An electrocardiogram (EKG or ECG) is a non-invasive diagnostic tool that uses ten electrodes to record the heart’s electrical activity as waveforms, capturing twelve different perspectives. The resulting tracing helps healthcare professionals identify potential issues like arrhythmias, coronary artery disease, or electrolyte imbalances. Proper placement of these electrodes is fundamental to obtaining an accurate reading.
Essential Preparation Before Placement
Preparing the patient maximizes conductivity and minimizes interference that could distort the final result. The patient should be positioned supine with arms relaxed at their sides and legs uncrossed to prevent muscle tension, which can generate artifacts on the tracing.
Skin preparation is important because dry or oily skin, lotions, and excessive hair significantly impede electrical signal transmission. Placement sites should be cleaned with an alcohol wipe to remove oils and dead skin cells, often requiring gentle abrasion to reduce skin resistance. Any substantial hair must be clipped or shaved to ensure the electrode patch achieves full contact with the skin surface. Using fresh electrodes with moist conductive gel and ensuring the EKG machine is properly calibrated and grounded are also necessary preparatory steps.
Locating and Attaching the Limb Leads
The four limb leads provide six views (Leads I, II, III, aVR, aVL, and aVF) by measuring electrical potential changes in the frontal plane. The right arm (RA) and left arm (LA) electrodes are generally placed between the shoulders and the elbows, often on the forearms or wrists. To reduce signal interference from muscle movement, it is beneficial to place them equidistant from the torso, such as on the upper arms or shoulders.
The remaining two limb leads are placed on the legs. The left leg (LL) electrode acts as the positive pole for several views. The right leg (RL) electrode functions as the electrical ground for the entire system to minimize interference. These leg electrodes are typically placed on the lower legs or ankles, and incorrect placement can result in changes to the heart’s electrical axis on the tracing, potentially leading to misinterpretation.
Precise Placement of the Chest Leads
The six precordial (chest) leads (V1 through V6) provide views of the heart’s electrical activity in the horizontal plane. These leads must be positioned accurately using specific anatomical landmarks to avoid creating artifacts that mimic serious cardiac conditions. Accurate placement begins by locating the sternal angle (Angle of Louis), the bony ridge adjacent to the second rib, which allows for systematic counting of the intercostal spaces.
Precordial Lead Placement
- V1 is placed in the fourth intercostal space immediately to the right of the sternal border.
- V2 is placed in the fourth intercostal space directly to the left of the sternal border. (Misplacement of V1/V2 can falsely suggest a heart attack.)
- V4 is located in the fifth intercostal space at the midclavicular line (an imaginary vertical line extending down from the center of the collarbone).
- V3 is placed midway in a straight line between the V2 and V4 positions. (V4 must be placed before V3 to ensure accurate positioning.)
- V5 is placed on the same horizontal plane as V4, positioned on the anterior axillary line (running vertically down from the front fold of the armpit).
- V6 is placed on the same horizontal plane as V4 and V5, positioned on the midaxillary line (running vertically down from the center of the armpit).
For female patients, the V3 through V6 electrodes should be placed underneath the left breast, ensuring the electrode is on skin and not breast tissue, while maintaining the correct anatomical lines and horizontal level. The nipple should not be used as a landmark for either sex, as its location is variable. This process ensures the precordial leads capture the true electrical vectors of the heart’s anterior, septal, and lateral walls.
Reviewing the Tracing for Accuracy
Once recording begins, the waveform tracing must be inspected for signs of electrical interference or technical errors. Interference not generated by the heart is called artifact, and it can obscure the true cardiac signal or mimic dangerous abnormalities. A common issue is a wandering baseline, which appears as a slow, undulating movement caused by patient movement, deep breathing, or poor electrode contact.
Muscle tremor, which appears as fine, rapid, irregular jaggedness, is often caused by a cold or nervous patient and can be resolved by ensuring the patient is warm and relaxed. Sharp, regular interference, known as 60 Hz artifact, is typically caused by nearby electrical equipment or improperly grounded machines and can be mitigated by unplugging other devices. Technicians must also check for lead reversal, indicated by inverted waveforms in leads that should normally be upright, requiring re-verification of cable connections.