Since its introduction in the 1960s, coronary artery bypass grafting (CABG) has offered millions of Americans renewed health and longer lives. But for some, this surgery affects their ability to concentrate and remember.
"Were talking about the ability of a person to perform mental tasks. Short term memory and quick calculations are most susceptible, says Patrice Desvigne-Nickens, MD, at the National Heart, Lung, and Blood Institute (NHLBI). These deficits can progress and affect quality of life, including independence.
The exact number of people who suffer postoperative cognitive changes from CABG is unknown. Researchers use different testing methods to assess mental functioning. Studies indicate anywhere from 20%-80% of bypass patients suffer some mental impairment. Initially, doctors thought the deficits were temporary. But researchers at Duke University Medical Center measured declines in 42% of patients five years after surgery.
A number of factors likely work together to cause the mental changes.
Were trying to understand this phenomena of neurocognitive decline, says Dr. Desvigne-Nickens, the leader of the Cardiovascular Medicine Research Group at the National Heart, Lung, and Blood Institute.
Bypass surgery is performed to treat coronary artery disease (CAD). CAD occurs when fatty plaque builds up in the arteries that supply the heart with oxygen. This buildup blocks blood flow to the heart muscle. During the surgery, doctors route blood flow around the blockages by using vessels from other parts of the body to restore blood flow. In the typical surgery, a patient is placed on a heart-lung machine, their heart is stopped, and the machine supplies the body with oxygen during the operation. Debate continues in the medical field as to whether the heart-lung machine plays a role in cognitive changes. One theory is that tiny air bubbles or blood clots could break off and travel to the brain, causing damage. Others suggest that the machine may not provide enough oxygen to the brain.New minimally invasive surgeries allow doctors to redirect blood flow without stopping the heart or using the heart-lung machine. But the success of these procedures, and whether they produce fewer cognitive problems, remains controversial. Doctors are also investigating other factors that may be contributing to cognitive changes after the surgery.In addition, the same disease process that caused the hearts blood vessels to clog is also likely clogging the arteries that supply the brain. In one study, patients given a battery of seven cognitive performance tests showed memory problems before surgery, though the changes were subtle. After the surgery, patients showed new cognitive impairments.
When you expose a brain thats already vulnerable (because of the arterial disease) to a major stressor like bypass surgery, you see new manifestations of problems, says Julian Keith, PhD, lead author of this study. Who Is at Risk?The Duke study also found that age and having less formal education increased a persons risk of long-term cognitive problems. Some speculate that the increased risk in age could be due to older adults being more likely to have existing cerebral disease, or younger people better tolerating decreases in brain blood flow during surgery. More education may increase the patients ability to compensate for cognitive difficulties, but doctors are still studying the reasons for this.As more information on cognitive decline and CABG is gained, doctors may due a risk assessment that includes tests to check for brain disease. Dr. Keith thinks educating patients about the risk would help them to better adapt if these changes occur. What Is Being Done?One of the most terrifying things a person goes through is the possibility of losing intellectual ability, especially memory, Dr. Keith said. Thats one reason why we need to find ways to better protect cognitive function.Dr. Desvigne-Nickens hopes making small changes to the surgery will help prevent cognitive changes. She also believes that these changes may be reversible, meaning there is the potential for treatment regardless of improvements in surgical techniques. Scientists continue to investigate strategies they think will protect the brain.
Greater use of angioplasty offers some patients an option. During this cardiac procedure, a doctor inserts a catheter (with a balloon) into an artery in the arm or groin. This catheter is threaded through the vessel to the heart, where the balloon is inflated and opens the artery. Doctors now typically place a mesh stent in the artery to keep it open. But not everyone is a candidate for the less invasive procedures. The risk of cognitive decline should not stop patients from having bypass surgery, especially since the majority of patients experience no memory problems afterward. RESOURCES: American Psychological Associationhttp://www.apa.org National Heart, Lung, and Blood Institutehttp://www.nhlbi.nih.gov CANADIAN RESOURCES: Health Canadahttp://www.hc-sc.gc.ca/index_e.html Mental Health Canadahttp://www.mentalhealthcanada.com/ References: Bronster DJ. Neurologic complications of cardiac surgery: current concepts and recent advances. Curr Cardiol Rep . 2006;8:9-16. Keith JR, Puente AE, Malcolmson KL, et al. Assessing postoperative cognitive change after cardiopulmonary bypass surgery. Neuropsychology . 2002;16:411-421. Newman MF, Kirchner JL, Phillips-Bute B, et al. Longitudinal assessment of neurocognitive function after coronary-artery bypass surgery. N Engl J Med . 2001;344:395-402.
Selnes OA, McKhann GM, Borowicz LM Jr, et al. Cognitive and neurobehavioral dysfunction after cardiac bypass procedures. Neurol Clin . 2006;24:133-145 Last reviewed May 2008 by Ryan Estvez, MD, PhD, MPHPlease be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.