Corpus: 12-lead ECG

A 12-lead ECG is an electrocardiogram that records 12 leads simultaneously.

The 12-lead ECG captures all 12 leads within the same time interval, making it the standard tool in cardiology due to its high diagnostic value. It consists of six limb leads and six chest leads:

• Einthoven leads (3)
• Goldberger leads (3)
• Wilson leads (6)

In a 12-lead ECG, four electrodes are placed on the limbs, and six electrodes are positioned on the chest. The limb electrodes follow the traffic light principle:

• Red – Right arm
• Yellow – Left arm
• Green – Left leg
• Black – Right leg (ground electrode)

The exact placement of the chest electrodes (V₁–V₆) is described in the article on Wilson's lead system.

In Germany, the standard paper speed for a 12-lead ECG is 50 mm/s. This allows for easy measurement of time intervals when using graph paper:

• 1 mm = 0.02 seconds
• 1 cm = 0.2 seconds

If the focus is on rhythm analysis ("rhythm strip"), the paper speed is reduced to 25 mm/s. In this case:

• 1 mm = 0.04 seconds

A 12-lead ECG should be analyzed systematically, ideally in comparison with previous ECGs. To ensure no abnormalities are overlooked, the following structured approach is recommended:

• Assessment of the heart rhythm
• Assessment of the heart rate
• Determination of the position type
• Measurement of the various time intervals (P wave, PQ duration, QRS complex, QT interval)
• Evaluation of the morphology of the waveform (analyzing all 12 leads individually)

Modern ECG machines often provide an automated interpretation, which can assist in assessment. However, these automated readings should be reviewed critically, as the final diagnosis remains the responsibility of the clinician.

Since placing chest electrodes and connecting the leads is time-consuming, alternative systems have been developed. These use vectorcardiographic techniques to derive a 12-lead ECG from only four electrodes. This method is particularly beneficial for portable ECG devices.