This study described the case of a patient with acute cerebral infarction after CABG, for whom CAS was successful performed. Despite improvements in anesthesia and surgical techniques, stroke remains a devastating neurologic complication of myocardial revascularization and a primary concern in assessing a patient’s cardiopulmonary bypass candidacy.  The prevalence of severe carotid artery stenosis (> 80% stenosis) among patients undergoing coronary artery bypass surgery has been estimated to be between 6 and 14% . However, some reports indicate that severe carotid artery stenosis alone is not a risk factor for stroke or mortality in patients undergoing CABG [4, 5].
In a staged approach (CAS or carotid endarterectomy followed by CABG after several weeks), the increased risk of myocardial infarction in the interval may represent a limitation. Moreover, the need for dual anti-platelet aggregation therapy for 3 to 4 weeks following CAS increases the risk of bleeding if surgery is urgently required in the meantime . Further, scattered reports suggest that a staged approach does not improve prognosis and may even increase risk [7, 8]. Simultaneous hybrid revascularization by CAS or carotid endarterectomy and CABG may be a viable alternative to the staged combination, particularly among patients for whom CABG cannot be postponed [15,16,17]. If a staged approach had been administrated in the present case, the patient might have developed a coronary attack in the interval. Considering that the carotid lesion worsened immediately following the coronary artery bypass procedure, simultaneous hybrid revascularization could have been considered.
The mechanism of perioperative stroke is still unclear, although calcific debris from a diseased valve, macroemboli of cardiac origin, introduction of air during the procedure, hypoperfusion arising from a severely stenotic carotid artery, or embolization from an ulcerated plaque have all been described in the literature . Moreover, since the primary causes of stroke during cardiac surgery have been thought to be cardiogenic embolism, intracranial arterial stenosis, or small vessel disease, preoperative carotid revascularization would not have a preventive effect for these events . In the present case, although there was severe stenosis of the carotid artery, it was determined that preoperative revascularization was not necessary, and the cardiac surgery was ultimately performed successfully. However, because of the potential for excessive coagulability, hypotension, and dehydration in the early postoperative stage, the carotid plaque at the bifurcation likely caused regional hypoperfusion and acted as an embolic source in the eventuation of stroke. Furthermore, in order to have predicted this phenomenon, quantitative evaluation of blood flow in the brain should have been performed preoperatively in addition to imaging evaluation.
Single-photon emission computed tomography is the most widely used method for evaluating cerebral circulatory reserve, and the rate of increase in cerebral blood flow obtained from its measurement before and after acetazolamide loading is used as an index of cerebral circulatory reserve . Kuroda et al. demonstrated that cerebral blood flow changes in response to changes in blood pressure, and even asymptomatic patients may tolerate perioperative reductions in cardiac output or blood pressure poorly with increased risk of cerebral infarction . However, acetazolamide has the potential to cause the serious side effect of acute pulmonary edema  and its use in cases with cardiac disease must be carefully evaluated. In accordance with these reports, it appears safe and feasible in most cases to conservatively manage CABG patients with severe carotid artery disease without the need for preoperative corrective carotid revascularization. However, if rapid progression of neurologic symptoms is observed postoperatively, immediate revascularization should be considered.
ASL in MRI detects perfusion without the use of exogenous contrast, instead relying on magnetic labeling of arterial blood . Zaharchuk et al. reported that ASL correlates well with mismatch with DWI as a substitute for perfusion-weighed image . Chalela et al. described that ASL in acute stroke successfully depicted perfusion deficits, restored perfusion, hyperperfusion, perfusion/diffusion mismatches, and delayed arterial transit in addition to providing quantitative cerebral blood flow determination . The mismatch between DWI and ASL represents the penumbra, or the tissue at risk of infarction .
Although the exact timing of the stroke was also unknown in this case, the decision to perform urgent revascularization was made because of neurologic findings that rapidly progressed within the examination alone, the possibility of penumbra on imaging, and the possibility of reversible recovery with revascularization. Although immediately post-surgical cardiac patients may not be amenable to transport for MRI imaging due to the placement of various infusion pumps and lines and the limitation of hemodynamics on prolonged imaging or movement, it is recommended that these issues be worked through so that non-invasive ASL may be performed in conjunction with head MRI imaging.