Which EKG leads are most closely associated with axis deviation?

• A. Leads II and aVL
• B. Leads aVF and I
• C. Leads III and aVR
• D. Leads V1 and V6

Answer: (B)

Axis deviation is determined by the direction of the QRS complex in the frontal-plane limb leads. The two limb leads that most directly reflect the overall frontal-plane axis are lead I and lead aVF, because they point in roughly 0 and +90 degrees, respectively. By looking at the QRS polarity in these two leads, you can tell which direction the axis is shifted: a QRS positive in I and negative in aVF suggests left axis deviation, while negative in I and positive in aVF suggests right axis deviation. Chest leads V1 and V6 view the horizontal plane and aren’t the primary tools for judging axis deviation, so they’re less informative for this purpose.