I've found that the dear wife's Apple IX watch is a real asset to following her Afib. (she only has overt symptoms when transitioning from NSR to Afib). We are one-third of the way in her process to get an ablation
So I have a question that I'd like to ask about the heart app that possibly some folks here have already sussed out.

The question is: when the Apple watch records a heart rate, over what period of time is the (apparent) pulse observed.

Dear wife is a nurse, and she would regularly take a persons pulse (by palpation) of the radial artery for 15 seconds, counting each beat than multiplying by 4 to get a BPM.

So my question is akin to that, over how many seconds does the watch observe beats for each recorded heart beat rate?

(Apple support could not answer this question because it's a "medical question" in other words they don't know)

Mine takes 30 seconds, but it's a Galaxy 4, and my newer 6 (which I only wear occasionally to keep it new...I like the rotating bezel which Samsung has only on some models) does the same. Neither watch reads constantly or even periodically. I must either initiate the ECG function or else go into settings and have the app do constant monitoring, which will obviously use up a lot of battery capacity.

Normal ER ECGs run for only 15 seconds. [www.wired.com]



Edited 1 time(s). Last edit at 07/23/2024 05:48PM by gloaming.

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Searching9
So my question is akin to that, over how many seconds does the watch observe beats for each recorded heart beat rate?

This link might be useful.

"When you use the Workout app, Apple Watch measures your heart rate continuously during the workout and for 3 minutes after the workout ends to determine a workout recovery rate." So perhaps this feature is something to experiment with.

I don't have an Apple Watch. If I want an accurate recording, I use a Polar H10 strap with an app that was designed to capture data for research purposes. I can download the RR (beat to beat length in ms) data to my computer and analyze it. I will sometimes capture the data overnight to analyze PAC and PVC frequency. I put the data in an ancient Polar Windows program as it will window the data to easily analyze it. I've posted screenshots from this program previously, for example in this post of an analysis of heart rate pattern with and without taping my mouth shut to encourage nasal breathing during sleep.

Perhaps it will become clearer if I give you a table of her resting heart rate that were recorded this morning (while she was at rest) !
This data is recorded from watch to her Apple Heart APP on her phone. Reading were taken automatically ( did not "request" a reading)

It's obviously doing a moving average so only the very first interval after turning it on has a sample period of more than 1 second. That's the only way you could get continuous readings at 1-second intervals. That's the same way the monitors in the hospital work that show a real-time display of heart rate, and exactly how I would expect it to work.

That's what I was originally thinking, however the moving average should not change significantly over a two second period.
For example, at 11:17:51 the moving average is 97, for the moving average to shift to 74 in a two second period, would suggest the during that "new" period rate would have to be near 0.

In other words the moving average would be relatively smoothed, provided that there were no really wild swings in the successive readings. So to shift the moving average from 97 to 74 would require a wild swing in the instantaneous rate. Oui ???

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Searching9
So to shift the moving average from 97 to 74 would require a wild swing in the instantaneous rate. Oui ???

Yes, which is common in afib.

Even sampling every second, you miss a lot of data, especially if rates are high.

I have an SpO2 ring that captures 4 second data and the comparison of those data vs RR (beat to beat) data captured at the same time can be pretty dramatic. The 4 second data mutes the HR variability dramatically.

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Searching9
for the moving average to shift to 74 in a two second period, would suggest the during that "new" period rate would have to be near 0.

And very well might have been. A 2-second pause wouldn't be unusual in afib, and even a single beat near the end of that 2-second period could produce that much change. Keep in mind the device is probably calculating in milliseconds.

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Carey

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for the moving average to shift to 74 in a two second period, would suggest the during that "new" period rate would have to be near 0.

And very well might have been. A 2-second pause wouldn't be unusual in afib, and even a single beat near the end of that 2-second period could produce that much change. Keep in mind the device is probably calculating in milliseconds.

I don't know about the AW and its plethysmographic sensor, but my Polar strap does not "see" PVC's, so a PVC beat rate is reported as 1/2 that of surrounding beats.

@Carey et al.
the moving average thought brought to mind another "experiment".
When the Apple watch calculates Heart Rate Variability, it measures the time (in milliseconds) between R-R complexes, but it also reports the instantaneous BPM between each R complex. Since the HRV determination runs for 3-4 minutes AND reports the BPM in fractions of seconds, one should be able see the BPM during the period that the HR is reported.

Here's what I found.:
The heart rate was recorded at 10:14:19.00 as 66.

However the beat to beat BPM ranged from 83 to 136 for the two minutes leading up to the 10:14:19.00.

How can that be?

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Searching9
Here's what I found.:
The heart rate was recorded at 10:14:19.00 as 66.

However the beat to beat BPM ranged from 83 to 136 for the two minutes leading up to the 10:14:19.00.

How can that be?

Is the 66 supposed to be an average during the two prior minutes or is it an instantaneous reading at that time? If the latter, was she in afib during the reading? If so, I'm not surprised.

