Certified Cardiographic Technician (CCT) Practice exam

In a standard 12-lead electrocardiogram (ECG), Lead I is specifically defined as the lead that measures the electrical potential difference between the left arm and the right arm. The left arm electrode is placed on the left arm, establishing it as a key reference point for this lead.

The configuration of Lead I provides valuable information regarding the heart’s electrical activity in the frontal plane, particularly how the heart's electrical signals progress from the right to the left side of the body. This information is crucial for diagnosing various cardiac conditions.

The other leads mentioned have different placements or configurations. For instance, Lead II connects the right arm to the left leg, Lead III connects the left arm to the left leg, and Lead aVR has its positive electrode on the right arm while referencing primarily from the other two limb leads. Therefore, among the provided options, Lead I is the one that is specifically associated with the left arm position, making it the correct answer.