An electrocardiogram (EKG or ECG) is a non-invasive diagnostic test that records the heart’s electrical activity. This procedure provides a graphic representation of voltage changes over time, revealing the depolarization and repolarization of cardiac muscle during each heartbeat. The EKG helps diagnose various heart conditions, including irregular rhythms, previous heart attacks, and issues with blood and oxygen supply. The test involves placing sensors, known as electrodes, on the skin, which connect to a machine that records the data. This guide details the standardized procedure for obtaining an EKG tracing for informational purposes only.
Preparation and Patient Setup
The process begins with explaining the procedure to the patient to alleviate anxiety and ensure cooperation. The patient must remove clothing from the waist up and any metallic objects, such as jewelry or watches, that could interfere with electrical signals. The patient is positioned supine on an examination table, with arms resting at their sides and legs uncrossed, to minimize muscle tension. The room temperature should be regulated for comfort, as shivering can produce muscle tremor artifacts that distort the tracing.
Achieving a high-quality tracing relies on proper skin preparation at the electrode sites. The outer layer of the skin is a poor conductor of electricity and can introduce artifact into the signal. Therefore, the skin must be prepared by clipping or shaving any excessive hair, as electrodes will not adhere properly over hair. After hair removal, the skin is cleaned with an alcohol wipe or abrasive prep pad to remove oils and dead skin cells, improving electrical contact. The electrode sites must air-dry completely before the adhesive patches are applied to ensure maximum conductivity.
The Standard 12-Lead Placement
Accurate placement of the ten electrodes is fundamental to acquiring a reliable 12-lead EKG, as incorrect positioning can lead to misinterpretation. These ten electrodes provide twelve distinct views, or “leads,” of the heart’s electrical field. The procedure involves placing four limb electrodes and six precordial (chest) electrodes at specific anatomical landmarks.
Limb Lead Placement
The four limb electrodes are placed on the arms and legs to establish reference points for the six limb leads (I, II, III, aVR, aVL, and aVF). The right arm (RA) electrode is positioned between the shoulder and wrist, avoiding bony areas. The left arm (LA) electrode is placed on the left upper limb, mirroring the RA placement.
The right leg (RL) electrode acts as the electrical ground, stabilizing the EKG signal by reducing interference, and is placed anywhere on the right leg. The left leg (LL) electrode is positioned on the left leg, typically on the calf, midway between the knee and ankle. These limb electrodes must be placed symmetrically on corresponding limbs to prevent misinterpretation caused by lead reversal.
Precordial (Chest) Lead Placement
The six precordial leads (V1 through V6) are positioned precisely on the chest to provide a detailed view of the heart’s electrical activity. Locating these positions begins by finding the fourth intercostal space (ICS), the space between the fourth and fifth ribs.
V1 is placed in the fourth intercostal space, just to the right of the sternum. V2 is placed directly across from V1, just to the left of the sternum. V4 is located next, positioned in the fifth intercostal space at the midclavicular line (an imaginary vertical line drawn down from the center of the collarbone). V3 is then placed midway between V2 and V4.
The final two leads are placed at the same horizontal level as V4 (the fifth intercostal space). V5 is placed at the anterior axillary line (running vertically down from the front of the armpit). V6 is placed at the mid-axillary line (running vertically down from the center of the armpit), ensuring V4, V5, and V6 align horizontally.
Acquisition and Quality Control
Once all ten electrodes are securely attached and connected, the acquisition process begins. The EKG machine must be properly calibrated before recording. Standard settings are typically a paper speed of 25 millimeters per second (mm/sec) and a voltage gain of 10 millimeters per millivolt (mm/mV). These settings ensure the tracing accurately represents the timing and amplitude of the electrical signals.
Before initiating the recording, the patient must remain completely still and breathe normally, as movement introduces interference. The standard 10-second strip records quickly, but the technician must monitor the screen for signs of artifact. Artifacts are non-cardiac electrical signals that distort the tracing.
Common Artifacts
A wandering baseline appears as a slow, undulating line, often caused by patient movement, breathing, or loose electrodes. Muscle tremor artifact presents as small, rapid spikes, caused by a nervous or cold patient, and is mitigated by ensuring comfort. Environmental interference, such as 60-cycle noise from electrical equipment, appears as regular, high-frequency waves. This can be resolved by ensuring the machine is properly grounded and moved away from wall outlets. Troubleshooting requires checking the security of each electrode and lead wire connection, and repeating the test if quality is compromised.
Post-Procedure and Documentation
After a high-quality EKG tracing is acquired, the lead wires are detached, and the electrodes are gently peeled away. The skin should be cleaned of any remaining adhesive or gel residue. The patient can then be assisted in getting dressed and returning to their normal activities, unless further medical attention is required.
Accurate documentation and filing of the EKG strip for physician review is essential. The tracing must be clearly labeled with the following information:
- Patient’s full name
- Medical record number
- The date and the exact time of recording
- The name or initials of the person who performed the test
Any noted changes to the standard lead placement should also be included. This record-keeping ensures the physician has all the information required for accurate interpretation.