A broad retrospective review of the effects of coronary artery bypass grafting (CABG) on memory and other brain functions concludes that, while there may be transient short-term effects, the procedure itself probably does not cause late or permanent neurological effects.
In an article published online April 25, 2005, in the Annals of Neurology, the authors argue that the late cognitive declines seen in some long-term studies are likely associated with progression of underlying conditions such as cerebrovascular disease rather than the surgery itself.
"We think that there are short-term cognitive changes after CABG in a subset of patients, but absent a frank stroke, these changes are generally mild and transient," said author Ola Selnes, Ph.D., professor of neurology at Johns Hopkins Hospital in Baltimore, Maryland. "We believe most patients who experience cognitive decline will return to their baseline by three months or sooner."
The exceptions, according to Selnes, might include older patients and those with risk factors for cerebrovascular disease or a history of stroke.
In their review article, Selnes and co-author Guy M. McKhann, M.D., also of Johns Hopkins, surveyed the published studies on cognitive changes following CABG. Confusing the issue, they point out, is the variability in the way this question has been approached.
Selnes and McKhann note that the surgical procedure itself varies among different institutions and surgeons. Similarly, there is wide variance in study populations and control groups, follow-up periods, and statistical analysis.
It is curious, the authors note, that studies should continue to find cognitive deficits despite the fact that CABG is a procedure in evolution, with surgical and anesthesiological techniques improving vastly over the past decades. This may be due in part to the reality that the population having the surgery is becoming older and sicker, with more hypertension, diabetes, previous strokes, and other disorders.
"In this paper, we reassessed what we think we know about cognitive decline attributable to the use of cardiopulmonary bypass versus cognitive decline due to pre-existing vascular disease of the brain," said Selnes. "Just about everyone agrees that some patients do suffer cognitive decline after CABG, but almost nobody agrees on how serious this decline is, and how long it lasts."
The authors find that the existing literature confirms the existence of mild deficits in the period up to three months after surgery, possibly due to minor disruption in blood flow that can be result from any major surgery, or other factors associated with surgery such as inflammation or complications of anesthesia.
But when they looked closely at the most authoritative studies -- those with appropriate control groups -- the authors failed to find strong evidence that cognitive deficits persist after three months in most patients.
"We believe that patients should not be discouraged from having CABG because of the risk of late cognitive decline," said Selnes.
He adds that their review emphasizes the need to have an appropriate control group when looking at cognitive outcomes after a surgical procedure.