Which ventricle has the larger muscle mass and thus contributes a stronger depolarization vector?

Which ventricle has the larger muscle mass and thus contributes a stronger depolarization vector?

• A. Left ventricle
• B. Right ventricle
• C. Atria
• D. Interventricular septum

Answer: (A)

The main idea is that the size of a chamber’s muscle mass directly influences the strength of its depolarization vector. The left ventricle has the thickest myocardium because it must generate high pressure to pump blood into the systemic circulation. That greater mass produces a larger electrical force during depolarization, so the net vector is strongest in the direction of the left ventricle. This dominance shapes the QRS complex, with larger amplitudes in the left-sided leads and a overall axis pointing leftward and slightly downward. The right ventricle, being thinner, generates a smaller depolarization vector and thus contributes less to the net QRS vector. The atria depolarize earlier and their vectors are much smaller in magnitude compared with the ventricles, and the septum—while it does contribute to early depolarization—adds a smaller component than the whole left ventricle. So the left ventricle’s mass makes it the primary determinant of the overall depolarization vector.

The main idea is that the size of a chamber’s muscle mass directly influences the strength of its depolarization vector. The left ventricle has the thickest myocardium because it must generate high pressure to pump blood into the systemic circulation. That greater mass produces a larger electrical force during depolarization, so the net vector is strongest in the direction of the left ventricle. This dominance shapes the QRS complex, with larger amplitudes in the left-sided leads and a overall axis pointing leftward and slightly downward.

The right ventricle, being thinner, generates a smaller depolarization vector and thus contributes less to the net QRS vector. The atria depolarize earlier and their vectors are much smaller in magnitude compared with the ventricles, and the septum—while it does contribute to early depolarization—adds a smaller component than the whole left ventricle. So the left ventricle’s mass makes it the primary determinant of the overall depolarization vector.