Apple Watch Series 4: ECG wherever you go

I bought an early first-generation Apple Watch back in 2015, and had been using it ever since. I kept meaning to upgrade to one of the newer series, and it was the features brought with the Series 4 which finally convinced. That and the fact that battery endurance of my old watch had fallen so it struggled to keep up with long working days.

I’ve had my new Watch nearly a month now, and the latest watchOS update to version 5.2 has just unlocked its full features in Europe. This article considers one of the most exciting of those: ECG.

Until I retired almost five years ago, I had spent much of my professional life looking at and trying to interpret ECGs. Plenty of doctors do, but what was unusual in my case was that these were being recorded live from people who were supposed to be healthy, not those with suspected heart problems or heart attacks, and that the great majority were ‘single-lead’ and in challenging circumstances. For example, we might be exercising a healthy person by running them on a treadmill in tropical heat, or immersing a volunteer in very cold water to assess their initial responses – which can sometimes include dangerous disturbances of heart rhythm.

Over the twenty-five and more years that I did this, we used a variety of ECG monitoring systems, some wireless, others using long leads. The very first that I used relied on analogue wireless telemetry, and the latest ran fully digital over Bluetooth. The Apple Watch Series 4 compares very favourably with all of these, at a tiny fraction of their cost.

Health or healthcare

In the great majority of countries, medical devices like pacemakers and ECG recording systems are very closely regulated, but those which we use in relation to health and fitness are essentially considered to be consumer devices and require less rigorous approval. Although my first generation Watch had the potential to do much more with its heartbeat data, Apple was careful not to enter medical device territory. It had to be, or the Watch and its Health software would have had to undergo approval as a medical device in North America, Europe, and most other markets.

What is remarkable is that Apple has seen sufficient potential in the healthcare uses of the 4th generation Watch to go through the lengthy, costly and demanding process of approval as a medical device. That isn’t something that you enter lightly.

Because of this close regulation, 4th generation Watches and their Health app can only provide limited support for what the ECG is capable of. I thus consider first what they provide the user, under the terms of their approval, then move on to what potential they have for the professional and the future.


A suitable iPhone running an enabled version of the Health app with a paired 4th generation Watch lets you access the ECG features. When you enable them, you have to work through a series of screens which lay down precisely what you’re getting.


This explicitly states that the ECG checks for atrial fibrillation (AF), one of a myriad of abnormalities which can be detected from an ECG such as that produced by a Watch.


This feature is age-restricted, so before going any further you have to enter your date of birth, which is also added to saved ECG records.


You are then given a set of explicit warnings as to what the current software cannot detect or be used for, and tells you that if you aren’t feeling well, you should obtain medical care. These aren’t Apple just playing it safe: these define what the rules of use are under the Watch’s approval as a medical device.

Once enabled, taking an ECG recording is extremely simple. You should be sat down, with your arms supported, and resting. You place one finger (typically the index) against the Digital Crown of the Watch after opening the ECG app on the Watch. You must then remain still for the thirty seconds which it takes to record the ECG. The Watch conveniently provides a countdown timer for this.

Once that is complete, the ECG is transferred back to the Health app on your paired phone, and displayed there.


The software provides a diagnosis in terms of AF, and you can scroll horizontally through its recording. Tap on Export a PDF for Your Doctor and the whole record will be saved ready to transfer from your iPhone to a healthcare professional.


When you follow the instructions, the ECG recorded is of very high quality, as that shown above. That is as good as an ECG made on a dedicated system costing ten or more times the price of a Watch, but it is only one out of the twelve leads which would normally be obtained from a dedicated system. The other eleven leads provide a great deal of additional information which help in diagnosis.

The purpose behind this is to screen the wearer for asymptomatic AF, which is not uncommon. In AF, the atria, which feed the ventricles with the blood to be pumped out to the lungs and the body, may become unco-ordinated in contraction. This allows clots to form within them, which can break off and cause serious health problems including stroke: you can read more about it here on Wikipedia, and on many healthcare sites.

AF is increasingly common, and according to figures quoted there, is thought to affect 2-3% of the population, although it is most common with advancing age, affecting 14% of those over eighty (who might not appear to be Apple’s biggest customers, yet). It can occur episodically too. Checking your ECG for AF shouldn’t be the sort of thing that you would do every day, but as you grow older it is worth keeping a check.

The other major health-related feature of Apple Watches which you should be interested in is its hard fall alerting system, which I will look at in another article. For those who are at significant risk of falls (again, largely the elderly) and anyone whose fall might not be witnessed by someone who can help, this could prove a life-saver.


The automated diagnosis available in the Health app looks solely for AF. A medical or related professional who examines this type of trace, often known as a ‘rhythm strip’, can see more detail which may be of value in other conditions and circumstances. However, care is required.


There is great temptation to do different with the Watch’s ECG recording feature. The trace above was obtained when I was walking briskly up an incline. This might appear attractive to many of the Watch’s younger users, perhaps, but even for a professional, interpretation is not easy. As exercise ECGs go, this is quite high quality but has plenty of artefacts resulting from footstrike on the ground and other movement.

What I see here looks like a normal healthy exercising ECG, but the artefact is sufficient for Health’s diagnostic software to consider that it may be AF.

If you know your way around rhythm strips well, there are plenty of opportunities where running an ECG like this can be informative. If someone collapses with cardiac symptoms in a populated area, you reach for the nearest defibrillator once you’ve started first aid, and that contains the necessary pads and system to perform life-saving diagnosis and treatment.

But when you’re a long way from such a facility or any form of medical assistance – out on the hills, perhaps – if you’re competent and still deliver good advanced first aid, slipping your watch onto a patient and getting a rhythm strip seems like a good idea while you’re waiting for help to arrive, for example.

It will be very interesting to see whether this new feature can be used to good effect in such circumstances.

Heart rate variability

Much of what the ECG feature brings is valuable, and has the potential when used properly to save lives. Time and statistics will tell whether this is an effective preventative measure. There is, though, a related feature which needs more than a pinch of salt: measurement of heart rate variability (HRV).


This isn’t apparently considered to be a healthcare feature, which in itself should alert you to the possibility that there’s a snake-oil salesman around. I have sat through several presentations by former physiologists who have been peddling various systems which claim to monitor ‘stress’ and other vague notions using this type of measurement.

The sad thing is that it’s easy to do with a good-quality heart-rate measuring system such as that in Apple’s Watches. But the numbers don’t actually mean anything. They vary greatly between individuals, and at times appear to be little more than noise. The theories often advanced about providing an index of ‘sympathetic versus parasympathetic tone’ or activity simply don’t make any sense either. I suggest that the wisest thing to do is just ignore them, and I’m sad that Apple included them at all.


Apple’s Watch Series 4 has two health features of value to users: ECG and hard fall detection. The quality of the ECG is superb, and forms a system for early detection of atrial fibrillation. Although the users most likely to benefit from this are those over sixty, it has the potential to be valuable for everyone when used according to its explicit instructions. Healthcare professionals may well be able to use ECG traces for other purposes, but those require training and experience in their interpretation, and are currently outside the Watch’s approval as a medical device.

I’m absolutely delighted with my new Watch, and look forward to Apple’s future developments. This is just a start.