An electrocardiogram, commonly known as an ECG, records the heart’s electrical activity. Analyzing these signals provides information about the heart’s rate, rhythm, and overall function. Accurate electrode placement is fundamental for a clear ECG tracing.
Preparing the Patient
Preparing the patient’s skin is important before applying ECG electrodes. The skin should be clean, dry, and free of oils or lotions, as these can impede signal transmission and electrode adhesion. Excessive hair at electrode sites may need to be shaved for proper contact. Gentle skin abrasion, such as rubbing with an alcohol pad, can remove dead skin cells and lower impedance, improving signal quality.
Ensuring patient comfort and relaxation minimizes movement and muscle tension, which can interfere with the ECG tracing. The patient should be in a supine or semi-Fowler’s position, with arms at their sides and legs uncrossed. A comfortable room temperature helps prevent shivering, which can create artifacts.
Placing Limb Electrodes
Four limb electrodes record the heart’s electrical activity from different perspectives: Right Arm (RA), Left Arm (LA), Right Leg (RL), and Left Leg (LL). The RA electrode is placed on the right arm, between the shoulder and elbow, or below the right clavicle. The LA electrode is placed on the left arm, symmetrically to the RA electrode.
The RL electrode can be placed anywhere on the right leg, below the torso and above the ankle, or on the lower right torso. The LL electrode is positioned on the left leg, symmetrically to the RL electrode, below the torso and above the ankle, or on the lower left torso. Placing electrodes on fleshy areas, rather than over bones, ensures better contact and reduces motion artifacts.
Placing Chest Electrodes
The six chest electrodes (V1-V6) provide a horizontal view of the heart’s electrical activity and require precise placement. Locating the sternal angle, a palpable ridge where the manubrium meets the sternum, is a starting point as it aligns with the second rib. From there, one can palpate down to identify intercostal spaces.
The V1 electrode is placed in the fourth intercostal space at the right sternal border. The V2 electrode is positioned in the fourth intercostal space at the left sternal border, mirroring V1. The V4 electrode is placed next, in the fifth intercostal space at the midclavicular line.
Following V4, the V3 electrode is positioned midway between V2 and V4. The V5 electrode is placed horizontally to V4, at the anterior axillary line. The V6 electrode is placed horizontally to V4 and V5, at the midaxillary line.
Avoiding Common Placement Issues
Incorrect electrode placement is a common issue that can distort ECG readings, potentially leading to misdiagnosis. A frequent error is the reversal of limb leads, such as swapping right and left arm electrodes. This can result in an inverted P wave, QRS complex, and T wave in lead I, and can mimic conditions like dextrocardia.
Misplacement of chest leads, particularly V1 and V2, is common, with electrodes sometimes placed too high or too low. Placing V1 and V2 too high can lead to abnormal R-wave progression and changes that might suggest a right bundle branch block or myocardial ischemia, even when the heart is healthy. Poor skin contact due to inadequate preparation, or patient movement like shivering or talking, can also introduce artifacts such as a wandering baseline or muscle tremor, obscuring the true cardiac signals.