what does this mean ?

My consultant cardiologist has written to my GP following my last appointment with him. The letter includes:

"I chased up the details from his previous pacemaker check (when he was an inpatient) and this showed an atrial fibrillation burden of 9% ie pretty low. Interestingly he also had a bit of atrial flutter during the pacemaker check at which point his pacemaker was pacing at the maximum tracking rate. This was managed by reducing the post ventricular atrial blanking period and changing the pacemaker to DDIR mode."

I understand AF. I think I understand maximum tracking rate. The final sentence defeats me. Can anyone help please?

What is DDIR mode and what mode would I have been on previously?

Why wouldn't I have been on DDIR mode before?

My background: I was rushed to hospital - a few days before I was due to race a half-ironman triathlon in June 2013. I was told I had A-V block. I came home with a St Jude Medical PM2112 (with Medtronic leads). On 30 April 2014 I had aortic valve replacement surgery (manmade valve) due to severe aortic stenosis. (I have had aortic regurgitation for 50 years when I had rheumatic fever at age 13 - one of the last in Britain I keep being told.)

I had my AVR surgery with minimal invasive method (4 inches scar) and was back to ironman triathlon training after two months.

I will be very grateful for help in understanding what my cardiologist has written.

Jon

9 Comments

Google is your friend

by Lurch - 2014-08-15 05:08:03

Sounds like a dual chamber device. Read this link:
http://www.ncbi.nlm.nih.gov/pubmed/1721153

thank you but .....

by ironmanjon - 2014-08-15 06:08:25

............. I had already read that old (1991) link and didn't feel any wiser about what DDIR actually means.

(Maybe I am just too stupid.)

Also there must be a reason why I wasn't on DDIR mode before - presumably DDIR mode has some disadvantages (otherwise it would be standard). What are the disadvantages of DDIR mode?

thank you Ian and Inga

by ironmanjon - 2014-08-16 02:08:48

Hi Ian and Inga

Thank you for both emails.

Ian: I don't seem to be able to find the website to which you refer. Can you let me have a link please.

Inga: on the basis DDIR responds to atrial tachyarrhythmias only when there is an atrial arrhythmia I don't understand why one might want a PM which automatically swaps between DDD and DDI modes?

What is the advantage of DDD mode (which presumably is what I was on before)?

I clearly do get atrial flutter at some times during the day because I had atrial flutter at my last pacemaker check-up (in June). I wasn't well at that time - I had an infection and my GP was concerned it could be an infection on my new aortic valve (which wouldn't be nice) so I was back in hospital feeling both poorly and worried. Maybe atrial flutter isn't usual for me during the day - but the hospital won't know that.

At a pacemaker check-up on 29 April (old mode) I was told in the previous six months I had had atrial pacing 19% of the time and ventricular pacing 5% of the time. So it seems I had AV block 5% of the time in the previous six months.

I think what you are saying is that the DDIR mode changes things only when I have some atrial arrhythmia combined with AV block at the same time.

There remains for me:

- the mystery of why the reduced ventricular atrial blanking period. Could this be an effort to help me if I am racing at a point I get AV block? (I hope this supposition is at least logical.)

- my lack of understanding on why I wasn't always on DDIR mode, given my AF was known before my PM was fitted. Also I don't understand the advantages of DDD mode even if DDIR mode isn't actually needed (ie no atrial arrhythmias)?

Thank you again.
Jon

Website

by IAN MC - 2014-08-16 06:08:24

Jon

Have a look at this; although it is referring to Medtronic pacing modes , the principles will be the same :-

Indications for Pacing and Mode Selection - Cardiac Study ...
cardiacstudycenter.com/images/page_images/resources/Indications.pdf
the definition of bradycardia varies with the patient s age and ... Mode Selection Decision Tree. DDIR with. SV PVARP. DDDR with. MS. N. VVI. VVIR. Are they.

Ian

Thank you Ian

by ironmanjon - 2014-08-16 07:08:29

Thank you Ian.

Interesting chart on page 41.

Its exact relevance to me is unclear because my AV conduction isn't 100% intact. I need to ask why this choice.

Jon

DDIR

by golden_snitch - 2014-08-16 09:08:23

Hi!

Maybe it does not have disdvantages, but is simply the better mode for someone who has episodes of atrial fibrillation and flutter? Modes and other parameters sometimes need to be changed, as our condition sometimes changes over the years.

DDD pacing can be a problem when you have episodes of of atrial tachyarrhythmias. During atrial fibrillation or flutter, there are so many sensed atrial events occurring at rapid rates that a DDD pacemaker responds with an attempt to track these events up to but not exceeding the upper rate. What you get is an often irregular ventricular paced rhythm at a mean rate just below the upper rate. If you have a functioning AV-node, then the ventricular rate can go faster, of course, but I think you have a complete block, right?

