A standard ECG consists of 12 leads on paper. The leads are created by the ECG device from 10 electrodes that are attached to the chest and limbs of the patient.
Each ECG lead requires two electrodes to display the ECG waveform. Lead I on a standard ECG has a positive electrode on the left wrist and a negative electrode on the right wrist, just like ECG watches.
ECG watches can typically capture lead I, which exactly matches lead I on a standard 12-lead ECG.
ECG Interpretation by Doctor Online
With ECG watches, you can sequentially capture the 12-lead ECG, which almost exactly matches the standard 12-lead ECG.
What you need
To capture the 12 leads using the watches, you need:
- ECG watches, I used the Apple Watch Series 9
- A 2-meter copper cable
- The patient must not have hairy chest or limbs because we will be applying the back part of the watches to the chest and limbs.
Limb Leads (I, II, III)
Limb leads (I, II, III) captured using the watches exactly match the standard 12-lead ECG.
Lead I
- The watches are typically worn on the left wrist. The back part of the watches touches the left wrist.
- We place the finger of the right hand on the crown of the watches and capture the ECG.
Lead II
- We place the back part of the watches on the left ankle.
- We place the finger of the right hand on the crown of the watches and capture the ECG.
Lead III
- We place the back part of the watches on the left ankle.
- We place the finger of the left hand on the crown of the watches and capture the ECG.
Chest Leads (V1, V2, V3, V4, V5, V6)
ECG watches, when capturing chest leads, cannot create the Wilson Central Terminal (WCT). The negative electrode is not located in the center of the heart as WCT but rather on the right side of the heart. This is because we place the finger of the right hand on the crown of the watches.
Therefore, chest leads from the watches may not exactly match the standard 12-lead ECG.
Chest leads from the watches are labeled as CR or CL. The back part of the watches is always applied to the chest exactly like standard chest ECG electrodes. The difference is which hand (specifically, which finger) you place on the crown of the watches.
- CR (Chest Right) - The back part of the watches is applied to the chest (Chest). The finger of the right hand (Right) is placed on the crown.
- CL (Chest Left) - The back part of the watches is applied to the chest (Chest). The finger of the left hand (Left) is placed on the crown.
CR leads are more accurate than CL leads.
V1 (CR1)
- We place the back part of the watches at the 4th intercostal space to the right of the sternum.
- We place the finger of the right hand on the crown of the watches and capture the ECG.
V2 (CR2)
- We place the back part of the watches at the 4th intercostal space to the left of the sternum.
- We place the finger of the right hand on the crown of the watches and capture the ECG.
V3 (CR3)
- We place the back part of the watches between V2 and V4.
- We place the finger of the right hand on the crown of the watches and capture the ECG.
V4 (CR4)
- We place the back part of the watches at the 5th intercostal space in the midclavicular line.
- We place the finger of the right hand on the crown of the watches and capture the ECG.
V5 (CR5)
- We place the back part of the watches at the 5th intercostal space in the anterior axillary line.
- We place the finger of the right hand on the crown of the watches and capture the ECG.
V6 (CR6)
- We place the back part of the watches at the 5th intercostal space in the midaxillary line.
- We place the finger of the right hand on the crown of the watches and capture the ECG.
Limb Leads (aVL, aVR, aVF)
These limb leads require a negative electrode, which is created by connecting two limbs. Therefore, we need a 2-meter copper cable.
We need to strip the copper cable at 3 places with a knife:
- We strip both ends of the cable. Each stripped section should be about 20cm long. We will wrap these stripped ends around the wrist and ankle.
- Then we strip the cable approximately in the middle. The stripped section should be about 2cm long. We will apply this stripped section to the crown of the watches.
Lead aVL
- We typically wear the watches on the left wrist. The back part of the watches touches the left wrist.
- We wrap one stripped end of the cable around the left ankle, and the other end around the right wrist.
- We hold the cable with the right hand by the stripped section and apply the 2cm stripped section to the crown of the watches and capture the ECG
Lead aVF
- We place the back part of the watches on the left ankle.
- We wrap one stripped end of the cable around the left wrist and the other end around the right wrist.
- We hold the cable with the right hand by the stripped section and apply the 2cm stripped section to the crown of the watches and capture the ECG
Lead aVR
- We wear the watches on the right wrist. The back part of the watches touches the right wrist.
- We wrap one stripped end of the cable around the left wrist and the other end around the left ankle.
- We hold the cable with the left hand by the stripped section and apply the 2cm stripped section to the crown of the watches and capture the ECG
12-Lead ECG from Apple Watches vs. Standard ECG
The watches capture 30 seconds of heart electrical activity, but they have only one lead, specifically lead I. When capturing a 12-lead ECG using the watches, each lead looks at a different 30 seconds of cardiac activity because we capture the leads sequentially.
A standard 12-lead ECG captures 4 seconds of heart electrical activity, but it captures all leads simultaneously. Each lead on the ECG paper looks at the same cardiac activity from a different angle.
Conclusion
ECG watches can typically capture lead I.
However, using the watches, all 12 ECG leads can be captured. The limb leads (aVL, aVF, aVR) are the most challenging to capture because you need a cable to connect two limbs and create a negative electrode.
The obtained leads from the watches expand the diagnostic utility in cardiology. Thus, the watches can partially replace the standard 12-lead ECG.
The watches can diagnose and localize conditions such as myocardial infarction, Brugada syndrome, accessory pathway, arrhythmogenic right ventricular dysplasia, left ventricular hypertrophy.
