Atrial Lead Amplitude

Battery life predictions

by crustyg - 2024-04-26 12:18:06

Fundamentally, a battery is a device to hold/store electrical charge.  Exactly how much is shown by the Ampere-Hour statement (or mAh) of capacity.

Each time the battery is used, some charge is removed and as that charge tends towards zero we say that the battery is depleted/empty/discharged.

Each activation that your device delivers pushes a tiny amount of charge into the heart muscle => activation.  But it's the charge delivered which is the main controller of battery life.  Charge delivered per activation is actually the product of pulse-width multiplied by current delivered during that time (where current, I, is given by V/R by Ohm's law).  Unless someone has gone gently mad, the reason why your pacing output voltage has gone up is because the resistance (R) has gone up too (as a marker of the lead-to-heart muscle connection becoming more fibrous) (yes, alright, I know it's actually impedance and not resistance, but for simplification let's keep all of this as DC and not AC).  So if lead-to-heart resistance has gone up sharply, then a higher voltage is required to push the desired current in (for the pulse-width that's been set).

So it's not correct (probably) to say 'doubled pacing output voltage => halved device battery life', but it *is* fair to say that it will have some detrimental effect on device longevity.

I think you're correct, that you're probably facing a lead removal sooner rather than later.

Hope that helps.

I would have a meaningful conversation with your EP

by Gemita - 2024-04-26 12:29:11

Hello Dave, Clearly with a new battery, your lead voltage can be increased to meet your needs for a little while longer.  I am not sure how high they can comfortably go before you would start noticing adverse symptoms.  What I would say is that as long as you are feeling comfortable and not experiencing any symptoms with what is likely a failing lead, you and your team have time to decide what needs to be done.  

In your shoes I would want to have a meaningful discussion with your EP about your next steps, whether you can afford to wait and see what happens or whether this is an early warning sign of a rapidly developing lead failure?  They will no doubt fully test your atrial lead.  You could also ask the EP whether this problem could be corrected by settings adjustments for a few years, or whether anything else could be done to fix the problem like opening the pocket if say it is a connection problem to the new device?? 

I am so sorry you are back in this position.  I wonder if there is going to be a silver lining to all of this?

Thanks!

by Good Dog - 2024-04-26 13:45:02

Genita & crustyg,

Thanks so much for your input! It is helpful and greatly appreciated. I never like negative surprises, but at least I received this one early-on with time to plan. Just when I was feeling good about getting my shiny new PM. The great unknown is; how soon will I be facing extraction. I don't want any more suprises, so I will work with my EP to try to develop a plan with regard to a threshold to trigger further action. Thanks for the suggestions! Gemita; I hope you are correct about the "silver lining".

Sincerely,

Dave

Ck with your doc

by Lavender - 2024-04-26 14:48:34

Dave,

Your clinic is tops. For your own peace of mind, I would call for more feedback. I have to think though...no one was alarmed enough to discuss this and sent you on your way. I'm kind of in a similar predicament with increased voltage. I was told this is what I need at this point, it's commonly done, and nothing else needs to be done right now. 
 

My policy is "don't worry in advance".  Easier said than done. However most of what we worry about never happens.  What does happen usually hits us totally without warning hence we don't even know what to worry about. 🙃

On other note, my son had his Achilles Tendon repaired this week. It will be a long recovery but I was delighted that his surgeon came from Cleveland Clinic! He is the Director of the Division of Foot and Ankle Surgery for our local hospital now. He came from the Cleveland Clinic Foundation where he served as Director of the Center of Foot and Ankle Surgery. I thought of you when I learned that😉

You are sooo right

by Good Dog - 2024-04-26 15:49:27

Lavender,

You are correct about worry! I do tend to worry about everything, but as you say; most of the stuff that I worry about never happens! Drat.......I usually end-up kicking myself in the end. I do try to work on that, but as you said; easier said than done! I just discovered this issue this morning after looking at my report in MyChart. I was wondering why nobody discussed it with me, but then they just did the interrogation yesterday. I am going to message my Doc over the weekend and will hope to hear back from him sometime next week.

