How do we identify a lead with unipolar characteristics?

To identify a lead with unipolar characteristics, it's essential to understand the definition and function of unipolar leads in electrocardiography. Unipolar leads are characterized by measuring the electrical activity at a single electrode relative to a reference point that is created by the average electrical potential of all other electrodes, typically referred to as the Wilson central terminal.

This means that unipolar leads focus on the electrical activity at one specific site on the body (one electrode), and compare it to a central reference, providing a specific reading that reflects the voltage in that location. This contrasts with bipolar leads, which measure the potential difference between two electrodes.

The other options do not pertain specifically to the identification of unipolar leads. For example, placing electrodes on the limbs describes the method of electrode placement rather than the characteristics of the lead itself. Calculating electrical resistance of the heart relates more to impedance measurements than to the electrical activity captured in unipolar lead configurations. Lastly, measuring overall blood pressure is unrelated to ECG and does not contribute to the identification or function of unipolar leads.

Therefore, measuring voltage at one electrode relative to the average of all electrodes is the definition that accurately identifies the characteristics of unipolar leads.