Gao Y; Centre for Heart Research, University of Toronto, Canada
Moayedi Y; Foroutan F; Verma B; Kim B; Luca E; Brum M;
Brahmbhatt DH; Duhamel J; Simard A; McIntosh C; Ross HJ

Nature Medicine. 32(3):924-933, 2026 Mar.

Heart failure (HF) involves cycles of remission and exacerbation, which
are poorly characterized by static disease measures. Consumer wearables
have an understudied potential for daily monitoring of HF symptoms. Here
we report results from an observational cohort of free-living patients
over a median of 94.5 d with HF in the Ted Rogers Understanding
Exacerbations of HF (TRUE-HF) study. The study measured the ability of
Apple Watch data to predict peak oxygen uptake (pVO2) as measured using
in-clinic cardiopulmonary exercise testing (CPET). A deep learning model
was trained with data from 154 patients (46 women, 108 men) and validated
on a held-out set of 63 patients (24 women, 39 men) for determining
wearable-derived daily pVO2, which correlated strongly with CPET-measured
pVO2 (Pearson’s correlation = 0.85). Each 10% drop in wearable-derived
daily pVO2 was associated with a 3.62-fold increased hazard ratio (HR) for
unplanned healthcare events (95% confidence interval (CI), 1.37-9.55; P <
0.01), which occurred at a median of 7.4 d after the first 10% drop in
wearable-derived pVO2. These findings were externally validated in an
independent external cohort from the All of Us Research Program using a
crossplatform model that accounted for the reduced-sensor capacities
available in this external cohort. Using this reduced-sensor variant of
the model, drops in wearable-derived daily pVO2 were associated with
unplanned healthcare utilization (HR 1.32, 95% CI 1.03-1.69; P = 0.03),
which occurred at a median of 21 d after the first 10% drop in
wearable-derived pVO2. These results indicate that wearable-derived daily
pVO2 provides earlier and improved risk discrimination compared with
existing wearable fitness estimates and established clinical markers and
offers a scalable and generalizable approach for longitudinal HF research
and monitoring.