Carney: Principal investigator
By Jim Dryden
March 23, 2001
School of Medicine investiga- tors have found that depression appears to interfere with the heart's ability to speed up or slow down in response to stress or exertion.
Principal investigator Robert M. Carney, Ph.D., professor of medical psychology in psychiatry, reported at the American Psychosomatic Society's annual meeting March 6, that even after other risk factors such as age, diabetes and smoking were taken into account, depressed heart-attack survivors were significantly more likely than medically comparable patients to have abnormally low variability in heart rate. Lower heart-rate variability is associated with increased risk of heart attack and death.
Carney: Principal investigator |
"Heart-rate variability is a good thing --more variability allows your heart to adjust to changes in demand," Carney said. "But we found significantly less variability in depressed patients than in individuals who were medically comparable but not depressed."
Normal people's hearts tend to speed up with increased activity or stress and slow down during relaxation. But people with lower heart-rate variability usually have higher resting heart rates and less fluctuation in response to exertion, stress and other things that require the heart to pump more or less blood.
Scientists know that depressed people with heart disease are three to four times more likely to have a heart attack or to die from heart disease. They also know that patients with heart-rate variability below a particular threshold are more than four times more likely to die during the two years following an initial heart attack.
The researchers --including scientists from Duke, Harvard and Yale universities and the National Heart, Lung, and Blood Institute --studied 380 depressed and 424 nondepressed patients recovering from heart attacks. Upon discharge from the hospital, all wore portable heart monitors for 24 hours.
The electrocardiogram tapes produced by the heart monitors revealed how the patients' heart rates varied during that time.
The findings suggest that depression and low heart-rate variability may be linked. Of the depressed patients studied, about 39 percent had heart-rate variability below the threshold that increases risk of death. Only about 20 percent of the nondepressed patients fell below that threshold.
"We have known that depression increases the risk of death from heart disease, but it's been unclear what physiologic mechanism explains that risk," Carney said. "This study would suggest that lower heart-rate variability could provide at least a partial explanation."
Smaller studies have suggested a link between depression and heart-rate variability, but other factors also were involved. Age, gender, diabetes and smoking can affect heart rate. Also, women, smokers and diabetics are more likely to be clinically depressed, and the incidence of depression rises as people age. So scientists studying depression and heart-rate variability were never sure whether they were seeing the effects of depression or one of these other confounding factors.
The large cohort of patients in this study allowed investigators to use statistical methods that could take those other factors into account.
"And after those adjustments, heart-rate variability was still significantly lower in the depressed patients," Carney said. "We feel it was low enough that it could possibly explain this increased risk for mortality that we and others have documented in past studies."
Carney believes that the large amounts of stress hormones produced by depressed patients may affect the body's autonomic nervous system, which controls heart rate. That could explain the link.
The researchers will follow the study patients for at least 18 months to learn whether the depressed and nondepressed patients have different mortality rates. They also will determine whether treatment for depression improved heart-rate variability. A small study has suggested a modest improvement, but Carney would like to follow those patients for a longer time.
"We know that depression is a risk factor for death from heart disease, but it's a treatable risk factor," he said. "Patients do feel better after therapy. What we don't know yet is whether their improved mood translates into higher heart-rate variability and reduced mortality. We suspect it might, but we still need to investigate that."
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