Electrocardiogram: 12 Lead (Ambulatory) - CE/NCPD

The content in Clinical Skills is evidence based and intended to be a guide to clinical practice. Always follow your organization’s practice.

ALERT

Be sure the placement of electrodes is correct to avoid incorrect interpretation of the 12-lead electrocardiogram (ECG), mistaken diagnosis, or patient mismanagement.^{undefined#ref2">2}

OVERVIEW

The standard 12-lead ECG is the most widely used noninvasive diagnostic tool in the management of cardiac disease and is a source of information about the heart’s electrical system.² The ECG has significant impact on medical decision-making, clinical management, and therapy. Common uses include diagnosing acute coronary syndromes, identifying arrhythmias and conduction disturbances, and determining the effects of medications or electrolytes on the heart’s electrical system (Box 1).

The ECG leads are the standard limb leads (I, II, III); augmented limb leads (augmented vector right [aVR], augmented vector foot [aVF], and augmented vector left [aVL]); and six chest leads (V₁ to V₆). The standard and augmented leads view the heart from the vertical or frontal plane (Figure 1), and the chest leads view the heart from the horizontal plane (Figure 2). The graphic display consists of the P, Q, R, S, and T waves, which represent electrical activity in the heart.²

If myocardial ischemia or injury is suspected, serial ECGs are done. Correct standardized electrode placement is crucial for accurate ECG interpretation.³

Advances in technology allow for the use of online or wireless transmissions, networking capabilities, computerized interpretation of the 12-lead ECG, wearable ECG devices, and artificial intelligence for the interpretation of rhythms.

SUPPLIES

See Supplies tab at the top of the page.

EDUCATION

• Give developmentally and culturally appropriate education based on the desire for knowledge, readiness to learn, preferred learning style, and overall neurologic and psychosocial state.
• Explain the equipment and the procedure.
• Tell the patient not to talk, to relax, to lie still, and to breathe normally.
• Encourage questions and answer them as they arise.

PROCEDURE

1. Determine if the patient has health literacy needs or requires tools or assistance to effectively communicate. Be sure these needs can be met without compromising safety.
2. Review the patient’s previous experience and knowledge of having a 12-lead ECG and understanding of the care to be provided.
3. Place the patient in a resting supine position and expose the torso while maintaining modesty. Pull the curtains around the patient or close the door to the room.
4. Ask if the patient is experiencing chest pain, shortness of breath, or palpitations.
5. Ask about the patient’s history of cardiac arrhythmias or cardiac problems.
6. Ask the patient about any current medications.
7. Ask the patient to remove any jewelry (e.g., wristwatches, necklaces, body jewelry) that may interfere with the ECG.
8. Check the cables and lead wires for fraying, broken wires, or discoloration.

   Rationale: Checking the cables and lead wires helps detect conditions that may give an inaccurate ECG tracing.

   If equipment is damaged, get different equipment and notify the appropriate health care team member for repair..

9. Plug the ECG machine into a grounded alternating current (AC) wall outlet or make sure that the battery-operated machine is functioning.
10. Turn the ECG machine on and input the required information.

    Rationale: Equipment may require a self-test and warm-up time. Multichannel machines may require input of information (e.g., data about the patient) to store the ECG appropriately (Figure 3).

    Follow the manufacturer’s recommendations and requirements for inputting information and warm-up time.

11. Make sure that the patient is in the supine position and is not touching the side rails.

    Rationale: The supine position gives good support for the patient’s limbs so muscle activity is minimal. Touching the side rails may increase the chance of distorting the tracing.

    The supine position is best, but Fowler or other positions may be used for comfort. If another position is required clinically, note the position on the tracing or in the comment space of the machine input.

12. Expose only the necessary parts of the patient’s legs, arms, and chest to give privacy and warmth.

    Rationale: A lack of privacy may induce anxiety, which can alter the ECG reading. Shivering interferes with the recording.

13. Wash the skin with soap and water and dry it briskly with gauze pads or a washcloth.¹ Be sure that the skin is dry before applying electrodes.

    Rationale: Moist skin is not conducive to electrode adherence. Wiping the electrode area with a washcloth or gauze dries and roughens the skin to enhance conduction.¹

    Do not use alcohol for skin preparation because it can dry the skin.¹

    For good skin contact with the electrodes, clip chest hair with surgical clippers as necessary.

14. Identify the lead sites. Mark the sites with an indelible marker if serial ECGs are anticipated.

Rationale: Identifying and marking the lead sites helps to make sure that the electrodes are accurately placed.

15. Prepare the electrodes.

Rationale: Preparing the electrodes will make sure there is appropriate impulse conduction.

1. For pregelled electrodes, remove the backing and test for moistness.

   Make sure that the gel is moist. Replace the electrodes if they are not moist.

2. For adhesive electrodes, remove the backing and check that the adhesive pad is sticky or moist.

   Replace adhesive electrodes if they are not sticky.

16. Place the limb electrodes in fleshy areas, equidistant from the heart and in approximately the same place on each limb (Figure 4). Avoid bony prominences.

