SAM event - respiratory sensor disabled

Not yet 'off' but I have had a vector change

by crustyg - 2023-10-23 05:21:28

I rely heavily on BostonSci's Minute Ventilation to increase my HR when road cycling and swimming.  I've had one SAM event which triggered a 'vector change'.  You probably know that MV works by measuring the impedance from the PM outer case to ring or tip of either of the two leads (if you have two), and if Signal Artifact Monitor detects too much interference it triggers a change.  If you are using PM<=>A-lead it switches to PM<=>V lead - and triggers an auto-calibration which can last up to 6 hours.  If already using V-lead then it turns MV off - for me, that's a disaster.  The one time it's happened to me I was cycling up a small mountain on the way home => RR stopped and I had to finish the climb with miserable cardiac output.  Not fun.  We have no idea what triggered the SAM event and all the usual culprits (pole-mounted mains transformers, arc-welding etc.) were absent.  So far, nothing on my leads suggests a problem there.

Happily I have two leads and every time I have an interrogation I check that we're using the A-vector.  Apparently, out-of-the-box SAM events aren't treated as Alarms, so don't meet the threshold for remote transmission and are easily missed during an in-person session - this can be changed.  It's the work of 2min to reset the MV-vector and another 2min to initiate a manual calibration (without which MV is still functionally useless).

So if you rely on MV for RR don't delay, get in to your EP-tech and get it reset.  If it starts to happen more often then you're probably going to want to get the damaged lead replaced - *IF* that's the lead in use when you have a SAM event.

Best wishes.

Jane & Crusty

by Penguin - 2023-10-23 08:06:27

'Anyone have any experience with the respiratory monitor being turned off by noise/artifact ? ' 

Hi Jane, 

My answer is 'not as far as I know' although I experienced a long period of oversensing recently.  Therefore I'm curious about SAM events and how a pacing clinic / pacemaker might recognise them. 

I have a normal PM, not a CRT

You and CrustyG may be talking about the same PM manufacturer / models - BScientific devices - so excuse me if my questions are irrelevant to other brands, but would you or CrustyG happen to know whether or not an alert gets triggered automatically on all pacemakers if SAM gets switched off during oversensing or is this an alert that the techs have to set up individually on a patient by patient basis when programming PMs?

Crusty - My PM is programmed to DDDR and doesn't use MV for rate response. It has an accelerometer. 

I'm not sure I understood your post that well and wondered if you could clarify whether or not the situation that you describe in your post could occur if my own device was oversensing artifact  due to a.sensing being set very low (below 2.0mv)? Could this cause switching from a.pacing to v.pacing as an auto calibration for 6 hours?

I have never heard of SAM before. 

SAM, Minute Ventilation and BostonSci devices

by crustyg - 2023-10-23 08:53:41

I hope I haven't waded into some nonsense of my own making here.  JaneJ doesn't state device vendor or model, but AFAIK only Boston Sci and one other vendor have a respiratory rate sensing capability for their PMs.  Hence my jumping to the conclusion about respiratory sensing being turned off by SAM that we were talking about the MV feed into RR in BostonSci devices.  Perhaps not.

Another cause of oversensing is near-field sensing: sometimes the electrical activation of the RV can provide enough of a signal that it is detected by the RA lead - PM sees a new activation and inhibits its output => low HR => low BP etc.  IIRC there was a discussion about this on the forum a couple of years ago.  It's uncommon, but real.  *IF* I understand this correctly, near-field sensing does not rely on retrograde conduction through the AV-node (which more commonly causes PMT) - but that may not be correct.

I would encourage all contributors here to fill in the basic details of their device - vendor + model but NOT serial number or lead information.  Help save me from myself!  A little bit of bio- is nice too.

Best wishes.

No Problem

by Penguin - 2023-10-23 08:59:05

Don't worry CrustyG. You are no doubt well informed about issues affecting your own device and tuned into that. I understand that.

I find you one of the most informative members here - so thanks for clarifying. 

thank you for updating your profile

by new to pace.... - 2023-10-23 14:43:40

thank you are udateing your profile.  will help with our answers to your query.

new to pace

Thanks!

by JaneJ - 2023-10-24 01:58:36

Thanks for all the helpful information!  My crt device is a boston scientific crt u128 pacemaker.  The rate response feature was working off of the atrial channel.  It completely got shut off, so I guess changing to the v lead did not work.  Will def be getting it turned back on when I go in next month.  I believe the accelerometer is still working so at least I have that, but my sinus node is toast, so I def need rate response on my device ( :  Thanks again for all the input on this!  This club is so wonderful!

"frayed lead"

by piglet22 - 2023-10-24 08:45:29

Lead damage is a bit concerning and is at least the second one reported here recently.

There are several layers in leads and the outermost one is the mechanical and moisture protective layer. It's most likely something like Silicone or Kevlar, maybe Teflon.

It won't be "frayed". They tend to split with movement over time.Having said that, some tubing like hosepipes are plastic with fabric reinforcement.

I'm guessing here, but for the sort of measurements going on with a PM, there will be a shield layer, sometimes a coaxial woven layer, and that can fray. Inside that will be insulators and other leads as part of the circuit.

What on earth are they doing as it reads, putting in a damaged lead? That doesn't fill me with confidence.

The last reported instance was repired with a suture sleeve, but even that would worry me.

The only repair I would think as even remotely acceptable would be something like a heat shrink sleeve, not gaffer tape.

A repair before insertion sounds bad but if it had to be done, it's a lot easier than an in-situ repair.