People are being warned not to rely on the accuracy of heart-rate apps after researcher found significant discrepancies in them.
Research published in the latest edition of the European Journal of Preventive Cardiology has found that there were differences of more than 20 beats per minute compared to ECG in over 20% of the measurements.
Dr Christophe Wyss, a cardiologist at Heart Clinic Zurich, Switzerland, and lead author of the report, said although heart-rate apps are installed on many smartphones, there is no law that requires their validation, which means consumers do not know if the results are accurate.
His study included 108 participants who tested the accuracy of four randomly selected commercially available heart rate apps using two phones, the iPhone 4 and iPhone 5.
Some apps used contact photoplethysmography – touching fingertip to the phone’s built-in camera – while others used non-contact photoplethysmography, where the camera is held in front of the face.
Dr Wyss and team tested the accuracy of the apps and compared them to the clinical gold standard measurements of electrocardiogram and fingertip pulse oximetry, which uses photoplethysmography.
The study participants had their heart rate measured by ECG, pulse oximetry and each app using each phone.
The researchers found differences of more than 20 beats per minute compared to ECG in over 20% of the measurements, with the contact apps performing better than non-contact apps, which tended to overestimate higher heart rates.
Dr Wyss said: “While it’s easy to use the non-contact apps – you just look at your smartphone camera and it gives your heart rate – the number it gives is not as accurate as when you have contact with your smartphone by putting your fingertip on the camera.”
The study also found that the performance of the two contact apps was also different. One app measured heart rate with comparable accuracy to pulse oximetry but the other app did not give the correct measurement.
“The one contact app was excellent, performing almost like a medically approved pulse oximeter device, but the other app was not accurate even though they use the same technology,” said Dr Wyss.
The researchers found that the variation could not be explained by camera technology, age, body temperature, or heart rate.
“The difference in performance between the contact apps is probably down to the algorithm the app uses to calculate heart rate, which is commercially confidential,” said Dr Wyss.
“It means that just because the underlying technology works in one app doesn’t mean it works in another one and we can’t assume that all contact heart rate apps are accurate.
“Consumers and interpreting physicians need to be aware that the differences between apps are huge and there are no criteria to assess them. We also don’t know what happens to the heart rate data and whether it is stored somewhere, which could be an issue for data protection.”
Coppetti T, et al. Accuracy of smartphone apps for heart rate measurement. European Journal of Preventive Cardiology 3 May 2017; doi: 10.1177/2047487317702044
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