Why do we have SA node pacing if the issue is only with heart block?

I hope I can clarify this for you

by crustyg - 2020-11-24 10:33:13

Hi John: If someone with complete heart block has a dual-lead, dual chamber pacemaker, the atrial lead will spend the entire time detecting the natural pace from the SA-node and then, a suitable delay later will fire off a pacing signal to the ventricular lead.  The atrial lead will not be pacing.  Normal SA-node, normal response to fight-or-flight, exercise, sleep etc.  All the PM is doing is collecting the timing information from the natural pacemaker (SA-node) and bypassing the block.

SA-node damage, folk need something to try and emulate the normal variations in HR needed, and then the PM delivers a pacing signal to the RA and the normal conduction pathway transfers the electrical activation down to the ventricles as nature intended.

Between these two extremes are folk with complex issues - perhaps incomplete HB and some SA-node issues, and that's where it becomes tricky.

Make sense?

I see

by quikjraw - 2020-11-24 10:54:19

That does make sense thanks Crustyg

sensing/pacing

by Tracey_E - 2020-11-24 11:01:26

If you look at a pacing report, it will show AS/AP and VS/VP which is atrial/ventricular sensing/pacing. The two numbers will add up to 100%. If pacing is needed it will jump in, the rest of the time it just sits there, keeping an eye on things. Having the second lead doesn't necessarily mean pacing with it, but it's still providing information. 

sensing/pacing

by Gemita - 2020-11-24 12:01:34

Hi Tracey, can I just confirm you are saying that

The values of AS/AP together with 

The values of VS/VP will add up to 100% ??

For example my recent checks showed 98% AP and 7% VP.  I do find my figures puzzling.  Many thanks

John, great question

Sensing and pacing

by Sisterwash65 - 2020-11-24 15:02:10

Youre not the only one who finds her numbers puzzling, Gemita. I was told I have complete heart block, 2nd and 3rd degree and intermittent heart block. At my device check on 10/29 my numbers were 12.3 % VP and AP 18.1%

First device check, 6/30 VP was 93% and AP was 5.9%.When I asked my EP what would cause such a discrepancy he had no idea except that in June my heart was getting used to the PM. He also said these numbers will be changeable.

Another reason this site has been so helpful is issues like this. It sure helps me to know other people have the same questions that I do. What I try to remember is that I feel great ! That’s the bottom line for me. 

Atrial pacing/Ventricular pacing percentages

by Gemita - 2020-11-24 15:22:09

Hello Sisterwash, Tracey_E,

I realise our pacing requirements may change second by second, minute by minute and that pacing percentages will change accordingly.  What puzzles me is that my 98% atrial pacing percentage + 7% ventricular pacing percentage does not add up to 100%.  What am I missing ?  Now if I saw 2% Ventricular pacing (98+2=100) I could understand.

Or should I factor in Atrial/Ventricular sensing percentages as well ?  Maybe I am overtired.  My report only shows AP/VP percentages, not sensing percentages

Atrial Pacing

by bobrichards55 - 2020-11-24 15:29:35

Hi,

I am in  similar situation to you.  I have intermittent third degree block so I have a two lead Medronics pacemaker.  I have no problems with my SA node.   My pacemaker is set to intiate an atrial pulse if my heart rate goes below 60.  I have asked several doctors/nurses why I have any atrial pacing and have always been given sort of vague answers.  It seems that they consider 60 to be a good normal low end pulse and do not want my natural pulse to go below this.  I only atrial pace at about 15% of the time.  I have a sleep mode which allows it to go down to 55 at night.  It might be that with MVP mode they are worried if I miss a ventricular beat or two I could get dizzy so this keeps the pulse up.  This might be the case for you too.

Pacing and sensing

by Sisterwash65 - 2020-11-24 15:32:13

Ok, I see what you mean, Gemita. I thought we were talking about each chamber being 100%. Since there are 2 leads that’s what I thought it was.

Now I’m confused too ! So if I total my 10/27 numbers, it would be 30.4% of the time I’m being paced ? 

Im certainly going to ask about this next chance I get !

