AFib below the threshold for detection?

I've been having what feels like an SVT at night most nights.  My Kardia 6L keeps saying either possible AFib or unclassified.  Had them run a check, no events recorded.  Threshold for recording is above 200BPM.  My last SVT was not AFib and was below the threshold.  The tech told me also fine AFib sometimes does not get picked up.  He said he changed the settings for me so that it would mode switch to 80 BPM V paced if I had any lower rate SVT and I would know because it would be a steady 80 BPM and I would likely feel the dysynchrony.  Sure enough same night he changed it I felt symptomatic took a Kardia 6L which said possible AFib and I was running at exactly 80 BPM.  Anyone heard of AFib not being picked up? I encouraged them to slap a zio patch on me like the last time I caught the low rate SVT but won't have results for a few weeks.


Missed Afib

by AgentX86 - 2023-03-09 21:55:08

Kardia isn't foolproof, nor is there one sort of Afib.  Most have a very high rate "irregularly irregular" pulse.  Some have a more normal rate (mine) but the same irregular pulse.  Some are more regular... Kardia isn't perfect at detecting all of these.  If you sent the strip to them (and paid to have it read) the could probably decode it.  It would be easier to just send the strip to your EP.

In short, Kardia will declare a strip "inconclusive" unless the result is obvious.

Yes AF is frequently missed which is why it can be so dangerous

by Gemita - 2023-03-10 04:11:22

Yes Anna, it is a common problem for many of us, especially as AF may be interspersed with other atrial tachy arrhythmias like multi focal atrial tachycardia, SVT, Flutter, even fast atrial premature beats (yes they do exist apparently) which rather confuses the picture.  However since my EP tends to place all my atrial tachy arrhythmias under the same umbrella, it is easy to see how short runs of a fast irregular AF might be missed.

As a matter of fact I have just had my Medtronic atrial lead sensitivity setting set to the lowest “sensitivity” possible from 0.30 mV to 0.15 mV since during a lengthy AF episode on the 4th February, a stored electrogram of the event failed to record the true AF burden during that day because I was rapidly flipping in and out of the arrhythmia.  

In your case, I see they have lowered the threshold for detection of high atrial rate episodes so that they will pick up more AF which can present at a slow, normal or fast heart rate.  As you know Anna, one arrhythmia can set another off so it is possible that you are having an assortment of in and out atrial arrhythmias at varying speeds too and it might be difficult to pinpoint the exact arrhythmia present at any given time.  Total atrial confusion?  Yes, which is why my EP lumps all my atrial arrhythmias “together”.  

I have always believed that longer term monitoring is the way to go and if longer term monitoring doesn’t pick anything up, then try the Reveal Linq implant - it won’t miss a thing and is far superior to our pacemakers for arrhythmia detection, analysis and recording (according to my experienced EP).

So yes, AF is frequently missed and it took a number of years for mine to be detected with the usual 24 hr, 7-10 day holter monitoring.  They eventually had to implant the Reveal Linq loop recorder which stayed in until battery depletion (3+ years) and this gave them all the information they needed to pick up my AF with a RVR and the occasional Syncope episode from the long sinus pauses that sometimes occurred when my AF converted back to normal sinus rhythm.

Still cannot quite believe we are chatting again.  

Pacemaker Model

by Penguin - 2023-03-11 06:48:46


Sorry to hear about the difficulties with your cardiac health previously and pleased to read that things improved after your last posts on here.  Fingers crossed that any improvement continues for you.  

I was wondering which pacemaker you have? 

I've spoken to a few manufacturers about programmable parameters for mode switch and AT detection. They vary but most devices will only detect SVTs and then mode switch at the patient's max tracking rate / sensor rate + 5-20 bpm.  The AT detection rates start at around 100 bpm and again these vary by manufacturer.

I'm no expert and may well be missing some vital piece of information, but it seems to me that these parameters make it difficult to detect low rate AT / AF during sleep / at rest (if AT/AF occurs below 100 bpm) other than via the ECG and more difficult still to get the device to mode switch as yours does. That's why I wondered which device you have. 

I hope that the dyssynchrony induced by your new settings is short term. I imagine it's very uncomfortable for you.  

Medtronic CRT-D with one of my leads shut off

by Asully333 - 2023-03-16 03:14:57

Honestly I don't know my current settings right now because I have had so much going on cardiac wise, I haven't been with an EP in well over a year.  Hopefully this year I will get established with one, I know the advanced team would like to do a lead revision so we can turn CRT back on.

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