Augmented Limb Leads of the Electrocardiogram
The electrocardiogram (ECG) utilizes a set of electrodes that are strategically placed on the limbs and chest during examination. Each resulting lead (the voltage between two electrodes) corresponds to a specific spatial direction of the heart’s electrical activity. The six limb leads, which provide the frontal plane orientation, comprise the three standard leads (I, II, III) and the augmented leads (aVL, aVR, and aVF). Together with the six precordial leads representing the horizontal plane, these leads give the healthcare provider a clear picture of electrical events that accompany various cardiovascular conditions.
When obtaining information from leads I, II, and III, three surface (skin) electrodes are used. Each of these leads uses one positive pole and one negative pole. Thus, these leads are called bipolar leads. Useful information can also be obtained by combining two of the three electrodes into one mutual negative pole. The remaining electrode is treated as the positive pole. The leads created in this way are called augmented limb leads. These augmented leads use the same electrodes used for leads I, II and III.
The augmented limb leads are named based on the placement of their respective positive poles. These leads are designated as:
- aVF - which stands for augmented Voltage Foot (left foot)
- aVL - which stands for augmented Voltage Left (left arm)
- aVR - which stands for augmented Voltage Right (right arm)
This short discussion of augmented limb leads introduces one of the core concepts of electrocardiogram interpretation. For a more detailed course on ECG reading and other related cardiovascular topics, please visit ExpertCollege.com, which contains illustrated exercises, diagrams and sample ECG tracings for self-study.