**7. Occasional frontally predominant brief 2/s generalized rythmic delta activity (GRDA)**

These EEG waves are bilateral, bisynchronous, symmetric activity of 4 Hz or less, intermittent, predominant anterior activities (**Figure 14**). It is the most EEG feature frequently seen in the ICU [39].

It is reported in various diseases and syndromes such as structural brain lesion, metabolic encephalopathy, epilepsy, neurodegenerative disorders.

Study has shown that this pattern is not associated with an increasing risk of seizures [23]. In general, this EEG feature represents a benign pattern and is associated with a good outcome.

*Periodic EEG Patterns in the Intensive Care Unit (ICU): Definition, Recognition and Clinical… DOI: http://dx.doi.org/10.5772/intechopen.95503*

#### **Figure 14.**

*Generalized Rythmic Delta activity (GRDA). Average montage. Note the brief (lasting 2 s), 2 cps, bilateral, predominantly anterior delta activity.*

### **8. Evolving lateralized rhythmic delta activity (LRDA)**

These interesting EEG features are unilateral rhythmic activity of 4 Hz or less, are found in various central nervous system lesions such as cortical and deep gray matter lesions, acute brain injury, and in chronic seizure disorder (**Figure 15**); there

#### **Figure 15.**

*LRDA in a 50 years old patient with NCSE. Note the right sided continuous lateralized focal predominantly fronto-temporal 3, 5 to 4 cps delta activity.*

are also seen in acute seizures in 63% of patients [40] and are frequently associated with LPDs; LRDA carries similar implications as LPDs [40].
