Electrocardiograms (ECGs) are a fundamental tool used to measure the electrical activity of the heart, providing waveforms that reveal rhythm and function. A clean ECG tracing is crucial for accurate interpretation, but the recording process is often complicated by artifacts, which are unwanted electrical signals or interference that distort the true heart signal. These artifacts can mimic serious cardiac conditions or obscure subtle changes, potentially leading to misdiagnosis or unnecessary treatment. Fortunately, the majority of these disturbances are preventable and can be traced back to three primary sources: the patient’s body, the connection between the patient and the machine, and the surrounding environment or equipment.
Addressing Artifacts Caused by Patient Factors
Artifacts originating from the patient’s body are primarily physiological, resulting from muscle activity or movement. The most common is somatic tremor, a rapid, choppy interference generated by skeletal muscle electrical activity, often due to tension, anxiety, or shivering. This tremor can resemble ventricular tachycardia on the tracing.
Minimizing this noise begins by ensuring the patient is comfortable and relaxed. If the patient is cold, offering a warm blanket stops shivering, a significant source of muscle artifact. Full limb support is also helpful, as unsupported muscles are prone to involuntary tension and movement.
Patient communication is a powerful tool for controlling artifact during the brief recording period. Instructing the patient to remain still and avoid talking or chewing gum prevents movement-related noise. For low-frequency baseline wander caused by respiration, asking the patient to take a deep breath, exhale partially, and hold it briefly can temporarily stabilize the baseline during the recording.
Ensuring Optimal Electrode Connection
The interface between the skin and the electrode is a high-resistance barrier, frequently causing poor signal quality and artifacts like baseline wander. Proper skin preparation is essential, as the natural presence of oils, sweat, and dead skin cells increases impedance, hindering the capture of the heart’s faint electrical signals.
To improve conductivity, the skin at the electrode site should be lightly abraded with a mild abrasive pad or gauze to remove the outermost layer of dead cells. Following this, cleaning the area with an alcohol wipe or soap and water removes skin oils and residue. Excessive hair should be shaved or clipped, as hair prevents the electrode from making firm, direct contact with the skin.
Electrode Application
The quality and application of the electrodes are equally important for maintaining a stable connection. High-quality electrodes with fresh, conductive gel should be used and checked for expiration. After skin preparation, electrodes must be firmly affixed to the correct anatomical position, avoiding placement over large muscles or bony prominences where movement is likely. Securing the lead wires near the patient’s body prevents cable movement from pulling on the electrodes, a common cause of intermittent signal loss and baseline drift.
Minimizing External and Equipment Interference
Artifacts not caused by the patient often stem from the environment or equipment, most notably electrical interference. The most recognizable form is alternating current (AC) interference, which appears as a thick, fuzzy baseline caused by 50 or 60 Hz electrical noise from power lines and nearby devices.
To combat this, the ECG machine must be properly grounded. The patient should be moved away from running electrical equipment, which acts as a source of electromagnetic interference (EMI). Common culprits include fluorescent lights, electrical beds, infusion pumps, and personal electronic devices like cell phones, which should be turned off or moved at least a meter away. Increasing the distance between the source of EMI and the cables significantly reduces artifact, as interference weakens rapidly with distance.
The equipment’s integrity and settings require attention to ensure a clean signal. Patient cables and lead wires should be periodically inspected for damage, cracks, or residue buildup on the clips, as this impedes conductivity. While not a substitute for proper preparation, the ECG machine’s built-in filters, such as the notch filter, can remove specific 50 or 60 Hz power line noise. However, filters can sometimes distort the true heart signal, meaning maximizing physical and electrical preparation remains the preferred first approach.