Glad to hear your son is on the mend. Not sure where you are, but how cool is it that his Doc is from the Clinic. Seems like a lot of Docs work there and then move-on. I had a couple Cardiologists in the past at different hospital systems that had also trained at the Clinic. That is pretty common around here, because the Clinic is local. Anyway.....

Thanks!

Sincerely,

Dave

I don't want you to worry only to think a little more!

by Gemita - 2024-04-26 15:53:47

Dave, I hope all that calcium they found in your pocket hasn’t accumulated again on the old atrial lead where it connects to the new device?  I know your surgeons cleaned it out before implanting the new device but I suppose you could ask about this?

In addition to finding out the state of your atrial lead, if you do find yourself heading for new leads or a complete CRT system in the near future, take a look at the following link.  Wouldn’t it be helpful if we could predict who would go on to experience left ventricular dysfunction from RV pacing and who would not and if our doctors could more reliably assess the best lead position for each one of us at the time of implant?  

The link discusses a method known as Ultra-High-Frequency (UHF) ECG, which can visualise the sequence of ventricular activation and identify patients with dyssynchronous ventricular depolarisation during pacing and helps predict patients at risk of decreased left ventricular ejection fraction due to pacing.  This information can assist the electrophysiologist in selecting a pacing location that avoids dyssynchronous ventricular activation.  

I wonder if UHF-ECG is routinely used for all new implant surgeries today or only used for CRT/physiologic conduction system pacing patients who are already showing signs of developing Pacing induced Cardiomyopathy?  Anyway, might be worth a glance - see the Abstract, Conclusion and Clinical Perspective box at end of link for a nice summary if you are short of time!

https://www.aerjournal.com/articles/ventricular-dyssynchrony-and-pacing-induced-cardiomyopathy-patients-pacemakers-utility

I'd Want It Sorted!

by Penguin - 2024-04-26 16:00:21

Dave, 

Lavender’s post is calming and she may well be talking absolute sense. I’m in no position to judge or tell.  I'm less calm and would want the worry removed if I was in your shoes. 

I remember your post about calcification in your pocket. Not sure if this means that there is similar build up around the electrodes (?) 

Atrial lead amplitude and battery drain

by AgentX86 - 2024-04-26 16:33:09

I wouldn't freak out about this.  It's the roller-coaster you're going to ride, no matter how bumpy it is from here to there.  As long as it doesn't run off the rails suddenly, you'll be fine.

To the technical glop. You say that your pacing voltage suddenly went up.  I assume, from this, that your pacemaker as the auto capture threshold feature turned on.  If not, someone turn it up. Why?

If you want to know the effect on the battery, change in battery power consumed, is the pacing voltage squared divided by the lead impedance[*]. If the lead impedance didn't change, you're using four times the battery as you were before. OK, you can look up the lead impedance in your last few reports.  BTW, the "lead impedance" includes the path through the heart, so either could change the impedance.

Why did it go up?  If the lead is damaged, and increases two-fold, to get the same current to the heart to trigger it, requires twice the voltage. Using the above relationship, the current didn't change, so the impedance must have doubled.  Crank the handle on the equation, and the battery drain is 2x, not 4x. Better but, no, not great. The energy delivered to the heart isn't the only drain on the battery.  The processor and all that stuff is burning the same power, no matter how much is being delivered to the heart.  This isn't a trivial component of the power, so the numbers aren't nearly as bad as the above would suggest.

Again, you can look up the numbers and see what's going on.  If the lead impedance didn't change, I'd want to know why the voltage increased so much.  Is the heart less sensitive to being paced (capture threshold increased?). Of did someone make a mistake?

Just after implant, the battery life projections are pretty bad.  They're bad until it gets very close to EOL/RRT. A change from nine years to seven may not be indicative of anything.

[*] Crusty, "Resistance" is a better term, in this case. The AC effects are so close to zero that they don't matter.  AC effects don't affect power, anyway.  "Impedance" sounds so much more intelligent than "resistance", but that's what it's listed under in the reports, so I use it.

