PMT Detection Settings

PMT "correction" settings!

by Gemita - 2024-09-01 20:09:43

Penguin, firstly are you okay or do you think you still have signs of pacemaker mediated tachycardia (PMT)?   I hope not.  

You might want to remind yourself of the several Pacemaker Mediated Arrhythmias there are by going to our FAQs (Learn-FAQs-the pacemaker/defibrillator, then scroll down to Part 3 - Can a pacemaker malfunction - PMT), where you will see a number of possible settings that may need adjusting to deal with PMT, like the reprogramming of the pacemaker to lengthen the PVARP since a retrogradely (backwards) conducted ventricular beat can only be sensed by the atrial lead if the PVARP (post ventricular atrial refractory period) has passed.  By increasing the duration of PVARP, there is less likelihood that retrograde conduction will be sensed, and PMT will be triggered. 

Another option would be changing the sensitivity of the atrial lead, so that sinus P waves are sensed, but not retrograde P waves.  

The rate at which PMT happens is dependent on the programmed AV delay and the Ventricular to Atrial conduction times. The rate of PMT is always equal to or less than the programmed upper tracking limit.  Retrograde P-waves are induced by ectopic ventricular beats, ectopic atrial beats, atrial sensing failure, atrial pacing failure, and a long AV delay. 

Definitive diagnosis of PMT is achieved by performing device interrogation and examining the intracardiac electrograms. This will show retrograde conduction with atrial sensed beats following ventricular paced beats, whereas in normal situations, the atrial sensed beats should precede ventricular pacing.  

I attach cardiocases links for Abbott devices, although I am sure you have seen these.

https://www.cardiocases.com/en/pacingdefibrillation/specificities/pm-av-delays-refractory-periods-management-tachycardia/abbott

https://www.cardiocases.com/en/pacingdefibrillation/traces/pm/abbott/pacemaker-mediated-tachycardia

I had my atrial lead adjusted to make it more sensitive (0.15 mV down from 0.3mV) to better detect an atrial tachyarrhythmia and it looks like the Mode Switch onset has been recently reduced from 171 bpm down to 150 bpm to trigger more frequent Mode Switching and to catch more atrial tachyarrhythmias.  I do sometimes get retrograde Ventricular to Atrial conduction.  

See also member Ukegirl’s post (link below) on her personal experience dealing with PMT and what worked for her:

https://www.pacemakerclub.com/message/44405/update-on-pacemaker-mediated-tachycardia

Not sure if any of this helps or whether I have answered your main question Penguin but it is not for want of trying.  Goodnight and stay safe xx

To sum up

by Gemita - 2024-09-02 00:30:03

The Pacemaker Mediated Tachycardia (PMT) detection rate as you know, determines at what rate the device becomes alert to the presence of a PMT.  This is a programmable rate between 90 and 180 bpm for Abbott I believe?  For Classic PMT detection, the rate set should always be equal to or less than the programmed upper tracking limit.  It cannot exceed it.  See Cardiocases links for more details. 

Then of course we have that awful RNRVAS (Repetitive Non-Re-entrant Ventriculo-atrial Synchrony) and pseudo RNRVAS.  RNRVAS usually occurs at rates slower than Classic PMT rates, so this should help differentiate between the two arrhythmias.   As we know, both true- and pseudo-RNRVAS are under-recognized because there are no device algorithms to reliably detect and document them.  

Pseudo-RNRVAS is seen in Abbott pacemakers.  Unlike PMT and true RNRVAS, Pseudo-RNRVAS can occur even in patients with VA conduction block.  

Appropriate lead sensitivity settings are important for accurate arrhythmia detection.  Mode Switch settings are also important to capture/detect atrial high rate episodes and assess arrhythmia burden.  A tachycardia is detected when the atrial rate exceeds the programmed arrhythmia detection rate during a programmable number of beats.  Intracardiac electrograms will help doctors give a definitive diagnosis, or follow up with further monitoring (like a surface ECG).

Differential Diagnosis for PMT can include any rapid atrial rhythm, like AT, AF, or Atrial Flutter, which can be sensed by the atrial lead and then result in ventricular pacing at the upper rate limit. Electromagnetic interferences and myopotentials from chest wall muscles can also be sensed by the pacemaker and cause pacing at the upper rate limit.  In pacemakers with rate response function, the sensor may be oversensitive, which may result in increased pacing rates in response to low-level activities.

Lots to consider 

PMT Detection Rate Query

by Penguin - 2024-09-02 12:52:20

Thank you for your full and helpful reply Gemita. Yes, I know the ropes and where to find the info on this forum that you so thoughtfully put together for us all. As you say - lots to consider.

