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)

Understanding how the frontal-plane QRS axis is labeled helps. The axis designation comes from the net direction of ventricular depolarization; when the resultant vector points toward the right side of the frontal plane and is very large, we call it extreme right axis deviation. In this case the vectors lie in the range from 180° to -90°, which effectively places the overall axis on the rightward half of the plane despite appearing in the upper-left quadrant on a basic diagram. The wrap-around across ±180° makes the dominant direction a strong rightward tilt, hence the designation of extreme right axis deviation. A normal axis would lie roughly between -30° and +90°, which this is not. Left axis deviation would place the net axis to the left (roughly -30° to -90°). Indeterminate axis is used when lead data do not point to a single, definite axis; here the data point to a consistent extreme right direction, so that label fits best.