An observational study of nearly 9,000 heart attack patients found people discharged from the hospital with a prescription for antidepressants had a 66 percent greater chance of all-cause death within one year.

Lead author Nadia Fehr, a medical student at the University of Zurich in Switzerland, presented the findings March 3 at Acute Cardiovascular Care 2018, a European Society of Cardiology congress in Milan.

“Previous studies have suggested that cardiovascular disease may increase the likelihood of being depressed,” Fehr said in a press release. “On the other hand, depression appears to increase the probability of developing cardiovascular risk factors. However, little is known about the impact of depression on outcome after a heart attack.”

The researchers used a Swiss nationwide registry for acute myocardial infarction to study outcomes of 8,911 patients admitted to hospitals in Switzerland from March 2005 through August 2016. A total of 6.3 percent of the patients were prescribed antidepressants upon discharge, and they were more likely to be older, have longer hospital stays and a greater burden of comorbidities, including hypertension, diabetes and dyslipidemia.

After adjusting for these characteristics, the researchers found the rates of stroke and subsequent heart attack were similar regardless of whether a patient was prescribed antidepressants or not. However, 7.4 percent of patients with antidepressants died within one year of follow-up compared to 3.4 percent of those who weren’t prescribed the medication.

Fehr pointed out the study was observational, so it couldn’t prove antidepressants directly caused the increased mortality risk.

“Our study showed that many patients are treated with antidepressants after a heart attack,” she said. “More research is needed to pinpoint the causes and underlying pathological mechanisms for the higher mortality we observed in this patient group.”