What is an ECG?

You might have seen the abbreviation ECG in any number of places, from hospitals to the specs sheet for your smartwatch, but what does it stand for?

The term ECG stands for Electrocardiogram, and it is a medical test that is performed in order to check the rhythm and electrical activity of the heart.

The NHS website states that an ECG can help to detect various cardiac conditions, including arrhythmia (when the heart beat is irregular), coronary heart disease (when fatty substances block the blood supply to the heart), heart attacks (when the heart’s blood supply suddenly stops), and cardiomyopathy (when the walls of the heart are enlarged).

If you were to have an ECG taken in hospital, you’d most likely have multiple electrode sensors attached to your arms, legs, and chest, and the test may be performed when you’re at rest or undergoing exercise. The strength and timing of the natural electrical impulses that flow from your heart are then recorded, in order to measure your heart health.

As a consumer tech website, we’re mostly concerned with ECGs when it is a feature of a smartwatch.

Which smartwatches have ECGs?

There are several smartwatches that are capable of performing an ECG scan on your wrist. These include the Apple Watch from Series 4 up to the current model (Apple Watch Series 7) though excluding the Apple Watch SE, and it’s also available on Samsung Galaxy Watch Active 2 and above.

You’ll also find an ECG feature on the Fitbit Sense, the Coros Vertix 2, and the Withings ScanWatch and Withings Move ECG.

However, this is by no means an exhaustive list of all smartwatches with the feature; if it is important to you to have ECG functionality on your smartwatch, we’d advise you to carefully check the features list before you buy.

Are smartwatch ECGs accurate?

Ultimately, this question depends on the smartwatch itself. It’s also hard for us to check when we review the devices as it generally only throws up alerts when something goes wrong, which thankfully hasn’t happened to any of our testers thus far.

Taking the Apple Watch series as an example, Apple claims that its ECG app “allows you to generate an ECG similar to a single-lead ECG without a prescription from your doctor”, going on to make the following statements which favourably compare the accuracy with that of a 12-lead ECG:

In studies comparing the ECG app on Apple Watch to a standard 12-lead ECG taken at the same time, there was agreement between the ECG app classification of the rhythm as sinus or AFib compared to the standard 12-lead ECG.

The ability of the ECG app to accurately classify an ECG recording into AFib and sinus rhythm was tested in a clinical trial of approximately 600 subjects, and demonstrated 99.6% specificity with respect to sinus rhythm classification and 98.3% sensitivity for AFib classification for the classifiable results.

Despite this, Apple advises that its ECG app cannot detect the following conditions: heart attacks, blood clots, strokes, high blood pressure, congestive heart failure, high cholesterol, other forms of arrythmia. The manufacturer advises users to seek the advise of their doctor if they feel unwell or believe they are experiencing symptoms, while if the user experiences chest pain, pressure, tightness, or any other signs of a potential heart attack then they should immediately call the emergency services.