When discussing cognitive decline after cardiac surgery, particularly with cardiopulmonary bypass (CPB), the first step is to define what is meant by cognitive decline. The Fifth Edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) divides neurocognitive disorders into 3 syndromes: delirium, mild neurocognitive disorder, and major neurocognitive disorder. The condition most commonly associated with CPB is mild neurocognitive disorder, defined as decline in 1 or more cognitive domains: complex attention, executive function, learning and memory, language, perceptual-motor skills, and social cognition.

Using this framework for cognitive decline, the authors report that the scientific literature has been inconsistent in its study methodology. In many cases, studies lack control groups, use different cognitive tests that do not assess the same functions, fail to distinguish between short- and long-term outcomes, or have incomplete follow-up. Together, these factors have created a misleading perception of a cause-and-effect relationship between cardiac surgery and permanent cognitive decline.

Through an exhaustive literature search and by distinguishing early cognitive decline (<6 months) from late cognitive decline (>6 months), this review analyzes the inconsistencies across different studies and relies on randomized clinical trials with large sample sizes to challenge the presumed causal role of CPB in cognitive decline.

COMMENTARY:

It is never easy to challenge what has become established in society or, in this case, within the scientific community. Even among physicians, certain beliefs persist beyond what can be refuted by a single study. Nevertheless, this should not prevent us from questioning concepts that we tend to take for granted.

In my view, the interest of this review lies in 3 main aspects: the findings of a meticulous analysis that exposes the inconsistency of the available studies, the importance of sound methodology, and the difficulty of dismantling established assumptions.

The results of this article highlight the lack of a clear link between cognitive decline and cardiac surgery or CPB. To do so, the authors analyze publications ranging from the earliest reports around the 1970s to the present day. They identify factors associated with cognitive decline after cardiac surgery, including postoperative pain, medication, general anesthesia, thromboembolism, baseline cognitive impairment, and age. They also report the use of 42 different tests, which not only assess different cognitive functions in different ways, but are also performed at different postoperative time points, often without subsequent follow-up and, in some cases, without baseline preoperative testing.

However, when randomized clinical trials such as CORONARY or ROOBY are analyzed, in which neurocognitive testing was performed before surgery, at 1 month, and at 1 year after cardiac surgery with and without CPB, no significant differences in cognitive decline at 1 year are demonstrated between procedures performed with or without CPB. Similarly, another study comparing percutaneous coronary intervention (PCI) with CABG with and without CPB not only showed no significant cognitive differences between these strategies, but also observed memory decline when off-pump CABG was compared with PCI, a finding that was not present when on-pump CABG was compared with PCI.

When cardiac surgery is not the main focus of analysis, epidemiological studies on the development of cognitive decline may provide further insight. In a study from the Rochester Epidemiology Project, which examined new cases of dementia over a 5-year period, previous cardiac surgery was not shown to be a risk factor for this type of cognitive impairment. This leads us to consider the hypothesis that cardiovascular disease itself may perhaps be an independent risk factor in the progression of cognitive decline.

Another point worth emphasizing is the importance of robust initial methodology in any type of research. From experimental studies to meta-analyses, we must be cautious when designing studies and critical when interpreting them. A well-designed baseline demographic assessment, including the variables needed to address the primary and secondary objectives, together with adequate follow-up, is crucial, especially when dealing with potentially reversible morbidities. We should also recognize the difficulty of comparing studies when the methods used to measure the same variable are different or even incompatible.

Finally, I would like to emphasize and acknowledge the complexity of challenging the evidence available to date. The early years of cardiac surgery were not easy, and it is possible that the first articles addressing cognitive decline after heart operations sought to question the safety of these procedures. For this reason, much of the value of this article lies in its critical reading of the evidence accumulated so far and in the authors’ ability to identify potential confounding factors that may have blurred the distinction between causality and coincidence.

REFERENCE:

Waterford SD, Whitlock EL, Ad N. Mind over heart: Is cognitive decline after cardiac surgery real? J Thorac Cardiovasc Surg. 2026 Apr;171(4):954-960.e1. doi: 10.1016/j.jtcvs.2025.11.001.