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The Johns Hopkins Hospital, 600 N Wolfe St, Tower 711, Baltimore, MD 21287
(Email: chogue2{at}jhmi.edu).
Maekawa and colleagues [1] report the findings from a study of 247 patients who underwent brain diffusion-weighted magnetic resonance imaging (DWI) prior to elective cardiac surgery. The method of DWI is a sensitive way to detect acute brain ischemic injury and to distinguish new from chronic brain lesions. The findings of this study adds to a growing appreciation of the rising frequency of cerebral vascular disease and brain infarction in patients before cardiac surgery. Indeed multiple studies have shown the frequency of pre-existing cerebral infarcts to be as high as 45% in patients scheduled for cardiac surgery. In most instances, these lesions are clinically asymptomatic and thus they go undetected in the absence of brain imaging.
The findings of this study have several implications for clinicians and researchers. First, these data support that with many patients who have widespread vascular disease, cardiac surgery is superimposed on a "natural history" of this disease; that is, affected patients will have a certain baseline frequency of ongoing brain injury that must be considered when investigating the effects of cardiac surgery on the brain. This is highlighted by the recent work of Selnes and colleagues [2] who found that the rate of cognitive decline for 6 years of follow-up in patients who had documented coronary artery disease was no different than that found in patients who had undergone coronary artery bypass grafting (CABG) surgery compared with patients undergoing medical treatment, including percutaneous coronary interventions. Thus, the performance of CABG surgery with cardiopulmonary bypass did not alter the rates of cognitive decline compared with a control group of subjects with vascular disease. Thus, inclusion of a control group was necessary to distinguish what neurologic changes could be attributed to surgery and what could be accounted for by natural progression of pre-existing cerebral vascular disease. A second implication from this study relates to future research in this field, and that is, that due to cost and convenience, preoperative imaging is often skipped. Usually, any acute postoperative infarcts (by DWI) are believed to have occurred at the time of or soon after surgery; however, the frequency of acute preoperative lesions in 4.5% of this large sample of patients emphasizes that some of these apparent postoperative infarcts may truly be preoperative (if they occurred within a few days before surgery, they will still appear "acute" postoperatively).
A final implication of the study by Maekawa and colleagues [1] is perhaps it is time to consider more widespread screening for cerebrovascular disease in patients scheduled for cardiac surgery. Identification of patients with recent cerebral injury might lead to a decision to delay surgery to avoid infarct expansion with the multiple perturbations from surgery. The authors advise this practice, but there is no clear evidence that the appropriate treatment plan should be in an individual with a preoperative acute infarction. The mechanism and recommendations may be quite different in an individual with an embolus related to cardiac catheterization, which was the likely cause in 10 of the authors' 11 patients who had acute preoperative infarcts or preoperative atrial fibrillation, as opposed to an individual with a large-vessel stenosis who might be at higher risk for ongoing cerebral injury. Brain magnetic resonance imaging is expensive and time consuming and the costs versus benefits of this method versus other diagnostic approaches would require careful study. Regardless, the study by Maekawa and colleagues [1] underscores the importance of considering pre-existing and often new brain lesions in our assessments of patients undergoing cardiac surgery.
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