Which axis designation corresponds to the quadrant described as indeterminate axis, located in the upper left quadrant with vectors between ±180 and -90 degrees?

Which axis designation corresponds to the quadrant described as indeterminate axis, located in the upper left quadrant with vectors between ±180 and -90 degrees?

• A. Extreme Right Axis Deviation
• B. Normal Axis
• C. Left Axis Deviation
• D. Indeterminate Axis

Answer: (A)

The main idea here is how the frontal plane QRS axis is categorized by its direction. The mean QRS axis is a vector that points the overall direction of ventricular depolarization. When that resultant vector lies in the upper-left region of the frontal plane and its angle falls in the range described (from about 180 degrees to -90 degrees, i.e., far to the right side of the frontal plane in axis terms), the labeled category is extreme right axis deviation. This reflects a markedly rightward (or inferior-right) axis orientation that is not normal and not simply a mild rightward tilt. A normal axis sits in a central range, a left axis deviation tilts more to the left (negative angles beyond the normal threshold), and an indeterminate axis is used when the axis can’t be confidently assigned from the available leads. The description given matches a true extreme right axis deviation, which is why that label is the most appropriate choice.

The main idea here is how the frontal plane QRS axis is categorized by its direction. The mean QRS axis is a vector that points the overall direction of ventricular depolarization. When that resultant vector lies in the upper-left region of the frontal plane and its angle falls in the range described (from about 180 degrees to -90 degrees, i.e., far to the right side of the frontal plane in axis terms), the labeled category is extreme right axis deviation. This reflects a markedly rightward (or inferior-right) axis orientation that is not normal and not simply a mild rightward tilt.

A normal axis sits in a central range, a left axis deviation tilts more to the left (negative angles beyond the normal threshold), and an indeterminate axis is used when the axis can’t be confidently assigned from the available leads. The description given matches a true extreme right axis deviation, which is why that label is the most appropriate choice.