Gemita & Penguin

by Good Dog - 2024-04-26 16:50:13

Penguin - Both you and Gemita made an excellent point relative to the calcium. It is one that never occurred to me. That is one of the reasons why I did not jump and immediately send a message to my Doc. I really wanted to think this through and put together a thorough as well as provocative list of questions in the hope of eliciting an enlightening response. So the questions that you offered are very helpful. I plan to use them. I do want to get to the bottom of this, because as you said; I want the worry removed, at least as much as possible. Thanks so much! 

I think that the point Lavender made was to do both; Contact the Doc with questions, but don't worry needlessly. So I do appreciate and can use all of the input.

btw: I am grateful for the fact that I do have a strong escape rhythm. That helps to remove some of the worry!

Gemita-  I have not yet had an opportunity to view that link, but will do so this evening and get back to you with my thoughts. It sounds really interesting. Thanks so much!

Sincerely,

Dave

Agentx86

by Good Dog - 2024-04-26 16:56:39

Nobody made any changes. I apparently do have the auto capture threshold feature turned on. So yes, the amplitude change was automatic. I did not download my interrogation report, so I need to go back and check the lead impedance. Too busy at the moment, but will do that asap.

The info you provided was helpful.....I think?

SEE POST BELOW THIS ONE

Thanks!

Dave

My atrial lead impedance

by Good Dog - 2024-04-26 17:15:05

The impedance measurements are not making a lot of sense and/or may not be indicative of a lead problem? Thing is; I am not sure what they should be and I have no point of reference beyond my own readings. So not sure? Nevertheless, the voltage increased on the lead from 2.5V to 5 V. So the question remains: why?

My atrial lead impedance (resistance)

04/14/2021 (old generator) - 554 ohms

11/10/2022 (old generator) - 572 ohms

02/14/2024 - (old generator) - 651 ohms

03/19/2024 (one week after implant of new generator) - 554 ohms

04/24/2024 - SUDDEN AMPLITUDE INCREASE FROM 2.5V TO 5.0V

04/24/2024 (yesterday) - 602 ohms

Why?

by AgentX86 - 2024-04-26 21:11:36

The only think I can think of is that your capture threshold increased by that much.  It might have been an error.  Either way, I think it's worth a call to your device tech, anyway.  Perhaps he can test the capture threshold manually and reset it, then see if it goes back to 5V with the automatic test.

Amplitude

by piglet22 - 2024-04-27 07:41:55

I would echo some of the comments.

What is important is the average drain on the battery (cell).

The processor (generator/microcontroller) will have periods of relatively low activity when energy usage is minimised and others, like pulse generation or when communicating, energy usage is higher.

I don't know enough about what the heart needs to function, be it voltage driven or current driven.

Clearly from Ohms law, if the resistance rises, say in the leads, then more voltage is needed to maintain the same current.

Of course it will affect the battery lifetime, but it might only be a small part of the overall picture.

I work a lot with batteries and one charactaristic is that if a battery is subjected to a short high load, it can take a little while to recover, maybe only minutes, but measuring the voltage immediately afterwards will give a different result to say 30 minutes later.

One thing you can be sure of is that the manufacturers will go to extraordinary lengths to maximise the efficient use of battery power to the extent of sleeping the device for even milliseconds.

On the scale of things, 600 Ohms is relatively low. It has to be low to allow enough current to flow. High reistance is measured in Megohms and only microamps would flow.

Resistance can be difficult to measure even with specialised equipment. Without knowing the measurement error, I wouldn't read too much into small changes. 600, 590, 610 all possible without anything actually changing.

Bear in mind, any digital device like the PM will measure values in steps. It's not like an old analogue voltmeter with an almost infinitely small resolution.

It's asking quite a lot of our devices to deliver lab grade measurents.

Check New Post Titled: Atrial Lead Impedance Update

by Good Dog - 2024-04-27 08:07:29

Check New Post Titled: Atrial Impedance Update