What HR does a stethoscope pick up?

My son is 17 months old and has had a Medtronic EnPulse dual chamber, rate responsive pacer his whole life due to complete congenital heart block. So while the atrial part of his heart works pretty well, the ventrical part does not ... because the atrial cannot communicate at all with the ventrical. His ventrical rate (which the doctors refer to as his underlying heart rate) is average 43 bpm. So when his pacemaker is working well, his natural atrial rate might be 150 and his natural ventrical rate 43. The pacemaker takes the 150 rate and tells the ventrical to match it. When I was pregnant, they could never get an accurate heartrate without doing a manual count on an ultrasound because the doppler detectors used in pregnancy would pick up the atrial rate at 150 but not the ventrical rate at 50 -- or both and not function correctly. Currently, my son has a fractured atrial lead .... so his ventrical lead is set to motion and he is operating at average, 80-90 bpm. Okay .... so the question ...

Recently we went to the pediatrician because my son had a cough. The pediatrician listened to him with a stethoscope and said he was getting the heartrate at about 50 bpm. I did a carelink phone check that night and everything is working fine. SO - when the doctor listens with a stethoscope, what does s/he hear??? The unpaced atrial rate (and unmatched to the ventircal), the paced ventrical rate, or something else the pacemaker is doing???

Thanks in advance - this really puzzles me! :)

Sterling

10 Comments

Good Question

by clichtenberg - 2007-12-29 08:12:22

You are more versed in all of this than I am. My son is almost 16 mo with a pacemaker.

I've been told that my son's setting is VVI 90. So the lowest bpm would be 90 bmp.

Does that help?

Cindy

I think you are right

by slarnerd - 2007-12-30 01:12:53

I think you are right - that the HR detected would be what the pacer is doing and if it isn't, it is the underlying rhythm. I will have to ask the EP when we go back.

My daughter has 2nd degree block too but it is Mobitz I which is less serious - I assume your son has 2:1 block or Mobitz II. In any case, from what I have read, a pacemaker is indicated and is a good, safe measure. I am so sorry that after going through OHS your son also developed rhythm problems and needed a pacemaker. You have obviously been through a lot with him and I hope everything is good and healthy going forward.

We do a monthly phone check and we just upgraded to Carelink which is more sophisticated since we are also monitoring the broken lead. We go to see the EP every 6 months too. Maybe because my son has complete block and is 100% dependent? I don't really know but you are right, everyone's experience is different.

If you like, you could join our yahoo group for parents with kids with heartblock/pacers.
http://health.groups.yahoo.com/group/heartblockkids/
There are a lot of informed moms there.

Sterling

Thanks!

by slarnerd - 2007-12-30 08:12:53

Thanks for responding Cindy but I think I made the question seem too complicated. Does your son have CHB too? And with a dual chamber pacer?

I will try to pose the question better ... My son has as many as 3 average heartrates - atrial 150, ventrical 43, and paced 85. If his pacer was working correctly, he'd have just one heartrate (I think) because everything would work together. But with a broken atrial lead, he is only paced in the ventrical. So does that mean he is operating with two heartrates? And if so, which one does the doctor hear with a stethoscope? Or taking his pulse - which might I pick up?

It seems like such a weird question but if the ventrical lead broke - I wonder if taking his pulse or listening with a stethoscope would do any good???

Sterling

I don't know

by clichtenberg - 2007-12-30 12:12:40

I'm sorry, I don't really know. But, I think what ever the stethescope picks up IS the bpm, the heart rate.

My son has 2nd degree heart block. He had OHS and never got his rhythm back after the surgery. For every 2 atrial beats the ventrical only gets one, so his heart rate would be too low, hence the pacemaker. Honestly, my husband understands it better than me. I've asked the EP over and over if my ds could ever get the pacemaker out and she says no. Even if he only needed it 1% of the time, that 1% could hurt him if he didn't have it.

He still sees the EP every 6mo. Until I'd read a few posts on here, I didn't know they did phone in's with babies. I'm really surprised. And from what I've read, no two experiences seem to be the same.

stethoscope sounds

by ElectricFrank - 2007-12-31 01:12:46

The sounds the stethoscope picks up are from the ventricles. They are the larger, more powerful part of the heart and make the most noise. Sometimes with defects, valves etc. can also be heard.
The pacemaker doesn't use those sounds though. With AV block the pacer has an electrode in the atrium that picks up the electrical signal when it contracts. It uses that to time the stimulus to the ventricles via another electrode. If all is working properly the heart sounds and wrist pulse should be at the atrial rate.
I hope this isn't too complicated.

frank

Thank you

by slarnerd - 2007-12-31 04:12:15

Thank you Frank - that is not too complicated at all, you explained it very well and that makes sense. In that case, because my son's atrial lead is fractured, will that HR be different? Thank you again - happy new year!

