Lead I records the heart's voltage difference between which two limbs?

Lead I in an electrocardiogram (ECG) specifically measures the electrical activity of the heart by evaluating the voltage difference between the right arm and the left arm. This leads to a representation of the heart's electrical activity in the frontal plane, with the positive electrode placed on the left arm and the negative electrode on the right arm. The significance of this lead lies in its ability to provide insight into the heart's rhythm and electrical activity as it travels between these two extremities, which is critical for diagnosing various cardiac conditions.

The configuration of Lead I allows clinicians to observe the heart's orientation within the chest cavity and to identify issues such as left or right axis deviation. In contrast, the other options specify combinations of limbs that do not correspond to Lead I's established configuration for recording the heart's voltage differences. By focusing on the relationship between the right and left arms, Lead I serves as a fundamental lead for cardiac monitoring and assessment.