Which leads are placed in the fourth column of the standard layout?

• A. V4, V5, V6
• B. I, II, and III
• C. aVR, aVL, aVF
• D. V1, V2, V3

Answer: (A)

In the standard four-column ECG layout, leads are grouped by region: the first column holds the standard limb leads I, II, and III; the second column contains the augmented limb leads aVR, aVL, and aVF; the third column carries the precordial leads V1, V2, and V3; the fourth column contains the remaining precordial leads V4, V5, and V6. V4, V5, and V6 are the left chest leads placed from the midline to the left side (V4 at the midclavicular line, V5 at the anterior axillary line, V6 at the midaxillary line), which is why they form the fourth column in this layout.