Pacemaker Entering Safe Mode Settings

I had a St Jude dual chamber rate responsive pacemaker placed in 2007, and the doctor said that I had 8-10 months left on the battery the last time I had an interrogation. Less than a month later I started having strange cardiac symptoms so I went to the ER and when they interrogated the pacemaker they discovered it had gone into safe mode, and had automatically changed the settings to preserve energy. The pacer worked correctly after they removed it from safe mode and corrected the settings. Is this a normal occurrence, especially the inaccuracy of battery life? I know that since I am 100 percent paced they said they can only guestimate the actual time of battery death, however have a general idea within 6 months of knowing when the battery needs a change. Unfortunately I just recovered from open heart surgery because the pacemaker lead became infected and had to be replaced before battery replacement surgery was performed. Now I have a Medtronic pacemaker and am wondering if it will also go into safe mode to preserve energy, or be inaccurate with remaining battery life. Has this happened to anyone before? I know I have many years before low battery life will be a concern, but I want to keep it in the back of my mind if I have to be mindful of this in the future. Thanks so much!

4 Comments

tactheemt

by zawodniak2 - 2015-07-02 10:07:21

My Medtronic rate responsive PM went into "end of life or safe mode" or preservation mode after 7 1/2 years at which time my heart rate was pulsed at a constant 65 bpm.regardless of my activity level (at rest or moderate activity). After about one week I could really feel my body wearing down and experienced major fatigue even when walking around the Walmart. After getting the PM replaced, it was like turning a dimmer switch back up and I felt normal immediately. My battery life went from 19 to 4 to 2 months in the last 6 months before replacement. So it appears that the battery life estimate becomes less accurate towards the end. When the interrogation showed 4 months, they scheduled me in for replacement and the Medtronic technician said they (guarantee??) 3 months of PM function once it goes into "End of Life"
Rodger

Thanks

by tactheemt - 2015-07-03 05:07:01

Thanks Rodger! Your info was helpful! :) Thank Donr! Your very descriptive info about batteries broadened the perspective of a pacer battery and it's life. To answer your questions they changed the settings because the rate response feature was suspended and I would become extremely fatigued with exercise. It never went into safe mode again because as I mentioned due to endocarditis, I had to have open heart surgery to remove the infected leads a week later, I actually never went home from the ER\hospital where they changed the settings, which the EP had instructed them to do, and the change in settings brought relief from exercise fatigue. They had said weeks before I had 8-10 months of battery life left and scheduled a follow up appointment for a year later, so I anticipated they expected it to go into safe mode before then which was fine. I expected anything as they always preached, we can only predict battery life. Now I've learned to be more aware in the future. I have ten to fifteen years on my new device now so no worries, I was just wondering how it worked, and why safe mode changes important settings to preserve energy life. The heart infection had nothing to do with it entering safe mode, or the change in settings. It was just by chance it happened together. Im just glad it's all over. Thanks again!

Let's talk batteries.

by donr - 2015-07-03 11:07:01

The battery is the weak link in the PM generator, while the leads are the weak link in the overall system.

Go to this link for a good history of WHY we have the current battery - the Lithium - Iodide Battery, also called the Li-ion battery.

http://heartdisease.about.com/od/pacemakersdefibrillators/f/My-Battery-Is-Low-So-Why-Does-My-Whole-Pacemaker-Need-To-Be-Replaced.htm

It is essentially the same battery found in modern hand tools, like drills, saws, sanders, etc.

One reason the author does not give for not having an infinite life battery is that the technology of the PM is evolving rapidly & if you had an infinite life battery you would be stuck w/ an obsolete PM device after a few yrs. As inconvenient as it seems to have to go through a battery change every few yrs, it turns out to be a decent compromise when it comes to up-grading capability of the computer chip in your chest. Let's have a show of hands on this - how many of you would like to have a PM w/ 1990's technology in it? Hmmm, just as I suspected, not very many.

