Swiss researchers assessed the accuracy of various heart rate apps and found their accuracy varied hugely with respect to medically rated measuring devices like the electrocardiogram (ECG). Although one of the apps was almost as good as the ECG, the rest were quite terrible, so consumers should be very careful when they choose to monitor their heart health with such apps.
Although heart rate apps are ubiquitous with many carriers pre-installing them on newly purchased devices, there is no legislation requiring developers to adhere to some strict medical performance guidelines. Consumers, on the other hand, might trust the results just as well.
To verify how accurate some of these heart rate apps are, a team led by Dr Christophe Wyss, a cardiologist at Heart Clinic Zurich, Switzerland, recruited 108 patients who had their heart rate measured. Four commercially available heart rate apps were chosen at random for the study and the results were then compared to the clinical gold standard measurements like the electrocardiogram (ECG) and fingertip pulse oximetry.
The apps were tested on the iPhone 4 and the iPhone 5. Some of these app work using photoplethysmography, essentially measuring the heart beat by placing the finger on the phone's fingertip sensor. Other apps use non-contact photoplethysmography and measure the heart heart just by taking a picture.
In one in five of the assessed measurements, the apps were as much as 20 beats per minute off compared to ECG. It's not surprising to hear that the apps that use optical analysis to determine the hear rate performed the worst, particularly at higher heart rates and lower body temperatures, as reported in the European Journal of Preventive Cardiology.
"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," Dr Wyss said.
One app measured heart rate with comparable accuracy to pulse oximetry, though. When the researchers tried to understand why this app was performing so well compared to others, the researchers found the variation could not be explained by camera technology (iPhone 4 versus iPhone 5), age, body temperature, or heart rate itself. The only thing that could explain this app's performance was the algorithm used to establish the heart rate -- but given it's a commercial app, the researchers didn't have access to the code.
The takeaway is that most heart rate apps are very poor. You might find a very good app, but you shouldn't trust it unless you compare results with a medical-graded device. Previously, blood pressure apps were also found to be inaccurate.
"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," Wyss said.
Since last year, Apple has been a lot stricter with what apps it allows developers to publish in the fitness or health section of the AppStore. Consumers, however, should still be very careful when using health apps. At most, use the monitored results as a rule of thumb or performance indicator. You should never take medical advice from a health app unless it's been recommended by your doctor.
"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," Wyss concluded.