Heart Block Diagnoses

by Greenspace - 2020-11-24 15:59:07

Hi all - this may be an unpopular and perhaps unuseful post, but I think the diagnosing aspect of heart block can be very complicated, and our EPs may not really know initially what is needed.  In my very limited experience, I was diagnosed with 2nd-3rd degree block based on maybe 90 seconds on the treadmill during a stress test (couldn't do any more).  Was wisked away via ambulance and received the PM implant the next day.  After a year of continuing SOB symptoms, it was pretty clear that more was needed, which turned out to be atrial pacing in my case.  The PM cliinic tech who did this second stress test repeatedly said that my situation was "special" but my guess from all of the great information-sharing on this site, is that this is actually a very common situation among some of us.  I'm sorry I can't speak to your specific question, but please know that you're not alone in wondering what's going on.

sensing/pacing

by Tracey_E - 2020-11-24 21:27:24

atrial sensing + atrial pacing = 100%

ventricular sensing + ventricular pacing = 100%

both leads are working at the same time, either sensing or pacing.  The report can be broken down into 

AS/VS both leads sensing

AP/VS only atrial pacing

AS/VP only ventricle pacing

AP/VP both pacing

for example mine is usually something like this: AP/VS 0, AS/VP 96, AP/VP 4, AS/VS 0

I pace 100% ventricle, 4% atrial. 

more clear?

Greenspace

by Tracey_E - 2020-11-24 21:31:44

I wouldn't say it's common but it's certainly not unheard of to have both sinus and block issues. If we are in block a lot of the time, we have no idea what the sinus rate is doing because our pulse is coming from the ventricles beating at random, not in sync with the atria. We assume it's ok, and most of the time it is, but sometimes it's not. Once the pacer is working and making sure the ventricles beat when the atria does, sometimes we suddenly find those sneaky sinus issues. This happened with me, hence the 4% atrial pacing mentioned above. 

Thanks Tracey

by Greenspace - 2020-11-24 22:16:53

I appreciate your response, Tracey. Your input on this site helped me formulate what questions to ask the EP and get setting adjustments that work for me. I'm forever grateful to you and all the other folks here.

Tracey_E

by Gemita - 2020-11-25 02:49:53

Tracey, yes a lot clearer!!  Did you get that Sisterwash?  No seriously Tracey I think I am almost there - just had a bit of a brain block over all of this but your explanation really couldn't be clearer and I am very grateful and very sorry if I have confused others as well as myself.   Just wish the reporting format was easier to understand.  It is certainly not written for patients.

Sisterwash I hope Tracey's clear explanation has worked well for you?  If not, we can always continue this analysis privately

Atrial pacing

by quikjraw - 2020-11-25 05:10:40

I get it now too Gemita!

Unless I am given a sound reason I need atrial pacing remaining at a lower limit of 60 I will insist on it being lowered.

Since my pacemaker was fitted I've been waking up at least twice a night.

I am certain that it's because of me not being used to having a sleeping heart rate of 60.

I don not know what my pre pacemaker pre heart block heart rate was but I know that sat down relaxed it was about 55 and has been for years. I have since asked two friends and my wife ( all the same age as me and all very fit) what their sleeping heart rate is and they all sleep at around 50bpm for large portions of the night.

heart rate setting at night

by Gemita - 2020-11-25 05:29:22

John,

Glad I wasn't the only one confused!

A lot of people cannot tolerate a higher heart rate at night, so it seems reasonable to me to ask them to lower it.  If it means getting a better night's sleep then this is what I would do. Heart block can change like all disturbances but I feel a rate of say 50 bpm at night would not cause you to pass out and your pacemaker would kick in anyway to prevent you from falling lower.  I would definitely ask them for example for a lower night rate.  I cannot see a problem with this.

Before my pacemaker, I had daily rates dropping to lower 40s bpm and at night to below 30s bpm and I was really unstable.

Mine is set at 70 bpm night and day which is perfect for me because I find it hard to stay warm (even in summer) with low heart rates.  My problem is low blood pressure which is not supported by my pacemaker but keeping a stronger pulse helps a lot.

You are keeping us busy thinking with all your questions!!  I'm learning a lot too John

Blood pressure

by quikjraw - 2020-11-25 06:57:59

I see so in your situation Gemita the fact you have a lower blood pressure means that combined with a lower heart rate it did cause you problems.

I had many blood pressures taken whilst in hospital but never thought to ask if it was high or low. Silly of me really now I think about it.

night mode

by Tracey_E - 2020-11-25 07:04:13

John, some pacers can be set to have a lower minimum rate at night. Ask if yours is one of them. That said, if your rate was too low for a long time, it can take some time to get used to a normal rate. It took a good 6 months for me to get used to it, what is perfectly normal felt crazy fast to me for a long time. Now it feels normal. 

Ask if you are pacing atrial at night. It's possible that like me, your natural sinus rate is well over 60 so the minimum rate on the pacer doesn't matter. My higher rate was all me. 

Pacing and Sensing

by Sisterwash65 - 2020-11-25 07:13:07

This explanation helps a lot ! Thanks so much all.

