An electrocardiogram, commonly known as an ECG or EKG, is a non-invasive medical test that records the electrical activity of the heart. This procedure involves placing small, adhesive patches (electrodes) on specific body areas to detect the heart’s tiny electrical impulses. The ECG machine translates these impulses into waveforms, providing a visual representation of the heart’s rhythm and electrical health. The 12-lead ECG offers a comprehensive view of the heart’s electrical function from multiple angles, aiding in cardiac condition assessment.
Preparing for the ECG
Thorough preparation of the patient and equipment is necessary for a clear and accurate ECG reading. The patient should be comfortably positioned, lying flat on their back, to promote relaxation and minimize muscle tension that could interfere with electrical signals. Remove any metal jewelry or electronic devices from the patient, as these can create electrical interference or artifacts on the tracing. The chest and limbs where electrodes will be applied need to be exposed.
The skin at the electrode sites must be clean and dry to ensure proper electrical contact and minimize resistance. Wiping the area with an alcohol swab can help remove oils or lotions that might impede conductivity. If the patient has excessive hair, it may be necessary to clip or shave it to allow the electrodes to adhere firmly to the skin. This helps prevent air pockets between the electrode and the skin, which can lead to a poor signal.
Electrode Placement
Accurate electrode placement is important for obtaining a reliable 12-lead ECG. Ten electrodes are used to create the twelve perspectives of the heart’s electrical activity. Four electrodes are placed on the limbs, and six are placed across the chest.
The limb electrodes are placed on fleshy, non-bony areas of the arms and legs, such as the wrists and ankles, or sometimes on the upper arms and thighs. The right arm (RA) electrode is positioned on the right wrist or shoulder, while the left arm (LA) electrode is placed on the left wrist or shoulder. The right leg (RL) electrode, which serves as a ground, is placed on the right ankle. The left leg (LL) electrode is positioned on the left ankle. Maintaining uniformity in limb electrode placement, such as placing both on wrists or both on shoulders, helps ensure consistent readings.
The six chest electrodes, labeled V1 through V6, are placed using anatomical landmarks:
V1 is positioned in the fourth intercostal space (the space between the fourth and fifth ribs) at the right border of the sternum.
V2 is placed in the fourth intercostal space, directly across from V1, at the left border of the sternum.
V4 is located in the fifth intercostal space at the midclavicular line, an imaginary line extending straight down from the middle of the collarbone.
V3 is then placed midway between V2 and V4.
V5 is positioned at the left anterior axillary line (an imaginary line extending down from the front of the armpit) at the same horizontal level as V4.
V6 is placed at the left mid-axillary line (an imaginary line extending down from the middle of the armpit), also at the same horizontal level as V4 and V5.
For female patients, electrodes V3-V6 should be placed underneath the left breast.
Connecting Leads and Recording
Once all ten electrodes are in place, connect the lead wires from the ECG machine to each electrode. Each lead wire is color-coded and labeled for correct attachment, adhering to either American Heart Association (AHA) or International Electrotechnical Commission (IEC) standards. For the limb leads, following AHA standards, the right arm (RA) lead is white, the left arm (LA) is black, the right leg (RL) is green, and the left leg (LL) is red. For the chest leads under AHA standards, V1 is red, V2 yellow, V3 green, V4 blue, V5 orange, and V6 purple.
Each lead wire connector is designed to snap onto the corresponding electrode. After all leads are connected, instruct the patient to remain still and quiet, avoiding movement, as this can introduce interference into the recording. The ECG recording is then initiated on the machine, capturing the heart’s electrical activity over several seconds, around 10 seconds.
Ensuring a Clear Reading
Even with careful setup, various factors can affect the quality of an ECG tracing, leading to a poor or unreadable result. Artifacts, which are unwanted disturbances in the recording, can appear as erratic or shaky lines on the ECG waveform. These can be caused by patient movement, muscle tremors, or even nearby electrical equipment.
Minimizing patient movement by ensuring they are comfortable and still during the recording helps reduce motion artifact. Baseline wander, where the entire ECG tracing drifts up or down, results from poor electrode contact or respiration. Rechecking that each electrode is firmly adhered to the skin and that the gel inside the electrode is making good contact can help stabilize the baseline. Ensuring lead wires are not tangled or pulling on the electrodes also contributes to a stable tracing. Electrical interference from other devices in the room can also disrupt the signal, so ensure electronic devices like smartphones are removed from the patient’s vicinity.