Reducing the Risk of Stroke in Coronary Artery Bypass Graft Surgery

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Abstract

Strokes are the biggest and most tenacious problem in coronary artery bypass graft (CABG) surgery today. CABG surgery has been the 'gold standard' treatment of multi-vessel coronary artery disease (CAD) since its development over 40 years ago. Despite continued improvement in the outcome for patients, strokes are still a persistent complication; however, we have been able to reduce the risk of stroke to a very low frequency. It has ranged from 0.4% to 5.4% for the last 15 years.

There has been more emphasis recently on the lifechanging effects of CABG surgery. Not only are we focusing on improving survival rates and reducing heart attacks, but also on decreasing the occurrence of neuropsychological problems. Measurement of these more subtle cognitive functions after CABG surgery has allowed negative events to be recorded from as few as 25% of cases to as many as 79% of CABG surgery patients when very stringent criteria are used. These changes are much more common at the time of discharge, but are reduced at six weeks and to even lower levels several months after surgery. Some studies have noted these changes even after five years. For elderly patients, the late effects tend to worsen with time after surgery and seem more pronounced. The neurological changes have been associated with the presence of diabetes mellitus, vascular disease and pulmonary maladies. Unfortunately, stroke rates associated with CABG surgery have not changed much in the last 15 years, even though CABG surgery has changed significantly.

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Not all central nervous system (CNS) events associated with CABG surgery are strokes. One can argue at some length about what is and is not a neurological change in a patient undergoing major surgery. Generally, neurological changes after surgery are divided into two groups. Devastating events or strokes (Type I) are motor and skill deficits, coma and death with usually easily identifiable radiological defects. Subtle cognitive changes (Type II) are less severe and can be difficult to measure because they frequently do not have associated identifiable radiological findings. These include cerebral functions involving memory loss, concentration deficits and complex reasoning abilities. Though more difficult to identify, they remain quite serious and life-altering.

Strokes and CNS changes are quantified financially to hospitals, as well as to individuals. Roach, et al. published in the New England Journal of Medicine a study of 2,108 CABG surgery patients. They found that the occurrence of a stroke (Type I) injury, seen in 3.1% of cases, added an average of eight days to an intensive care unit (ICU) stay and seven days to the ward recovery stay. Type II dysfunctions still added four ICU days and seven days to the ward recovery stay. Many institutions estimate that one stroke will cost a facility in excess of US$40,000 over the course of the patient's treatment. Individual loss is much more difficult to measure; however, it is usually quite substantial, if not devastating, financially.

This spectrum of effects and the persistence of the problem have caused surgeons and scientists to examine the neuropsychological changes after heart surgery. New understanding of these principles has allowed innovative people to develop new strategies and enabling technologies to combat strokes after heart surgery. This article examines the most tested and studied operation performed on humans: the CABG surgery.

Traditional CABG surgery is a dramatic event. A blood pump called a heart-lung machine and a large (about six inches) frontal chest incision are employed most commonly to complete the task.

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