Left axis deviation is defined as QRS axis between -30° and -90°. It is often seen with which conditions?

Left axis deviation is defined as QRS axis between -30° and -90°. It is often seen with which conditions?

• A. RVH
• B. LVH
• C. Left bundle branch block
• D. Normal axis variation

Answer: (B)

Left axis deviation occurs when the overall direction of ventricular depolarization shifts more toward the left, so the QRS axis falls between -30° and -90°. The left-sided heart muscle becomes the dominant generator of the depolarization vector, so the mean electrical axis moves leftward. The classic situation producing this shift is left ventricular hypertrophy, where increased left ventricular mass strengthens the leftward depolarization forces and pulls the axis toward the left. That’s why LVH is the best-known condition associated with left axis deviation. In contrast, right axis deviation (seen with right ventricular hypertrophy or conditions that stress the right heart) pushes the axis toward the right. Left bundle branch block can alter the QRS morphology and may affect axis, but it’s not the defining association for LAD, and normal axis variation is, by definition, not leftward.

Left axis deviation occurs when the overall direction of ventricular depolarization shifts more toward the left, so the QRS axis falls between -30° and -90°. The left-sided heart muscle becomes the dominant generator of the depolarization vector, so the mean electrical axis moves leftward. The classic situation producing this shift is left ventricular hypertrophy, where increased left ventricular mass strengthens the leftward depolarization forces and pulls the axis toward the left. That’s why LVH is the best-known condition associated with left axis deviation.

In contrast, right axis deviation (seen with right ventricular hypertrophy or conditions that stress the right heart) pushes the axis toward the right. Left bundle branch block can alter the QRS morphology and may affect axis, but it’s not the defining association for LAD, and normal axis variation is, by definition, not leftward.