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Department of Neuroscience, Joan C. Edwards Marshall University School of Medicine, 1600 Medical Center Drive, Suite G500, Huntington, WV 25705
(Email: mark_stecker{at}yahoo.com).
Pre-existing brain or neurovascular injury increases the risk of neurologic complications of cardiac operations. The main question is how to optimally quantify these conditions so as to facilitate the process of preoperative neurologic risk stratification. The state of large extracranial cerebral vessels can be easily measured using ultrasound, and the large intracranial vessels can be evaluated with transcranial Doppler. However, the smaller intracranial vessels (ie, the highest resistance component of the cerebral circulation) that control cerebral perfusion are more difficult to assess. Techniques providing measures of perfusion, such as computed tomographic perfusion, magnetic resonance perfusion, single photon emission computed tomography, O15 positron emission tomography, and xenon-cerebral blood flow can be useful at predicting the risk of neurologic injury, according to some small studies, but these tools are not generally available.
Morimoto and colleagues [1] propose using the presence of a white matter abnormality, leukoariosis, seen on routine magnetic resonance imaging studies as a simple surrogate index of the status of these small intracranial vessels. In a set of patients undergoing aortic arch reconstruction with circulatory arrest and selective antegrade cerebral perfusion, patients with higher degrees of leukoariosis had a higher risk of perioperative stroke. This finding must be tempered by the fact that the sample of this study may not be representative of other groups of patients undergoing cardiac operations, because factors such as carotid disease, duration of circulatory arrest, and age, which in other studies of both cardiac and aortic surgery have been correlated with the risk of stroke, did not correlate with the risk of perioperative stroke in this study.
Morimoto and colleagues [1] also demonstrated that the degree of hippocampal atrophy (although it did not correlate with the risk of perioperative stroke) was associated with an increased risk of postoperative transient neurologic dysfunction, as did the presence of severe leukoariosis. This relationship is expected because pre-existing brain injury is a known risk factor for postoperative neurologic dysfunction, and the susceptibility of the hippocampus to cell loss from dementia or ischemia makes it a sensitive marker for brain injury.
Despite the limitations of this study, it underscores the importance of finding preoperative markers of susceptibility to neurologic injury. It also suggests the importance of investigating the potential role of more direct measures of cerebral perfusion, such as computed tomographic perfusion on outcomes of cardiac operations, as these become increasingly more available.
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