Final answer:
In a posterior 12-lead EKG, lead V9 should be placed along the paraspinous border to capture the heart's posterior electrical activity.
Step-by-step explanation:
The EKG technician performing a posterior 12-lead EKG should place lead V9 along the paraspinous border. In a standard 12-lead electrocardiogram (ECG or EKG), ten electrodes are used to measure the electrical activity of the heart from different angles, providing a comprehensive view of the heart's function. When performing a posterior ECG, which is often done to assess for possible posterior myocardial infarction, additional leads V7 to V9 are placed on the back of the chest. Specifically, lead V9 is positioned to the left of the spine, in line with lead V6, which is necessary for capturing the electrical activity emerging from the posterior aspect of the heart.