Swimming and Oversensing

Any swimmers out there? Using Boston? I’m a 3-year recipient of a dual sensor Boston Accolade, and it’s been working fine. EXCEPT for some recent issues with the MV (Minute Ventilation) sensor.

In the last month, the MV sensor was twice disabled by the SAM monitor. This is a safety function to guard against oversensing. When I studied the dates and times, I realized that in both cases, I was swimming (in an outdoor, club, 50m pool). The snapshots clearly show noise on both leads.

After the first one, I went back to the Device Clinic and had them check for any physiologic issues (doing arm movements and such while watching the online programmer during interrogation), and everything was clean and fine. No lead problems. Everything within range. And then they turned the MV sensor back on. Only to have it go out again a couple weeks later.

They (the docs, the nurses, the Boston reps) think it’s an external EMI event causing this. But I’ve studied the pool in question, talked to the head of maintenance there, and even done my own metering of AC/DC current (which is the suspected cause). Nothing shows up. (FYI: there are no underwater lights in that pool) And adding to the mystery is that the problem is INTERMITTENT, i.e., the sensor did NOT shut down on a couple of pool visits between the visit to the device clinic and the second shutdown of the MV sensor.

So the MV sensor is currently off, and my EP is okay keeping it that way for a while. I have partial inherent conduction at higher BPMs, so currently don’t really need pacing while swimming (or doing anything else that raises my heart rate), and the other sensor (Accelerometer) is working fine. 

But in the meantime I’m struggling to understand the mystery behind what’s causing this oversensing and the MV sensor shutdowns. 

Anyone else have similar experiences? Thanks for your inputs.


4 Comments

Not experienced that myself

by crustyg - 2020-07-31 13:14:28

Hi: Do you have a complete BostonSci setup?  Your profile is more bare than sparse!

I have Accolade + Ingevity leads, 14months in.  Full MV, carefully tuned for road cycling, fine for running, not effective for my swimming, even though I had the accelerometer sensitivity increased by two notches 8 weeks ago.

The MV sensor is *VERY* sensitive to external magnetic fields (static bikes esp magnetic-braking auto-power, but also my fluid-braked cheap turbo-trainer).  But in my case all this does is remove the MV feed into rate response so my HR stays too low (SSS+CI) which is a pain.  Nothing in my log about activation of SAM (which *is* on) - even on occasions when I can guarantee that the MV has effectively been stopped.  I *think* the great BostonSci MV problem from 2017 (think that's right) was mostly related to non-Boston leads.

So I don't think it's a MV magnetic field issue, I *suspect* it's more likely to be PM/lead connector producing noise as you swim.  It's an exercise where the PM is moved around a lot in the pocket and that could easily produce electrical noise esp if you've non-Boston leads.  I don't think it's an external EMI event causing your noise problems.  Tell me you're on 320uA excitation of MV and not the lower setting of 80uA?  Do you know if your MV sense vector changes (it can use either lead, mine always uses atrial), as this *might* suggest a lead => heart muscle impedance problem.  It can be set to use A, V or auto and this might be worth exploring.

Sorry I don't have the answer.  I would be going *mad* if my MV were switched off and I had to go and have it re-enabled.  I posted late last year ('How happy patients become unhappy') about the nonchalant comment from an EP tech about how their team always disabled MV.  My (not very grown up) response was along the lines of  'touch that and die' - without MV my PM is useless for me.  I empathise!

PM me with your recent settings reports if you want to discuss this further.  You do *have* your settings reports....?

Replying to crustyg

by Henry55 - 2020-07-31 18:40:04

Hi crusty! Thanks very much for your detailed reply. Let me respond to your points and elaborate a bit. And I may also take you up on a PM later.

YOU: “Do you have a complete BostonSci setup?”

ME: Yes. Complete. All Boston. Accolade MRI L311

-----

YOU: “Full MV, carefully tuned for road cycling, fine for running, not effective for my swimming, even though I had the accelerometer sensitivity increased by two notches 8 weeks ago.”

ME1: Not sure why “not effective for my swimming”. The point, for me, is that, as with cycling, there is little thoracic movement, although some lateral rotation involved (in freestyle swimming). But definitely no “bouncing up and down.” I’m curious why you think this.

ME2: I’m 38 months in now and I had to dial DOWN the accelerometer early on because it was activating when I did things like stretching and yoga.

-----

YOU: “So I don't think it's a MV magnetic field issue, I *suspect* it's more likely to be PM/lead connector producing noise as you swim.  It's an exercise where the PM is moved around a lot in the pocket and that could easily produce electrical noise esp if you've non-Boston leads.”

ME: All the docs, nurses, tech reps are saying it’s definitely NOT the device/leads causing this; it’s external. Do I believe them? Not sure. What I can say is that I’m a highly skilled swimmer with a very “smooth stroke,” although there is some movement + the flip turns at the pool ends. And again, they had me replicate my swimming movements while being hooked up and wanded, and no noise showed up at all.  

-----

YOU: “I don't think it's an external EMI event causing your noise problems.”

ME: But that’s exactly what all of them are saying it is.

YOU: “Tell me you're on 320uA excitation of MV and not the lower setting of 80uA?”

ME: Yes. 320. Always has been.

YOU: “Do you know if your MV sense vector changes (it can use either lead, mine always uses atrial), as this *might* suggest a lead => heart muscle impedance problem.  It can be set to use A, V or auto and this might be worth exploring.”

ME: The default vector has always been RA, but when it oversensed, it Auto Switched to RV. Then it disabled the sensor soon after.

-----

YOU: “Sorry I don't have the answer.  I would be going *mad* if my MV were switched off and I had to go and have it re-enabled....”

