Heart Rate Part 2: simple machines - AF Association

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Heart Rate Part 2: simple machines

In "Heart Rate Part 1" I asked about the efficacy of manually determining heart rate (as applies to AFers).

I was amazed and heartened by the great response. Thanks!

Now, proceeding from manual method to simple machines...

For an AFer, what’s the efficacy of using a:

- Cuff: I suspect no better than the manual approach. I don’t exactly know how they work—but know the cuff is a reliable way to find out blood pressure. Blood pressure can be very important to AF patients. I have extremely low blood pressure. (Low enough to earn me helicopter trip #2.) Almost all medications relating to AF (specifically to ensure heart rate doesn't go too high, too often) decrease blood pressure—so you can see my quandary.

- Pulse Oximeter: I understand that well oxygenated blood is important, but I still don’t know how this device relates to, or measures, heart rate.

PLEASE DON’T DISCUSS MORE COMPLICATED MACHINES LIKE THE FITBIT, KARDIA, and the ER-room cardiac monitor. These are reserved for "Heart Rate Part 3". But if any other devices fall into the “simple machine” category, please pipe in.

HOWEVER, AS FAR AS I’M CONCERNED, BOTH CUFF and PULSE OXIMETER ARE ESSENTIALLY USELESS BECAUSE THEY PROVIDE ONLY SINGLE DIGIT HEART RATE ANSWERS (more specifically--they do not display TRENDS) and I can’t see how a single digit response (e.g., heart rate = 120 bpm) relates in any useful way to a person with a heart in AFib.


21 Replies

You missed our wist monitor!! They are pretty inaccurate when in AF. I did a cross check of a well known make against a Kardia and found inaccuracies of up to 50%.

Finger oximeters / pulse monitors are pretty inaccurate when in AF. I did a cross check of one that I bought (for use to check my SpO2 level) make against a Kardia and found inaccuracies of up to 35%.

I thought that, and I was led to believe, that the SpO2 reading would be accurate. On the second occasion seeing my sleep apnoea consultant told me that for SpO2 level if someone is in AF they are not accurate but they are more accurate than the pulse function.

Cuff monitors fall into three categories.

First are those specifically designed for AF. Often designated A or Afib or the like. One model is on the main AFA website. BP element is good. The HR element is sometimes inaccurate and sometimes reasonably accurate. I have Microlife WatchBPHome A (A for Afib) and have cross checked against Kardia (simultaneously for some tests and consecutively on a daily basis). Sometimes the consecutive readings are very close but from memory at other times the inaccuracy can be up to 15% to 20%. Note that I have found that there have been occasions where my cuff monitor has NOT shown me as being in AF whereas the Kardia has. I am in persistent AF. Probably around 2% to 3%. However I have found a glitch with my Microlife (that relates to the model and not just my machine) in that it stores (but only displays Error on the screen) all the error readings and all these are not classified as AF and are also included in the averages function which they shouldn't be.

The second category are ones approved by the British Hypertension Society but not designed for AF. Some I believe are BP only and some both BP and HR. Obviously these won't tell you that you are in AF. From gut feeling these won't be any better than cuff ones designated AF but could well be worse. I haven't done any cross checks. However if someone has one they shouldn't just throw it out unless they want to update to an AF model for BP and being told they are in AF (or disregarding the HR functionality).

Long winded but hope this helps.


Not long-winded at all…In fact, it provoked a lot of questions.

I was not told about the SpO2 level discrepancy. On the other hand, I was also told the PO provided superior heart rate info than the (cuff) pulse function.

Q1:But how does the PO determine heart rate?

Q2: Why would Afib affect one’s SpO2 level at all?

RE "cuff…3 categories..." Nothing was ever said to me (USA) about different kinds of cuffs—only that you could get one at the local pharmacy and that there were two types, strap and wristlet.

Q3: How does a cuff monitor “tell you you are in Afib”? Every one I’ve tried has just given me three numbers: heart rate & (blood pressure)systolic/dystolic.

(Story) There was a night we were with friends and everyone passed around the cuff. (This is what children of the 60s do when they’re old!) Everyone had their respective heart rates…(this was before I knew I had afib)… when my turn came…my heartrate registered at 35! (I wasn’t particularly concerned [I would not have put an exclamation point behind it then] So I tried it again and …35 again (never “ERR”)! In some way I thought it a badge of honor—(I said to myself that the lower my heart rate—the less beats per minute— the longer I might live (since I wasn’t using up my (beat) allotment.

Q4: I suspect this ‘theory’ doesn’t hold water…Right?

Q5: What does persistent/2-3% afib mean? Does it mean you have AF 2-3 percent of the time?


Re SpO2 level. A few things due to the arrythmia and "circulation" issues. Your actual SpO2 level may not being recorded properly due to fact that blood is not reaching the extremities properly. That is why fingers and thumbs are always colder first. Your reading may be low but not not normally higher than actual. For me pre ablation reading nearly always in 88% to 96% range. Post ablation nearly always >96% even though back in AF. The overall circulation is impaired. In addition warfarin certainly affects circulation. The testing is from the small capillaries.

EP told me only to get a cuff monitor approved by the British Hypertension Society (BHS) and gave a brief explanation. A more detailed explanation is that there are essentially four types of cuff monitors. (1) Those designated for AF - see my previous reply.. (2) ones tested by (BHS).. (3) ones where manufacturer claims compliance usually by self testing.. (4) the rest which should not be considered and many are inaccurate.