@ GeorgeN & Cary

Yes she is currently in AFIB.

If the reported heart rate at 10:14:19 is 66, it could NOT have been any averaging of prior beats (see above); the 66 appears to be a rate based on a single R-R interval (aka an instantaneous rate).

I'll have to check some of her hospital 12 lead ECG recordings taken while in AFIB, but I would bet that the heart rate reported is the average of the R-R (nstantaneous) rates. (or simple count of QRS complexes identified during recording period).

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Searching9
@ GeorgeN & Cary

Yes she is currently in AFIB.

I'll have to check some of her hospital 12 lead ECG recordings taken while in AFIB, but I would bet that the heart rate reported is the average of the R-R (instantaneous) rates. (or simple count of QRS complexes identified during recording period).

My Kardia device reports the average of the RR beat rates (or more likely the sum of the RR times divided by the number of beats & then converted to BPM) for a 30 second reading.

I assume your (or her) objective is to see if the average rate is > 100 BPM, or something like that?

My immediate objective is to understand how the Apple watch reports the heart rate in their phone application.
Is it an counting of QRS complexes during a period of time? and if so what is that period of time.

(for example, if I count the number of QRS complexes on my 6L Kardia for the first 15 second, and then do the same for the next 15 seconds, I can get two different BPM when the R-R interval is chaotic - indicative of AFIB.)

What I do NOT know, but would like to find out, is what period of time is used by an Apple watch. My suspicion is that it's a short period of time, just from observing how the display changes on the watch face. BUT, as Carey suggested this initial display may be a longer period of time (say 10 seconds) , and subsequent displays are updates to the moving average. Those subsequent displays could change every second.

WE visited with our GP today, and prior to his arrival the nurse determined wife's heart rate by palpation over 15 seconds and reported a BPM of 124, however when the Dr came in he asked the nurse to repeat the heart rate, but now count the beats over 60 seconds. Now her BPM was 78.

I'm not suggesting that either determination was incorrect, but each determination needs to be understood in the context of how the determination was made.

The alternative is that heart rate determinations taken during AFIB with RVR are essentially meaningless.

If you open the heart sensor on the watch it reads the pulse every 5 seconds. If you open the heart sensor and place your finger on the crown it reads it every second. Apple says if you want a faster reading “with fidelity” placing your finger on the crown should be done.

I am surprised RN only took pulse for 15 seconds in a patient that is having cardiac issues.



Edited 1 time(s). Last edit at 07/25/2024 01:20PM by JakeS.

Hi Jake,
Re: "nurse", the pulse rates were taken by a CNA, not an RN. But that is beside the point, the point is that the apparent pulse rate can vary as a function of the period of time of observation. In the first case beats "averaged" over 15 sec versuis beats "averaged" over 60 seconds. That distinction is important to understand when attempting to report BPM for a patient with AFIB with RVR.

I take from what you've said is that the normal activation of the heart sensor (not using the crown), is a potentially new rate display each 5 seconds The only question I've got with respect to that is: is it a display that is completely independent of beats prior to that 5 second window, or is the newly displayed rate influenced by the prior 5 seconds. ( that is to say, a moving average that is updated each 5 seconds).

Also, if you know, the heart rate display when touching the crown..... Is this "type" of heart rate drawn from the ECG function (where actual electrical signals are used) versus using the photoplethysmography principle used in the non-crown determination?

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JakeS
I am surprised RN only took pulse for 15 seconds in a patient that is having cardiac issues.

I'm not. That's pretty much the standard that all medical providers are trained to. It's unlikely you're going to find anything new by counting longer. It's plenty of time to feel the quality, strength, rhythm and rate, and anything else you need to know is better obtained with an ECG.

@Carey, JakeS, George N:

Finally found someone at Apple that was able to clarify.
The normal "touch the heart icon" on the watch face: captures and counts the number of beats for the next 5 seconds and multiplies by 30 to report and record the heart rate. That value is NOT influenced by what occurred before. And each time the display is updated it only looks at the number of beats per minute in that five second interval.

Holding the crown utilizes the same sensor (not the ECG sensors), but accelerates the reading and updating to 1 second intervals (should be almost the identical values as one might see in the Beat-to-Beat data used in Heart Rate variability function).

Also, health data including all the raw heart data is capable to be stored in iCloud. That data is encrypted (so not viewable like photos, notes, files etc).

The health data will be maintained in iCloud as long as there is available space. If a person runs out of available iCloud storage, older heath data may be deleted to make room for new data.

One of the things I've noticed if I use a plethysmograph (and your fingers will notice this if taking a pulse as well) is that in afib, there is large variability in pulse wave amplitude as well as pulse rate. The amplitude can get very small and hard for a device to detect (and hard for your fingers to detect as well). If the plethysmograph device displays amplitude, you can see this pulse wave amplitude variability as well.