A very simple question

if you have some level of AV block from long PR interval to full heart block does anybody know how it is decided what the Paced AV delay should be set at?

Is it individual or is there an agreed optimum Paced AV in general?


5 Comments

A simple question that doesn't have a simple answer

by crustyg - 2021-04-27 18:38:32

There is no one answer to this Q.  1: modern PMs typically have two settings, Fixed AV-delay and Paced-AV delay (AV delay is progressively reduced as HR increases (just like a normal heart....).  Sometimes there's a third mode: BostonSci call this Sensed-AV delay.

In the normal heart the AV-node's refractory period (when it will block conduction from A=>V) is quite long at rest, and progressively reduces under the influence of cardiac Sympathetic drive and also circulating Adrenaline.  This is why folk in AFlut/AFib can see their Vent rate increase as they exercise - the normal drive to the AV-node reduces the refractory period, and one can see 5:1 block become 4:1, 3:1, 2:1 and even 1:1 (this is SCD territory for AFlut).

A modern PM tries to replicate this natural reduction - A=>V sync isn't well maintained if atria are activated at 160BPM but a huge AV delay messes up the vent response.

Your EP team will usually set you up with typical settings and then adjust them to suit you.

AV Delay Strategy

by Terry - 2021-04-27 20:33:09

Some doctors prefer to extend the AV delay if doing so results in natural ventricular activation. The intent is to avoid paced ventricular activation and the risk of "pacing induced cardiomyopathy." That is, unless the lead is positioned to produce natural ventricular activation, "His-pacing."

Simple question lmao!

by asully - 2021-04-27 21:38:40

Sorry I just saw the irony in that as I did not know the answer off the top of my head.  Crusty G did a very good breakdown.  QuickJRaw I noticed most of your questions fall under the difficult section, no problems with that I like learning when you do get an answer to a question!

Still not sure

by quikjraw - 2021-04-28 04:23:43

Yes it does seem a more complicated question than it seems.

I know that I have exactly the same settings as another member on here and we are very different in both our heart issues and in many other ways so how can that be?

My Paced AV is 180ms and my sensed AV is 150ms.

I am going to bet that a large proportion of people on here with a medtronic device is set at these parameters. I am interested to know if that is the default setting on the device and if so what initiates a change to it?

Have other people had these values changed over the years and if so what was the reason?

Yes.

by PacedNRunning - 2021-05-21 04:26:16

The can set the delays individual. They usually find out what your own PR is and try to beat it or extend it to allow your own newer to work. I tend to have long PR intervals myself so 180/150 Would pace me 100% because I can't beat that at all. My delays are longer than most in order for my own heart to work under 90bpm. I have dynamic delays so as my heart rate in increases with exercise or exertion AV delay shortens. I've done a lot of research on this and studies have found that dynamic delays are the best for good hemodynamics. Fixed not so much. Exercise PR is 70-80ms not paced. So most doctors program the shortest delay for dynamic delays 80-100'ms depending on what you need. Try and find out what your natural PR interval is and either beat it or lengthen it to allow your heart to work. 

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