What direction does the normal axis of an ECG indicate during heart contraction?

The normal axis of an electrocardiogram (ECG) during heart contraction refers to the overall direction of electrical activity as the heart depolarizes. During systole, which is when the heart is contracting, the normal electrical impulse travels from the sinoatrial (SA) node through the atria, leading to their contraction, and subsequently moves through the atrioventricular (AV) node into the ventricles.

The electrical axis is primarily influenced by factors such as the orientation of the heart within the thoracic cavity, the vector of depolarization, and the relative size of the ventricles. In a healthy adult, the average electrical axis ranges from -30 to +90 degrees in the frontal plane, with the most common axis being approximately -30 to +60 degrees, which is directed toward the left side of the body and slightly downward.

The option indicating "down and to the left" accurately reflects this typical direction of the normal electrical activity during ventricular contraction. It accounts for the anatomical positioning of the heart, where the ventricles have a dominant electrical vector that flows downward and leftward, especially during the depolarization of the left ventricle, which is larger and generates a more significant electrical impulse compared to the right vent