This Instructable shows you how to extend the ECG feature of Apple Watch® series 4 from the basic Lead I recording to simulate a full 12 lead ECG. The ECG is “simulated” because of course the readings cannot be taken simultaneously, so it's therefore of limited diagnostic value.
For entertainment purposes only. For adults only. This procedure is not intended to diagnose any medical condition. Any recordings made by following this procedure should not be interpreted as demonstrating or disproving the existence of any cardiac abnormality or heart disease. If you have any health concerns, consult a qualified medical professional. This document and procedure are not endorsed by Apple Inc.
Apple Watch® series 4
About 3 metres of insulated copper cable (any gauge will do)
Some Velcro® strap or similar to secure the stripped cable to limbs
Useful but not essential: a partner to assist you with the later readings
Step 1: Prepare Your Cable and Straps
- Strip 3-5cm of insulation from each end of your cable.
- About one third of the way along the cable, carefully remove another 3-5cm of insulation. Be careful not to cut the cable.
- Make three straps to hold the cable to your limbs by cutting lengths of Velcro® tape. Make one long enough to go round your ankle.
Be aware that standard electrostatic discharge (ESD) wrist straps used for handling static-sensitive devices are not suitable, because they are fitted with an inline 1MΩ safety resistor. For this to work, we need a direct, low resistance electrical connection between limbs.
Step 2: If Your Watch Has a Passcode, Disable It
If your watch has a passcode enabled, you will find it much easier to make the recordings if you disable it before proceeding. To do this:
- Open the Watch app on your phone
- Tap My Watch at the bottom left
- Scroll down to Passcode
- Choose Turn Passcode Off (you may need to unlock your watch first)
If the option to turn the passcode off is greyed out, it’s probably because your phone (and therefore the watch) is managed via an installed corporate profile policy or similar. You may need to contact the device administrator before proceeding.
Be aware that any cards attached to Apple Pay on your watch will need to be re-added when passcode lock is restored.
For some recordings you will need to attach the watch to your left ankle.
If your strap permits, that is the best way to ensure good contact. If your strap is a loop type, you may have to remove one end from the watch to wrap the strap round your ankle. If you cannot secure the watch with your existing strap, your partner may have to hold it in place for you. For best results, choose a fleshy area of your ankle to position the watch. Just as with the standard watch ECG (Lead I), try to maintain a relaxed posture throughout the readings. Any accidental muscle activity may cause the graphs to drift vertically, making them harder to visualise.
Step 3: If Necessary, Set Your Watch to the Default Wearing Arrangement
These instructions are written for the most common wearing arrangement of the watch: left wrist, digital crown on the right. If your arrangement is different, please temporarily change your “Watch Orientation” settings to match the picture above, which you can find under “General” in the Watch app. (Sorry, left-handers!)
If you don't do this, some ECG recordings may be the wrong way up.
Step 4: Let's Take the First Reading: Lead I
This is the normal Lead I reading.
- Place the watch on your left wrist.
- Perform a normal ECG recording using the watch ECG app. The result will be sent to the Health app on your phone as normal.
Step 5: Next, Let's Take a Lead "aVL" Recording
- Using your prepared cable and straps, connect bare sections of cable between your right wrist and left ankle.
- Make an ECG recording by touching the crown with your right index finger. The trace will automatically upload to your phone.
Step 6: Next, It's Lead II
For the next three recordings, you'll need to attach the watch to your left ankle.
If your strap permits, this is the best way to ensure good contact. If your strap is a loop type, you may have to remove one end from the watch to wrap the strap round your ankle before reattaching.
If you cannot secure the watch with your strap, your partner may have to hold it in place for you. For best results, choose a fleshy area of your ankle to position the watch.
Just as with the standard watch ECG (Lead I), try to maintain a relaxed posture throughout the readings. Any significant muscle activity may cause the graphs to drift vertically, making them harder to visualise.
- Remove the cable connecting your right wrist and left ankle.
