Understanding the Apple Watch electrocardiogram app

It may classify a recording as a sinus rhythm, possible atrial fibrillation, a high or low heart rate, or inconclusive. Those labels are screening information rather than a complete interpretation of the heart.

A watch tracing observes the electrical signal through contact with the wrist and a finger. A clinical electrocardiogram uses electrodes placed at several body locations, giving clinicians more views and detail.

The app cannot rule out a heart attack, angina, heart failure, a blood clot or every abnormal rhythm. Movement, poor skin contact, electrical interference and an unsuitable recording position can cause noise or an inconclusive label. Some irregular rhythms also come and go between recordings.

Rest the supported arm on a table or your lap, keep still, ensure the watch sits snugly, and follow the app instructions. Save the tracing with notes about symptoms, activity, caffeine, illness and medicine timing.

Repeated unusual or inconclusive recordings warrant a clinical discussion, particularly with palpitations, dizziness or reduced exercise tolerance. A clinician may review the trace, examine you and arrange a standard ECG or longer rhythm monitoring. Do not start, stop or change heart medicine based only on the app classification.

Call emergency services for chest pressure or pain, severe breathlessness, collapse, new confusion, or symptoms suggesting a stroke such as facial drooping, arm weakness or speech difficulty. Seek help on the basis of the symptom, even if the app says sinus rhythm or cannot classify the recording.

Prompt medical advice is appropriate for new recurring palpitations, fainting or near-fainting, or an unusual rhythm alert accompanied by weakness or breathlessness. Avoid driving yourself if you feel faint or seriously unwell.

Bring saved recordings and a symptom diary. Ask whether the pattern could be atrial fibrillation or another rhythm, whether a clinical ECG or longer monitor is needed, and which symptoms should trigger emergency care. Include all medicines and supplements when discussing possible rhythm triggers.