Burst–suppression Pattern
Other Names
Burst–suppression activity
Suppression–burst pattern
Description
The burst–suppression pattern (BSP) is characterized not so much by the features within the burst or the suppression but by their contrasting, adjacent amplitudes. The amplitude of a burst may vary from low (<20 μV) to high (>100 μV), but most often it is between 20 and 100 μV. Similarly, a suppression may vary in amplitude but it is almost always within the range of electrocerebral inactivity to medium amplitude (<50 μV). Since the abrupt change in amplitude is the essential definition of this pattern, the amplitude difference must be clearly visible, and this difference is usually close to or greater than a 50% decrease. A threshold amplitude decrease cannot be defined because BSP may have amplitude differences as little as 10 μV if the bursts are 15 μV, but a 10 μV decrease is not significant if the higher amplitude activity is 60 μV.
The temporal relationships between the bursts and suppressions vary considerably with the possibility that either the bursts or the suppressions may be longer in duration. Some definitions specify that the term burst–suppression indicates that the bursts are longer than the suppressions and suppression–burst indicates that the suppressions are longer (Fisch, 1999). However, the term BSP is commonly used without such specificity. Individual bursts typically have a duration of 1 to 3 seconds and, regardless of the duration, often recur quasi-periodically (Bauer, 1999; Fisch, 1999).
Bursts may comprise multiple and intermingled sharps and spikes, or occur as rhythmic activity. The rhythmic activity may be regular or irregular and have a predominant frequency anywhere in the spectrum from the delta through the beta ranges. Bursts of delta frequency range activity usually have superimposed faster frequencies. Regardless of whether the bursts are rhythmic or not, burst morphology usually is not conserved across occurrences within an EEG; however, the rhythms within the bursts may have conserved regularity and frequency. Bursts usually are bilaterally synchronous and commonly are generalized but may be unilateral. Asynchronous BSP has been reported and is ascribed to abnormality within the corpus callosum, as may occur from diffuse axonal injury or agenesis (Savard and Huot, 2008). The activity that is present during suppressions is typically in the delta frequency range. In general, suppressions within the range of normal EEG amplitudes include activity that is closer to the normal background frequencies. Thus, suppressions may contain rhythms in the alpha frequency range (Bauer, 1999).
Distinguishing Features
• Compared to Periodic Epileptiform Discharges
Similar to BSP, periodic epileptiform discharges (PEDs) constitute a paroxysmal, recurring pattern that includes spikes or sharps and amplitude that is higher than the background’s. PEDs also may be bilateral (BiPEDs) and they have distribution that is similar to BSP’s. Furthermore, many clinical situations that produce BSP, such as anoxic injury, can instead produce PEDs, especially BiPEDs. Differentiating these two patterns depends mostly on waveform. Unlike the bursts of BSP, PEDs typically are briefer and have minimal differences in waveform across recurrences. They also include a preserved temporal relationship between sharply contoured transients (spikes or sharp waves) and slow waves within an occurrence. Moreover, the relationship among the wave elements in PEDs is epileptiform with the slow wave following a sharp wave or one or more spikes, and this is not true for BSP. Occasionally, bursts have stereotyped waveforms, but they comprise multiple sharply contoured waves and slow waves without the epileptiform pattern (Hughes, 1986). Bursts also are usually longer in duration than PEDs and, unlike PEDs, commonly have durations longer than 1 second.
Co-occurring Waves
BSP always occurs in the context of diffuse cerebral dysfunction; therefore, it is accompanied by other EEG features of such states, especially generalized
polymorphic delta activity. Some clinical situations that lead to BSP also produce myoclonus, and the myoclonus of such states commonly accompanies the bursts. Other movements that may accompany the bursts of BSP include tonus, ocular movements, and orofacial movements, and each of these movements has their own characteristic muscle or movement artifact (Fisch, 1999; Fernandez-Torre et al., 2008; Reeves et al., 1997). As such, muscle artifact may be superimposed on the bursts with a slight lag from the burst’s beginning. Rarely, the muscle artifact accompanies suppressions (Pourmand, 1994).
polymorphic delta activity. Some clinical situations that lead to BSP also produce myoclonus, and the myoclonus of such states commonly accompanies the bursts. Other movements that may accompany the bursts of BSP include tonus, ocular movements, and orofacial movements, and each of these movements has their own characteristic muscle or movement artifact (Fisch, 1999; Fernandez-Torre et al., 2008; Reeves et al., 1997). As such, muscle artifact may be superimposed on the bursts with a slight lag from the burst’s beginning. Rarely, the muscle artifact accompanies suppressions (Pourmand, 1994).
Clinical Significance
The BSP occurs in the context of diffuse cerebral dysfunction with coma and indicates a clinical severity that is greater than generalized slowing but less than electrocerebral inactivity. Such situations include cerebral anoxia (diffuse ischemic encephalopathy), hypothermia, end-stage status epilepticus, severe epileptic encephalopathies of infancy, and high levels of sedation (Niedermeyer, 2009
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