A systematic review of randomized, controlled trials and prospective cohort studies found little evidence to suggest older adults experience long-term cognitive decline following cardiovascular procedures.

However, lead researcher Howard A. Fink, MD, MPH, warned better evidence is needed and recommended physicians continue to discuss the possibility of cognitive impairment. He and his colleagues published their findings online July 21 in the Annals of Internal Medicine.

Fink, who runs a memory loss clinic at the Veterans Affairs Healthcare System in Minneapolis, said none of the 21 studies he evaluated reported on the occurrence of a new diagnosis of dementia or mild cognitive impairment as defined by an objective criteria. The majority of studies examined incident cognitive impairment, but the definitions of the term differed.

“I don’t think we can make definitive conclusions,” Fink told Cardiovascular Business. “It would have been nice to have found more, bigger studies that had less risk that the results could have been biased by some methodological problem. We had to qualify all these statements about what the results mean because of limitations in the study size or because no two studies used the same definition for new cognitive impairment or incident cognitive impairment."

"Because of differences in the studies," he continued, "we didn’t feel like it was appropriate to mathematically pool [studies]…We would have liked more studies and stronger studies.”

The researchers reviewed articles, analyzed databases and used other sources to identify studies published between 1990 and January 2015 that involved coronary or carotid revascularization, cardiac valve procedures or ablation for atrial fibrillation among adults who were at least 65. Each year in that age group, there are approximately 200,000 CABG surgeries, 50,000 carotid revascularizations, 50,000 cardiac valve replacements or repairs and 10,000 catheter ablations for atrial fibrillation performed.

They included randomized, controlled trials or prospective cohort studies that reported clinically diagnosed cognitive impairment or results of neuropsychological tests or global cognitive screening tests at least three months following the cardiovascular procedures. All of the studies measured cognition before and after the procedures and had a control group.

Of the 21 trials that met the eligibility criteria, 17 were randomized, controlled trials and four were prospective cohort studies. Sixteen evaluated CABG, two studied cardiac valve replacement and three studied carotid revascularization. Each of the studies included baseline results of neuropsychological tests such as attention, memory and executive functioning. The mean age of patients was 68, and 80 percent were men.

For ablation for atrial fibrillation, none of the studies met the eligibility criteria.

“It’s hard to say much about that,” Fink said. “There are studies that didn’t meet the criteria that have mixed results. Some say it is a problem, some say it isn’t. The jury’s still out on that.”

For the valve repairs, there weren’t many studies, either. He said one study raised concerns with the transcatheter aortic valve replacement procedure, although the trial had several issues with its methodology.

The most evidence was found with CABG, carotid revascularization and other bypass surgeries. The researchers said cognitive function did not differ after the procedure between on- and off-pump CABG, hypothermic and normothermic CABG or CABG and medical management. They added that one study found lower risk for incident cognitive impairment with minimal versus conventional extracorporeal CABG, while two trials found no difference between surgical carotid revascularization and carotid stenting or angioplasty.

“We didn’t see real evidence of decline [after bypass surgeries],” Fink said. “When you looked within groups and you looked between groups, there really wasn’t much difference from prior to the procedure to the follow up. That could be reassuring for CABG…The studies that were there [for carotid revascularization] also suggested there may not be decline in the people who had the procedure.” 

As of now, there is no consensus about how to define incident cognitive impairment. Fink said it would help if there could be an agreement on a definition and tests that could be done to quantify and compare the impairment.

“It’s not that what’s being done is inherently bad,” Fink said. “It’s just really hard to make any general conclusions from the different studies when every study takes a different approach.”