dropped beats

HI. At a recent visit with a new cardiologist they said that the settings on the boston scientific biventricular pacemaker were "too close to the threshold" and that there could have been dropped hearbeats. Has anyone heard of this or experienced this before? They didn't explain very well (a) how that could happen, in terms of the science behind it and (b) how a person would feel if that did happen. Any information would be much appreciated! 


Capture threshold

by AgentX86 - 2022-09-10 17:44:02

Sure, there is a setting called the "pacing capture threshold" (or just "capture threshold"), which is the voltage at where the heart muscle will contract.  If this is set too low, the pacemaker doesn't reliably do its job.  There is also a "capture margin" that is an indication of how much safety margin is programmed into the pacemaker by your EP.

On the other side of the coin, there is also a "capture sense threshold" that is set to differentiate between noise and a valid heartbeat.  This has to be set low enough to reliably sense a natural heartbeat but high enough that the pacemaker doesn't oversense because of noise.  There is also a "sense capture threshold" equivalent to the pacing capture threshold.

Ventricular Capture threshold

by Rch - 2022-09-11 00:04:26

If your pm-tech or the provider didn't get a chest X ray or a surface ECG to check the lead connection or position and you have no symptoms, he's probably not too much concerned about it. The tech may have run a manual ventricular capture test and reprogrammed the device. Also, all modern day pacemakers give a backup jolt if more than 2 loss of captures occur, and retry the capture test. In addition, I know the Boston Scientific pms run automatic capture tests every 21 hrs and plots a graph over time. Mine will kick-in in about 5 minutes for today's test, and I really don't like the feeling!  It feels like a continuous string of ectopic beats for about a minute!

Nonetheless, in your case, I would suggest you arrange for a follow up if you experience any symptoms. 

Automatic capture tests

by AgentX86 - 2022-09-11 00:15:04

The automatic tests are one of the parameters controlled by pacemaker settings.  Many can't deal with the test and it doesn't work well enough for others. I have a Medtronic but their test doesn't work for me and my EP isn't big on it anyway. He'd rather have more control over the capture margin. It's really important that it be done right with plenty of margin for dependent people.

been there done that

by dwelch - 2022-09-20 08:40:31

My first device, over 30 years ago, not as high tech as today.  today much of this is more automatic.  it took a bit that first year to get mine dialed in.  

For each of us, our hearts, our leads, how the leads are secured in the heart muscle, the device, etc.  Too high of a pulse and the pulse can echo around and beat twice.  Too low and the muscle wont fire at all or wont fire every time. 

LIke parking your car against a curb.  not enough gas and the car doesnt move, too much and you jump the curb, there is a window of just right.

if this continues they may want to put a halter on you that you wear for a day or so and then they can look at every beat and see if the device is responding as it should and then make some adjustments as needed.

I now have a biventrical as well and if they bump up the left lead? (the one the side normally not used) then you get what one nurse called belly bumps.  It can be tricky to get that side dialed in, because a little too much juice and not only will your heart muscle fire but your belly muscles will as well.  I have this happen from time to time, I think it is funny, but some folks it is all the time and they cannot sleep cannot function and need it fixed.  For me I have to be standing or sitting just right, happens on deep breaths just before breating in all the way and i get one kick.  If I am tired, etc etc.  so very rare.  if i could do this on demand, it would be a nice party trick.   anyway, for the normal side for a single ventrical lead they have a wider window to hit.  On this other side they cant go over or you will be calling them about it firing off other muscles and it is literally driving you crazy....

You have had the device for a few years based on your profile, so they should be dialed in by now, so maybe it just needs a tiny adjustment, no big deal.  Brand new leads change their resistance over the first so many months as scar tissue forms and they settle in, thus the visit a few months after implant.  but you are not in that situation.

How would it feel?  If it was a single ventrical and say you had complete heart block, and it was for a period of time like seconds or minutes then you would feel like you did before the device or in other words you would feel like you feel when they turn off the device during the interrogation, a bit hollow inside, maybe like someone is sitting on your chest.  but biventrical, are both sides low for a period of time and not firing or is only one side?  I would expect you not to be able to notice.  They probably already do, but if you want to feel it they should be able to disable one lead at a time during the interrogation.  And or if they already do, which I assume, they can tell you what they are doing during the interrogation so you know what each of the effects are.


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