Technology Insight: brain MRI and cardiac surgery—detection of postoperative brain ischemia

Abstract

Annually, an estimated 1 million patients undergo heart surgery worldwide. Unfortunately, stroke continues to be a frequent complication of cardiac surgery, with the specific cerebrovascular risk depending upon the particular surgical procedure performed. Neuroimaging has an integral role in the initial evaluation and management of patients who present with acute stroke symptoms following cardiac surgery. The aim of this paper is to review the role brain MRI has in detecting postoperative brain ischemia in these patients. Multimodal MRI--using diffusion-weighted MRI (DWI), perfusion-weighted MRI, and gradient-recalled echo imaging--has an excellent capacity to identify and delineate the size and location of acute ischemic strokes as well as intracerebral hemorrhages. This differentiation is critical in making appropriate treatment decisions in the acute setting, such as determining patient eligibility for thrombolytic or hemodynamic therapies. At present, DWI offers prognostic value in patients with strokes following cardiac surgery. Additionally, DWI could be a valuable tool for evaluating stroke preventive measures as well as therapeutic interventions in patients undergoing CABG surgery.

A Preliminary Prediction Model with MR Plaque Imaging to Estimate Risk for New Ischemic Brain Lesions on Diffusion-Weighted Imaging after Endarterectomy or Stenting in Patients with Carotid Stenosis

“…However, there is increasing evidence that the cumulative burden of ischemic lesions causes neuropsychological deficits. 28,29 The latest randomized study demonstrated that CAS had a small but statistically significant detrimental effect on cognitive functioning at 6 months after treatment for symptomatic carotid stenosis, an effect not observed with CEA, probably because of a more than 2-fold higher rate of new ischemic lesions on DWI after CAS than after CEA. 30 Accordingly, considering the low stroke and death rates of CEA and CAS in recent clinical trials 31,32 and the current study, even subclinical infarction might be a factor to be reckoned with for treatment strategy.…”

Brain Protection in Cardiac Surgery

“…[1–4] Sensitive diffusion-weighted magnetic resonance imaging of the brain, for example, may reveal brain infarction in 45% of patients after cardiac surgery. [3,5] These ischemic brain infarctions may or may not be associated with stroke or postoperative neurocognitive dysfunction (clinically “silent”), but the long-term implications of these lesions on neurological function have not yet been extensively evaluated. The importance of cardiac surgery on long-term cognition recently has been challenged by controlled studies in which the cognitive function of patients who have undergone coronary artery bypass graft (CABG) surgery with cardiopulmonary bypass (CPB) was compared with that of non-surgical patients who have coronary artery disease and are undergoing medical management and/or percutaneous coronary artery interventions.…”

Neurological Complications of Cardiac Surgery

“…Leary and Caplan have emphasized that multimodal MRI, includ-ing DWI, perfusion-weighted MRI, and gradient-echo imaging, be used for patients with concern for postcardiac surgery ischemia. 47 MRI with DWI is more sensitive than CT scanning in general for detecting new ischemic injury; this is also true in the post-CABG surgery population. This is particularly important because many patients with stroke after CABG surgery have multiple small embolic or watershed-territory infarcts that are less easily detected by CT scanning.…”

“…Most strokes occurring as a result of cardiac surgery are either embolic-appearing in distribution (in multiple vascular territories) or in watershed territories between major cerebral arteries. 48,49 Stroke in this setting is almost exclusively ischemic; intracerebral hemorrhage is rare, 47 occurring in less than 1% of most patient populations and only up to 1 to 2% in patients undergoing valvular surgery. 50 Figure 2 Probability of postoperative stroke.…”