Which electrodes are considered bipolar?

Bipolar electrodes are those that measure the electrical potential difference between two points, typically positioned on opposite sides of the heart. The electrodes that are traditionally categorized as bipolar in a 12-lead ECG system refer to the standard limb leads: Lead I, Lead II, and Lead III, which are represented by the first three choices.

Lead I is the difference between electrodes on the left and right arms, Lead II is between the left leg and the right arm, and Lead III is between the left leg and the left arm. These configurations capture the heart's electrical activity from various angles and allow for a comprehensive view of its function.

In contrast, the other options feature electrodes that do not fit into the bipolar classification. The augmented vectors (aVR, aVF, and aVL) are unipolar leads that measure the electrical potential at one point compared to a reference point. Likewise, the chest leads V1, V2, and V3 are unipolar leads, focusing on the heart's electrical activity in the horizontal plane.

Thus, understanding why Lead I, II, and III are classified as bipolar is essential for properly interpreting ECG readings and recognizing the heart's electrical dynamics.