The increased risk of death from any cause holds true whether the depression immediately follows the heart disease diagnosis or occurs even years later, according to Heidi May, from Intermountain Medical Center Heart Institute in the US.
The findings point out the importance of screening for and treating depression even years after someone is diagnosed with heart disease, she said.
Researchers found that post-coronary artery disease depression was the single biggest predictor of death, and remained so even after they controlled for the other factors.
"Depression was the strongest risk factor for dying, compared to any other risk factors we evaluated. That included age, heart failure, diabetes, high blood pressure, kidney failure, or having a heart attack or stroke," she said.
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That association did not change for patients who were previously diagnosed with depression before their heart disease diagnosis or for patients whose angiograms were performed for various reasons, which included stable angina, unstable angina, or heart attack, researchers said.
Patients with depression were also placed into subcategories based on how long after their heart disease diagnosis the depression was identified.
In all, 15 per cent, or 2,646 patients, were diagnosed with depression at some point during follow-up.
This study reinforces previous research investigating the link between depression, heart disease, and increased risks of death, researchers said.
The study did not explain the reason for the elevated risk of death, although May said one possibility is that depression impacts how closely patients follow their treatment plans.