Rate Response

I need the help of all the techies out there to help me understand what I just did.

Last Friday my EP turned off the Rate Response (acclerometer) in m St. Jude Dual Chamber device. Since its implantation, I have never felt whole or even close -- labored breathing, tiredness etc. Almost immediately, I felt better, and I'm into my 5th day. 

Even though I didn't have the condition for which a rate response was needed, the EP said turning it off would not improve my condition. But it did. Amazingly! Now I wonder if the sudden and strange appearance of VTs over the past six weeks (after 15 months of feeling terrible) were the result of the RR being on when it should have been off. I've read about RR sensitivities being the culprit in pacemaker mediated tachycardias (PMT).

Since I didn't have the  "rate imcompenence" for which the rate response was made, how would it create PMT in me? I understand the direction and evolution of the native cardiac electrical current. I get the concept of unwanted retrograde currents created by a PM. But I cant understand how RR could possibly create PMT. But it can, according to what I have read. 


1 Comments

Here goes

by crustyg - 2019-12-13 12:08:46

I don't think RR necessarily *causes* PMT, but I can see how it can *enable* it.

If you are set for DDDx, then your box is watching for activation pulses in atrium and ventricle - the idea being that your SA node is still working and providing the variable HR that you need - slow for rest, increased for activity.

Whether you are set for DDD or DDDR, if you have retrograde AV conduction (i.e. V=>A conduction), your device can detect inappropriate atrial activations which it faithfully replicates down to your ventricle - and then sense the same activation some time later back up in the atrium and trigger another ventricular contraction - and so go faster and faster.  With RR enabled, your PM's rate control software is able to increase paced rate quite quickly.

Documentation that I have access to acknowledges that this can happen regardless of whether RR is enabled (pax, MrTech), *BUT* I can see how it might take off much more quickly if you have RR enabled.  So disabling RR might have the effect of abolishing the PMT problem in some patients.  I don't think it's correct to say that retrograde conduction is caused by the PM, but the PM's sensing of the retrograde-derived impulse when it arrives in the atrium and then acting on it is the problem.  Without a PM sensing this activation, nothing would happen.

Really glad that you're feeling better, and it's good that your EP tried the change.

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