Contributed by James A. Rowley, MD, Wayne State University, Detroit, MI
What is the artifact indicated by the arrow? What are possible causes of the artifact?
Artifacts are generally classified as physiologic or electrical. Physiological artifacts arise from the patient while electrical artifacts arise from the PSG system itself. The artifact at the arrow appears as a very rapid continuous waveform (60 Hz) in the EMG lead. This finding is often consistent with an electrically-generated artifact. 60Hz artifact is commonly caused by unbalanced electrode impedances, improper or broken electrode connections, electronic interference (location near transformers, motors, power supplies) and long unshielded wires. Therefore, 60 (50) Hz artifact is best prevented by using shielded wires, proper shielding in the ceilings/walls of patient rooms, keeping impedance low (<5 kΩ) and ensuring proper electrode connections. As a last resort 60 Hz artifact can be eliminated by using a 60Hz or notch filter; however, a notch filter should not be routinely used to prevent this artifact.
Further Reading:
Chokroverty, S., Bhatt, M., and Goldhammer, T. (2005) Polysomnographic recording technique. In Atlas of Sleep Medicine (Chokroverty, S., Thomas, R., and Bhatt, M., eds), Elsevier, Philadelphia, PA
Beine, B. (2005) Troubleshooting and elimination of artifact in polysomnography.Respir Care Clin N Am 11, 617-634
