What is an ECG
An electrocardiogram (also called an ECG or EKG) is a test that records the timing and strength of the electrical signals that make the heart beat. By looking at an ECG, a doctor can gain insights about your heart rhythm and look for irregularities.
How to use the ECG app
The ECG app can record your heartbeat and rhythm using the electrical heart sensor on Apple Watch Series 4 and then check the recording for atrial fibrillation (AFib), a form of irregular rhythm.
The ECG app records an electrocardiogram which represents the electrical pulses that make your heart beat. The ECG app checks these pulses to get your heart rate and see if the upper and lower chambers of your heart are in rhythm. If they’re out of rhythm, that could be AFib.
Here's what you need
- The ECG app is available in the United States, Puerto Rico, Guam, and the U.S. Virgin Islands.
- You need Apple Watch Series 4 with watchOS 5.1.2, paired with iPhone 5s or later with iOS 12.1.1.
Set up the ECG app
- Make sure that the software on your iPhone and Apple Watch is up to date.
- Open the Health app on your iPhone.
- Follow the onscreen steps. If you don't see a prompt to set up, tap Health Data > Heart > Electrocardiogram (ECG).
- After you set up ECG in the Health app, the ECG app appears on your Apple Watch.
Take an ECG
You can take an ECG at any time, when you’re feeling symptoms such as a rapid or skipped heartbeat, when you have other general concerns about your heart health, or when you receive an irregular rhythm notification.
- Make sure that your Apple Watch is snug and on the wrist that you selected in the Apple Watch app. To check, open the Apple Watch app, tap the My Watch tab, then go to General > Watch Orientation.
- Open the ECG app on your Apple Watch.
- Rest your arms on a table or in your lap.
- With the hand opposite your watch, hold your finger on the Digital Crown. You don't need to press the Digital Crown during the session.
- Wait. The recording takes 30 seconds. At the end of the recording, you will receive a classification, then you can tap Add Symptoms and choose your symptoms.
- Tap Save to note any symptoms, then tap Done.
How to read results
After a successful reading, you will receive one of the following results on your ECG app. Regardless of the result, if you aren't feeling well or are experiencing any symptoms, you should talk to your doctor.
A sinus rhythm result means the heart is beating in a uniform pattern between 50 and 100 BPM. This happens when the upper and lower chambers of the heart are beating in sync. A sinus rhythm result only applies to that particular recording and doesn’t mean your heart beats with a consistent pattern all the time. It also does not mean that you're healthy. If you're not feeling well or are feeling any symptoms, you should talk to your doctor.
An AFib result means the heart is beating in an irregular pattern between 50 and 120 BPM. AFib is the most common form of serious arrhythmia, or irregular heart rhythm. If you receive an AFib classification and you have not been diagnosed with AFib, you should talk to your doctor.
Low or high heart rate
A heart rate under 50 BPM or over 120 BPM affects the ECG app’s ability to check for AFib, and the recording is considered inconclusive.
- A heart rate can be low because of certain medications or if electrical signals are not properly conducted through the heart. Training to be an elite athlete can also lead to a low heart rate. Learn more about low heart rates from the American Heart Association.
- A high heart rate could be due to exercise, stress, nervousness, alcohol, dehydration, infection, AFib, or other arrhythmia. Learn more about high heart rates from the American Heart Association.
An inconclusive result means the recording can’t be classified. This can happen for many reasons, such as not resting your arms on a table during a recording, or wearing your Apple Watch too loose. Learn how to get the best results.
If you consistently receive an inconclusive result
If you consistently receive an inconclusive result, even after trying the steps above, it could be due to one of the following situations:
- Your heart rate is between 100 and 120 BPM.
- You have a pacemaker or implantable cardioverter defibrillator (ICD).
- The recording may show signs of other arrhythmias or heart conditions that the app is not designed to recognize.
- Certain physiological conditions may prevent a small percentage of users from creating enough signal to produce a good recording.
If you need help, contact Apple Support.
View and share your Health information
The ECG waveform, its associated classifications, and any noted symptoms will be saved in the Health app on your iPhone. You can also share a PDF with your doctor.
- Open the Health app.
- Tap the Health Data tab, tap Heart > Electrocardiogram (ECG).
- Tap an ECG result, then tap Export a PDF for Your Doctor.
How to get the best results
- Rest your arms on a table or in your lap while you take a recording. Try to relax and not move too much.
- Make sure that your Apple Watch isn’t loose on your wrist. The band should be snug, and the back of your Apple Watch needs to be touching your wrist.
- Make sure that your wrist and your Apple Watch are clean and dry.
- Make sure that your Apple Watch is on the wrist that you selected in the Apple Watch app. To check, open the Apple Watch app, tap the My Watch tab, then go to General > Watch Orientation.
- Move away from any electronics that are plugged into an outlet to avoid electrical interference.
A small percentage of people may have certain physiological conditions preventing the creation of enough signal to produce a good recording — for example, the positioning of the heart in the chest can change the electrical signal levels, which could impact the ECG app’s ability to obtain a measurement.
Liquid-free contact is required for the ECG app to work properly. Use of the ECG app may be impacted if the Apple Watch and/or skin aren't entirely dry. Make sure that your wrist and hands are thoroughly dry before attempting a reading. To ensure the best reading after swimming, showering, heavy perspiration, or washing your hands, clean and dry your Apple Watch. It may take up to one hour for your Apple Watch to completely dry.
Things you should know
- The ECG app cannot detect a heart attack. If you ever experience chest pain, pressure, tightness, or what you think is a heart attack, call emergency services immediately.
- The ECG app cannot detect blood clots or a stroke.
- The ECG app cannot detect other heart-related conditions. These include high blood pressure, congestive heart failure, high cholesterol, or other forms of arrhythmia.
- If you’re not feeling well or are feeling any symptoms, talk to your doctor or seek immediate medical attention.
How the ECG app works
The ECG app on Apple Watch Series 4 generates an ECG that is similar to a single-lead (or Lead I) ECG. In a doctor’s office, a standard 12-lead ECG is usually taken. This 12-lead ECG records electrical signals from different angles in the heart to produce twelve different waveforms. The ECG app on Apple Watch measures a waveform similar to one of those twelve waveforms. A single-lead ECG is able to provide information about heart rate and heart rhythm and enables classification of AFib. However, a single-lead ECG cannot be used to identify some other conditions, like heart attacks. Single-lead ECGs are often prescribed by doctors for people to wear at home or within the hospital so that the doctor can get a better look at the underlying rate and rhythm of the heart. However, the ECG app on Apple Watch Series 4 allows you to generate an ECG similar to a single-lead ECG without a prescription from your doctor.
In studies comparing the ECG app on Apple Watch to a standard 12-lead ECG taken at the same time, there was agreement between the ECG app classification of the rhythm as sinus or AFib compared to the standard 12-lead ECG.
The ability of the ECG app to accurately classify an ECG recording into AFib and sinus rhythm was tested in a clinical trial of approximately 600 subjects, and demonstrated 99.6% specificity with respect to sinus rhythm classification and 98.3% sensitivity for AFib classification for the classifiable results.
The clinical validation results reflect use in a controlled environment. Real world use of the ECG app may result in a greater number of strips being deemed inconclusive and not classifiable.