Ann Thorac Surg 2004;77:603
© 2004 The Society of Thoracic Surgeons
Ola A. Selnes, PhD
Department of Neurology, The Johns Hopkins Hospital, Meyer 100, 600 N Wolfe St, Baltimore, MD21287, USA
Postoperative cognitive impairment continues to be a major concern for patients undergoing coronary artery bypass grafting (CABG) with conventional cardiopulmonary bypass. Previous studies have identified some patient characteristics that predict postoperative cognitive impairment, including older age, diabetes, and degree of severity of aortic atherosclerosis. The study by Ho and colleagues adds cerebrovascular and peripheral vascular disease to this list of patient characteristics associated with cognitive decline. In the absence of a control group, the authors estimated the incidence of significant decline from baseline to 6 months using three different methods: 1 SD decline, 0.5 SD decline, or 20% decline. With use of these methods, the incidence of decline ranged from 8% to 37%.
In light of findings from previous studies that have suggested patients with cognitive decline during the immediate postoperative period tend to recover by 36 months after surgery, these numbers may seem high. Why would a subset of patients in this study continue to have worse performance at 6 months than at baseline? Is the use of cardiopulmonary bypass circuitry responsible for this decline? Their finding that bypass time was inversely related to neurocognitive decline may suggest that the factors that predict decline 6 months after surgery may be somewhat different from those that predict immediate postoperative decline. There is now considerable evidence that, even in the absence of cardiac surgery, having one or more risk factors for cerebrovascular disease is associated with mild cognitive decline over time when compared to individuals free of such risk factors.
This brings up the importance of having a control group for these kinds of studies. What proportion of patients with risk factors for cerebrovascular disease similar to those of the CABG patients in this study, but no surgery, would have decline in cognitive performance 6 months after their baseline assessment? This is an important question, not just for understanding the impact of CABG on cognition, but also for postsurgical management of patients with cerebrovascular disease. There is some evidence suggesting that late cognitive decline after CABG can be minimized with stricter medical management of hypertension, diabetes, and other risks for cerebrovascular disease after the surgery. Therefore, for at least some patients, what happens to them during the months and years after surgery may be as important for their long-term cognitive prognosis as what happens during the bypass surgery itself.