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Ann Thorac Surg 2002;73:S367
© 2002 The Society of Thoracic Surgeons
1 Department of Radiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina, USA
2 Department of Medical Engineering, Wake Forest University School of Medicine, Winston-Salem, North Carolina, USA
3 Department of Cardiothoracic Surgery, Wake Forest University School of Medicine, Winston-Salem, North Carolina, USA
4 Department of Anesthesiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina, USA
Magnetic resonance imaging (MRI) is a common clinical imaging tool for the evaluation of the wide spectrum of brain disorders and injuries, including postsurgical brain injury related to ischemia. Conventional and advanced MRI techniques offer the ability not only to image the sequellae of injury but also to identify some factors that may result in increased risk of brain injury from embolic and hypoperfusion events resulting from surgical cardiac intervention. Diffusion weighted imaging (DWI) is a powerful newer technique that allows for both the identification of acute ischemic injury and differentiation from chronic ischemic changes. DWI is abnormal within the first day of an infarct and should detect all but the smallest lesions. We present our current findings in an ongoing study comparing brain injury in patients undergoing cardiac surgery on and off cardiopulmonary bypass. So far, the data demonstrate a trend toward increased risk of brain infarcts for patients undergoing coronary artery surgery on conventional cardiopulmonary bypass compared with minimally invasive surgery on the beating heart (p = 0.26 Fisher’s exact test).
Evaluation of the DWI sequences in patients undergoing coronary artery surgery, randomized to the two arms, demonstrates a significantly higher number of infarcts in patients on cardiopulmonary bypass. A total of 22 randomized patients have been imaged, of which 9 are on-pump and 13 off-pump. A total of four infarcts have been detected in the 22 patients, three in the on-pump and one in the off-pump group. A total of 33.33% of patients on-pump have had detectable infarcts on DWI and only 7.69% off-pump, and 75% of the infarcts detected on MRI have occurred in the patients on-pump.
Additional advanced MRI techniques are available, including perfusion weighted imaging (PWI) techniques and MRI spectroscopy. A form of noninvasive MRI perfusion, flow-sensitive alternating inversion recovery (FAIR), has also been performed in our study patients. The FAIR MRI perfusion studies give a measure of cerebral blood flow in traditional units of mL/100 g/min without requiring exogenous administration of contrast or tracer as with other perfusion techniques. Thus far, MRP data demonstrate an increase in the degree of asymmetry in cerebral perfusion compared with normal volunteers. However, PWI has not shown any significant difference in perfusion asymmetry between the on and off-pump patients. A larger sample size may be required to demonstrate a statistical significance in PWI results.
Supported by a grant from the National Institutes of Health (NS-38242), a grant from the Charles A. Dana Foundation, and Medtronic Inc, (Minneapolis, MN).
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