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 [1,2].
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.
Getting erlectrodes to stick
There’s nothing more frustrating than being unable to obtain an artifact-free ECG when time is of the essence. The surface of the skin where the electrode will make contact must really be free of oil and perspiration in order for the electrode adhesive to stick well.
Consider these suggestions to improve electrode contact:
- Don’t “preload” the electrodes! Opening the foil bag containing the electrodes, or attaching them to the cables without immediately using them on a patient will cause the electrodes to dry out prematurely. While the gel surface may feel “wet”, it is not reliable.
- For diaphoresis, use clean gauze or a towel to wipe away the perspiration. Using gauze has the added benefit of slightly “roughing” the skin’s surface that improves adhesion.
- Skin oil can be removed with an alcohol pad. Scrub the surface with moderate pressure to remove the oil and disrupt the uppermost layer of the epidermis. Use multiple alcohol pads, as they dry quickly.
- If there is obvious hair on the chest, use a razor to remove it before applying the electrodes.
- Connect the monitoring cables to the electrodes first. Then, when you apply the electrode to the skin, press down firmly on the center of the electrode, over the point where the conducting gel is concentrated. This will help ensure solid contact between the gel and the skin and maximize signal reception.
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.
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 to locate 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.
Electrode placement for pregnant patients
Despite the appearance of the abdomen during advanced pregnancy, 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.
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.
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.
Acquisition tips to minimize artifact
Movement of any sort has the potential to create excessive artifact 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 breath normally and keep their hands by their sides. This prevents them from gripping the hand rails too tightly, which can cause minute muscle tremors that show up on the ECG as artifact.
- 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.
References
1. ECC Committee, Subcommittees and Task Forces of the American Heart Association. 2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2005 Dec 13;112(24 Suppl):IV1-203. Epub 2005 Nov 28.
2. ECC Committee, Subcommittees and Task Forces of the American Heart Association. Part 8: adult advanced cardiovascular life support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010 Nov 2;122(18 Suppl 3):S729-67.
