Electroencephalography findings in patients with acute post coronary artery bypass graft encephalopathy

Discussion

Our study showed that patients with aPCE who’s EEGs showed lateralized slowing, focal epileptiform discharges, PLEDs, and electrographic seizures had acute cerebral ischemic insults. Altered level of consciousness was the most common symptomatology in our cohort, and could be due to hypoxic, toxic, or metabolic etiology. Generalized theta intermixed with diffuse delta were the most common EEG findings in our study. Neurological assessment of the delirious and unresponsive patient is limited, only a few biochemical tests can provides clues, with significant limitations. However, electrophysiologic investigations provide a window into cerebral function, and are sensitive, quite safe, readily available, and inexpensive.5 Electroencephalography provides data that helps clinicians in decision-making in the setting of epilepsy related situations like hypoxic encephalopathy.5 Periodic lateralized epileptiform discharges on EEG are most commonly associated with cerebral infarctions, but may also be seen in encephalitis, tumor, or demyelination. Studies using computer EEG monitoring show that brain electrical activity recording demonstrates moderate sensitivity and high specificity in detecting brain ischemic alterations.4 A decrease in EEG amplitude, and or EEG slowing indicates a fall in mean cerebral flow below 22ml/100gm/min. An initial decrease in fast rhythms, namely, alpha and beta are followed by appearance of delta rhythms, and a further decrease in perfusion causes flattening of the EEG activity.4 Apart from the diagnosis of encephalopathy, the degree of severity can also be ascertained by EEG.

The degree of diffuse slowing of the normal background plus abnormal mixed rhythms in the EEG correlates with the severity of encephalopathy. Various studies have shown that EEG and neuropsychological deficits were found in almost 40% of patients after a week of CABG. It is estimated that worldwide the number of CABG’s carried out per year is around one million,6 and this number is increasing every year. The pathophysiology of post CABG encephalopathy is not very well understood, because there are many possible causes: infection, cardiac, or renal failure, and hypnotic medications. Diffusion weighted MRI studies indicate multiple small vascular lesions in patients after CABG, some of whom have reported to have encephalopathic features. The relatively old age of the patients who undergo CABG, and their widespread atherosclerotic disease are possible reasons for vascular sequelae particularly those leading to neurological dysfunctions.3 In our cohort, most of the patients had comorbid medical conditions increasing their risk of postoperative neurocognitive impairment. Post operatively, patients are intubated in intensive care units, which is a difficult setting for patients who develop aPCE and would require neuroimaging. We found that EEG is a simple tool that can be easily performed using portable EEG machines without delay.