May 2006
The impact of heart surgery on the brain is being tested in a study that could have a major impact on how and under what circumstances the surgery is performed.
Report: Diane Squires
As a cardiac surgeon, Professor Julian Smith is often approached by patients or their relatives who are concerned about subtle changes in personality after they or their loved ones have had heart surgery.
In his role as Monash University's Head of Surgery and Monash Medical Centre's Head of Cardiothoracic Surgery, Professor Smith has encountered family and friends of heart patients who have noticed memory loss, lack of balance or impaired vocabulary. Sometimes the patients do not admit any changes have occurred or they may not be aware of them, he says.
Now, a study being undertaken by Monash's Psychology and Surgery departments is determining whether heart surgery does, in fact, result in subtle changes in brain function and whether certain types of heart surgery may be more likely to affect cognition.
The study, by PhD candidate Ms Kathryn Bruce and her supervisors, Associate Professor Stephen Robinson, Dr Greg Yelland and Professor Smith, assesses cognition before and after heart surgery.
As well as testing motor coordination, memory and verbal fluency, the study uses the Subtle Cognitive Impairment Task (SCIT) test, developed in 2001 by Dr Yelland and Dr Robinson and doctoral students Mr Timothy Friedman and Mr Chris Hutchison, all from the School of Psychology, Psychiatry and Psychological Medicine (see below for more information on SCIT test).
Ms Bruce says the SCIT test, which relies on the subconscious, gives reliable results because participants cannot practise or remember answers from previous sessions.
"We get a clearer picture of whether there have been any changes to cognition because people can't cheat on the test the second or third time they do it," she says.
The tests are performed on heart patients before surgery, then one week and again three months after surgery to determine whether cognitive impairment is present and ongoing.
The study is looking at 90 patients aged over 55 who have undergone coronary artery bypass, valve surgery or keyhole and robotically-assisted surgery.
Initial indications show all surgery has some impact on cognitive function, but the effects of different types of surgery are yet to be assessed.
Professor Smith says his team wants to help guide doctors to use the surgical techniques that provide the best outcomes overall.
The impact of different types of surgical procedures could have major implications for how and under what circumstances they are performed in the future.
"It is important to know whether there are any differences in cognitive function between the ways in which surgery is done to know what overall impact it is having," he says.
"This study may lead to further modifications in the way we do surgery, or further adoption of minimally invasive surgery if we find that other surgeries have a greater cognitive impact.
"It may be that the stress on the body as a whole is less with keyhole surgery, which may in turn have less of an impact on cognitive function, or we may find there is nothing we can do about it and that all surgery results in some cognitive impact."
Focus on cognitive impairment
The SCIT test assesses subtle forms of impairment caused by alcohol abuse, shift work, sleep deprivation and neuro-degenerative diseases such as Alzheimer's. It is also used to measure cognitive impairment in HIV sufferers and autism in children.
Participants are asked to watch as two lines of differing lengths are flashed onto a computer screen for varying periods of time. The image is flashed so quickly that participants do not register having seen it, but the image is registered by the subconscious.
This screen is followed by a mask screen -- a series of dots on a white field -- which blocks the previous image from memory. The participants are then asked to make a decision about the length of one of the lines, and the process is then repeated.
The test compares the accuracy of response to the duration that the image is on the screen. The longer the images need to be flashed on the screen for patients to produce correct responses, the higher the level of impairment.
Dr Yelland says initial tests on cognition in the elderly have found the test is the most sensitive available. "This test can determine much earlier than any other test whether cognition is affected," he says.
Dr Robinson helped develop the test because of his interest in Alzheimer's disease.
"There is currently no test that is able to pick up the first signs of impairment in ostensibly healthy people," he says.
"Once we have a cure, we have to be able to give it to people at the beginning of illness to prevent further neural damage, so if we have a test that can pick up impairment in its earliest stages, that will be very useful."
For more information contact Diane Squires on +61 3 9905 9315 or email diane.squires@adm.monash.edu.au.
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