New study finds heart has a back up SA node

What a discovery

by Gemita - 2021-03-05 05:36:12

https://www.frontiersin.org/articles/10.3389/fphys.2021.592229/full

Thank you John.  That was a gem of a finding!  It led me to the above link for further reading on subsidiary atrial pacemaker (SAP) in goats.  

If the SAP is shown to be capable of kicking in after the SA node fails (say from an ablation for Inappropriate Sinus Tachycardia which we know can be tricky to eliminate) I wonder what the implications are of the SAP kicking in with other SA node conditions requiring treatment with a pacemaker?  It raises many interesting questions which I cannot begin to understand.

Thanks John...very interesting

by IAN MC - 2021-03-05 06:18:55

It all shows that we still have lots to learn about the heart !

Isn't it surprising that electrophysiology cardiac mapping procedures  ( which are routinely done before ablations ) haven't identified the presence of a subsidiary sinus node before now ?

I have always liked goats and will look at them with even greater appreciation in future !

Ian

Do you think they thought is was the AV node?

by quikjraw - 2021-03-05 06:57:07

Hi Therese,

Yes the more I think about it the more it raises questions I cannot answer. Is it possible the SA node and SAP work independently sometimes? Could the SAP kicking in independant of the SA node cause extra beats and tachycardia?

If the SA node is causing problems will that mean the SAP will cause the same problems.

Hi Ian, I am also suprised this has not been noticed before but a study I read the other day reminded me that ECG leads pick up the signals externally so to really know what was going in the heart would you not need leads of the heart itself?

I wonder how this finding explains certain implantable pacemaker issues?

Something of an old goat?

by Selwyn - 2021-03-05 07:08:37

"The team are confident the discoveries are highly relevant to the human heart, as the organ in goats has similar anatomy and physiology, producing a similar heart rate."

Not sure about the 'highly relevant' bit!  If the SAP was available in humans, given all the anatomy and electrical mapping of the human heart, I wonder why this has not been noted. How clinically relevant could this be? They do make the point that this could be a cause for some ablation failures, however, "when the malfunctioning SA node is removed by cardiologists in a procedure known as ablation, the new structure discovered by the team carrying out the research in goats took over as the dominant pacemaker, which also drives electrical activity of the heart."

My point being,  that Billy goats may not be the same as Billy!

Only some additional thoughts John - built on no scientific evidence !

by Gemita - 2021-03-05 07:48:31

Hi John, not sure what you mean by “do you think they thought it was the AV Node”?  

The AV Node is generally easy to ablate (and stays effectively ablated most of the time after a first attempt AV node ablation, although it can rarely fail).  The SA node seems more resistant to being damaged from an ablation procedure for IST for example, when it can be difficult to stop the arrhythmia, although the risk of needing a pacemaker afterwards is always present.  

Could an SA node and SAP work independently sometimes?  Well I suppose so if you mean as in Sick Sinus Syndrome when sometimes the SA node may not function at all and at these times, the subsidiary atrial pacemaker might kick in?

As Ian says, it is surprising that mapping during say complex ablation procedures for difficult arrhythmias, have in the past failed to detect a subsidiary atrial pacemaker signal in humans.  I too find that hard to believe.  Maybe they always detected a signal but called it another arrhythmia, who knows.

Yes if the SA node is causing problems, the backup pacemaker (SAP) being a part of the electrical system of the heart would certainly be capable of producing its own disturbances I would think?  This is why the electrics are so hard to fix John.  There are endless possibilities.  Perhaps now we understand why our doctors may be reluctant to change anything in a hurry and adopt a “wait and see policy”.  I think they have an incredibly difficult job. 

I wonder what the intrinsic SAP heart rate is.  Would it be the same as the SA node rate of 60-100 bpm?  More questions than answers

I checked the date - had April come early?

by crustyg - 2021-03-05 08:02:00

Well apparently it's still March.

This sounds really interesting for goats, but I'm more than a little sceptical about how much of this translates to humans.  We've been using internal electrical mapping technology inside the heart for more than a decade (or two?) so it's a little odd that no-one has noticed this cluster firing off before.  Or perhaps they are so close to the SA-node they are destroyed by the same disease processes that wreck the SA-node to start with.

Maybe if this had been shown in pigs that would be more relevant - we use pig valves for humans as they are so close to our tissue types.

I still think it is a potentially exciting discovery

by Gemita - 2021-03-05 08:37:13

Oh you old cynic crustyg.  Where is your sense of wonder?   I feel quite “excited by this discovery”.  Let us see where this leads us before we draw any conclusions.  It is still very early days

I hope I'm a sceptic...

by crustyg - 2021-03-05 12:18:41

A sceptic is one who is suspicious of the motivations of others so is cautious about believing things without good evidence. I believe reasonable scepticism is healthy.

A cynic is one who doesn't believe in the possibility of altruism, and this is a really nihilistic outlook.  Not healthy at all, IMHO.

And a pedant is one who...

Oh, I see you've stopped reading...

Yes you are a sceptic of course

by Gemita - 2021-03-05 13:19:29

Quite right crustyg and well said.  You are indeed a sceptic and I enjoyed the lesson in grammar - a very important one too

It could be worse Crusty .....

by IAN MC - 2021-03-05 13:52:00

At least you're not a septic !

Interesting

by AgentX86 - 2021-03-05 19:41:13

Interesting but I too would like to see more than a press release.  I'm cynical ;-) about press releases.  I've seen a few too many "nuclear fusion is just around the corner" press releases to know what the game is.

It's been long known that any nervous cell in the heart has the capability of becoming a "pacemaker".  This is why ectopics exist.  Everyone wants to be king.  Some wannabes are slower than others so we get the hierarchy we see in excape rhythms.

This "new" finding is strange in that this "new SI node" hasn't shown up in that heirarchy.  If it is there, how does it get turned on?  As others have questioned, how fast is it?  Does it have chronotropic competence?  I'd think some of these questoins wouldn't be all that hard to find out.

Press release

by quikjraw - 2021-03-06 13:30:32

Sorry I think some of you may have missed Gemita's post.

I posted the press release from one of the university's involved in the study. Gemita posted the actual study which is an extensive report. I suppose my point is that it is not a press release it is a scientific paper.

https://www.frontiersin.org/articles/10.3389/fphys.2021.592229/full