Right axis deviation is defined as QRS axis between +100° and +180°. It is seen with which conditions?

• A. Conduction abnormalities
• B. Left anterior fascicular block
• C. RVH, significant pulmonary disease, or conduction abnormalities
• D. Normal axis variation

Answer: (C)

Right axis deviation means the overall direction of ventricular depolarization is shifted toward the right, with a QRS axis in the +100° to +180° range. This happens when the right side of the heart becomes the dominant ventricle or when the activation vector is redirected to the right.

In practice, conditions that push the depolarization vector to the right include right ventricular hypertrophy, which enlarges the right ventricle and pulls the mean vector rightward; and significant pulmonary disease (such as COPD or pulmonary hypertension) that causes chronic right ventricular strain or hypertrophy. Both scenarios increase rightward forces on depolarization, yielding right axis deviation.

Conduction abnormalities can also alter the activation pattern in ways that favor a rightward axis, further contributing to RAD.

Left anterior fascicular block tends to shift the axis to the left, not the right, so it doesn’t fit right axis deviation. Normal axis variation stays within the typical range and does not reach +100° to +180°.