What I’m actually asking is whether there are any restrictions that I don’t know about when programming a PMT detection rate? For example, we discovered that when programming the AT Detection Rate on my PM, it has to be programmed at least 20 bpm above the MTR.  As you know these 'rules' for arrhythmia detection vary by manufacturer. 

Thinking along the same lines, I wondered whether there are any similar rules for PMT detection that I am not aware of, given that PMT usually occurs at or below the MTR?  I've checked and there is sufficient room within the parameters for PMT detection (90-180 bpm) to capture the PMT that has been evidenced in my case, but as the detection rate is too high, I'm wondering if there is some rule or other which is preventing the techs from changing it. (It's bog standard PMT as far as I know - which I am not always aware of).  

Whether or not there is something else going on and hitting my upper rate limit when I become very symptomatic, I don't know.

I'm hoping that somebody else might have some answers. 

My technicians are flexible with Mode Switch detection rate

by Gemita - 2024-09-02 14:28:02

Hi Penguin, I will try to keep this short to hopefully allow others to comment.  They don’t want you hitting your MTR and forcing a Mode Switch too early.  My MTR is only 130 bpm, so my new tachy setting of 150 bpm is acceptable.  Recently though I had 171 bpm as the rate that I had to reach before a mode switch would be triggered.  Mode Switch can be quite difficult to tolerate though if it happens too often.

Since we will all have our own very unique reasons for developing tachycardia and will require different adjustments, the upper detection rate has to be set to suit the patient’s condition.  For example now that I have developed chest pain, clearly my doctors will want to know if and when I hit dizzy heights (above 171 bpm).  That seems to be why they have reduced my Mode Switch detection rate to 150 bpm, to help prevent worsening symptoms.  Another reason is because they wanted a more accurate count of the time I actually spend in AF (since AF can come in at slower rates too), to see whether I will need an ablation.

For you I would imagine that the more flexible they can be with your detection rates, the more likely they will pick up more in the way of disturbances and give you some answers.

Gemita

by Penguin - 2024-09-02 15:29:56

'Since we will all have our own very unique reasons for developing PMT and will require different adjustments, the upper detection rate has to be set to suit the patient’s condition.'   There's just one detection rate programmed for PMT. There's no upper and lower detection rate (?) The PM verifies PMT over 9 cycles or so and then terminates it, and , if programmed to do so it adds it to the diagnostic EGMs and event counter.  If the detection rate is too high to trigger the algorithm the PMT carries on.  That's not good in the long term. 

It seems to me that if PMT is evidenced beneath the detection rate programmed, it would be helpful to reduce the detection rate accordingly as terminating the rhythm is pretty important! 

Your pacing mode won't trigger PMT Gemita, but DDD(R) pacing is definitely susceptible to it!

'For example now that I have developed chest pain, clearly my doctors will want to know if and when I hit dizzy heights (above 171 bpm).'  .... which they knew before didn't they? 

'That seems to be why they have reduced my Mode Switch detection rate to 150 bpm, to help prevent worsening symptoms'   That's a useful move. How have they done that and does this still trigger a mode switch or does the pacemaker behave differently?

'Another reason is because they wanted a more accurate count of the time I actually spend in AF (since AF can come in at slower rates too), to see whether I will need an ablation.'  Of course! Although you[ve said previously that there's too much evidence to collect on the device's EGM.  I take it there's been a change of mind towards gathering the max amount of evidence.  Lucky you! 

I will hope for more answers and evidence for myself.  It's about time!  Not sure my heart is going to take much more of this. 

Further Digging

by Penguin - 2024-09-05 07:04:09

I recently put up a post about PMT detection at rates lower than the PMT detection rate.  I’ve done a bit of digging around since and found this article, which provides an example of what can happen when PMT occurs below the max tracking rate and below the rate which is technically recognised as ‘tachycardia’ by pacemakers.  PMT at lower h/rates may be due to slow retrograde conduction. 

The article explains that PMT detection algorithms are not triggered when what is ‘technically’ a pacemaker mediated tachycardia (recognised via ECG pattern) occurs below the lowest PMT detection rate and below the programmed MTR. 

The key points seem to be:

At h/rates below the lowest PMT detection rate devices will not recognise the rhythm as ‘tachycardia’ and will not trigger the usual response to PMT.  

Slow retrograde conduction can cause PMT below this rate. 

The usual method of extending PVARP will not work if there is slow retrograde conduction if the conduction cycle length is above  the max programmable PVARP length.  (In this example the max PVARP setting is 500ms and the cycle length is 520ms). 

Max PVARP length is programmable, and may also be built into the PMT prevention algorithm.  Max PVARP length may also vary by manufacturer. 

The article suggests that, ‘in the case of very slow retrograde conduction, prevention of PMT may only be possible by prolonging the post ventricular atrial refractory period (PVARP) after a premature ventricular beat.’  

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8283539/

I hope this is helpful to someone.