In the Duke study, 261 patients having bypass surgery were tested for their cognitive capacity (i.e. mental ability) at four different times: before surgery, six weeks, six months, and five years after bypass surgery. Patients were deemed to have significant impairment if they had a 20% decrease in test scores.
This study had three major findings
- Cognitive impairment does indeed occur after bypass surgery. This study should move the existence of this phenomenon from the realm of locker room speculation to the realm of fact.
- The incidence of cognitive impairment was greater than most doctors would have predicted. In this study, 42% of patients had at least a 20% drop in test scores after surgery.
- The impairment was not temporary, as many doctors have claimed (or at least hoped).
The mental impairment was not due to the patients' age (which averaged 61). The results from the Duke study were compared to results from a similar study among patients of the same age who did not have bypass surgery. The decline in mental capacity in those who had bypass surgery was 2 -3 times higher over five years than in patients who did not have surgery.
The authors could not say what, exactly, caused the impairment in mental capacity. The most common speculation is that the mental changes are due to the showering of the brain with tiny particles (microemboli) related to the use of the bypass pump (the heart/lung machine, that oxygenates and pumps the blood while the heart is stopped during surgery.) If this is the case, then newer surgical techniques such as beating heart surgery (in which the bypass pump is not used) should help to minimize the problem. The Duke study was completed prior to the use of such procedures.
Doctors have reacted to the Duke study with mixed feelings. While most believe the Duke study was extremely well designed, many criticize it saying that "in my hospital we don't see this," or that surgical techniques have improved in the 5 years since this study was done, or that publicizing this study will discourage patients from getting necessary surgery.
What should patients think about this study?When making major decisions such as whether or not to have a major procedure like coronary artery bypass grafting you want a doctor who will take into account all the potential risks and benefits.
The Duke study is the best information available right now, and must be taken into account. So when considering bypass surgery, make sure you have the answers to the following questions:
- Is the surgery likely to prolong my survival, or is it being done electively, simply to relieve symptoms?
- Are there any other viable alternatives, such as medication, angioplasty, or stenting? (This question is becoming particularly relevant, with stent technology advancing as rapidly as it is.)
- If I must have bypass surgery, is there any reason I cant have some form of minimally invasive surgery where the bypass pump is avoided? (While it is not proven that the bypass pump causes the cognitive problem, it does seem to be the leading suspect at this point.)
If you do need to have bypass surgery, keep in mind that the majority of patients in the Duke Study had no significant deterioration their mental capacity, and further, of the ones who did, many never noticed it in their day-to-day lives.
Nonetheless, if you are told you ought to have bypass surgery, unless it is vital that bypass surgery be performed immediately, the Duke study ought to provide one more reason to seek a second opinion before choosing this option.