Repeat smartwatch ECGs cut AI false alarms for low ejection fraction

Clinical takeaway: A positive smartwatch result is a reason to consider an echocardiogram, but it's not a diagnosis. One that holds across several days carries more weight than a single reading. 

Left ventricular systolic dysfunction (LVSD), meaning an ejection fraction of 40% or less, can cause no symptoms. Without treatment it can progress to symptomatic heart failure. Finding it takes an ultrasound of the heart, which leaves clinicians deciding who gets sent for one. 

Consumer smartwatches record a 30-second, single-lead ECG, which makes them a possible first screen. This study tests whether AI software interprets those tracings consistently across two watch brands and across days of recording at home. 

Requiring a positive AI result on two of three consecutive days halved false positives to 9 from 18 among the 70 recorders without LVSD, compared with acting on any single positive day. The same rule caught 31 of the 38 recorders with LVSD against 33 on single positive days, so it missed two more. Both comparisons cover the 108 recorders who logged at least five days. 

The model separated patients with and without LVSD about equally well on the Apple Watch and the Galaxy Watch. At one cutoff set in advance on separate Galaxy Watch data, 9% of the 2,211 patients were classified positive on one watch and negative on the other. 

Among the 146 home recorders, 81% of those with consistently positive results had LVSD confirmed by echocardiography, versus about 6% of those with consistently negative results. Nearly half had a mix of positive and negative results, and 40% of them had confirmed LVSD. LVSD was more common in these referred patients than in the general population, so those rates would run lower outside such a group. 

Adults were enrolled in two groups at Incheon Sejong Hospital, a single site in South Korea. The first group, 2,211 adults scheduled for an echocardiogram at an outpatient cardiology clinic, had ECGs recorded on both an Apple Watch and a Galaxy Watch during the same visit. The second group, 146 outpatients, recorded ECGs at home on their own watches, 94% of them Galaxy Watches. The first week of home recordings fed an exploratory comparison of repeat-testing rules. Echocardiography confirmed LVSD in both groups, with ECGs recorded within 14 days of the scan. 

The study did not test whether flagging patients with the model leads to earlier treatment, fewer hospitalizations or improved survival. Larger studies, the researchers say, are needed to settle how best to use a positive result. 

The findings were presented at the American Heart Association Scientific Sessions 2026 and have not yet been peer reviewed.

“Some people have reduced heart pumping function without noticeable symptoms,” said Hak Seung Lee, MD, chief medical officer of Medical AI, the company that developed the model. “Our study explored whether AI analysis of smartwatch ECGs could help identify people who may benefit from additional screening for LVSD or other heart conditions.” 

Source: Lee HS, et al. (2026 Nov 9) American Heart Association Scientific Sessions 2026. Abstract 27869. Consumer Smartwatch Artificial Intelligence-Enabled Electrocardiogram for Left Ventricular Systolic Dysfunction: Cross-Manufacturer Validation and Serial Home Monitoring