Cardiac rehabilitation patients who have symptoms of depression take longer to return to their normal heart rate after taking a treadmill stress test, researchers report in the American Heart Journal.

Heart rate recovery after a treadmill stress test is an indication of how the autonomic nervous system is functioning. Patients who take longer to recover their normal heart rate also have an increased risk of mortality, according to study co-author Dr. Joel W. Hughes, of Kent State University, Ohio, and colleagues.

The autonomic nervous system helps the body to adapt to changes in the environment, adjusting or modifying body functions in response to stress. It also regulates functions such as blood pressure, heart rate, airflow to the lungs, as well as the digestive process, insulin secretion, urinary function and sexual response.

The researchers suggest the alterations in autonomic nervous system function may help explain the relationship between depression and cardiac death.

The findings come from a study of 260 patients entering phase II cardiac rehabilitation who completed an exercise treadmill test, which assessed exercise capacity and heart rate recovery two minutes after exercise. The Beck Depression Inventory was used to assess symptoms of depression.

Heart rate recovery after exercise was slower among patients with higher scores on Beck Depression Inventory, the researches report. This association remained after factoring in the effects of patient age, sex, and the use of beta-blocker drugs.

The relationship between depression score and heart rate recovery was not statistically significant after factoring in the effects of exercise capacity, indicating that exercise capacity may partly explain this relationship.

“A role of physical fitness in the relationship between depression and heart rate is not surprising in light of the evidence that heart rate recovery is highly correlated with exercise capacity, depression predicts physical inactivity among patients at risk for heart disease, and depression symptoms are associated with reduced exercise capacity for patients with coronary artery disease,” Hughes and colleagues explain.

They conclude that altered exercise capacity may be one mechanism whereby depression leads to autonomic dysfunction and poor prognosis among cardiac rehabilitation patients. If so, treatment programs that focus on improving physical fitness may benefit depressed cardiac patients.

SOURCE: American Heart Journal, May 2006.