Even on approved ones accuracy is a bit variable (I am used to reading technical specifications and parameters).

The majority of pharmacies do not stock AF ones because they are more expensive and less demand. Also many don't know they exist. In addition many GPs and other medics don't know of them.

Picture of this morning's reading wil be inserted in post when I can.

Re story. Your HR was almost certainly not as low as that but cuff not picking it up.

No there is I defined number of beats I have learnt that for some people 60 is normal and for others 90 could be normal.

Q5 not heard that term how ever by definition persistent could not be AF only 2% to 3% of the time.

I also have moderate to severe leakage in triscuspid valve.


So how does a Pulse Oximeter determine heart rate?

Re Q5: You said " I am in persistent AF. Probably around 2% to 3%." That's what I had a question about.


I used to have very warm hands and feet—so much so it would cause comment. Now my hands are always FREEZING (no medical seems concerned)!

My SpO2 readings are almost always 98-99 ( I don’t do the PO often).


@PreterWH The Omron most expensive model upper arm bp monitor cuff has an icon for irregular heart rhythm. It cost under $100 usd and was purchased at Walmart in NYS. OMRON sells on line internationally--so you can do an internet search for that . It is very accurate--but as with all LED bp monitors I just replace it once a year.


Thanks but I bought my Microlife over 18 months ago.


I have a newer Omron, (Canada) with the irregular heartbeat icon, and it picks up the AFib every time.


I would agree that automatic BP machines are largely useless, giving both erroneous pressure and rates. It is for this reason that medical staff should be encouraged to use the old fashion manual method where they actually have the knowledge to do this and not all do.

There may be one or two machines which members have found to give reasonable results but I have not found one.


A year ago the Microlife WatchBPHome A is actually the only one recommended by NICE for use with AFib and was the only one on the AFA website.


Just for the record, I have a pulse oximeter TempIR and the reading I get for a pulse rate is the same as I get from my Kardia and indeed from previous hospital readings.

I have found this very useful as I can see the range I am in instantly to give to medics when asked.


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How does a pulse rate reading you get from your pulse oximeter show you "the range you are in"?


When in AF the oximeter displays continuously the changing heartbeat.


What is a Kardia please.


Basically, Kardia, previously known as AliveCor, is an ECG which is capable of being downloaded onto most smart phones and some tablets. A clinical grade ECG recording is taken in 30 seconds. It will instantly detect AF and has the ability to communicate results direct to your doctor if required

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Why does a person who knows s/he has afib need to purchase/use a device that tells h/er/im s/he has afib?


My monitor tells me a lot more than whether I have AFib or not. I get a brief analysis - irregular heartbeat, or fast and irregular heartbeat, or deviating or fast and deviating and so on.

What I like is to be able to scroll along and look at the heartbeats. Are they all random chaos or do I have long or short runs of normal beats with P waves along with the wildness? If I'm getting just 'irregular heartbeat' I am usually mostly sinus with one or two or several random beats now and then. I don't always find it easy to tell when I am fully back in NSR as just one pair of beats out of sync will bring up 'irregular'. Always nice to see 'stable waveform' eventually. Very reassuring.

I would not be without the monitor and always have it with me if I am away. I rarely use it.

On top of that, I can take a reading and show it to anyone to demonstrate what my heart is doing or has been doing. My other half finds this very helpful, as do both my GP and my EP. I don't need to try and describe - or indeed remember - what's been going on. Loads of stored info for the trained eye. OK, it's not the same as a proper ECG, but I have arrived at A & E 23 miles away with a heartbeat that is far removed from what prompted me to go there and my monitor enables instant recording of anything untoward.


Of course none of these devices are essential and could make some people quite OCD. Reassurance is probably the reason they are bought.

Personally I believe in being proactive and if that means having a few devices in my possession then so be it.

As far as the pulse oximeter goes, I find it useful on two fronts. Firstly because it reassures me on my Spo2 level, as I've had heart failure in the past, and then as previously explained the pulse range.

I'm new to the Kardia ECG mobile. I know that this is not an essential item but it is jolly useful. it's good to know that if I go Into a continuous fast but regular rate then I can send a recording over to my EP via his arrhythmia nurse for analysis. And yes, it would confirm what I probably already know, that I'm in AF. instead of worrying that it could be a dangerous arrhythmia.

I haven't got round to buying my own stethoscope like some on the forum but that won't be far off!



It was my other half who bought my pocket ECG because he thought it would inform us both. And indeed it does.

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At the end of the day regular readings from devices like the Kardia (AliveCor) and a proper approved BP machine can tell Consultants and GPs far more than a single snapshot reading taken in a clinic or surgery can (even if a person doesn't have white coat syndrome!!!). Both mine have been used to adjust medications at least every two months and without them I would have been medicated too much (Bisoprolol) and also not been given BP tablets.

If you look at a single day snapshot then my HR and BP was fine. If you look at the daily readings BP in particular had gone from being low (circa 95 to 105 / 65 to 70) to being high (130 to 140 / 95 to 100). This was a step change in circa one to two weeks and stayed there. Went to GPs three weeks ago but next hospital appointment is not to 9th September so would have been high for at least 6 weeks and possibly longer if on the 9th it happened to have slipped back o normal (it does seem to on an odd day for some reason).

In the early 1990s my father was one of the very early diabetics who had a tester that was linked to the PC and recorded sugar levels and gave insulin dose amounts. Nowadays they are so common!!!


What does AF mean?


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