The thing is, you do NOT want the pacemaker to track atrial tachyarrhythmias. This is where the DDIR comes into play. In DDIR mode there is no tracking of atrial events. If there is a sinus or other atrial sensed event, the pacer will inhibit atrial pacing output. DDIR is a non-tracking mode, the ventricular lead will not track the atrial arrhythmia, but simply pace you at the programmed base rate or, with the rate response switched on ("R"), at a rate that the rate response sensor has determined to be appropriate. Thereby, the problem of inappropriate tachycardia caused by an atrial tachycardia is solved.

Nowadays, most pacemakers can automatically switch from DDD(R) into DDI(R) or VVI(R) when an atrial arrhythmia occurs. My Biotronik Evia, for instance, switches into DDIR when the atrial rate exceeds 200bpm. Apparently your St. Jude pacemaker is not able to do that, otherwise your cardio had programmed a mode switch and not permanent DDIR.

PVARP or Post-Ventricular Atrial Refractory Period = a pacemaker will “close its eyes” for a prescribed interval after each QRS complex, whether it’s a native QRS complex or a paced QRS complex. It ignores all p-waves that fall into this period. Why your cardio shortened this? Difficult to say. Usually, the PVARP shortens with higher rates. Maybe your cardio wanted to enable the pacemaker to better track fast atrial rates? But that makes no sense, because he just put you in DDIR to prevent tracking fast rates. So, no idea why your cardio did this.

Inga




DDIR - fog has lifted slightly but still hard to make sense of

by ironmanjon - 2014-08-16 11:08:34

Hi Inga

Thank you for your reply and very full and helpful attempt to enable me to understand.

It sounds like I'll need to ask the cardiologist a number of questions when I next see him. (My next appointment isn't due until January.)

When I saw the cardioligist last month he told me he reckons my pacemaker is pacing me only when I'm asleep. He said he doubts it is pacing me at all when I am active. (I do not know what causes him to think this.)

Unless he is totally wrong I don't have total A-V block.

My pacemaker was fitted at a different hospital from the one I now attend (and where I had my AVR surgery three and a half months ago). I find the cardiologist much better compared with the previous hospital where I was taken by ambulance from GP surgery when I visited due to shortness of breath and inability to raise HR (just before race in 2013). The previous hospital took advice from another very large hospital on choice of pacemaker for me. I had to wait three days for the recommended one to arrive. I was told it was chosen in an attempt to suppress my paroxysmal AF.

My AF seems to have disappeared - or become totally asymptomatic - in the last couple of months. But when I do get - or notice - AF it seems to occur a low HRs. Typically - say - 70.

(As an athlete I am used to a resting HR of 40 or less. Immediately post-op it was 60 but has now fallen to 50. I hope it will fall lower. My PM is set for a base rate of 35.)

It seems surprising - although possible of course - the PM chosen for me isn't sophisticated enough to choose appropriate mode.

Also my AF has decreased since my op - although the atrial flutter may be new (or rather newly identified - I am never aware of it) - so it seems odd I haven't always been on DDIR mode given I have had AF since before my PM was fitted. Unless there is a reason for not being on DDIR mode.

But as you say why should the post ventricular atrial blanking period be reduced rather than increased?

Coming back to my main point if the PM isn't pacing me most of the time how is that consistent with being on DDIR mode? I understand what you say is that on DDIR mode the PM simply decides its own ventricular rate (based on rate response mechanism which my PM has).

Also - unless I am misunderstanding (very possible) - what you say about DDIR mode would mean I would have 100% ventricular pacing. Yet I thought a high level of ventricular pacing should be avoided because it can lead to hear failure?

I am very grateful for your help so far but further comments will be very welcome.

Jon

DDIR

by golden_snitch - 2014-08-16 12:08:05

No, you don't pace 100% in the ventricle. What I explained about how DDIR responds to atrial tachyarrhythmias applies only when you have an atrial arrhythmia. When you have an episode of atrial tachy, the pacemaker will not deliver any atrial impulses, and will - when you have a complete block - pace your ventricles at a rate that the sensor decides is appropriate. But only then, during that episode, not all the time.

Your pacemaker still paces and senses both chambers, if necessary. If your AV-conduction is working, and you never have bradycardia during the day, the pacemaker will let your heart do as much work as possible on its own.

Inga

Hi Jon

by IAN MC - 2014-08-16 12:08:51

Just to add to your confusion, and to probably thicken the fog :-

Out of curiosity I Googled " DDIR Definition " and found an excellent site which shows a decision tree used to determine which PM mode you should have.

It suggested that DDIR is recommended if you have brady-tachy syndrome and ONLY when you have intact AV conduction i.e. if you don't have AV block.

Is it possible that your mode was changed because they have realised that you do not have AV block ?

I'm sure that I've added nothing to your thinking and I do hope that your cardiologist provides some answers !

Ian

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