Cardiac Surgery Not Linked to Cognitive Decline

Batya Swift Yasgur, MA, LSW

December 28, 2018

Cardiac surgery does not appear to have adverse cognitive effects in comparison with cardiac catheterization, according to new research results.

In a study of more than 3000 adults aged 65 years and older, investigators compared patients who had undergone cardiac catherization to those who had undergone cardiac surgery and found little difference between the two groups in postprocedural memory changes.

"We found that people who reported undergoing heart surgery were cognitively indistinguishable from those who reported undergoing cardiac catherization," lead author Elizabeth Whitlock, MD, assistant professor, Department of Anesthesiology, University of California, San Francisco, told | Medscape Cardiology.

"This should be reassuring to clinicians who perform heart surgery, as well as patients for whom noninvasive methods of addressing serious heart disease are not an option," she said.

The study was published online December 18 in the Annals of Thoracic Surgery.

Anecdotal Reports

Like other major surgery, cardiac surgery is often followed by cognitive decline, leading to "widespread alarm" that cardiac surgery and general anesthesia may "cause durable and sometimes catastrophic cognitive decline," the authors write.

"There is a lot of information in both the popular media — mostly anecdotes — and the research world about postoperative cognitive decline," Whitlock commented.

However, research has mainly been conducted on small groups of patients, with follow-up of limited duration, "in most cases, 3 months or less," she noted.

Moreover, previous research has often compared "patients with serious disease who undergo surgery — which may have cognitive implications itself — to healthier patients," she added.

"We used a large database that is representative of the US population to examine the question of whether postoperative cognitive change is a major health problem from a different perspective," she said.

The researchers conducted a retrospective study of data drawn from the Health and Retirement Study (HRS), a population-based longitudinal study of community-dwelling American adults who undergo detailed interviews every 2 years from entry into the cohort until either death or withdrawal from the study.

The study collects data on demography, health, quality of life, cognitive status, and other factors.

The present analysis focused on HRS participants who reported undergoing a cardiac procedure at an interview between 2000 and 2014, at which time they were ≥65 years old.

At each HRS evaluation wave, participants were asked if they had undergone "cardiac catheterization" and/or "cardiac surgery" in the past 2 years.

The researchers categorized participants into the "surgery" group if they reported having undergone cardiac surgery (regardless of whether they reported having undergone cardiac catheterization) or into the "catheterization" group if they reported having undergone cardiac catheterization but not heart surgery.

All participants in the study took both the preprocedure and the postprocedure surveys.

"We selected cardiac catherization as a control because it is usually performed because of significant heart disease, yet does not require general anesthesia, ICU recovery, and a lengthy hospital stay," Whitlock explained.

The primary outcome consisted of change in memory score from the preprocedure to the postprocedure interview.

Subjective memory decline was the second outcome measure, assessed through postprocedural responses to the question of whether the participant's memory was better than, the same as, or worse than it was 2 years ago.

Potential Cognitive Benefit?

The researchers adjusted for a wide range of variables, including demographic measures, current tobacco use, medical comorbidities, financial assets, marital status, depression symptoms, independence of daily living, and presence of pain.

In addition, the following covariates were used for propensity modeling with respect to factors that differentiated patients who underwent coronary artery bypass grafting (CABG) from those who received percutaneous coronary intervention (PCI): frailty; heart failure (HF); new myocardial infarction (MI); angina at the preprocedure interview; lung disease requiring oxygen; and active malignancy.

Covariates were assessed at the preprocedure interview, with the exception of new MI, which was assessed post procedure and was used as a surrogate for urgent/emergent revascularization in the propensity model.

Of the 3105 participants, 1921 reported having undergone cardiac catheterization, and 1184 reported having undergone cardiac surgery.

Participants who underwent surgery were more likely to be male, white, married, have total financial assets greater than the cohort median, have higher educational attainment, have fewer medical comorbidities, and have less difficulty with activities of daily living.

The average preprocedure memory scores were similar between the groups.

At the preprocedure interview, 41.6% of the surgery participants and 56.7% of the cardiac catheterization participants reported heart problems, compared with 97.7% and 93.9%, respectively, post procedure.

Prior to the procedures, the modeled rate of cognitive change was −0.054 memory units per year (95% confidence interval [CI], −0.062 to −0.046 memory units per year).

During the 2-year interval spanning the cardiac procedure, the average memory change was −0.031 units (95% CI, −0.060 to −0.002 units; P = .033) greater than the modeled rate of cognitive aging before the cardiac procedures.

Participants who underwent surgery experienced an additional decrement of −0.021 memory units (95% CI, −0.046 to 0.005 memory units; P = .12) in comparison with patients who underwent cardiac catheterization.

Results were nearly identical in adjusted and unadjusted analyses.

The researchers further contextualized this coefficient by comparing the memory decrement seen with surgery to the rate of cognitive aging in the cohort (ie, −0.054 memory units per year) and found that the additional memory change of −0.021 points in the surgery group was approximately equal to 4.6 months of cognitive aging.

The researchers related these findings to a hypothetical 75-year-old patient.

A decrement in memory score of 0.021 units, that is, the predicted difference between cardiac surgery and catheterization, "implied an absolute risk increase in inability to manage finances independently of 0.26% (95% CI: 0.24% to 0.28%) and an absolute risk increase for inability to manage medications independently of 0.19% (95% CI: 0.18% to 0.21%)."

If there were indeed a causal association between cardiac surgery and additional memory decline, then 1 of 383 cardiac surgery participants would lose the capacity to independently manage money as a result of their surgery, and 1 of 513 would lose the capacity to manage their medications, they explain.

The findings remained after the researchers adjusted for covariates.

"Concerns about cognitive effects must be counterbalanced against evidence that CABG in appropriately selected patients results in more durable revascularization and improved revascularization-related outcomes, compared with PCI delivered by cardiac catheterization," the authors comment.

In fact, some evidence has "suggested this clinical benefit could translate into a cognitive benefit, as well, favoring surgical revascularization," they state.

"Subtle" Impact

Commenting on the study for | Medscape Cardiology, Mark Neuman, MD, associate professor of anesthesiology and critical care, Perelman School of Medicine, University of Pennsylvania, Philadelphia, who was not involved in the study, described it as "very interesting and very well done statistically."

He called the comparison with other cardiac disease patients who underwent cardiac catherization "clever" and noted that the HRS cohort was "unique because it was a representative cohort and also included cognitive measures."

The study has "important take-away lessons," said Neuman, who is the chairman of the American Society of Anesthesiology's Committee on Geriatric Anesthesia.

"These findings can be used for counseling patients who might have questions about heart surgery vs cardiac catherization," he said.

However, he warned that it is important "to keep the potential limitations of the study in mind, since it is a retrospective design and therefore not fully definitive."

The authors acknowledge the limitations of the retrospective design, with its potential for residual confounding.

They also note that there is a "possibility of a long-term decrement after cardiac surgery that does not manifest within the first few years."

Nevertheless, they conclude, "the population-level impact of cardiac surgery, compared with cardiac catheterization, on intermediate-term cognition, if it exists, is likely to be subtle."

Funding for the study was provided by the National Institute of General Medical Sciences of the National Institutes of Health; the National Institute on Aging; and the Foundation for Anesthesia Education and Research. The HRS is sponsored by the National Institute on Aging and is conducted by the University of Michigan. The study authors have disclosed no relevant financial relationships. Dr Neuman's research has utilized data from the HRS, but he reports no conflicts of interest.

Ann Thoracic Surg. Published online December 17, 2018. Abstract

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