Which lead is placed on the left arm in a 12 lead EKG?

Which lead is placed on the left arm in a 12 lead EKG?

• A. aVR
• B. aVL
• C. aVF
• D. II

Answer: (B)

In a 12-lead EKG, the lead positioned on the left arm is aVL. This lead is specifically defined as an augmented unipolar limb lead that measures the electrical activity of the heart from the left arm's perspective. The aVL lead provides information about the heart's electrical activity in the lateral aspect, focusing particularly on the region supplied by the left circumflex artery.

To understand why aVL is the correct answer, it is essential to recognize that the 12-lead EKG includes three standard limb leads (I, II, III), three augmented leads (aVR, aVL, aVF), and six precordial leads (V1-V6). The left arm is specifically used for aVL as it references the electrical potential from the left arm to the center of the heart, allowing for a unique perspective on the heart's activity.

The other leads, such as aVR and aVF, have different reference points and do not correspond to the left arm. For instance, aVR measures from the right arm and focuses on the right side of the heart, while aVF looks at the heart from the foot's perspective. Understanding these distinctions aids in interpreting the EKG and the information provided by each lead.