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Heart surgery--particularly coronary artery bypass graft (CABG) surgery--is one of the most common surgical procedures in the United States, with more than 650,000 CABG surgeries performed each year. Advances in surgical techniques have made heart surgery safer--even for patients formerly not considered candidates for surgery, including older patients and those with other medical conditions such as kidney disease and diabetes.

The goals of surgery are to reduce symptoms, improve quality of life and ultimately improve survival. Unfortunately, a percentage of patients complain of mental changes, even five years after bypass surgery. Family members report the patient is “not the same” as before surgery. This condition, termed neurocognitive dysfunction, may include symptoms of being short-tempered, memory loss, inability to concentrate or perform basic mental tasks.

Several studies have focused on determining why neurocognitive changes occur and who is at risk. Unfortunately, the research that is published often leads to more questions than specific answers.

What brain-related problems can occur after heart surgery?

The most common problems related to the brain and cognition (ability to think) that can occur after cardiac bypass surgery include:

• Delirium – An obvious state of mental confusion. It occurs in 10 percent to 15 percent of patients and may be related to many causes including the aftereffects of anesthesia, pain medications, fever or postoperative infection, or withdrawal from habitual alcohol use. Delirium is usually of short duration but may result in a prolongation of hospital stay.
• Short-term cognitive changes -- Problems with memory, attention and concentration can occur in 33 percent to 83 percent of patients. These short-term cognitive changes generally improve over time.
• Long -term cognitive changes --- Inability to process complex problems, follow directions or plan actions. These changes are often more subtle and careful testing has demonstrated that they can occur in 20 percent to 60 percent of patients after bypass surgery. Patients may also develop a delayed worsening of cognitive function. In a 2001 study, published in the New England Journal of Medicine, Newman et al showed that a decline in cognitive function was present in 42 percent of patients 5 years after bypass surgery. This is now thought to be related to the effects of underlying vascular disease (atherosclerosis which led to the heart surgery) rather than a delayed effect of the heart surgery itself.

A less common but more serious brain-related problem that may be associated with bypass surgery is stroke. The risk of stroke is primarily related to the complexity of the heart operation being performed. The incidence of stroke ranges from 1-5 percent after coronary artery bypass surgery alone but can be as high as 20 percent when bypass surgery is combined with valve replacements or repairs or aortic reconstruction procedures.

What happens during heart surgery that causes changes in cognitive function?

Experts believe there are several factors that may contribute to problems with mental functioning after heart surgery:

• During heart surgery, the patient's body temperature is lowered (hypothermia), which allows the heart to remain stopped longer without damage. Lowering body temperature also has a protective benefit to the brain. Some researchers believe the brain's protection may be decreased if the body is warmed too quickly after heart surgery, placing sensitive brain tissue at risk for damage.
• During many heart surgeries, patients are placed on cardiopulmonary bypass, a machine that oxygenates the blood and circulates it throughout the body during surgery. It is not known for sure, but cognitive changes may be related to emboli (tiny particles, most commonly cholesterol or blood clots) that are dislodged when the heart-lung bypass machine is removed from the aorta.
• Reduced blood flow to the brain, which can be further reduced in the setting of blockages of the brain arteries can also result in cognitive changes postoperatively.

Who is at risk for neurological complications?

Recent studies suggest that cognitive decline after open heart surgery may be caused by underlying patient factors. These risk factors:

• Older age
• Previous stroke or “mini-strokes” or TIAs (transient stroke warning symptoms)
• Evidence of cognitive dysfunction before surgery
• Atherosclerosis or “hardening of the arteries” involving the aorta, the blood vessels supplying the brain (carotid arteries) or the limbs (peripheral vascular disease)
• Chronic kidney failure
• Diabetes
• High blood pressure
• Chronic alcohol use

There also may be a genetic basis and involvement of the inflammatory response. Further investigation is needed to increase our understanding of early and late cognitive decline associated with bypass surgery.

What can be done to protect the brain during heart surgery?

An initial step in helping to protect the brain during heart surgery is to identify patients who might be at increased risk for neurological complications before their operation. For some patients, additional consultation with a neurologist, imaging of the brain or brain arteries, or laboratory tests can provide helpful information which may result in adjustments in their medications or adjusting the surgical procedure, when possible. Improvements in coronary artery bypass procedures are always being developed to help preserve cognitive function. These include heart-lung bypass machine improvements, warming procedures, and the beating-heart bypass surgery procedure. Beating heart surgery does not use the heart-lung bypass machine during surgery (click here for more information) .

What can you do?

Some people may become frustrated during recovery from heart surgery because they are not as sharp mentally as they were before surgery. The entire body, including the brain, was seriously stressed during surgery. With time, in most cases, normal cognitive functioning returns but in the interim, the patient may need assistance with complex activities, such as finances, or supervision with their medications to ensure they are complying with their treatment plan.

If cognitive changes persist, further evaluation is needed to determine if the symptoms are related to depression or neurocognitive changes. If the patient’s symptoms are related to neurocognitive changes, an evaluation with a neurologist and diagnostic tests will be needed to determine the underlying cause.

Tests that may be helpful in diagnosing neurocognitive changes include an MRI or CT scan of the brain, formal neurocognitive testing (also called psychometric testing), a psychiatric evaluation if depression is suspected, and blood tests. 

Treatment is dependent on the underlying cause. Neurocognitive rehabilitation programs, often part of speech therapy programs, and medications can help some patients.

If you have concerns about neurocognitive changes after surgery, please talk to your doctor.