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DURHAM, N.C. – In the largest and longest study of its kind, researchers at Duke University Medical Center have definitively shown what previous studies have hinted at – depression is a strong independent risk factor for death in patients who have undergone coronary artery bypass surgery to restore blood flow to the heart.
Because depression appears to double the chances of death, the researchers believe that bypass surgery patients should be screened to assess a patient's likelihood of depression.
The findings of the Duke team's study were published in the August 23, 2003, issue of the journal Lancet. The study was supported by numerous grants from the National Institutes of Health.
In analyzing the medical records of more than 800 patients who underwent bypass surgery at Duke, the researchers found that those patients with moderate to severe depression at the time of their surgery -- or those with mild depression prior to surgery that persisted for at least six months following surgery -- were more than twice as likely to die during the follow-up period. Some patients were followed as long as 12 years after surgery, with the average follow-up being 5.2 years.
"Despite our advances in surgical and medical management of patients after coronary artery bypass surgery, depression is an important independent predictor of death after surgery and should be carefully monitored and treated if necessary," said clinical psychologist James Blumenthal, Ph.D., lead author on the Lancet article. "We believe that psychological assessment before and after surgery could be a low-cost and relatively easy way of potentially saving lives."
Because bypass surgery, which has been performed for more than 30 years, has been so successful in saving lives, past studies with small samples have had so few deaths that it has been difficult for researchers to make statistically significance conclusions. However, the Duke researchers have been collecting clinical and psychological data on heart surgery patients for more than two decades, which allows them to perform these long-term outcomes studies.
"We were very surprised at the strength of the association between depression and mortality," said Mark Newman, M.D., chairman of anesthesiology at Duke and co-investigator of the study. "As we statistically controlled for other risk factors, we began to worry that the association might be due to the advanced age and other illnesses, which could be a reason for the depression.
"But, after all the statistical analyses, we found that depression is truly separate from every other risk factor as a robust and significant independent risk factor," Newman said. "The key for us now is to determine whether or not treating the depression – whether by medications, psychological approaches or exercise – can positively affect outcomes."
PHOTO CREDIT: This photo is the property of Duke University Medical Center. Use of this photo requires credit to Duke University Medical Center. If you have any questions, please contact the Duke University Medical Center News Office at 919-684-4148. |
The Duke team analyzed the records of 817 patients undergoing bypass surgery from 1989 to 2001. During that time period, 122 patients, or 15 percent, died. Patients who were already being treated for depression or other mental illnesses were excluded from the analysis.
All of the patients took a standardized test to assess symptoms of depression the day before surgery as well as 6 months after surgery. The test is known as the Center for Epidemiological Studies – Depression (CES-D) survey, a 20-question self-report instrument that can be administered by psychologists in less than 15 minutes.
"Of that group of patients, thirty-eight percent met the criteria for being depressed," Blumenthal said. "Specifically, twenty-six percent we considered to be mildly depressed, and and additional twelve percent with moderate to severe depression."
Patients who scored below 16 on the CES-D were considered non-depressed, with a score between 16 and 26 being considered mildly depressed. Patients scoring above 27 were considered moderate to severely depressed. The researchers then examined the relationship of the depression scores with the subsequent mortality data.
During the 12-year follow-up period, 10 percent of the patients who were never depressed died, compared to 19 percent of patients who were persistently depressed, the researchers said.
"Interestingly, patients with mild depression – a score between 16 and 26 – before surgery and who had scores that remained high six months later had the same risks as those with moderate to severe depression before surgery," Blumenthal explained. "However, those mildly depressed patients whose scores decreased after six months were at no more risk than those who weren't depressed to begin with."
The researchers point out that, while their study demonstrated a strong association between depression and mortality, it could not determine the mechanisms involved. Although there a many theories, further studies that pinpoint the mechanism will be important to developing a successful intervention, they said.
Depression has been linked to other such cardiovascular risk factors as insulin resistance, hypertension, obesity, increased cigarette smoking, alcohol abuse and physical inactivity. The Duke researchers are currently investigating several potential mechanisms, including the effects of depression on platelet aggregation and heart rate variability.
"The overall goal of all our efforts is to improve the quality and quantity of life for patients undergoing bypass surgery," Newman said. "This study is just one part of progress toward achieving that goal."
Other members of the Duke team included Heather Lett, Michael Babyak, Ph.D., William White, Peter Smith, M.D., Daniel Mark, M.D., Robert Jones, M.D., and Joseph Mathew, M.D.
Journal
The Lancet