Your Smartwatch Has Flagged AF — Here is Exactly What to Do Next

The alert that is changing how we diagnose AF

Every week in my clinic I see patients who have walked in holding their phone or watch — and on the screen, an alert reading some variation of: ‘Irregular rhythm. Possible atrial fibrillation detected.’ For some, the notification came during a rest on the sofa. For others, it appeared mid-workout, or in the middle of the night.

Wearable ECG devices — the Apple Watch Series 4 and above, the Kardia Mobile by AliveCor, the Withings ScanWatch — have genuinely transformed the landscape of AF detection. Before these devices existed, countless patients lived with paroxysmal AF for years, experiencing unexplained palpitations or fatigue, before a 12-lead ECG happened to capture an episode. Today, many patients are walking through my door with months of recorded data on their wrist.

The question I am asked most often is: the watch says I have AF. What do I do now? Here is my step-by-step guide.

Step One: Do Not Panic — But Do Not Ignore It Either

An AF notification from a smartwatch or handheld ECG device is not a clinical diagnosis. It is a signal that something may need investigating. The Apple Watch’s photoplethysmography-based irregular rhythm notification algorithm has been validated in the Apple Heart Study of over 400,000 participants, with a positive predictive value of around 84% when the notification was followed by a Holter-confirmed AF episode. This means most AF notifications reflect genuine AF — but a minority are false positives, often caused by ectopic beats, artefact, or movement.

The reason you should not ignore the notification is clear: AF carries a significant stroke risk if unmanaged. Early detection and proper assessment are the interventions that prevent the serious consequences.

Step Two: Record More Tracings

If your device allows you to record a single-lead ECG — and both the Apple Watch and Kardia Mobile do — record your heart rhythm the next time you feel palpitations or notice an irregular heartbeat. Save these tracings. Both devices allow you to export a PDF trace that can be shared with a doctor. Also record some tracings when you feel entirely well — a normal baseline tracing is extremely useful for comparison.

Keep a brief symptom diary. Note when your symptoms occur, how long they last, what you were doing at the time, and whether they resolved on their own. This kind of history is invaluable in clinic.

Step Three: See Your GP

Contact your GP to discuss the alert. They should arrange a 12-lead ECG — the gold standard diagnostic test — at your earliest opportunity. If your 12-lead ECG shows AF, the diagnosis is confirmed and management can begin. If the ECG shows normal rhythm — which is common in paroxysmal AF, where episodes come and go — your GP may arrange a 24-hour or 7-day Holter monitor to attempt to capture an episode. Some GP practices are now able to review Kardia Mobile traces directly within the consultation.

Step Four: Consider a Specialist Consultation

If AF is confirmed — or if there is strong clinical suspicion based on your symptoms and device tracings — I would recommend a consultation with a cardiologist or electrophysiologist for a full assessment. This would typically involve:

• Review of all your device recordings and any ECGs performed
• An echocardiogram to assess heart structure and function
• Calculation of your CHA₂DS₂-VA stroke risk score
• Discussion of treatment options, including anticoagulation, rate or rhythm control medication, and ablation
• Assessment of modifiable risk factors — weight, blood pressure, alcohol intake, sleep apnoea

I see patients for this kind of first AF consultation at OneWelbeck Heart Health on a regular basis. In many cases, a single focused consultation is enough to put a proper management plan in place — and to give patients the clarity and reassurance they deserve.

A Note for GP Colleagues

Wearable ECG recordings — particularly those from Kardia Mobile — are clinically validated to medical-grade standards and suitable for use in clinical decision-making. The Kardia 6L device has CE marking and FDA clearance for AF detection, and its tracings are printable and file-able in the patient record. Patients presenting with smartwatch AF alerts and clear single-lead recordings showing irregularly irregular rhythm without visible P waves should in most cases be treated as if they have a probable AF diagnosis, with appropriate risk assessment and onward referral.

Concerned about an irregular heart rhythm? Book a specialist consultation — drboonlim.co.uk or call 0208 187 9888