mode switching due to far-field R wave

It's all anatomy

by crustyg - 2021-03-07 13:31:35

Usually, an atrial lead is placed in the Right-atrial appendage.  Nice and easy to find, good stable location, reasonably close to the SA-node so fairly physiological.  Trouble is, it's also quite close to the top of the R-ventricle and apparently it's not uncommon for the RA lead to pick up the electrical signal from the RV-contraction.  But as it's quite some time after an activation of the RV, it can seem to be another atrial activation, which the PM hasn't initiated.  PM fails to detect RV-activation (because there was no real RA-activation), happens again and after a couple of missed RV-activations, PM switches to save-your-life mode (VVI) and only attempts to pace your RV.

The EP-doc/tech has increased the 'ignore time' - PVAB, Post-Ventricular Atrial Blanking - to try and stop this happening, but you can't make this time too long, or the PM will miss a genuine, natural atrial activation and then fail to deliver the matching RV-activation that's important for folk with HB, like you.  The long-term solution might be to remove and replace the RA lead, placing it much higher up in the RA, further away from the RV-outflow tract, although a quick search shows an old paper (2006) evaluating individually tuned PVAB reducing inappropriate mode switching to VVI for folk like you.

Hope that helps.

MODE SWITCHING DUE TO FAR-FIELD R WAVE

by Ms Rutledge - 2021-03-07 14:13:07

Thank you,  I do understand more clearly, except for your last statement, do they not recommend not  increasing the PVAB with patients with complete heart block?

I think it's quite individual

by crustyg - 2021-03-07 15:43:54

I suspect that was very clear in their minds, hence the fairly high degree of willingness to consider replacing your RA lead.

MODE SWITCHING DUE TO FAR-FIELD R WAVE

by Ms Rutledge - 2021-03-07 16:10:27

Thank you.  You have been most helpful.

Mode switching, R wave and escape rhythms

by Gemita - 2021-03-08 21:55:49

Hello Ms Rutledge,

Firstly thank you for your post which I found so interesting.  It was good to read crustyg’s clear explanation of your EP’s assessment of your position.  Crustyg has explained the most crucial, complicated part of your question and I have learnt much from his response but I thought I would try to answer one or two of your additional questions:  on R wave and Escape rhythm just for completeness and as much for my own benefit as perhaps for yours!  

R Wave:

https://www.nottingham.ac.uk/nursing/practice/resources/cardiology/function/r_wave.php

I came across this useful site above and attach a link explaining R wave.  Actually the site is very informative in a simple to understand way, so we can learn about other Waves as well and a lot else, if you care to take a peep.

Escape Rhythms:

When I was considering an ablation of the AV node for my atrial fibrillation which would have made me totally pacemaker dependent, my main concern was if my pacemaker failed, would I die?   My EP quickly reassured me that most of us have back up pacemakers, in the form of Escape Rhythms, albeit running at much slower rates than that of the heart’s natural pacemaker (the SA Node) but sufficient to keep us alive long enough to seek help in the unlikely event of pacemaker failure.  These Escape rhythms/escape beats are heart beats arising from an ectopic focus in the atria, AV junction, or ventricles and when the sinus node fails in its role as pacemaker or when the sinus impulse fails to be conducted to the ventricles as in complete heart block, these escape rhythms hopefully will take over.  The ventricular escape beat follows a long pause in ventricular rhythm and acts to prevent cardiac arrest. It indicates a failure of the electrical conduction system of the heart to stimulate the ventricles (which would lead to the absence of heartbeats, unless ventricular escape beats occur).  

I hope that your reprogramming will be successful and that you will not need lead revision.  I also have lots of mode switching going on for atrial tachyarrhythmias, some of it inappropriate too apparently and have been told there have been some sensing difficulties, so I was particularly interested in crustyg’s response.  However I do not have heart block but sick sinus problems (tachy/brady).  Good luck.  

Mode switching

by Ms Rutledge - 2021-03-09 20:19:37

Thank you for your response, I appreciate all the information.  

This post literally happens to me today!

by asully - 2021-03-11 20:16:48

I read this post a few days ago, and funny thing is I had my appointment with my new EP today who discovered my settings were programmed incorrectly, in addition he said that I was oversensing in my far field r wave.  I then said "increase the pvab?" and he said yeah and called his Medtronic guru to make sure he did it right. Anyways, had I not read this post I would have had no clue what was going on! Y'all keep me on top of my game lol!

R wave sensing

by Ms Rutledge - 2021-03-13 16:33:34

  Who would have thought this would occur.  On another note we lived in Newnan Ga from 1991 to 1995, on Happy Valley Circle.  You are a little younger than my children, however it is sure is a small world.