Single-lead ECGs may not be as accurate in detecting AF as previously thought

A new study has challenged previously reported accuracy of atrial fibrillation (AF) detection with single-lead electrocardiograms (ECGs) technology.

“Single-lead ECG may not be as accurate for AF detection in patients with cardiovascular disease as previously thought,” said lead study researcher Dr Andre Briosa Gala, from Oxford University Hospitals NHS Trust, Oxford, UK, who reported their results at EHRA 2023.

“The CART-I ring demonstrated superior AF sensitivity and specificity compared with the Apple Watch,” which missed AF in one in three patients, Gala added.

The researcher pointed out that while the use of wearable technology to detect episodes of AF is becoming more common, studies that have tested the accuracy of these AF detection algorithms using single-lead ECGs have mainly involved patients who have either normal heart rhythm or AF. As such, the sensitivities and specificities of AF detection algorithms are likely overestimated.

Lower than previously reported

In the study, Gala and colleagues compared the diagnostic accuracy of the Apple Watch and CART-I ring AF algorithms in a cohort of 400 consecutive patients with pre-existing cardiovascular disease. These participants underwent simultaneous 12-lead ECG recordings with a 30-second single-lead ECG from an Apple Watch Series 6 and a CART-I ring. The order of devices was randomly assigned.

The presence of AF on 12-lead ECG data was evaluated by two cardiologists who worked independently, and any discrepancies were resolved by a third cardiologist. The algorithm used by the wearable devices categorized ECGs as either “AF,” “not AF,” or “unclassified.” McNemar's test was used to compare the sensitivity and specificity of each device, as well as to determine their diagnostic accuracy.

Of the participants, seven had suboptimal 12-lead ECGs and were excluded. The median age of the remaining 393 patients was 63 years, and 73 percent were men. These participants contributed a total of 1,573 ECG data for analysis. There was an excellent level of agreement between the Apple Watch (89.1 percent) and CART-I ring (91.15 percent).

Looking at all ECGs, Gala and colleagues found that CART-I ring had higher sensitivity and specificity for detecting AF when compared with Apple Watch (sensitivity: 86.6 percent, 95 percent confidence interval [CI], 80.6–91.1 vs 67.4 percent, 95 percent CI, 60.0–74.1; specificity: 89.4 percent, 95 percent CI, 84.7–92.8 vs 74.9 percent, 95 percent CI, 68.9–80.1). [Gala AB, et al, European Heart Rhythm Association 2023]

Of note, Apple Watch had 78 “unclassified” ECGs, whereas CART-I ring had only two. The “unclassified” Apple Watch ECGs were grouped into the following categories: heart rate <50 bpm (14.1 percent), heart rate >120 bpm (10.21 percent), and inconclusive (76.9 percent).

“When ‘unclassified’ ECGs from Apple Watch were excluded, AF sensitivity and specificity improved by 16.33 percent (p=0.002) and 13.38 percent (p<0.001), respectively,” Gala noted.

In light of the findings, Gala advises caution when using such wearable devices. “As the guideline states, we always should look at ECGs rather than algorithms.”