Night mode

by quikjraw - 2020-11-25 08:15:26

Yes I will ask that Tracey. I think the datasheet suggested it did 

I really wish I'd bought a heart rate watch ( one that didn't need a band) years ago. I'd know what normal was for me especially at night and might have seen a progression.

I see things a bit clearer now

by Gemita - 2020-11-26 06:35:30

My fog has finally lifted.  Yes, I know, I am very slow.  I thought I would just post my findings John. 

With reference to Tracey_E’s sensing/pacing info numbers, I was focussing on arriving at a 100% pacing figure from both leads and I was failing to factor in the capacity for each lead to pace up to 100% on its own.  Therefore my pacing figures of 98% Atrial Pacing and 7% Ventricle Pacing makes complete sense to me now.  I am clearly atrial paced with very little pacing in my right ventricle which I know is a very good sign indeed.  Recently my total right ventricle pacing has again dropped to nearer 2%, so I am well pleased.

The only aspect of Tracey_E’s sensing/pacing example report figures that still challenges me is why is AP/VS reported as “0” when we know she had 4% Atrial Pacing and why is AS/VS reported as “0” also when I would have assumed some sensing was occurring during the given period?   An explanation of these "negative" figures would be helpful?

Oh the complexities of recording our electrical disturbances and fixing them!

my numbers

by Tracey_E - 2020-11-26 10:26:09

I always pace ventricle, there is never a time when my ventricular lead only senses. 4% of the time both leads pace at the same time, 96% of the time the ventricular lead paces while the atria lead senses. 

Your numbers Tracey

by Gemita - 2020-11-26 10:57:20

Yes I can see now that with your condition those numbers are perfectly normal for you.  I should have realised that.  What a good way to learn and to get us all thinking about our numbers and how they will be so different for each one of us depending on our condition and degree we are affected by our condition.

Thank you Tracey and everyone

Atrial v. Ventrical (SSS vs. HB) & night time pacing

by AgentX86 - 2020-11-26 15:05:26

Think of a pacemaker as two generators, one for the atria and the other for the ventricles.  If the atrial part doesn't sense a pulse within it's set time, it generates a pulse.  This takes care of any sinus node problems. In pacemaker parliance, the first character of the pacing mode is either an 'A' (atrial pacing only), or 'D'' (atrial and ventricular pacing). The second character being sensing, again 'A' or 'D''.

The other half is the ventricular part.  If it doesn't sense a beat in the RV within some set period after it senses or generates the atrial beat, it supplies the impulse to the ventricles.  This replaces the AV node in the case of heart block (either permanent or intermittent).  The pacemaker codes would be 'V' for ventricular pacing only (HB only) or 'D' for both (SSS and/or HB). Likewise the second character would be 'V' or 'D'.  It could also be 'O' if there is no sensing going on - it just paces 100% without looking at what's happening naturally (asynchronous mode).

So 100% atrial means that the SI node is never fast enough, perhasps CI as well as SSS, so the pacemaker supplies all beats.  100% ventricular means that the heart block is total.  There can be any combination from 0% to 100% in either case.  They're independent numbers.

Night time pacing is a great idea if your PM supports it.  You might look up its datasheet on the web to see.  This information should be burried in there somewhere.  Because of PVCs my normal HR is set to 80pm.  I didn't like it, particularly at night, so my pacemaker tech set a night mode to 50bpm.  The only problem is after DST/SDT time changes.  My heart  get off by an hour.  It's a minor prolem because rate response is set quick enough and long enough that it doesn't take long to recover and once it does, I'm alright exercising.

AgentX86

by Gemita - 2020-11-26 17:13:47

Thank you so much for taking the time to explain Atrial v Ventrical (SSS v HB) and how the pacemaker works. I like the idea of the pacemaker being two generators both capable of performimg up to 100% of the time depending on the condition being treated and the degree of need.  My problem was I was trying to see my dual lead pacemaker as one generator and this was distorting my pacing percentages.

I have made a fool of myself in this thread haven't I and exposed myself to admitting how little I know about pacing.  Oh well I will just have to swallow my pride and carry on.  It has been a good lesson AgentX86 but at least I am among friends so I don't feel so bad

Gemita

by AgentX86 - 2020-11-27 00:23:19

We all  make mistakes and have a lot to learn about these aliens.  I'm just a geek at "heart" so try to understand the nuts and bolts (and have a long way to go). You're right much more often than wrong so it's nothing to worry about.   You help a lot of people in more ways than one so keep up the good work.