Neuropsychological outcomes of coronary bypass surgery

Investigators:
Associate Professor James Tatoulis, Cardiothoracic Surgical Unit, The Royal Melbourne Hospital; The team from the Heart Research Centre included Dr Marian Worcester, Dr Christine Ernest, Dr Peter Elliott, Dr Barbara Murphy, Ms Rosemary Higgins, Dr Alan Goble, Mr Michael Le Grande,  Associate Professor David Andrewes, Department of Psychology, The University of Melbourne.

A recently completed two-year study compared neuropsychological outcomes of two surgical techniques being used to perform coronary bypass graft surgery at The Royal Melbourne Hospital, undertaken together with Associate Professor James Tatoulis. This study was part of a randomised controlled trial being undertaken by the Cardiothoracic Surgical Unit at The Royal Melbourne Hospital.

Mood disturbances and cognitive deficits commonly occur after conventional bypass surgery using the heart bypass pump. Subtle neuropsychological changes occur in 20% to 60% of patients. However, past research suggests that patients who are operated on without cardiopulmonary bypass ("off pump") have a better recovery and fewer medical complications than patients whose surgery is undertaken using the heart bypass pump ("on pump"). Improved physical outcomes are thought to be associated with improved neuropsychological performance.

Our team measured cognitive functioning in patients enrolled in this trial of "on pump" versus "off pump" techniques to see whether the new surgical approach improved cognitive outcomes, including memory. Patients were assessed before surgery and at two and six months to measure cognitive functioning using 11 standardised cognitive tests, covering a variety of domains. One hundred and twenty patients were recruited to the study.

Results showed there were no differences in cognitive test scores between the "off pump" and "on pump" groups at any time. Neither were there differences between "off pump" and "on pump" groups in the incidence of cognitive deficits, with the exception of a test measuring verbal fluency. Overall findings suggest that the off pump group is generally comparable to the on pump group in terms of short-term and long-term post-surgical cognitive outcomes. However, there is some suggestion that the off pump technique may result in subtle post-surgical cognitive benefits specific to verbal fluency.

The use of data modelling methods that allowed for linear and non-linear models of change is an important strength of the study.  Most cognitive test scores changed over time in a non-linear fashion, with more rapid changes in the early post-surgical months.  Results of this study were presented at the annual meeting of the Cardiac Society of Australia and New Zealand.

While many studies have investigated cognitive impairment in patients following coronary bypass graft surgery, few have evaluated their pre-surgical cognitive functioning. We compared the neuropsychological functioning of 109 patients in the above study with that of a healthy control group and published normative data. Cognitive test scores of candidates for surgery were reduced compared with those of a healthy control group and published normative data. These findings are consistent with those of a growing number of studies. One explanation for pre-bypass cognitive difficulties could be emotional distress prior to surgery. The cardiac disease process itself has been implicated as a cause of poor cognitive performance before surgery.  Unrecognised cerebrovascular disease may accompany cardiovascular disease, since the underlying pathophysiology of both disease processes is similar.

Relatively little is known about the impact of cognitive difficulties upon patients in their everyday lives. A further investigation is planned to examine the effects of cognitive difficulties, such as poor memory.

Funding: Percy Baxter Charitable Trust; The Royal Melbourne Hospital Research Foundation ; The Eirene Lucas Foundation