture threshold or changed contact.
   In any of these situations, ventricular depolarization does not follow each pacing pulse, and the intrinsic rhythm falls to a very low rate (e.g. 27 bpm).
3. Drop in cardiac output
   A HR of 27 bpm, especially in a single-chamber ventricular system that depends on pacing, is almost certainly associated with a major fall in cardiac output. This may be partially offset by:
   • Increased stroke volume.
   • Peripheral vasodilation.
   But overall, organ perfusion is likely reduced.
4. Peripheral vasodilation –> PI = 20
   In response to low cardiac output and high vagal tone, the peripheral circulation in the fingers dilates strongly. This gives a perfusion index of 20, which is much higher than the baseline PI of around 4–5 at bedtime.
5. Renal hypoperfusion and very low nocturnal urine output
   The kidneys are very sensitive to changes in effective circulating volume and blood flow.
   • Normally, the patient urinates ~250 ml at the first nocturnal void.
   • This time, only 50 ml: that is marked oliguria for this patient.
   This is perfectly consistent with a period of reduced renal blood flow during the time of low heart rate and low cardiac output.
6. Why no symptoms at 2:30–3:00 AM?
   Despite the bradycardia and low cardiac output, the patient reports no symptoms:
   • No dizziness.
   • No presyncope.
   • No chest pain or dyspnea.
   Possible reasons:
   • Very gradual drop in cardiac output that brain and body partially adapt to.
   • Supine (or lateral) position reduces the gravitational stress on circulation, so the brain still receives enough blood.
   • The patient may have a generally good cardiovascular reserve.
7. What happened between 3:00 and 6:00 AM?
   It is very plausible that:
   • The low heart rate (around 27 bpm) and/or intermittent non-capture persisted for part or most of this period.
   • At some point, the pacemaker resumed reliable capture or the intrinsic rhythm improved, bringing the heart rate back up to around 50 bpm by 6:00 AM.
   During this whole time:
   • The kidneys remained relatively underperfused, explaining continued low urine output at 6:00 AM (50 ml instead of the usual 150 ml).
8. Why the big discomfort in the morning?
   When the patient finally wakes up at 6:00 AM:
   • Heart rate is back to 50 bpm.
   • SpO₂ is 97%.
   • PI is down from 20 to 5.
   Now the body is “re-entering” a more normal hemodynamic state:
   • The kidneys are suddenly receiving improved blood flow after a period of relative hypoperfusion.
   • There may be changes in visceral perfusion, local metabolites, and sympathetic tone.
   The subjective sensation of a “big discomfort, close to pain” can reflect:
   • Visceral discomfort from splanchnic and renal circulation readjusting.
   • Muscle and soft-tissue “washout” of metabolites.
   • Possibly a generalized feeling of malaise after a night of hemodynamic instability.
9. Why does swimming resolve the discomfort?
   During swimming:
   • Cardiac output increases.
   • Peripheral and visceral perfusion improve further.
   • Muscle pump, breathing patterns, and autonomic changes stabilize circulation.
   The fact that the patient can swim 30 minutes without pain or discomfort strongly argues against:
   • Fixed severe coronary ischemia as the main driver.
   • Severe structural pump failure that cannot handle modest exertion.
   Instead, it fits a picture of:
   • Transient nocturnal hemodynamic disturbance (most likely pacing related).

4. The most likely overall explanation

What probably happened during the hours the patient was sleeping?

The most plausible, unified explanation is:

There was a prolonged period during deep sleep in which the Aveir VR LP did not consistently capture the ventricle (nocturnal non-capture), or the heart rate fell to a very low intrinsic rate (around 27 bpm) despite pacing stimuli, likely favored by:

• Very high nocturnal vagal tone.
• Right lateral sleeping position possibly altering the leadless device’s contact or increasing capture threshold.
• A temporary mismatch between programmed pacing output and the momentary capture threshold.

This caused:

• Severely reduced heart rate (27 bpm) → low cardiac output.
• Compensatory peripheral vasodilation → very high perfusion index (PI 20).
• Renal hypoperfusion → markedly reduced nocturnal urine output (50 ml instead of 250 ml and later 50 ml instead of 150 ml).

Once pacing and/or intrinsic rhythm recovered toward morning, circulation improved but left a period of:

• Visceral and systemic “readjustment” → perceived as big discomfort on awakening.
• With increased activity (swimming) and stable pacing, circulation normalized and the discomfort disappeared.

5. Clinical implications and next steps

This scenario is significant and should be discussed with a cardiologist or, ideally, an electrophysiologist experienced with leadless pacemakers. Points to address:

• Device interrogation:
  • Check for episodes of low rate, loss of capture, or high capture thresholds during the night (especially around 2:00–3:00 AM).
  • Review the history of auto-threshold measurements, if available.
• Programming review:
  • Consider increasing the pacing output voltage and safety margin at night.
  • Verify or adjust lower rate limit (e.g. 60 bpm during the night in some patients).
  • Review the auto-capture algorithm and its settings.
• Position testing:
  • In the clinic, check capture threshold in different body positions (supine, left lateral, right lateral) to see whether right-side sleeping significantly worsens capture.
• Laboratory and clinical context:
  • Check electrolytes (especially potassium and magnesium) that influence capture thresholds.
  • Review hydration status, especially fluid intake and diuretics in the evening.
• Home monitoring:
  • Continue pulse-ox and heart rate recordings, especially between 2:00 and 4:00 AM.
  • Temporarily avoid sleeping on the right side, to see whether events improve.

6. Short, direct answer

In summary: During the hours the patient was sleeping, there was most likely a prolonged episode of severe bradycardia due to pacemaker non-capture or inadequate pacing, favored by high nocturnal vagal tone and right lateral position. This led to low cardiac output, marked peripheral vasodilation, and reduced kidney perfusion, explaining the very low heart rate, very high perfusion index, oliguria, and the morning discomfort that resolved once normal circulation was restored with activity.