Psychological depression is as significant as high cholesterol, hypertension, and even the ability of the heart to pump blood, in contributing to worse medical outcomes for patients with heart failure, new research suggests.

Depressed patients were over 50 per cent more likely to die or be hospitalised for their heart condition, according to a team of US researchers who took into account disease severity, strength of heart muscle contractions, the underlying cause for the heart failure, age and medication use.

An estimated one in every 100 people in the UK have heart failure, a condition marked by the inability of the heart muscle to pump enough oxygen and nutrients in the blood to the body’s tissues. A variety of factors can cause heart failure, including infections of the heart, coronary artery disease, high blood pressure, previous heart attacks and a malfunctioning heart valve.

"While many studies have linked depression to worse outcomes for patients with heart disease, there has been uncertainty about the extent to which depression is related to the adverse medical outcomes independent of known medical risk factors," said Dr James Blumenthal, Ph.D.

Researchers still don’t understand why depressed heart patients have worse outcomes. Possible causes are that depressed patients are known to have a lower ability to clot blood properly and a decrease in their heart’s ability to react appropriately to the stresses of everyday life. Depressed patients may also be less likely to comply with their medical treatments, may not be as motivated to stick with exercise or rehabilitation programs, may miss doctor’s appointments and tend to make unhealthy lifestyle choices in such areas as diet and smoking.

What made this analysis different from other such studies was that the researchers coupled the psychological assessment with a relatively new blood test that measures what are known as "B-type natriuretic peptides." These chemicals are released into the bloodstream by the heart tissue when the heart is unable to pump effectively and are now being used in the diagnosis of heart failure.

"As expected, high levels of BNP predicted worse outcomes in our study, but even taking this and other disease makers into account, we found that depressive symptoms were still independently associated with worse outcomes," said lead investigator Dr Andrew Sherwood. "Our findings underscore the importance of assessing heart failure patients for depression, so that where treatment is indicated, both the quality and quantity of their lives may be improved.”