ME: Well, I appreciate very much what you have answered.

Luckily for me, my MV is not that needed at this time. Of course, that may—probably will—change over time, so I do need to figure this out. But agree that going in to have the MV turned back on is (A) a lot of trouble, and (B) costly (for us Americans with the world’s worst healthcare system ;-).

The current plan is to let things stay as they are until the next remote transmission on Aug. 12. Then take a look at that report <b>—[NOTE: I’m fastidious about getting my Full Combined Follow-up Report and even take a camera into the device clinic and photograph the Decades Bins screens as Boston says those cannot be included in the Combined Reports, although they ARE included in the Remote Transmision Combined Reports. Why that’s the case is beyond me and I’ve complained to them about this obvious design flaw.]—</b> Then see how things are going before my next in-person Device Clinic interrogation and discussion with the EP in November. That’s the plan anyway.

Further thoughts???

Where to start....

by crustyg - 2020-08-01 17:42:13

Pardon me for being blunt: you don't specify your leads.  They are a critical part of your setup.  I specified Ingevity leads for me.

Me: MV not effective for swimming - as in my PM doesn't drive my HR high enough. I've checked it several times over the last few weeks and I don't get above 100bpm - not nearly enough.  My f/s stroke isn't great - a lot of resistance and poor arm technique - so I really need something >120bpm.  I'm told that open-water swimmers are trained to rotate the chest *much* more than pool/lane swimmers (partly to clear the airway for inspiration, partly to visualise the destination marker) and this can really help the accelerometer with a feed into RR.  Mine was set to factory default (8), at my request, but is now at 10.  Hasn't helped.

Not sure how to be polite about the replicating swimming movements and your EP team saying 'see, there's no noise' so I'll be blunt. *IF* they knew what they were doing, they would *KNOW* that MV is DISABLED during a wand session.  It actually says so in the BostonSci Brady reference manual,  but you do have to actually read it to know this!'    Table 2-4, appendix c is the clue. As I mentioned, MV is *VERY* sensitive to magenetic fields, the big thing about the inductive wand is the huge magnet at the end of the wand.

It's not obvious to the EP techs but any BostonSci rep should know this.  They *MUST* use Zoom telemetry if they going to investigate this function.

If MV changed sensor vector so quickly that might suggest that *both* of your leads are not BostonSci *or* that both leads didn't have their locking screws tightened adequately (or perhaps both leads are showing increased impedance).

I know and accept and acknowledge that I'm the patient from hell, given my background. There's a BostonSci rep for my area that I won't allow within 50feet of me, but fortunately for me, my EP doc is smart enough to have arranged for my PM tuning with another BostonSci rep who really knows the details.  But in your case, I would be seriously challenging their claimed expertise. From what you've said so far, they sound as though they are well out of their depth.

Calming down a little: there's no doubt that charm achieves more than insults.  Somehow you have to find a way to achieve your goal with as little wasted time/money as possible.  I have the advantage of living 5miles from the teaching hospital where I trained, but in general I try to/have to behave as any ordinary patient.  But at least it's convenient and close for me to get my PM tweaked, and it's foc (actually it's pre-paid).  The more that *you* learn, the  more you can convince them by the power of your logic. Last Dec my EP tech said 'your pacing voltage is fixed and not set to auto-calibrate', as though this was a significant issue.  I checked and called later and explained that for *my* PM in my pacing mode, auto-calib of pacing voltage is disabled.  The EP tech didn't know this - but given the huge array of PMs and ICD they deal with, it was not a great surprise.  No-one knows everything about all of this kit, me included.

It still sounds like a lead noise issue - there is almost certainly no great EMI source in your swimming pool - and if this is the *only* place where MV generates a noise alarm in SAM, a vector change and then disabled, it's most likely related to lead noise and not induced interference.  To an electrical engineer, Noise is not the same as signal swamping (e.g. from external mag field, as in watt-bike, turbo-trainer, mains transformer on a pole right above you), which might explain why my MV signal drops sometimes when I'm in the countryside, but never fails at other times.

misunderstandings and clarifications

by Henry55 - 2020-08-02 23:49:01

No problem with you being blunt or needing to be polite, but I think some clarifications are in order from my side...

1. SETUP: I said “all Boston”: the can and the leads. (Q: Why would anyone use third-party leads?)

2. SWIMMING: I swam today. 2,000m total in an hour, typical for me. My highest BPM was 112. I rarely go over that. NOTE: I’m 72 and like to target 65-75% of max rate for upper target range (and although I don’t really believe in the 220-minus-age formula, if using that with 75%, that puts me at 111). I like to stay in the 100-112 range for my moderate-to-vigorious workout portions. But again, I’m not pacing much in that range. My PM is primarily for extreme Bradycardia with my Lower Rate Limit set at 50.

As I said, I’m a very skilled swimmer. I paid attention today, and my torso never exceeded a gentle “rocking” motion (technically, a “roll” around the directional line of forward movement). Max is 45% but usually less. In open water, it might be a little more but doubt it. (I’ve done dozens of open-water swim races; I sight by lifting my head, and I just turn my head more to breathe)

3. PHYSIOLOGIC TESTING: I did not know that the MV is turned OFF during a wand session. News to me. And maybe news to the Boston field rep who was there doing the wanding??? Kinda hard to believe. But I’ll be questioning this on my next visit.

4. NOISE: You think it’s internal (lead noise), but all of the EP nurses, the Boston field rep, and the Boston Patient Services reps are indicating it’s external. So what’s a patient to do? ***Get a second EP opinion???

Thanks for your continued inputs.

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