In this multicenter observational cohort study of patients after ACS, we found that patients whose symptoms of depression persisted after hospitalization were at higher risk for not adhering to recommended preventive behaviors, including quitting smoking, exercising, attending cardiac rehabilitation, and taking medications regularly. Furthermore, we found that there were no statistically significant differences in adherence between patients whose symptoms of depression remitted and patients who were never depressed.
Depression is associated with poor motivation, low self-esteem, and low energy, characteristics that may be necessary for the maintenance of healthy behaviors and lifestyle changes. While it is possible that depressed patients are informed differently than nondepressed patients about the importance of secondary prevention behaviors, in our study it is unlikely that persistently depressed patients would have been informed differently than the remittent depressed group as they both started out depressed in hospital. Assuming that both remittent depressed and persistently depressed patients received equal advice from their health care providers about secondary prevention, then the lower rate of engagement in these activities by persistently depressed patients is more likely due to the effect of the persistent depressive symptoms on patients' ability to adhere to recommended behaviors.
This evidence confirms and extends previous findings that have shown that depression is a risk factor for poor adherence after ACS. Whereas previous authors have noted that depression at hospitalization is a risk factor for poor adherence 4 months later, we have shown that it is the persistence of depression that may confer this risk of poor adherence as there were no significant differences in adherence among those whose depressive symptoms remitted and those who were never depressed.21
In addition to incorporating repeated measures of depressive symptoms, another strength of our study is the diversity in the patient sample in terms of sex, race, and ethnicity, as well as the enrollment of patients from multiple hospital sites. Although there were significant differences in the socioeconomic status of our patients when analyzed by depression status, the association between depression status and adherence remained robust when we accounted for these variables.
There were several limitations of this study. First, we had a moderate rate of refusal to participate in the study among potentially eligible subjects. Patients who refuse to participate in research studies might have poorer adherence. As a result, our findings may overestimate the true rates of adherence to secondary prevention behaviors among post-ACS patients. Second, we may not have been able to account for all possible confounders. For example, we were not able to adjust for the number of medications prescribed, which some research has shown is associated with adherence.33
Similarly, some studies have shown that income correlates with poor adherence; we used employment status as a surrogate marker for income. Third, we were unable to account for the effect that identification and treatment of depressive symptoms by providers may have had on adherence. Providers, however, were not made aware of BDI results from the study. Finally, information pertaining to adherence behaviors was primarily derived from self-report. It is possible that patients who have experienced ACS may adhere to recommended behaviors at similar levels but only report differently according to the influence of their depressive symptoms. According to some psychological studies, depressed patients may be more likely to accurately report maladaptive behaviors than their nondepressed counterparts.34,35
Our study corroborates prior research that has shown poor overall rates of adherence to healthy lifestyles after ACS.36,37
Previous studies have shown that poor adherence is associated with poorer outcomes after ACS.38
For example, in the Beta Blocker Heart Attack Trial, patients who did not adhere to the study medication after MI, whether or not the medication was placebo, were 2.6 times more likely to die within 1 year.39
This finding is consistent with the hypothesis that decreased adherence to healthy secondary prevention behaviors may be a mediator in the association of depression and mortality after ACS.
Researchers are beginning to study the effectiveness of screening for and addressing poor adherence among patients with chronic illnesses such as diabetes mellitus and heart disease.40
In some populations, such as patients with human immunodeficiency virus infection and diabetes mellitus, treatment of depression has been to shown to improve adherence.41,42
Among patients with diabetes mellitus, some trials have shown that enhanced treatment of depression can lead to improvements not only in adherence, but also in diabetic outcomes.43
Accordingly, the American Diabetes Association has added screening for mood disorders to its guidelines for standard diabetic assessments.44
Two major randomized control trials of post-ACS patients have failed to demonstrate that enhanced depression treatment can improve post-ACS outcomes.45,46
None of these trials specifically attempted to impact the adherence of patients. Future studies should assess whether enhanced screening and treatment of depressive symptoms can improve adherence in patients after ACS and whether improved adherence, in turn, can improve post-ACS mortality. These studies should also assess whether the BDI is an optimal tool for diagnosing depression in the post-ACS setting. Our study suggests that among patients who have experienced ACS, resources for screening and treating depression may be best directed at patients who are depressed at follow-up, not only in the hospital. In addition, our study suggests that it may be important to include adherence counseling as part of depression treatment programs in post-ACS patients.47