How to do a 12-Lead ECG?

DEC 12 ,2022


Since the American Heart Association’s recommendation to obtain prehospital 12-lead electrocardiograms on patients with acute coronary syndrome, EMS providers have played an increasingly important role in identifying these patients, beginning the appropriate treatment, and transporting them to appropriate hospitals capable of emergency angioplasty.

The acquisition of the 12-lead ECG in the field is theoretically not different from those obtained inside the emergency department. However, due to the unique prehospital environment, there are several tips and pearls to consider when placing the patient electrodes.

1. Conditions Requiring an ECG

A 12-lead isn’t just for chest pain. Obtain a 12-lead for possible strokes, altered levels of consciousness, weakness, dizziness, fatigue, palpitations and otherwise vague medical complaints. Remember that diabetic patient, younger women and various ethnicities often have atypical presentations and may have “silent myocardial infarctions.” Be vigilant. You may just save a life.

2. Proper acquisition of the 12-lead ECG

Proper acquisition of the 12-lead ECG is paramount to getting the most out of this tool. An improperly acquired 12-lead doesn’t provide diagnostic-quality information and can render the tracing mostly useless. Here are a few tips to making sure you get it done right:

3. Skin Preparation

It’s important to prepare the skin by cleaning it with an alcohol prep and by abrading it with a cloth towel to remove dead skin cells. You may need to wash the area with saline and dry it. Remove excess body hair by shaving. For females, place the leads under the breast tissue. You may need to lift and clean the skin underneath the breast to get a clear tracing.

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4. Lead Placement

Traditionally, the limb leads go on the limbs, and while it’s acceptable to move them closer if you have to, try to avoid placing the leads over bony prominences or overly fatty areas. Look for a generally flat, clean, intact area of skin with muscle generally underneath.

  • The V-Leads go on the chest in a specific pattern. Leads V1 and V2 go in the 4th intercostal spaces (between the ribs) on either side of the sternum. To find these, go about three finger widths up from the xyphoid process, or bottom of the sternum. V1 is on the patient’s right, V2 is on the left.
  • V4 should be placed next; it goes one rib down in the 5th intercostal space, on the midclavicular line. Place V3 in between V2 and V4.
  • V5 goes in the anterior axillary line (front of the armpit) and V6 goes in the mid-axillary line. They go in the same horizontal line as V4.


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5. Electrode Placement for Women

Asking a female patient to disrobe can be uncomfortable for the EMS provider, at first. Be professional. Explain to the patient what you plan to do in terms of electrode placement; emphasize that several of the chest leads may need to be placed around and under the left breast.

Have a patient gown available for the patient to use after removing her clothing.
If the patient’s left breast is large enough to cover the V3, V4, or V5 placement area, it will have to be lifted up for proper electrode placement. If possible, you can ask the patient to lift her own breast. Alternatively, use the back of your straightened hand to displace the breast.

6. Electrode Placement for Bariatric Patients

Obese patients may appear to be more difficult at first to accurately place electrodes. The trick is to spend a few extra moments locating the anatomic landmarks. Palpate more deeply to feel the sternal border and Angle of Louie to place leads V1 and V2. V4 is usually located in a straight line below the nipple at the fifth intercostal space. Then, imagine a line track straight down the left lateral side of the chest. Along this line, at the mid-axillary line is the location of lead V6.

Once these leads are placed, then V3 is placed halfway between V2 and V4. Finally, V5 is placed halfway between V4 and V6.

7. Electrode Placement for Pregnant Patients

Despite the appearance of the abdomen during advanced pregnancy, the placement of the electrodes is the same. You can use the technique above if necessary.

Note that left-axis deviation on the ECG may appear in both pregnant and obese patients. This is due to the abnormal position of the heart as the diaphragm pushes high into the thoracic cavity.


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8. Electrode Placement for Pediatric Patients

Use smaller electrodes specific to children. Adult electrodes will overlap and potentially cause inaccurate placement. For preschool-age children and older, take time to explain what you are doing. Young children will be fearful of the procedure and may imagine that it will hurt, or that you will shock them. Having a parent close by will help provide reassurance.

9. Obtaining 12-Lead ECG in Extreme Environments

Extreme heat or cold will affect the integrity of the electrode’s conducting gel. During the cold winter or hot summer months, check to make sure that the electrode bag is kept in a location that minimizes dramatic temperature shifts.

10. Acquisition Tips to Minimize Artifact

Movement of any sort has the potential to create excessive artifacts in the ECG. Consider these tips:

If your patient is shivering, cover the skin with a light sheet and consider using a small heat pack to provide a sense of comfort. Turn the thermostat in the ambulance up to keep the patient warm.

The patient should be in a semifowler’s position.

Ask the patient to simply breathe normally and keep their hands by their sides. This prevents them from gripping the handrails too tightly, which can cause minute muscle tremors that show up on the ECG as artifacts.

There should be some “slack” in the patient cables. If the cable is taut between the electrode and the monitor, adjust the cable to release the tension.

With practice and preparation, obtaining a clean 12-lead ECG every time will be easier to accomplish. Your confidence in acquiring an accurate tracing will decrease the time it takes to decide how to manage and transport the patient who is experiencing ACS, and increase the chance of survival and recovery.

11. Baseline

A quality 12-lead ECG has a smooth, flat baseline (called the isoelectric line). Baseline wander, or the vertical motion of the ECG line, can mask important findings in the ECG tracing and result in a non-diagnostic ECG.

The patient should remain motionless and lay as close to supine as possible for the acquisition of the tracing and the ambulance should be stopped and not move during the process. It sometimes takes a few minutes for the ECG tracing to normalize and you should wait for it to do so. The goal is to be able to see the entire cardiac waveform clearly and be able to measure accurate ST-segment levels. Skin prep is important to reduce artifacts. A tracing with artifact or baseline wander can mask serious ECG findings and may cause a patient to be misdiagnosed.

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