Limitations of the study, according to the investigators, included the possibility of confounders and selection bias.
"These findings argue for expanded efforts to understand the influence of recovery expectations and the potential benefits of attempts to modify them," Barefoot's group concluded.
However, the potential efficacy of such efforts is uncertain, according to Dr. James Kirkpatrick, of the University of Pennsylvania in Philadelphia.
"Whether a patient's outlook can be changed (or patients can change their outlook) and improve results, and whether there are other factors which might make these patients do better, is unknown. One of those factors might be that cardiovascular providers give better care to patients with a positive outlook — perhaps spending more time with them or being more conscientious," wrote Kirkpatrick in an email to MedPage Today and ABC News.
"Future studies will need to take this possible mechanism into account," wrote Kirkpatrick.
The study was supported by the National Heart, Lung, and Blood Institute and the National Institute on Aging.
One author has a patent pending on an allele as a marker of cardiovascular disease and stress, and is a founder and major stockholder in Williams LifeSkills Inc.
Editorialist Gramling is funded by the National Palliative Care Research Center and the Greenwall Foundation.