But, back to the battery we now have. There are several very big advantages to the Li-ion battery - one is that its voltage remains stable & constant for most of its life useful span. For those of you who have Li-ion powered hand drills, this is manifested by the way that device works fine for a long time, then just very suddenly it croaks & stops turning.

That same thing happens in your PM. The battery works fine for a long time & suddenly just rolls over onto its little back, legs crossed over its chest & little x's where its eyes were.

Now the battery is not perfect in this way. There are ways to test it to detect very small voltage drops & current drops & they are used to predict how much life is left in your battery. They are not perfect, however. Go back to your battery powered electric drill - most of them today have an indicator system telling you the life left in the battery. That system uses LED lights of some sort. My Bosch drills have three small LED's. 3 lit means full power left; 1 lit means it is about to croak. Then it suddenly just stops - dead.

The time to stopping dead on my drill depends on a lot of things - what am I drilling into, how fast am I drilling,what is the temperature of the battery, a whole bunch of factors.

Ditto for your PM battery & its life predictor. When the battery is brand new, it is trying to predict something years into the future w/ zero idea what may happen several yrs ahead. Contrary to the last comment, i foundt hat my Medtronic predictor became more accurate as time passed & we approached the EOL point. Why? Because it knew more precisely what was being demanded of it from usage & it had a better idea how my battery was losing capability to operate the PM's digital computer. Now the predictor algorithm NEVER predicted remaining life in hours or days. It was always months and a RANGE of months. At least till the end, when it just gave a prediction of so many months w/o a range. it just does not have the capability to define it more closely - yet. So how close did my predictor work? Missed the EOL coming by three days. It predicted essentially a Tues. The device entered EOL on the previous Sat.

Considering all the variables that the predictor algorithm has to deal with, it really does a pretty good job predicting the future.

You said that after predicting 8-10 months it switched into Safe Mode after less than a month. followed by the ER "Correcting" the settings. WHY did they CORRECT the settings? What was different about them? How long before it went into safe Mode again after the setting change? Further, they said they can only "Guesstimate" to within 6 months when you are 100% paced. Sounds to me like they made that 6 months. with a range of 8-10 months & switching to Safe Mode about a month later, they were well within 6 months of the middle of the range they gave.

Personally, as an engineer, I would think that w/a KNOWN power drain rate (100% paced full time) you could more accurately predict the demise of the battery. Especially after having many years data on how that particular battery was functioning.

NO matter what, you may trust me on this much: If the designer of the algorithm that predicts life remaining in a battery 5,6,or more years into the future could do any better at it, he/she would not be designing algorithms. The would be making their fortune predicting the stock market & making their fortune that way.

Donr



I owe you an apology for...

by donr - 2015-07-04 08:07:14

...mis-reading your first post. Talk about dumb mistakes - I read 8-10 months as 6-8 for some cockamamie reason & came up w/ 7 months as the mid point when I said that 6 months was pretty close to 7! Must be the new glasses that were cut from the bottoms of old Coke bottles.

One of the reasons they stop everything but default steady pacing at a fixed rate at the EOL point is so they can control the energy use rate & have a more predictable life span for the battery.

When my PM went into EOL at 1222 on Sat, I suddenly felt like something I stepped on in the back yard after the dogs had been out. I felt that way till Mon at about 1600 when it struck me what had happened & I had Dear Wife check my pulse & it was 66 BPM. Close enough to 65, Medtronic's default HR. Called my Cardio's office & was told to get there as soon a possible. They checked my PM & sure enough it went into EOL at 1222 on Sat - explaining why I suddenly felt so bad at that time.

By 1730, Mon, I had a scheduled PM change for Thurs.

When I went to the hosp for the procedure, they asked me to WALK to the OR, then climb up on the table. Rodger mentioned fatigue after going into EOL. I had all I could do to get on the table w/ the help of a stool to step up on.

Post op, I just didn't wake up, so they stuck me in a room. Woke up about 2200. Blink!!! there I was wide awake & the first words I uttered were "I'm hungry!"

You know you're wired when...

You fondly named your implanted buddy.

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