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Abstract & Commentary
Source: Stolz E, Gerrietz T, Kluge A et al. Diffusion-weighted magnetic resonance imaging and neurobiochemical markers after aortic valve replacement. Implications for future neuroprotective trials? Stroke. 2004;35:888-892.
Cardiac surgery may be complicated by ischemic stroke as well as more non-specific cognitive disturbances. These events are largely attributed to the release of micro- and macro-embolic particles from complex atherosclerotic aortic arch disease. Diffusion-weighted MRI imaging may be effective in diagnosing these emboli not only when they are symptomatic, but also when they occur silently. Unless patients are scanned prospectively, however, the true incidence of these events is difficult to estimate. Even more importantly, the true clinical significance of these lesions is unclear. Could prophylactic neuroprotective strategies be employed in the setting? The data of Stolz and colleagues brings us one step closer to answering these questions.
A total of 45 consecutive patients underwent MRI scanning prior to and immediately following aortic valve replacement (AVR). Pre-existing T2 bright lesions were found in 26 patients. Postoperative diffusion-weighted infusion (DWI) lesions were found in 14 patients, 2 with territorial infarcts and the remainder with one or more punctate lesions. All patients were seen by a neurologist. Only 3 patients had a neurological deficit, 2 with territorial lesions and the third with a small white matter lesion. Measurements of S100B and neuron specific enolase (NSE), known markers of neuronal damage, were made sequentially. S100B values on days 2-4 postoperatively correlated with the presence of DWI lesions. In addition, DWI lesions were associated with increasing patient age and the presence of pre-existing T2 lesions on MRI. After additional analysis of these, only pre-existing T2 lesion volume was found to be a relevant predictor of DWI positivity. Stolz et al suggest that such T2 lesions may reflect prior microcirculatory damage and identify patients who are unable to optimally clear microembolic particles.
These data suggest that in the absence of a significant territorial infarct, DWI-positive lesions following cardiac surgery are largely asymptomatic and below the detection threshold of a detailed neurological examination. Such lesions may nevertheless be important and likely do contribute to long-term adverse neuro-psychiatric outcomes in these patients. The presence of pre-existing T2 lesions appears to be predictive of perioperative ischemic lesions and suggests that we may be able to preoperatively risk stratify patients undergoing cardiac surgery. While most patients may be able to clear microemboli easily, there may be a subset with an impaired microcirculation for whom these emboli present a much more serious problem. — Alan Z. Segal
Dr. Segal, Assistant Professor, Department of Neurology, Weill-Cornell Medical College, Attending Neurologist, New York Presbyterian Hospital, is Assistant Editor of Neurology Alert.