Ann Thorac Surg 2003;76:435
© 2003 The Society of Thoracic Surgeons
Original article: cardiovascular
Invited commentary
Sotiris Stamou, MD, PhDa
a Department of Cardiac Surgery, Georgetown University Hospital, 3800 Reservoir Road, NW Washington, DC 20007, USA
e-mail: cvsisfun{at}hotmail.com
The incidence of clinically obvious strokes after coronary artery bypass graft operations is reported to be between 0.8% and 5.2%. It is estimated that between 5,000 and 35,000 new strokes develop as a result of this procedure, which possibly makes coronary artery bypass surgery the single largest cause of iatrogenic stroke in the U.S. In this study, Likosky and colleagues present a prediction model for stroke based on intraoperative and postoperative factors. By virtue of the sample size of this multiinstitutional study, they were able to create a powerful model to identify intraoperative and postoperative risk factors that are more likely to be associated with this outcome in patients who had coronary artery bypass with cardiopulmonary bypass (so-called on-pump patients). Their findings are confirmatory of previous reports of predictors of stroke after coronary artery bypass. Prolonged inotropic support (use of 
inotropes at 48 hours) emerged as the most potent risk factor, while use of intra- or postoperative intra-aortic balloon pump, return to bypass, and low cardiac output failed to emerge as independent risk factors of postoperative stroke. Factors such as postoperative atrial fibrillation and prolonged cardiopulmonary bypass seem more obvious.
The study by Likosky and colleagues focused solely on patients who had cardiopulmonary bypass as part of the surgical procedure. Previous studies suggest that coronary bypass surgery without cardiopulmonary bypass is associated with a lower risk for stroke. To date, there is no randomized trial evidence to suggest a lower incidence of stroke after off-pump surgery. Moreover, the occurrence of clinically obvious stroke, the outcome measure in this study, likely represents only the tip of the iceberg. Postoperative cognitive impairment that may not necessarily fall under the rubric of "stroke," possibly represent multiple territory cerebral microinfarcts occurring as a result of embolic phenomena. These patients may be classified in other categories, such as delirium, depression, or dementia. Thus the 1.5% complication rate of clinically obvious stroke reported in the current article most likely represents an underestimate. Unfortunately, diagnosing these patients has traditionally been difficult in the past. Newer modalities may show promise in that regard.
The typically poor postoperative course of patients who develop stroke after coronary artery bypass surgery underlines the need for timely recognition, prevention/modification of factors that predispose to stroke. Information from this multi-institutional study may help design therapeutic strategies to decrease the incidence of this catastrophic complication. A modification of the surgical strategy, such as the "no-touch technique" described by Mills and Everson, might also be important in these patients. Furthermore, the increasing recognition of the role played by aortic atheroma, and the innovative steps taken to minimize this risk including epiaortic scanning and the potential for intra-aortic filtration, are all currently undergoing large-scale, prospective evaluations. Previous authors have demonstrated that use of epiaortic scanning and of a "Y" graft, which uses the radial artery joined to the pedicled left internal mammary artery in a Y-graft fashion, was associated with a significantly decreased incidence of cerebral embolization secondary to aortic instrumentation. In addition, pharmaceutical agents such as gangliosides, glutamate receptor antagonists, and antioxidants may potentially minimize neuronal damage and decrease the occurrence of stroke. It has also been suggested that prostacyclin infusion during cardiopulmonary bypass may lower the incidence of encephalopathy and stroke during coronary artery bypass by preventing adhesion of platelets to the extracorporeal tubing and subsequent microembolization. Further studies are needed to prospectively investigate the potential benefits of pharmaceutical agents in reducing the incidence of stroke after coronary artery bypass. Coronary artery bypass without cardiopulmonary bypass needs further investigation as an approach for decreasing the incidence of stroke, and should potentially be considered in patients with carotid artery disease or other high-risk characteristics for stroke. However, the benefits of this technique have not been evaluated in a prospective randomized setting.
