By Jim Dryden
November 9, 2001
Investigators at the School of Medicine have found that depression appears to interfere with the heart's ability to speed up or slow down in response to stress or exertion.
Reporting in Circulation: Journal of the American Heart Association, principal investigator Robert M. Carney, Ph.D., professor of medical psychology in psychiatry, said 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.
"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."
The study followed a subset of participants from the Enhancing Recovery in Coronary Heart Disease study who were admitted to coronary care units between 1997-2000. Carney studied 307 patients with depression and 366 who were not depressed. All had suffered heart attacks in the 28 days before enrolling in the study.
Upon discharge from the hospital, all the patients wore portable heart monitors for 24 hours to measure changes in heart-rate rhythm. The tapes from those monitors were used to assess their heart-rate variability.
Normal 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.
In this study, 16 percent of depressed patients had heart-rate variability readings so low that it was a risk factor for death during the first two-and-a-half years after a heart attack. Only 7 per-cent of nondepressed patients had readings that low.
"We have known for some time 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."
Carney believes 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 continue to follow the study's patients to learn whether the depressed and nondepressed patients will have different mortality rates. They also hope to determine whether treatment for depression will improve heart-rate variability.
"We know that depression is a risk factor for death from heart disease, but
it's a treatable risk factor," Carney said. "Patients do feel better after therapy.
What we don't know yet is whether improved mood translates into higher heart-rate
variability and reduced mortality."
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