The major finding of this study was that self-reported medication nonadherence is significantly higher in adults with HF who have even relatively mild rates of EDS (using a cut-point of ≥ 6 rather than the usual cut-point of ≥ 11 on the Epworth Sleepiness Scale). The other major finding was that the relationship between EDS and medication nonadherence may be explained by selective attention. That is, adults with HF and EDS appear to be missing medication doses or taking their medicines late because of poor attention and a lack of vigilance.
The link between EDS and medication nonadherence is compelling. Most HF investigators cite medication nonadherence rates between 40% and 60%,(52
) which is consistent with the rate of nonadherence identified in this study. Medication nonadherence has been shown to be associated with hospitalization and death in adults with HF. For example, Murray and colleagues found that hospitalization was higher in HF patients low in medication taking adherence compared to patients who were adherent with taking their medications.(60
) Wu et al documented that medication adherence predicted event-free survival before and after controlling for age, gender, ejection fraction, NYHA class, angiotensin-converting enzyme inhibitor use, and beta-blocker use.(61
) The findings of these authors demonstrate the importance of medication adherence, while the results of the current study provide a focus for interventions that may improve it.
In a recent review of the factors associated with medication nonadherence, forgetfulness was one of the most common barriers to adherence identified.(62
) This result is supported and explained by our finding that attention may be the mechanism by which EDS influences medication nonadherence. Lim and Dinges argue that the ability to sustain attention is fundamental to all other aspects of cognition and that vigilance is the process most affected by sleep deprivation.(63
) If alertness and sustained attention are necessary for successful information processing, memory, judgment, and decision-making, HF patients with EDS may not be able to sustain the attention needed to remember to take their medicines with any regularity.
Only one prior study of sleepiness and medication adherence was located. In a study of 173 HIV infected women, Phillips et al.(64
) found a significant difference in adherence to highly active antiretroviral therapy between good sleepers and poor sleepers. Elements of cognition such as vigilance were not tested as mediators in this study. They did find, however, that depression mediated the relationship between sleep and medication adherence, which was not surprising in this population. The women were single, low income, African-American women, 39 years of age, on average, living in a rural community. In our HF population, both depression and impaired cognition are common issues and depression was adjusted in our analyses. But, future research should explore the contribution of depression to the relationship between EDS and adherence.
Strengths of the current study include a large sample enrolled from three diverse sites and the relatively large sample of women and minorities. The primary limitation of this study is the self-report method of assessing medication adherence, although self-report is generally considered a central component of adherence assessment. It is possible that subjects with a mild cognitive decline may not remember if they took their medications. However, inaccuracies in the self-report approach most likely would under report the occurrence of skipped doses and late administrations. Thus, true medication nonadherence is most likely even higher than the self-reported rate presented here. In addition, demographic differences in age, education, race, and premorbid intellect between the cohorts is a limitation that is difficult to account for statistically and complicates our interpretation of the cognitive tests. Selection bias is possible also, as many patients were ineligible for inclusion in the study. Further, it is plausible that subjects with cognitive decline may have been adherent to the medication regimen because a caregiver assured adherence. This possibility was not accounted for in the analysis.
Further research is needed to describe the factors other than sleep quality influencing simple attention or vigilance in this population; it may be that these factors could be amenable to intervention. It would also be useful to test an association between EDS and other forms of self-care prescribed for adults with HF. It may be that EDS is also associated with failure to comply with daily weighing, a sodium restricted diet, and the response to symptoms when they occur. Research is also needed to describe how EDS changes over time in adults with HF. It has already been established that persons with HF do not experience as much EDS as other adults in the same age group.(34
) However, further research is needed to explain this observation.
In summary, we found that even a relatively low level of EDS is associated with significantly more self-reported medication nonadherence in adults with HF. An inability to maintain vigilance and pay attention may be the mechanism responsible for the link between EDS and medication nonadherence in adults with HF.