In a wide retrospective review of the effects of coronary artery bypass grafting (CABG) on memory and other brain functions a team of U.S. researchers has concluded that, while there may be transient short-term effects, the procedure itself probably does not cause late or permanent neurological effects.
The authors of the review Ola Selnes, Ph.D., professor of neurology at Johns Hopkins Hospital in Baltimore, Maryland and Guy M. McKhann, M.D., also of Johns Hopkins, say that the late cognitive declines seen in some long-term studies are most likely to be associated with the progression of underlying conditions such as cerebrovascular disease rather than the surgery itself.
They believe that there are short-term cognitive changes after CABG in some patients, but other than a stroke, these changes are generally mild and transient and most patients who experience cognitive decline return to their baseline by three months or sooner.
According to Selnes, the exceptions might include older patients and those with risk factors for cerebrovascular disease or a history of stroke.
In their review article, the pair surveyed the published studies on cognitive changes following CABG. The variability in the way this question has previously been approached confuses the issue as the surgical procedure itself varies among different institutions and surgeons and there is a wide variance in study populations and control groups, follow-up periods, and statistical analysis.
The authors found it curious that studies continue to find cognitive deficits despite the fact that CABG is a procedure in evolution, with surgical and anaesthesiological techniques improving vastly over the past decades. This they feel could 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.
Selnes says that 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 and they have attempted in their study to reassess what is known about cognitive decline attributable to the use of cardiopulmonary bypass, versus cognitive decline due to pre-existing vascular disease of the brain.
They found 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 as a result of major surgery, or other factors associated with surgery such as inflammation or complications of anaesthesia.
But when they looked closely at the most authoritative studies they failed to find strong evidence that cognitive deficits persist after three months in most patients and say that patients should not be discouraged from having CABG because of the risk of late cognitive decline.
Selnes emphasizes the need to have an appropriate control group when looking at cognitive outcomes after a surgical procedure.
The article is published online April 25, 2005, in the Annals of Neurology.