The 12-lead ECG is a vital tool for EMT’s and Paramedics in both the prehospital and hospital setting. It is extremely important to know the exact placement of each electrode on the patient. Incorrect placement can lead to a false diagnosis of infarction or negative changes on the ECG.
|V1||4th Intercostal space to the right of the sternum|
|V2||4th Intercostal space to the left of the sternum|
|V3||Midway between V2 and V4|
|V4||5th Intercostal space at the midclavicular line|
|V5||Anterior axillary line at the same level as V4|
|V6||Midaxillary line at the same level as V4 and V5|
|RL||Anywhere above the ankle and below the torso|
|RA||Anywhere between the shoulder and the elbow|
|LL||Anywhere above the ankle and below the torso|
|LA||Anywhere between the shoulder and the elbow|
The 12-lead ECG is grouped into two electrical planes. The frontal leads (Lead I-III, aVR-F) view the heart from a vertical plane, while the transverse leads (V1-V6) view the heart from a horizontal plane.
|Lead||(-) Electrode||(+) Electrode||View of Heart|
|aVR||LA + LL||RA||None|
|aVL||RA + LL||LA||Lateral|
|aVF||RA + LA||LL||Inferior|
One of the most common questions regarding a 12-lead ECG is why there are only 10 electrodes. It’s important to fully understand what the term “lead” actually means. A lead is a view of the electrical activity of the heart from a particular angle across the body. Think of a lead as a picture of the heart and the 10 electrodes give you 12 pictures. In other words, a lead is a picture that is captured by a group of electrodes.
The heart’s electrical signal is very small and unfortunately this can be combined with other signals of similar frequency to create artifact. It’s not uncommon for 12-lead ECG’s to have some form of artifact; however, it’s important to try to reduce any interference to ensure an accurate ECG. Below is a list of guidelines that will help reduce artifact when performing ECG’s.
Visit the ECG section to learn how to interpret 12-lead ECG’s and identify the different types of heart rhythms.