A smartwatch ECG is a small medical sensor system that can record an electrical snapshot of the heart from the wrist. It matters because abnormal heart rhythms can be brief, easy to miss, and important to discuss with a clinician. By placing electrodes in the watch back and digital crown, the device can measure a voltage signal related to each heartbeat.
The result is a single-lead electrocardiogram that can help screen for irregular rhythms such as atrial fibrillation.
Key Facts
- A smartwatch ECG records a single-lead ECG, similar in idea to Lead I in a clinical ECG.
- The ECG signal is a tiny voltage difference measured between two electrodes on the body.
- Heart rate can be calculated by HR = 60 / RR, where RR is the time in seconds between two R peaks.
- Sampling frequency matters: higher sampling rates capture fast changes in the ECG waveform more accurately.
- Atrial fibrillation often shows irregular RR intervals and no consistent P waves.
- A smartwatch ECG is a screening tool, not a full diagnosis, so concerning results should be reviewed by a healthcare professional.
Vocabulary
- Electrocardiogram
- An electrocardiogram, or ECG, is a recording of the heart's electrical activity over time.
- Single-lead ECG
- A single-lead ECG measures one view of the heart's electrical signal using two main contact points.
- Electrode
- An electrode is a conductive contact that detects tiny electrical signals from the body.
- RR interval
- The RR interval is the time between two neighboring R peaks in an ECG waveform.
- Atrial fibrillation
- Atrial fibrillation is an irregular heart rhythm in which the atria beat in a disorganized pattern.
Common Mistakes to Avoid
- Calling a smartwatch ECG the same as a 12-lead ECG is wrong because it records only one electrical view of the heart, not twelve views from different directions.
- Assuming a normal smartwatch ECG proves the heart is healthy is wrong because some heart problems are intermittent or not visible in a single short recording.
- Moving the wrist or finger during recording is a mistake because motion can create electrical noise that distorts the ECG trace.
- Interpreting every irregular beat as atrial fibrillation is wrong because skipped beats, poor contact, and normal rhythm variation can also change the spacing between peaks.
Practice Questions
- 1 A smartwatch ECG shows 15 R peaks in a 10 second recording. What is the average heart rate in beats per minute?
- 2 Two neighboring R peaks are 0.80 s apart. Use HR = 60 / RR to calculate the heart rate.
- 3 A user gets an irregular rhythm alert after recording while walking and moving the watch hand. Explain why repeating the ECG while seated and still could give a more reliable result.