Escape Beats; The Hearts Back Up Pacemakers – Simplified

A Real Human Heart

The Hearts Multiple Pacemakers – Safety in the Workplace

Now if you are unfamiliar with the conduction system then you can read my article on How the Heart Beats and it will bring you up to scratch.
I wanted to do a post on something quite remarkable that the heart does, which should also put the mind at rest a little when discussing conductive tissue disease (disease affecting the hearts natural electrical circuitry).
You see quite brilliantly the heart has a safety net at each stage of the conduction system. If part of the system fails, the next link in the chain takes the reins.
If this safety net wasn’t in place, failure of the hearts natural pacemaker (The S.A. Node) would mean your heart will stop beating…..

Back-Up Natural Pacemakers – How it Works!

Now the S.A. Node is autonomous, this is jargon which basically means it will fire (initiate a heart beat) of its own accord – it naturally paces the heart between 60-100 BPM.
Now most other cells in the heart are heteronomous (pronounced; i-‘m not-Sure), these are cells that won’t contract unless the cell next to them tells them to! 
Now if the S.A. Node was the only structure in the heart that could ‘Start’ a heart beat and it failed – then your heart wouldn’t beat and your long term health prospects have just been greatly affected.
This is where the clever bit comes in, there are groups of cells within the heart that have heteronomous properties (so when the cell next to them activates they follow suit) AND autonomous properties (they will activate off of their own back). 
This means that if everything goes to plan and they receive a signal from the S.A. Node, they will just pass on the signal as planned. However if they fail to receive a signal from the the part of the circuit before them…. they decide to start a heart beat of their own.
To stop the various pacemakers within your heart competing, they each wait longer and longer before they intervene, which presents itself as a slower and slower heart rate.
In the picture below, (that I drew myself!) you can see the structures in the conduction system which have the capability to initiate a heart beat and at what rate they will pace the heart at if they are called into action because of disease to other parts of the conduction system.
The contraction rates of different parts of the cardiac conduction system
Now rhythms that are originating in these different parts of the heart get less and less desirable from a long term health point of view and is often why people require pacemakers. I have never shared this analogy, but in my head I have always likened escape rhythms to people you would want flying your plane! 
Comparing a conduction system cardiac with an Aeroplane
A comparison that only makes sense if you read the article…
Now these people might keep your plane in the air for a bit… but you would probably need more urgent assistance the further down the safety chain you went!
I hope that analogy isn’t too crude but it is how it is! In fact I think this is quite heart warming that there are safety mechanisms in place (I apologise for the terrible pun). 
Time for Football Training
Thanks for Reading
Cardiac Technician
Image courtesy of ddpavumba / FreeDigitalPhotos.net

Comments 4

  1. Great explanation, Cardiac Technician! This sets the stage for why it is crucial for some pacemaker patients, especially those who may have been paced into heart failure due to pacing that has bypassed the conduction system, to pace the red line near the A. V. Node at the His bundle. If you Google PacemakerPatientAdvocacy you will see why.

  2. In the over quoted words of Albert Einstein "If you can't explain it simply, you don't understand it well enough." So, I have every faith you understand it so well you don't need to hide behind jargon 🙂

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