Sterling

Fractured atrial lead

by ElectricFrank - 2008-01-01 01:01:28

A fractured atrial lead if it has completely failed would keep the pacemaker from synchronizing the ventricles to the atrium. It would need to pace the ventricles at its own rate. In this case I would think the bad lead would need to be replaced as soon as possible as it is necessary to make the heart function normally. You mentioned the carelink showed all was working OK, so how do you know there is a defective atrial lead?
There may be good reason to wait to replace the lead, but you deserve an understandable explanation. Unfortunately, the medical community has a tendency to make decisions based on convenience and profit unless you keep them honest. I have had to hold their feet to the fire on several occasions.
I suggest asking for a copy of the pacemaker interrogation reports. Even if you don't understand all the technical language it tends to keep them honest. Also, there are several of us here that can help you understand the report.

Thank you

by slarnerd - 2008-01-01 02:01:31

We used to do a regular ECG phone check, once a month. In November, we got a call right after the transmission (at 8 pm!) saying that our son's atrial lead was either pulled out or broken. His pacemaker is implanted in his abdomen and the leads are attached to the outside of his heart. They asked us to come in the next morning. He had an echo, xrays, and a pacer check. That confirmed that his atrial lead had fractured on Oct 13 (only days after our last phone check!) and the pacer had shut down to it's base rate of 80 bpm. The xrays showed an apparent complete fracture near to the generator. The EP said that it appears not to have been caused by an injury but due to a kink as the leads uncoiled as my son grew. I am hoping that Medtronic will be able to do a failure analysis on it when it is removed.

Anyway, the EP shut off the atrial lead and reprogrammed the ventrical lead to work on motion. So if he is walking, rolling, tantruming, etc, it will kick his HR up. Still - he used to be set at 80-200 bpm, rate responsive. Now he is averaging 80-90 bpm. The EP said that this is how they used to pace all CCHB kids before the dual chamber, rate responsive pacers came out - and I know of several older kids that are still paced this way.

I have to admit (shamefully) that I have been somewhat blissfully ignorant about how exactly the pacemaker works until recently. All I knew before was that my son nearly died and because of this pacemaker and the great staff at Stanford, he is alive and doing well. But he had so many other little problems (reflux, developmental issues, etc) that I didn't educate myself about the pacer enough. Now, I have read a lot about heart function, different pacer models, lead failure rates, negative effects of long-term pacing, etc. But I am still so overwhelmed by it.

The EP said that we would use Carelink monthly to keep a closer eye on the ventrical lead (which is the one he obviously needs the most). I do get the Carelink reports via email but as you suggest, I understand very little of it. I would love it if someone else would assess the information but it seems to be about 10+ pages and I don't even know what questions to ask! We go in for an echo, etc in Feb - to make sure there are no heart function problems and to possibly schdule surgery. I think you are totally right about the surgery being delayed due to convenience and profit (though I was glad not to need to do it over the holidays - if it wasn't needed) ... the EP said that since he still has 2+ years left on his battery, they want to use as much of that as possible until replacing the lead together with the battery. It isn't so easy to do the surgery and recovery on an 18 month old who isn't able to stay still for even a minute.

I am so sorry that I have rambled on so - I am just so grateful to have a knowledgable, helpful ear!

Happy, healthy New Year!

Sterling

It's the ventricular rate

by slarnerd - 2008-01-06 02:01:04

We went in to the EP to have my son's ventricular base rate turned up from 80 to 110. She said that a stethoscope (and taking his pulse) would get the ventricular rate b/c it is the noisy one. She also said that until a child is about 9-10 years old, they don't see the problems with lack of syncronization between the atrial and ventrical ... this is because before this age, the heartrate is more constant. While a younger child is more active through the day - s/he isn't really getting the heart revved up like an older kid or adult does doing aerobic activity or sports. I have seen this with both my kids on their holters ... their heartrates remain pretty even and while they do get their heartrates up high screaming or playing, it isn't a maintained higher rate. I hope that makes sense ... and that it is true!

Sterling

Followup

by ElectricFrank - 2008-01-16 02:01:52

It sounds like the EP's approach is reasonable. I'm not knowlegeable about the cardiac norms for an 18 month old. It does make sense to hold off on invasive procedures if you can. Hopefully by the time he needs a replacement it can be implanted under his skin like most of us are use to having. I suppose though that it will require surgery to remove the old one.

good luck,
frank

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