CABG Not a Contributor to Long-Term Cognitive Decline

Caroline Cassels

October 18, 2007 (Washington, DC) — Contrary to previous findings, a new study suggests that coronary artery bypass graft (CABG) surgery does not contribute to long-term cognitive decline, which rather is related to underlying cerebrovascular disease.
Presented here at the 132nd Annual Meeting of the American Neurological Association, preliminary 6-year results of a prospective, longitudinal study found no significant differences in the degree of late cognitive decline following on-pump CABG surgery compared with other types of coronary artery disease (CAD) treatment.
"We don't think there's any selective long-term decline after CABG surgery that cannot be attributed to significant coronary artery disease or that a risk of late [cognitive] decline should be an issue when it comes to the choice of procedure," principal investigator Guy McKhann, MD, from Johns Hopkins University, in Baltimore, Maryland, told conference attendees.
Investigators conducted the 4-cohort study comparing short- and long-term cognitive outcomes in individuals who had undergone traditional on-pump CABG surgery with those in 3 control groups — off-pump CABG surgery; medical treatment including the use of stents; and heart-healthy controls with no major risk factors for CAD. Subjects were compared at baseline, 3 months, 1 year, 3 years, and 6 years.
At baseline, said Dr. McKhann, individuals with CAD had lower cognitive function than heart-healthy controls, but not across all cognitive domains.
In addition, they found approximately 25% of patients who underwent CABG experienced short-term cognitive problems that generally resolved within 3 months of surgery.
Controversial Area
While baseline memory and language are relatively well preserved in individuals with CAD, they have decreased motor speed, psychomotor speed, and executive function compared with those without CAD, findings that are generally associated with cerebrovascular disease, said Dr. McKhann.
"We didn't see any difference in performance between surgery and nonsurgery patients at 3 months or from there on out. We tell patients there is a risk of cognitive decline and that they are likely to have problems with their memory but that they will get better," he said.
In addition, he said, preliminary 6-year follow-up findings showed no cognitive differences between individuals who underwent on- or off-pump CABG surgery.
According to Dr. McKhann, the long-term cognitive impact of CABG has been a controversial issue. Several research groups have reported cognitive decline between 6 months and 5 years following CABG surgery. However, he said, none of these studies have included appropriate control groups.
A 2001 study reported an association between CABG and a 42% incidence of cognitive decline at 5 years (Newman MF et al. N Engl J Med 2001;344:395-402).
The research, he said, became "a very important paper in the field" and was part of the motivation behind his current study comparing cognitive outcomes in CABG patients with groups with similar cardiovascular risk factors who had not undergone this procedure for treatment of CAD.
Higher Incidence of Watershed Stroke
CABG is associated with higher rates of stroke and encephalopathy, which occur in 3% to 5% and 10% to 15% of patients, respectively. Watershed stroke is particularly common in CABG patients, and Dr. McKhann said preliminary evidence from this study suggests it may be related to fluctuations in blood pressure during the procedure.
However, he pointed out that his team, as well as other research groups, have developed predictive models based on the presence of standard cardiovascular risk factors, including hypertension, diabetes, and previous stroke, to identify potential CABG candidates at high risk for these complications.
The mortality, length of hospital stay, and long-term disability in such patients is high, he said, and may warrant the consideration of preoperative imaging studies and/or possible alternative procedures to on-pump CABG surgery to mitigate their risk.
However, the study's bottom-line is CABG surgery does not appear to contribute to long-term cognitive decline.
"We believe late decline is due to cognitive changes associated with cerebrovascular disease. These patients wouldn't be undergoing surgery or having stents put in if they didn't have significant coronary artery disease. Real attention should be placed on modifying their [CAD] risk factors, because unless something is done to modify their underlying vascular disease they're not going to do well," he said.
The study was supported by the National Institutes of Health.
132nd Annual Meeting of the American Neurological Association. Presented October 10, 2007.