Depression is associated with a twofold rise in the risk of heart disease patients dying within seven years, a study suggests.
The research was conducted by Dr Alexander Glassman and his colleagues from Columbia University College of Physicians and Surgeons.
They suggest that, rather than either condition causing the other, both may aggravate one another.
Most depressive symptoms in patients with acute coronary syndromes (ACS) begin before an acute coronary event, even though they may be attributed to the stress of a particular event, the researchers said.
They suggest that patients with ACS should be aggressively treated for depression, alongside promotion of adherence to cardiovascular medicines.
Dr Glassman and his team assessed depression symptoms in patients admitted to hospital for a cardiac event.
Patients diagnosed with major depressive disorder were given either a placebo or the antidepressant sertraline and assessed for six months for symptoms of depression.
Dr Glassman and his team then followed up the patients seven years later. During the intervening period, 75 of the 361 patients assessed had died.
The study found that patients with severe depression were 2.3 times more likely to have died than those with less severe depression. Also, those whose symptoms had failed to improve were 2.4 times more likely to have died than those whose symptoms had improved.
The researchers said that, despite uncertainty as to whether treating depression reduces mortality, their findings pointed to the risks of failing to treat depression successfully.
'When patients with major depressive disorder after ACS do not respond to antidepressant treatment, a special effort should be made to promote lifestyle improvements and cardiovascular medication adherence,' they said.
'Lack of adherence to cardiovascular drug therapy increases mortality after an MI and depression reduces adherence.'