What does lead III represent in an EKG?

What does lead III represent in an EKG?

• A. The potential difference between the left arm and left foot
• B. The potential difference between the right arm and left foot
• C. The potential difference between the left arm and right arm
• D. The potential difference between the right arm and left leg

Answer: (A)

Lead III in an electrocardiogram (EKG) measures the electrical potential difference between the left arm and the left foot (or left leg). This lead is part of the standard 12-lead EKG system and specifically assesses the activity of the heart in the inferior leads.

In an EKG, leads are characterized by their viewpoint of the heart's electrical activity. Lead III provides information from the perspective of the left arm to the left foot, helping to establish the heart's axis and revealing how electrical signals propagate through the cardiac tissues. This is essential for diagnosing various heart conditions related to rhythm and conductivity.

Understanding the specific potentials that each lead measures aids in accurately interpreting the heart's electrical dynamics and identifying abnormalities. Hence, this understanding reinforces why the choice stating that lead III represents the potential difference between the left arm and the left foot is the correct identification of lead III’s role in EKG analysis.