- Strap the watch to your left ankle and perform a normal ECG recording with your right index finger touching the crown. The trace will automatically upload to your phone.
Step 7: Now Lead III
With the watch still on your left ankle, follow the same procedure as Lead II but using your left index finger instead.
Step 8: Next, Lead "aVF"
- Leave the watch on your left ankle. Using your prepared cable and Velcro® straps, connect bare sections of cable between your left wrist and right wrist.
- Make an ECG recording by touching the crown with either index finger.
Step 9: Now the Sixth Lead: "aVR"
- Remove the wire attached to your wrists.
- Move the watch to your right wrist.
- Using your prepared cable and straps, connect bare sections of cable between your left wrist and left ankle.
- Make an ECG recording by touching the crown with your left index finger.
Step 10: The Final Six Readings: the Chest Leads
For the final six readings you will need to remove the strap from your watch. Although it's possible to do the final six readings on your own, it will be easier if you have a partner to hold the watch in the correct positions for you.
For every remaining reading, use the bare sections of your prepared cable to connect left wrist, right wrist and left ankle.
Study the diagram above and practise locating the correct positions for the watch. To help you to feel for the correct locations, follow this procedure:
- Place your left index finger on the top of your sternum just below the clavicles [A].
- Slide your finger down about an inch. You will feel a bony bump. This is the sternal angle [B]. (The "bump" is more prominent in men than in women.)
- Slide right and drop into a space between your ribs. This is the 2nd intercostal space [C].
- Move downwards between each rib to reach the 4th intercostal space [D].
V1: 4th intercostal space, right sternal margin
V2: 4th intercostal space, left sternal margin
V4: 5th intercostal space, left midclavicular line.
V3: Midway between V2 and V4
V5: Anterior axillary line (forward crease of armpit) level with V4
V6: Mid axillary line (mid point of armpit) level with V4
Step 11: Let's Begin With Lead V1
Reminder: for every remaining reading, use the bare sections of your prepared cable to connect left wrist, right wrist and left ankle.
Be careful to avoid any direct skin contact between you and your partner’s bodies (at least until you've finished!).
- Press (or ask your partner to press) the watch at the V1 location.
- Make an ECG recording by touching the crown with either index finger.
Step 12: Now for the Remaining Five Readings
For leads V2 to V6, repeat the procedure for lead V1 using the chest lead positions as shown in the diagram.
Step 13: Putting It All Together
You should now have 12 ECG traces saved on your phone.
- On your phone, open the Health app, go to the Heart section and locate the ECG traces. They will be listed in reverse chronological order. (Except for Lead I, disregard any diagnostic report given by the software.)
- For each trace, tap it and then tap "Export a PDF for your doctor". (Of course, we're not really sending them to a doctor.)
- Using your preferred method (Airdrop, email and so on), get them all on to a device running your preferred page layout program. Just about anything will do.
- After you've transferred all 12 files, list them in chronological order and rename them accordingly. The lead order for the first six leads was I, aVL, II, III, aVF, aVR. For the chest lead traces, rename them V1-V6, assuming you did them in numerical order.
You'll probably notice that some of the chest lead traces are cropped at the bottom edge. This is due to the watch software being designed for a Lead I ECG, which is always a predominantly positive deflection. To maximise readability for Lead I, the baseline is therefore shifted downwards on all the other graphs, which crops some of them. Although annoying, it's not a big deal.
Step 14: Formatting and Displaying Your Recordings
- In your chosen graphics layout program, create a blank landscape format document.
- For each of your twelve saved pdf files, crop them to show three adjacent consistent waveforms. Ensure the 1cm reference (at the beginning of each trace) is the same size for each cropped section and resize if necessary.
- Arrange them as shown in the example above.
And there you have it! A 12-lead ECG simulation using your Apple® Watch series 4.
This whole procedure was devised and developed by my brother and ECG guru Mike. I supplied the watch (and the ankle).