Sky Labs' smart ring tops Apple Watch in AFib comparison

A smart ring developed by South Korean healthtech Sky Labs has outperformed the Apple Watch in a head-to-head comparison of their ability to detect atrial fibrillation (AFib).

The study, published in the journal Heart Rhythm O2 and carried out at three clinical centres in the UK, looked at the sensitivity and specificity of the two devices' automatic AFib detection algorithms using single-lead electrocardiograms (SL-ECG) data, which was subsequently interpreted by physicians.

Sky Labs' CART-I ring – described as a cardio tracker – achieved 84.6% sensitivity compared to 69.1% for the Apple Watch, with the latter device recording a higher number of unclassified SL-ECG readings.

Put another way, CART-I missed one of seven AFibs identified later by physicians, while the Apple Watch missed one in three, with unclassified SL-ECGs coming in at 1.9% and 20.1%, respectively. The study also included patients with atrial flutter, with one in four cases missed by CART-I and two in five with Apple's device.

While the results of the 483-subject study hand a win to Sky Labs' device and reinforce the potential of wearable tech for identifying AFib, the researchers – from Oxford University Hospital, University Hospital Southampton, and Queen Elizabeth Hospital – that the devices alone are not yet sufficient for diagnosing specific arrhythmias, such as atrial flutter or atrial tachycardia.

As long as physicians subsequently reviewed the data, sensitivity for both devices rose above 94%, although, they performed poorly in detecting non-AFib arrhythmias, according to the researchers.

A version of the CART-I ring known as CART BP has already been approved in South Korea for use as a 24-hour blood pressure monitoring device, and is reimbursed under the national health insurance system with more than 1,300 clinics using it to support patients.

The devices deploy photoplethysmography (PPG) technology – the use of infrared light to measure changes in blood volume in blood vessels – which has been shown to be a reliable way to detect AFib and is increasingly seen in wearable devices.

The authors of the paper note that, while wearables are increasingly used to detect AFib, most validation studies have measured only sinus rhythm or AFib, which they suggest could potentially overestimate diagnostic performance by excluding other clinically relevant arrhythmias.

"The variability in sensitivity and specificity highlights the importance of caution when incorporating wearable devices' automated detection into patient care without adequate physician interpretation," they conclude.

AFib is a type of irregular heart rhythm where the upper chambers of the heart beat out of sync with the lower chambers, and affects around 2% of people under the age of 65 and 9% of those older. Apple first received FDA clearance for its irregular heart rhythm notification on its watch in 2021.