Frontal plane axis with Lead I negative and Lead aVF positive.

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Multiple Choice

Frontal plane axis with Lead I negative and Lead aVF positive.

Interpreting the frontal plane QRS axis relies on how the mean depolarization vector projects onto the limb leads. A positive QRS in a lead means the vector is moving toward that lead’s positive electrode; a negative QRS means it’s moving away. With Lead I negative, the axis is directed away from the left arm (toward the right side). With Lead aVF positive, the axis also points downward toward the foot. Put together, the mean axis lies in the lower-right quadrant of the frontal plane, which is right axis deviation. For context, left axis deviation would show Lead I positive and Lead aVF negative; a normal axis usually has both leads positive (within about -30 to +90 degrees); extreme (northwest) axis would have both leads negative.

Interpreting the frontal plane QRS axis relies on how the mean depolarization vector projects onto the limb leads. A positive QRS in a lead means the vector is moving toward that lead’s positive electrode; a negative QRS means it’s moving away.

With Lead I negative, the axis is directed away from the left arm (toward the right side). With Lead aVF positive, the axis also points downward toward the foot. Put together, the mean axis lies in the lower-right quadrant of the frontal plane, which is right axis deviation.

For context, left axis deviation would show Lead I positive and Lead aVF negative; a normal axis usually has both leads positive (within about -30 to +90 degrees); extreme (northwest) axis would have both leads negative.

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