What is the moderator band?

• A. A fibrous band between the aorta and pulmonary trunk
• B. A thin membrane within the left atrium
• C. The largest of the trabeculae carneae that connects the lateral wall of the right ventricle to the intraventricular septum and houses part of the right bundle branch
• D. A ligament anchored to the annulus fibrosus

Answer: (C)

The moderator band is a muscular bridge inside the right ventricle, also called the septomarginal trabecula. It is the largest trabecula carneae in that chamber and runs from the interventricular septum to the wall of the right ventricle, near the area of the anterior papillary muscle. Its important role is to contain part of the right bundle branch, a component of the heart’s conduction system, which helps rapidly transmit electrical impulses to the right ventricular myocardium and the papillary muscles. This arrangement supports synchronized contraction of the right ventricle and efficient valve function.

Other structures described in the choices aren’t features of the moderator band. The ligament between the aorta and pulmonary trunk is the ligamentum arteriosum, a remnant of fetal circulation. A thin membrane in the left atrium doesn’t describe this muscular band, and a ligament anchored to the annulus fibrosus isn’t the moderator band either.