Einthoven’s Triangle Unlocks 12-Lead ECG Interpretation

How well do you know leads I, II & III?



Robert Girardeau, BS, NREMT-P | | Tuesday, March 13, 2012

Besides coining the actual term “electrocardiogram” and in turn “ECG,” Willem Einthoven also established the general principal of ECG as we know it. The foundation of 12-lead ECG analysis is grounded in the basic understanding of Einthoven’s Triangle.

The triangle is composed of the leads I, II, and III forming the shape. Leads aVL, aVR and aVF perpendicularly intersect each side to the triangle. Together, these six leads can paint a large picture of the patient’s overall cardiac health. Using these leads to assess axis and aid in rhythm determination will greatly influence and strengthen your ability to provide thorough and factually based patient care. However, we will focus on leads I, II, and III, which are also known as the limb leads.

These limb leads are bipolar, meaning they have a positive pole and a negative pole. Lead I extends horizontally from the right arm to the left arm, with the actual left arm electrode being the positive pole. Lead II forms one of the vertical arms of the triangle and stretches from the right hand to the left leg with the electrode positioned on the left leg being the positive pole. Finally, lead III forms the other vertical arm and extends from the left arm to the left leg. Take caution here with this lead as this left arm electrode plays double duty and is now positive for the purposes of lead III.

These leads, in conjunction with the augmented limb leads (aVL, aVR and aVF), will provide you with a fairly detailed three-dimensional picture of the heart’s electrical wiring. Lead I shows left side of the heart, while leads II and III generally focus on the bottom and parts of the right side of the heart.
Practicing and understanding the role and views of each of these leads will strengthen your ability to form a three-dimensional picture of the heart. Additionally, this tool will certainly aid you in grasping more complicated aspects of electrocardiography with much more ease.


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Related Topics: Training, 12-lead ECG


Robert Girardeau, BS, NREMT-PRobert Girardeau, BS, NREMT-P, is a ranked member of the faculty and the clinical coordinator for the Good Fellowship Training Institute in West Chester, Pa. He’s also a paramedic in the Greater Delaware Valley and the Harrisburg metropolitan area. Contact him at rgirardeau@goodfellowship.com.


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