Digital biomarkers for heart failure
Decompensation develops over days before it becomes an emergency. That window is exactly what a scheduled appointment is likely to miss.
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Heart failure is a condition of episodes. People are relatively stable for periods and then decompensate, and decompensation typically develops over days before it becomes an emergency. That timeline is what makes continuous measurement attractive here: the window in which deterioration is detectable but not yet critical is exactly the window a scheduled appointment is likely to miss.
The digital measures used in heart failure fall into two groups. Physiological measures track the state of the circulation, including resting and nocturnal heart rate, rhythm, and the vascular and fluid related signals that indicate congestion. Functional measures track what the person can and does do: daily activity, walking speed, time spent sedentary and time spent upright.
Functional measures matter more than they might appear to. Exercise intolerance is the defining symptom of heart failure, and daily activity is its continuous expression. A fall in activity that precedes hospitalisation is a meaningful signal, and because it is behavioural rather than symptomatic it can appear before a person recognises that anything is wrong.
Digital biomarkers used in heart failure research
How these measures are used
Remote monitoring for early detection of decompensation is the dominant application, and it is one of the more commercially developed uses of digital measurement in cardiology. The clinical goal is to intervene during the days when a medication adjustment can prevent an admission.
In trials, activity measures are used as functional endpoints alongside conventional exercise testing. A treatment that improves a supervised six minute walk distance but does not change how much a person moves at home has produced an ambiguous result, and reporting both makes that visible rather than leaving it unexamined.
These measures are typically paired with a disease specific quality of life questionnaire, since symptom burden and functional capacity are related but distinct, and treatment decisions in heart failure weigh both. Nocturnal heart rate is a common addition because it is measured under relatively standardised conditions, with the person at rest, which removes much of the day to day noise that confounds daytime readings.
What the evidence supports today
The evidence base here divides between well established physiological measures and less established functional ones. Resting and nocturnal heart rate are dependable measurements with clear prognostic associations in heart failure. Rhythm monitoring is mature. Implantable haemodynamic monitoring has trial evidence for reducing hospitalisation, though that sits outside the wearable scope of this library.
Wearable activity measures have consistent observational evidence linking reduced daily activity to worse outcomes, and increasing use as trial endpoints. What they largely lack is an established minimal important difference in this population, which limits their interpretation as standalone endpoints rather than as supporting measures.
The practical limitation in heart failure is that many patients are older, may have limited device tolerance, and often have comorbidities that independently reduce activity. Attributing a change in daily walking to cardiac status rather than to arthritis, fatigue or a change in living circumstances requires care, and studies that do not collect that context will misread their own data.
Common questions
Can wearables predict heart failure decompensation?
Research consistently shows that physiological and activity changes appear in the days before decompensation, and remote monitoring programmes are built on that observation. Prediction at the level of an individual is harder than the group level pattern suggests, and false alarms are a genuine burden on both patients and services.
Why is nocturnal heart rate used rather than daytime heart rate?
Because it is measured under more standardised conditions. During sleep the person is at rest, not exerting, not caffeinated and not stressed by an appointment, so night to night comparison is cleaner. Daytime heart rate carries the same physiological signal plus a large amount of behavioural noise.
Do activity measures add anything beyond a six minute walk test?
Yes, and the two can disagree. The walk test measures capacity under supervision and encouragement. Daily activity measures what the person does across ordinary days, when motivation, breathlessness and fatigue all intervene. A treatment that changes one without the other has produced a result worth understanding rather than glossing over.
What confounds activity measurement in this population?
A great deal. Heart failure patients are often older and frequently have musculoskeletal, respiratory or cognitive comorbidities that limit walking independently of cardiac status. Weather, living situation and availability of support also shape daily activity. Studies need to record that context or they will attribute ordinary life variation to disease progression.
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