Which leads are included in a bipolar lead?

In a bipolar lead system, the leads are structured to measure the electrical activity of the heart using two different electrodes to derive the readings. The primary bipolar leads in the standard 12-lead electrocardiogram (ECG or EKG) are lead I, lead II, and lead III.

Lead I records the voltage difference between the left arm (positive electrode) and the right arm (negative electrode). Lead II measures the difference between the left leg (positive) and the right arm (negative), while lead III captures the difference between the left leg (positive) and the left arm (negative). This arrangement allows for the assessment of the heart's electrical activity from multiple angles, providing valuable insights.

The other answer options consist of different combinations of leads which are not classified as bipolar. For instance, V1, V2, and V3 are unipolar leads placed on the chest wall that measure voltage at specific locations relative to a common reference point. Similarly, the combination of II, III, and aVR includes a bipolar lead (II and III) along with a unipolar lead (aVR). The last option contains leads I, aVL, and aVF, which also mixes bipolar with unipolar leads.