What physiological structure does the left bundle branch depolarize during an EKG?

The left bundle branch plays a crucial role in the electrical conduction system of the heart, specifically during the depolarization phase depicted on an electrocardiogram (EKG or ECG). The left bundle branch is responsible for transmitting electrical impulses that result in the contraction of the left ventricle by depolarizing the left side of the heart.

When the left bundle branch depolarizes, it primarily stimulates the muscles of the left ventricle and also plays a key role in depolarizing the intraventricular septum—the wall that divides the left and right ventricles. This is vital for a synchronized contraction of the ventricles, allowing for effective pumping of blood into the systemic circulation through the aorta.

In contrast, the other structures listed do not receive direct depolarization from the left bundle branch. The atria are primarily depolarized by the electrical impulses originating from the sinoatrial (SA) node and transmitted through the atrioventricular (AV) node. The pulmonary artery and the aortic valve do not play a role in the electrical conduction of the heart but are involved in the circulatory flow of blood. Thus, the left bundle branch's function directly relates to depolarizing the intraventricular sept