CHB pacing

I'm just curious.

Currently I have a CHB without a PM.

Without a PM, the AV node is pacing itself at a lower rate, hence the 30-40bpm bradycardia commonly found in CHB people.

My understanding is that a pacer will "follow" the SA node to trigger the AV node, with an appropriate delay .

So when a PM, would the AV node continue its original independent pacing in addition to the one induced by the PM? Does the PM wait for the AV self-pulse to occur and only trigger it when it doesn't?

 

3 Comments

The fastest wins

by AgentX86 - 2020-11-01 10:48:27

In this case the pacemaker would listen to the SI node to fire (if it didn't before some timeout, it would supply the pacing pulse), then wait some time and supply the pacing signal to the ventricles. The AV node won't supply the pacing signal to the ventricles because they got "reset" by the previous heartbeat. The fastest pacer wins and the others are suppressed. The same thing happens in a normal heart.

pacing

by Tracey_E - 2020-11-01 11:22:29

The pacer always allows the ventricles a chance to beat on their own before kicking in with a paced beat. Most of us pace every beat. The random beats don't happen on their own, hey are too far apart and the pacer almost always beats it. 

Some muddled thinking here

by crustyg - 2020-11-03 07:00:16

Hi Koala:

You have CCHB, so your SA-node should be fine.  Therefore, even with a dual-chamber PM, your PM won't be pacing your RA - your SA-node will.  The PM's atrial lead will detect the electrical impulse from your normal SA node and then transfer that to your ventricle(s) so bypassing the AV-node block.  Your SA-node should respond normally to activity, excitement/fear, relaxation and sleep, and your PM wil faithfully 'copy' the SA-node activation to your ventricles.  In almost all cases, your SA-node will produce an activation before any other source of electrical activity (usually the AV-node *below* the level of the block - the little clump of cells that have kept you alive so far).  The same nerves that make your heart thump in a scary film make your SA-node beat faster and your AV-node more likely to pass a much faster stream of impulses as your body is readied for fight-or-flight.

HTH.

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