Advanced magnetic resonance imaging measurements of brain connectivity in comatose patients who recently suffered a heart attack can help determine whether the patient will recover cognitive abilities a year later, according to a new study.
Investigators in Europe and the United States formed the Neuroimaging for Coma Emergence and Recovery Consortium to map changes in the brain in patients after several types of neurological injury. The study of comatose heart attack victims, recently published in the Radiology journal, sought to assess whether imaging brain connectivity was associated with their long-term outcomes.
A majority of patients who suffer heart attacks and survive don’t regain consciousness immediately after the medical emergency; they stay in a coma for hours, weeks or even longer, making it particularly difficult to determine their long-term recovery potential. A patient can emerge from a coma with anywhere from full cognitive function to significant cognitive impairment.
Current models don’t accurately predict which patients are more likely to emerge from a coma with cognitive impairment, and patients with similar characteristics after a heart attack can have very different outcomes.
The researchers used advanced MRI technology and a multimodal MRI sequence that included resting-state functional and structural MR imaging of 46 comatose patients less than four weeks after their heart attacks and compared the results with a control group of 48 healthy age-matched participants. They analyzed higher order brain networks that consider both intra-network and inter-network connectivity.
Resting state functional MR imaging indicates that the brain is organized in discrete large-scale functional networks with features congruent with known sensorimotor and cognitive systems.
The resting state networks change over time and in relation to processes such as learning and sleep.
They found abnormalities in the resting networks between the comatose patients compared with the control group. However, the abnormalities were different among the patients; the 11 who recovered with full or almost full brain function one year later had greater preservation of connectivity within the resting networks, particularly within the default mode resting network and the salience resting network, suggesting that the higher connectivity was linked to a higher likelihood of cognitive recovery.
“The results demonstrate that abnormalities in long-range connectivity occur within and between canonical brain networks in the acute phase of anoxic brain injury, and these abnormalities are associated with long-term functional outcome,” the study authors said. “These data suggest that anatomic and functional disconnection occurs early after [cardiac arrest] and could represent a biomarker of recovery potential,” they added.
A related editorial in the same issue noted that the imaging methods used in the study were better at predicting patient outcomes than other imaging tools, such as electroencephalography. The editorial also noted the potential significance of the study. “In the initial stage of coma after cardiac arrest, a prediction of the outcome is of paramount importance both for the relatives and treating medical team.”
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