Generalized periodic discharges and ‘triphasic waves’: A blinded evaluation of inter-rater agreement and clinical significance

• Generalized periodic discharges characterized as ‘triphasic waves’ present similar risk for the development of seizures as those without triphasic appearance.
• ‘Triphasic waves’ have only fair inter-rater agreement (k = 0.33) and are not reliably associated with underlying toxic-metabolic encephalopathy.
• Conventional association of ‘triphasic waves’ with specific clinical conditions may lead to inaccurate EEG interpretation.

ObjectivesGeneralized periodic discharges (GPDs) are associated with nonconvulsive seizures. Triphasic waves (TWs), a subtype of GPDs, have been described in relation to metabolic encephalopathy and not felt to be associated with seizures. We sought to establish the consistency of use of this descriptive term and its association with seizures.Methods11 experts in continuous EEG monitoring scored 20 cEEG samples containing GPDs using Standardized Critical Care EEG Terminology. In the absence of patient information, the inter-rater agreement (IRA) for EEG descriptors including TWs was assessed along with raters’ clinical EEG interpretation and compared with actual patient information.ResultsThe IRA for ‘generalized’ and ‘periodic’ was near-perfect (kappa = 0.81), but fair for ‘triphasic’ (kappa = 0.33). Patients with TWs were as likely to develop seizures as those without (25% vs 26%, N.S.) and surprisingly, patients with TWs were less likely to have toxic-metabolic encephalopathy than those without TWs (55% vs 79%, p < 0.01).ConclusionsWhile IRA for the terms “generalized” and “periodic” is high, it is only fair for TWs. EEG interpreted as TWs presents similar risk for seizures as GPDs without triphasic appearance. GPDs are commonly associated with metabolic encephalopathy, but ‘triphasic’ appearance is not predictive.SignificanceConventional association of ‘triphasic waves’ with specific clinical conditions may lead to inaccurate EEG interpretation.