Cardiac Surgery and Cerebrovascular Disease: What are the Risks, Options?
AbstractS & Commentary
By Dara G. Jamieson, MD, Associate Professor, Clinical Neurology, Weill Medical College, Cornell University. Dr. Jamieson is a consultant for Boehringer Ingelheim and Merck, and is on the speaker's bureau for Boehringer Ingelheim, Merck, Ortho-McNeil, and Pfizer.
Synopsis: The neurological risk of cardiac surgery is still not well characterized, but post-operative strokes occur in 3-9% of patients. A decrease in intra-operative blood pressure and increased cardiopulmonary bypass time may result in watershed infarcts. Carotid stenting followed by cardiac surgery is an option for patients with coexistent disease.
Sources: Newman MF, et al. Central Nervous System Injury Associated with Cardiac Surgery. Lancet. 2006;368:694-703; Gottesman RF, et al. Watershed Strokes after Cardiac Surgery: Diagnosis, Etiology, and Outcome. Stroke. 2006;37:2306-2311; Oscar M, et al. Synchronous Carotid Stenting and Cardiac Surgery: An Initial Single-Center Experience. Catheter Cardiovasc Interv. 2006;68:424-428.
Central nervous system injury after cardiac surgery includes ischemic stroke, encephalopathy, delirium, and neurocognitive decline. Prediction of risk and understanding of mechanism of injury should lead to improved post-operative outcome. Newman and colleagues reviewed studies that evaluated neurological consequences of cardiac surgery and outlined issues and controversies in the field. Questions that need further study include: 1) Does off-pump cardiac bypass surgery decrease post-operative complications and 2) Is neurocognitive decline related to the surgery? While atrial fibrillation is associated with increased post-operative neurological abnormalities, its contribution to post-operative cognitive decline is less certain. Do genetics, pre-existing cerebrovascular disease, and anesthesia factors also predict risk? The review in Lancet described issues for further investigation without reaching specific conclusions about risk reduction.
The multiple mechanisms for strokes associated with cardiac surgery include emboli from the heart and/or aorta and cerebral hypoperfusion. Improved cardio-pulmonary bypass techniques with arterial filtration and membrane oxygenation have decreased embolic risk, but intraoperative hypoperfusion may still lead to watershed infarcts, with poor outcome. The deleterious effect of more subtle changes in cerebral perfusion pressure has not been established. Watershed-distribution infarcts are seen more frequently in patients after cardiac surgery than in the general stroke population.
The study by Gottesman and colleagues evaluated 98 patients who had an MRI, including diffusion-weighted imaging (DWI), to evaluate a stroke occurring up to 10 days after cardiac surgery. The reviewers of the 98 MRI films and 109 CT films were blinded to the patient clinical information. Prospective data entered into the Cardiac Surgery Stroke database included pre-operative blood pressure. Intra-operative blood pressure was defined as mean arterial pressure (MAP) while on cardiopulmonary bypass (CPB), excluding blood pressure measurements for patients operated on an off-pump. Change in MAP was calculated by subtracting the intra-operative average measurement from the pre-operative blood pressure value.
Watershed infarcts were noted bilaterally on 48% of DWI studies and 22% of CT scans, with unilateral watershed infarcts on 68% of DWI studies and 37% of CT scans. Patients with bilateral watershed infarcts were more likely to have undergone an aortic procedure and to have had longer CPB time. Bilateral watershed infarcts were more likely to result in an increased length of hospital stay. Poor outcome was associated with bilateral infarcts, with these patients more likely to be discharged to a long-term care or rehabilitation facility, or to die in hospital.
Patients with an intra-operative drop in MAP of at least 10 mm/Hg were 4.06 times (adjusted odds ratio; 95% CI, 1.03, 15.98) more likely to develop bilateral watershed strokes than those patients who had a smaller or no drop in blood pressure. A decrease of 10 mm MAP was the dichotomized threshold for a larger watershed stroke volume. Increase in CPB time did not reach significance as an effect on the development of bilateral watershed infarcts.
Preoperative carotid duplex results were available for 84 patients. No significant interaction was found between change in blood pressure and presence of bilateral carotid disease (defined as > 60% stenosis bilaterally) in the development of bilateral watershed infarcts. However, the small sample size limited the conclusion.
This study emphasized the utility of DWI, as compared to CT scanning, in the post-operative evaluation of the cardiac surgery patient. The decrease from the pre-operative to the intra-operative MAP appeared to be a more important risk factor for watershed infarction than was the absolute intra-operative blood pressure value. A prolonged CPB time also appeared to increase risk for watershed infarction. Limitations of the study included the lack of standardization of neurological evaluation. The intra-operative blood pressure measurement was episodic, and duration of hypotension may also factor into stroke risk. Further evaluation of the risk factors for intra-operative stroke, including stenosis of cerebral vessels should improve outcome after cardiac surgery.
Coexistent carotid stenosis and cardiac disease increases risk for intra-operative stroke, but operative management prior to cardiac surgery is controversial. Synchronous or staged surgical procedures may be considered, but carotid stenting is an option to decrease stroke risk. Oscar and colleagues reported their experience with 30 patients who received carotid stenting, followed immediately by cardiac surgery, from 1995 through 2005. The patients were 80% male, with an average age of 72 years; about 77% of patients had hypertension. Five patients had a previous stroke or TIA. Carotid stenting was performed on > 70% symptomatic or > 80% asymptomatic carotid stenosis. Patients were pre-treated with aspirin alone, and were given bolus heparin during the carotid stenting. Immediately after the stenting, the patients underwent coronary artery bypass grafting with or without valve replacement. Three in-hospital deaths were due to non-neurological complications. No strokes occurred in-hospital or after a mean follow-up of 18 months. The synchronous carotid stenting and cardiac surgery had low neurological risk and is an acceptable strategy for appropriate high-risk patients.
The neurological risk of cardiac surgery is still not well characterized, but post-operative strokes occur in 3-9% of patients. A decrease in intra-operative blood pressure and increased cardiopulmonary bypass time may result in watershed infarcts.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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