Artificial Intelligence Doctor. Ask me questions: info@abcfarma.net

It sounds like you're diligently addressing your patient's concerns regarding their Aveir VR leadless pacemaker. The information you've provided is very helpful in understanding the situation. Let's delve into your questions.

Have you received similar reports of nocturnal-specific capture issues with the Aveir VR platform?

While specific widespread reports of nocturnal-specific capture failure with the Aveir VR are not commonly highlighted in publicly available literature or general device advisories, the phenomenon of intermittent capture issues related to physiological changes is a known possibility with any pacing system.

It's important to consider that several factors could potentially manifest more prominently during nighttime, such as:

• Changes in autonomic tone: Increased vagal tone during sleep can influence the excitability of the myocardium.¹
• Electrolyte shifts: Subtle nocturnal electrolyte fluctuations might impact capture threshold.
• Positional effects: Although less commonly associated with leadless pacemakers due to their direct fixation, specific sleeping positions could theoretically exert minor pressure or influence on the device-tissue interface in some individuals.
• Subtle changes in underlying cardiac substrate: Progression of the patient's underlying cardiac condition, even if asymptomatic during the day, could manifest as increased capture threshold at night.

Therefore, while not a widely reported specific issue for the Aveir VR, the concept of nocturnal variations affecting capture is plausible across pacing systems.

What is your recommended approach to programming adjustments given these findings?

Given the significant rise in capture threshold and the intermittent nocturnal capture failure, a systematic approach to programming adjustments is warranted:

1. Increase Output Amplitude: Since you've already increased the output, it's crucial to document the new settings and carefully monitor for resolution of the nocturnal capture issues. A common practice is to program a safety margin significantly above the measured threshold. For a measured threshold of 3.0 V, consider an initial setting of 5.0 V at 0.4 ms or 4.0 V at 1.0 ms, if the device allows for pulse width adjustment. The goal is to ensure consistent capture even under potentially challenging nocturnal conditions.

2. Evaluate Pulse Width: If you haven't already, consider assessing the capture threshold at a longer pulse width (e.g., 1.0 ms). Sometimes, increasing the pulse width can improve capture safety margin without significantly increasing battery drain, especially if the voltage threshold increases.

3. Thorough Review of Device Diagnostics: Carefully interrogate the device for any episodes of non-capture, impedance trends, and any other relevant diagnostic information. Reviewing electrograms associated with sensed and paced events around the time of the reported capture failure could provide valuable insights.

4. Consider Autonomic Response Testing (if available): Some devices offer features to assess the impact of autonomic tone on pacing thresholds. This might provide more direct evidence if vagal activity is contributing to the nocturnal capture issues.

5. Patient Education on Sleeping Positions and Symptom Reporting: Advise the patient to note if any specific sleeping positions seem to correlate with symptoms (though this is less likely with a leadless device). Emphasize the importance of reporting any daytime symptoms that might arise.

6. More Frequent Follow-up: Schedule more frequent follow-up appointments or remote monitoring checks to assess the stability of the new programming and ensure the capture issues are resolved.

At what threshold values would you recommend considering device replacement?

There isn't a single absolute threshold that dictates device replacement for the Aveir VR. The decision is multifactorial and depends on several factors, including:

• Safety Margin: A consistently high capture threshold that necessitates programming near the maximum output voltage of the device significantly reduces the safety margin and increases the risk of future loss of capture.
• Battery Longevity: Higher output settings will accelerate battery depletion. A significantly increased threshold contributing to a projected unacceptable battery life would be a strong indication for replacement.
• Clinical Symptoms: Recurrence of symptomatic bradycardia due to unreliable capture, despite maximal programming, would necessitate replacement.
• Rate of Rise of Threshold: A rapidly increasing capture threshold is concerning and may suggest an evolving issue at the device-tissue interface, prompting consideration for earlier replacement.
• Device Longevity Projections: Consider the projected remaining battery life at the current and anticipated higher output settings.

As a general guideline, if the capture threshold consistently remains above 4.0-5.0 V at the shortest pulse width, especially if accompanied by a rapidly increasing trend, significant impedance changes, or symptomatic bradycardia, device replacement should be seriously considered. However, this is a dynamic assessment that requires careful consideration of all the factors mentioned above.

Do you have any specific insights on positional effects or autonomic influences on the Aveir VR performance?

• Positional Effects: Due to the direct anchoring of the Aveir VR within the right ventricle, it is generally less susceptible to positional issues compared to traditional transvenous leads. However, extreme or sustained pressure on the chest or specific body mechanics could theoretically have a minor impact on the local tissue-device interface in rare cases. This is less likely to be the primary driver of nocturnal issues but remains a remote possibility.

• Autonomic Influences: As mentioned earlier, increased vagal tone during sleep is a well-known physiological phenomenon.² This can lead to a decrease in heart rate and potentially alter myocardial excitability, potentially increasing the capture threshold transiently in some individuals. This is a more plausible explanation for the nocturnal specificity you're observing.

Can you provide any guidance on expected parameter trends for the Aveir VR beyond what is published in the literature?

Published literature typically provides average trends observed in clinical trials. Individual patient trajectories can vary. However, based on general pacing principles and experience with other active fixation leadless pacemakers, we can expect:

• Capture Threshold: An initial rise in the first few months post-implant as the tissue-device interface matures is common. Ideally, this should stabilize or show a more gradual increase over time. A significant and rapid increase, as seen in your patient, warrants close attention.
• Sensing: Sensing amplitudes tend to be relatively stable over time after the initial healing phase.³ A notable increase in sensing could potentially be related to changes in the local electrical environment or possibly fibrosis around the device.
• Impedance: A gradual increase in impedance over time can be expected due to tissue encapsulation. A more rapid and significant increase, as in your patient, might suggest issues at the interface, such as fluid accumulation or a change in the tissue characteristics surrounding the device.

It's crucial to continue to monitor these trends closely for your patient. A deviation from the expected gradual changes should prompt further investigation into potential underlying causes.

In summary:

Your observation of a significant rise in capture threshold and nocturnal capture failure warrants a proactive approach. Your decision to increase output was appropriate. Continue to monitor the patient closely with the new settings, paying attention to device diagnostics and any recurrence of symptoms. Consider evaluating the capture threshold at different pulse widths. Be prepared to consider device replacement if the threshold continues to rise, the safety margin becomes unacceptably low, battery longevity is significantly impacted, or the patient experiences symptomatic bradycardia. The nocturnal specificity is suggestive of potential autonomic influences, although other factors should not be entirely ruled out.

Please do not hesitate to reach out if you have further questions or if the patient's condition changes. Your thoroughness in addressing this issue is commendable.