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Table 2 Electroencephalography patterns and findings of the study patients according to electroencephalography timing

From: Background frequency can enhance the prognostication power of EEG patterns categories in comatose cardiac arrest survivors: a prospective, multicenter, observational cohort study

EEG findings Total (N = 489) Patients with EEG < 72 h
(N = 353)
Patients with EEG of 72 h to 7 days
(N = 136)
P value
EEG background frequency     0.220
 Predominant alpha waves 106 (21.7%) 84 (23.8%) 22 (16.2%)  
 Predominant theta waves 127 (26.0%) 87 (24.6%) 40 (29.4%)  
 Predominant delta waves 90 (18.4%) 67 (19.0%) 23 (16.9%)  
 Undetermined 166 (33.9%) 115 (32.6%) 51 (37.5%)  
Categorization     0.934
 Highly malignant pattern 199 (40.7%) 144 (40.8%) 55 (40.4%)  
 Malignant pattern 124 (25.4%) 88 (24.9%) 36 (26.5%)  
 Benign 166 (33.9%) 121 (34.3%) 45 (33.1%)  
Highly malignant pattern     
 Suppressed background without discharges 154 (31.5%) 106 (30.0%) 48 (35.3%) 0.261
 Suppressed background with continuous periodic discharges 10 (2.0%) 8 (2.3%) 2 (1.5%) 0.733
 Burst-suppression 35 (7.2%) 30 (8.5%) 5 (3.7%) 0.064
Malignant rhythmic or periodic features 67 (13.7%) 44 (12.5%) 23 (16.9%) 0.2
 Periodic discharges (≥ 50%) 30 (6.1%) 19 (5.4%) 11 (8.1%) 0.264
 Rhythmic spike-and-wave (≥ 50%) 28 (5.7%) 21 (5.9%) 7 (5.1%) 0.732
 Unequivocal seizures or status epilepticus 53 (10.8%) 37 (10.5%) 16 (11.8%) 0.683
Malignant background 85 (17.4%) 64 (18.1%) 21 (15.4%) 0.527
 Discontinuous (> 10% suppression) 16 (3.3%) 10 (2.8%) 6 (4.4%) 0.399
 Low voltage (< 20 μV) 61 (12.5%) 47 (13.3%) 14 (10.3%) 0.365
 Reversed anteroposterior gradient 14 (2.9%) 11 (3.1%) 3 (2.2%) 0.766
  1. Values are expressed as number (%)
  2. EEG, electroencephalography