ECG Lead Placement

· by · in

The electrocardiogram (ECG) is an extremely important diagnostic tool for the evaluation of electrical activity in the heart. The information helps identify functional abnormalities and to guide the decision-making process. In order to formulate an accurate idea about the health of the heart, it is critical that the provider have a comprehensive understanding of proper ECG lead placement. Failure to place electrodes at the appropriate locations can result in a non-standard result that makes it more difficult to diagnose and treat the patient.

Spatial Orientation and Einthoven’s Triangle


Electrical signals travel through the cardiac tissue along a complex network of nerves and intercellular connections. While signals pass through the heart, they can be detected by sensors that are placed on the patient’s body. Because these signals move along different spatial planes, the electrocardiogram must be capable of providing information about each plane. This is why there are standards for the number of electrodes used and proper ECG lead placement. The system used today can credit its existence to Willem Einthoven who first used the letters P, Q, R, S, and T to describe a variety of deflections recorded by a string galvonometer in the early 1900s. The three triangular limb leads that represent the spatial electrical activity in the heart were theorized by Einthoven and are now known as Einthoven’s triangle.


The ten electrodes used in most electrocardiograms today are important for capturing data about electrical activity in 3 different axial planes. The first axis runs from one shoulder to the other with the negative electrode on the right and the positive electrode on the left. The second axis runs from the right arm to the left leg with the negative electrode on the shoulder and the positive electrode on the leg. The third axis runs from the left shoulder to the left leg with the negative electrode on the shoulder and the positive electrode on the leg. Axis 1 – 3 form Einthoven’s triangle. The twelve leads in the standard electrocardiogram gather information about activity in specific spatial orientations as follows…

  • Lead I: Right Arm (-) to Left Arm (+)
  • Lead II: Right Arm (-) to Left Leg (+)
  • Lead III: Left Arm (-) to Left Leg (+)
  • aVR: Right Arm (+) to Left Arm and Left Leg (-)
  • aVL: Left Arm (+) to Right Arm and Left Leg (-)
  • aVF: Left Leg (+) to Right Arm and Left Arm (-)
  • V1, V2, V3: Posterior to Anterior
  • V4, V5, V6: Right to Left

ECG Lead Placement

The following is the standard orientation for the 10 electrodes that are used in the twelve lead electrocardiogram…

  • V1: Fourth Intercostal Space Adjacent to the Right Sternal Border
  • V2: Fourth Intercostal Space Adjacent to the Left Sternal Border
  • V3: Midway Between V2 and V4
  • V4: Fifth Intercostal Space at the Midclavicular Line
  • V5: Same Level as V4 at the Anterior Axillary Line
  • V6: Same Level as V4 and V5 at the Midaxillary Line
  • RL: Generally Somewhere Along the Right Leg Above the Ankle
  • RA: Generally Somewhere Along the Right Arm Between the Shoulder and Elbow
  • LL: Generally Somewhere Along the Left Leg Above the Ankle
  • LA: Generally Somewhere Along the Left Arm Between the Shoulder and Elbow

It is important for the leads to be placed properly to collect reliable and informative data. While different types of systems vary slightly when it comes to ECG lead placement, these variations should not have a significant impact on the exam outcome. Misplaced electrodes can cause abnormalities that mimic cardiac conditions such as a myocardial infarction and T wave inversion. The reversal of electrodes can cause unusual results and need to be considered in cases where an odd QRS complex is observed.

Artifact Interference


Odd electrocardiogram results are not always caused by improper ECG lead placement and can result from situations that create artifact interference. To reduce the chance of artifacts, patients should be encouraged to lie flat with their arms at their sides. The legs should not be crossed and all electronic devices should be set aside so that they do not interfere with the electrodes. The areas where the electrodes are to be placed needs to be shaved and cleaned. The technician should also ensure that gel has been applied and there is good skin contact.