    Rationale: Accurate electrode placement results in correct electrical tracing of the heart from the vertical and frontal planes.²

17. Place the chest electrodes (Figure 5).

    Rationale: Accurate electrode placement results in correct electrical tracing of the heart from the horizontal plane. Slight alterations in the position of a precordial lead may alter the ECG significantly and can have an impact on diagnosis and treatment.²

    1. Identify the sternal angle, also called the angle of Louis (Figure 5).

       Rationale: The sternal angle helps identify the second rib for placement of precordial leads in the appropriate intercostal spaces (ICSs).

       1. Palpate the upper sternum to identify where the clavicle joins the sternum (suprasternal notch).
       2. Slide the fingers down the center of the sternum to the obvious bony prominence; this is the sternal angle, which identifies the second rib and gives a landmark for locating the fourth ICS.
    2. When the fourth ICS is located, place the V electrodes in the appropriate locations.
       1. V₁ at the fourth ICS, right sternal border
       2. V₂ at the fourth ICS, left sternal border
       3. V₄ at the fifth ICS, midclavicular line
       4. V₃ equidistant between V₂ and V₄
       5. V₅ horizontal to V₄ at the anterior axillary line
       6. V₆ horizontal to V₄ at the midaxillary line

          Variations in precordial lead placement can result in important diagnostic errors, such as septal ischemia or infarction.²

          If leads cannot be accurately placed, clearly document the actual location of the electrode placement on the 12-lead ECG.

          Place precordial electrodes under the breasts of a patient who has large breasts.

18. Attach the lead wires to the electrodes.
19. Program the ECG machine according to the manufacturer’s instructions for use (IFU). Most machines have automatic settings for programming paper speed and calibration and do a self-test when turned on.
20. Input patient information required for appropriate storage of the ECG into the machine according to the organization’s practice.
21. Get the 12-lead ECG recording.
    1. Tell the patient to remain still while the machine senses and translates the heart’s electrical activity to electrical waveforms on paper.

       Rationale: For correct interpretation, the ECG must be marked accurately and have a clear baseline without artifact.²

    2. Get a rhythm strip if needed.

       Rationale: A rhythm strip is a long recording of a specific lead; lead II is commonly used because P waves are best seen in lead II.

       Refer to the manufacturer’s IFU for instructions on getting a rhythm strip.

22. Examine the 12-lead ECG tracing to make sure that it is clear; repeat the ECG if it is not clear. Compare the 12-lead ECG with previous 12-lead ECGs if possible.

    Rationale: A comparison helps to show normal and abnormal findings.

    Examine the ECG and determine whether the recording must be repeated while the patient is still connected to the machine.

23. The clinical team leader interprets the recording, per the organization’s practice, and looks for:
    1. Rhythm
    2. Rate
    3. Presence and configuration of P waves
    4. Length of P–R intervals
    5. Length of QRS complexes
    6. Configuration and deviation of the ST segments
    7. Presence and configuration of T waves, length of Q-T intervals, presence of extra waves (e.g., U waves)
    8. Arrhythmias
    9. Signs of ischemia, injury, infarct, and other significant myocardial alterations

       Rationale: An evaluation identifies pathophysiologic processes that may require further evaluation or treatment.

24. Disconnect the equipment, clean the gel off of the patient (if necessary), return any removed clothing, and help the patient resume a comfortable position.

    Follow the manufacturer’s IFU and the organization’s practice for electrode use and removal.

25. Clean the ECG leads and machine. Return the equipment to its assigned storage space.

EXPECTED OUTCOMES

• A clear 12-lead ECG recording is obtained (Figure 6).
• Abnormalities are promptly identified.

UNEXPECTED OUTCOMES

• Altered skin integrity
• Inaccurate lead placement or limb lead reversal (Figure 7)
• AC interference, also called 60-cycle interference (Figure 8)
• Wandering baseline (Figure 9)
• Motion artifact (Figure 10)

DOCUMENTATION

• Education
• Reason for the 12-lead ECG (documented by the clinical team leader)
• Patient signs and symptoms of cardiac arrhythmias or cardiac problems (e.g., chest pain, syncope, dizziness, palpitations)
• Any altered lead placement or patient position and reason for change
• Need for follow-up to the 12-lead ECG, as indicated
• Unexpected outcomes and related interventions

REFERENCES

1. American Association of Critical-Care Nurses (AACN). (2018). AACN practice alert: Managing alarms in acute care across the life span: Electrocardiography and pulse oximetry. Critical Care Nurse, 38(2), e16-e20. doi:10.4037/ccn2018468
2. Brady, W.J., Harrigan, R.A., Chan, T.C. (2019). Chapter 14: Basic electrocardiographic techniques. In J.R. Roberts and others (Eds.), Roberts and Hedges’ clinical procedures in emergency medicine and acute care (7th ed., pp. 275-287). Philadelphia: Elsevier.
3. Muzzy, A. (2024). Procedure 51: Twelve-lead electrocardiogram with right and left posterior leads. In K.L. Johnson (Ed.), AACN procedure manual for progressive and critical care (8th ed., pp. 480-489). St. Louis: Elsevier.

ADDITIONAL READINGS

Smith, S., Maisrikrod, S. (2025). Wearable electrocardiogram technology: Help or hindrance to the modern doctor? JMIR: Journal of Medical Internet Research Cardio, 9, e62719. doi:10.2196/62719

Clinical Review: Genevieve L. Hackney, MSN, RN

Published: May 2025