What are EEG triphasic waves?

Updated: Sep 24, 2018
  • Author: Kalyani Korabathina, MD; Chief Editor: Tarakad S Ramachandran, MBBS, MBA, MPH, FAAN, FACP, FAHA, FRCP, FRCPC, FRS, LRCP, MRCP, MRCS  more...
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Triphasic waves (TWs) are a distinctive but nonspecific electroencephalographic (EEG) pattern originally described in a stuporous patient in 1950 by Foley as "blunted spike and wave." In 1955, Bickford and Butt coined the term "triphasic wave." Since their findings were limited to patients with hepatic failure, triphasic wave encephalopathy (TWE) became synonymous with hepatic encephalopathy. Since then, TWE has been associated with a wide range of toxic, metabolic, and structural abnormalities. [1, 2]

TWs are high-amplitude (>70 µV), positive sharp transients that are preceded and followed by negative waves of relatively lower amplitude. They are diffuse and bilaterally synchronous with bifrontal predominance. They often repeat periodically at a rate of 1-2 Hz. [3]

See the image below.

An 89-year-old man with end-stage liver disease. N An 89-year-old man with end-stage liver disease. Note the frontally predominant, sharply contoured waveforms with a triphasic morphology, characterized by 3 phases: negative (wave 1), positive (wave 2), and negative (wave 3). Also note the periodicity with 1-second intervals.

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