March 3, 2008 -- Depressed heart attack patients have a higher risk for sudden death in the months following a heart attack. Now a team led by researchers from Washington University School of Medicine in St. Louis has found that the risk continues for many years.
"There's a two- to four-fold increase in a person's risk of dying following a heart attack if they also happen to be depressed," says Robert. M. Carney, Ph.D., lead author of the new study and professor of psychiatry at Washington University. "Previously we thought the impact of depression was strongest for the first three to six months following a heart attack and then gradually dropped off within a couple of years. Instead, we found that the effect lasts for at least five years."
Carney, with colleagues from Duke University Medical Center, Harvard University, Yale University, the National Heart, Lung and Blood Institute (NIH) and the Mayo Clinic, followed more than 750 heart attack patients for five years. The findings will appear in an upcoming issue of the Journal of Affective Disorders and are currently available online.
Patients followed in the study had participated in the NIH-funded project Enhancing Recovery in Coronary Heart Disease Patients (ENRICHD). A little less than half were diagnosed with depression.
In the five years following a heart attack, 106 patients died. Of those, 62 had been diagnosed with depression, while 44 had not. In gauging the effects of depression, the investigators also considered other risks including age, smoking, hypertension, gender and diabetes.
Some of those factors, like younger age and female gender, lower mortality risk. Smoking and diabetes tend to raise the risk of dying. Carney says his team used statistical methods to evaluate the ways in which the various factors influenced mortality risk. Then they removed the influence of all other factors from the risk equation in order to consider the statistical impact of depression itself.
"We found that after adjusting for those risk factors, depression continues to play a statistically significant role," he says.
One possible explanation for depression's lingering influence on mortality is its recurring nature. Because the disorder can come and go over many years, it also may continue to increase the risk of death for many years.
"People typically are depressed for a while, then they'll either get better with treatment or it may subside on its own," Carney says. "But depression can always recur, and we think that because it is a recurring problem, whatever depression is doing to mortality risk after a heart attack, it continues doing for quite a long time."
Past studies have differed over how much depression affects survival following a heart attack. But Carney believes these new findings are more reliable because all of the patients in this study were personally interviewed to determine their depression status, whereas other studies have relied on self-reporting.
"In our experience, self-reporting tends to overestimate the risk because it's often not possible to evaluate the causes of various symptoms on self-report questionnaires," he explains. "Say somebody reports having sleeping problems — that would go into the depression column as a symptom. But it's possible they are sleeping poorly because of a bad back or because they have to get up and go to the bathroom frequently during the night. During an interview, we can determine whether an individual symptom is related to depression or can be explained in some other way."
Carney's team also found that any clinically relevant depression increases the risk of death in heart attack patients. The risk was elevated both for patients with major depression, which requires the presence of five or more symptoms, and minor depression, which requires between two and four symptoms for diagnosis. Major depression was associated with higher risk, but minor depression also was associated with a significant increase in mortality risk.
Even with mounting evidence of a link between depression and death in heart attack patients, only about 25 to 30 percent of these patients receive antidepressant drugs or other depression treatments.
That doesn't surprise Carney. His team reported in 2003 in the Journal of the American Medical Association that providing treatment for depression seemed to have little effect on whether patients survived or had a second heart attack. This could be because the treatments don't work for all patients, Carney says, and he suggests if current depression treatments could be improved, survival rates might increase, too.
To this end, his team is studying whether omega-3 fatty acids — the fatty acids found in fish oil — might improve antidepressant therapies in heart patients. They're giving an antidepressant drug and a special formulation of omega-3 to some heart patients and comparing them to depressed heart patients who receive an antidepressant but no omega-3.
"We have not been satisfied with the effectiveness of standard antidepressants at alleviating depression in this population of patients," Carney says. "We're studying omega-3, because there's preliminary evidence that the fatty acids also might make depression therapies more effective, both in treating depression and in improving heart health."