Among patients with coronary disease, we found that depressive symptoms were strongly associated with health status outcomes, including symptom burden, physical limitation, quality of life, and overall health. In contrast, 2 physiological measures of disease severity—left ventricular ejection fraction and ischemia—were not. Exercise capacity by treadmill testing was also predictive of health status outcomes, but depressive symptoms remained associated with health status in all strata of exercise capacity. Although the causal pathways between depressive symptoms and health status outcomes cannot be determined by this cross-sectional study and are almost certainly bidirectional, our results suggest that depressive symptoms are an important factor in the perceived health status of patients with coronary disease.
We found that depressive symptoms were associated with overall and disease-specific health status, independent of cardiac function. Indeed, depressive symptoms were as strongly associated with disease-specific health status as was exercise capacity, one of the primary variables used to validate the Seattle Angina Questionnaire.17
Previous studies have demonstrated an association between depressive symptoms and health status outcomes in patients with coronary disease,10,25-28
but these studies did not measure severity of cardiac disease simultaneously. Other studies have found that symptoms of anxiety and depression lead to poor health status, independent of the degree of angiographic stenosis, but these studies did not assess cardiac function by measuring exercise capacity, ejection fraction, or ischemia.11,28,29
Our results suggest that efforts to improve the health status of cardiac patients should include assessment and treatment of depressive symptoms. Treatment of depression leads to improvements in health status,30,31
and improved health status is associated with better health outcomes.14,32-36
Some antidepressant therapies, such as selective serotonin reuptake inhibitors, may even improve cardiovascular outcomes among patients with coronary disease.37,38
Health care professionals can easily identify depression by administering 2 simple screening questions (“During the past month, have you often been bothered by feeling down, depressed, or hopeless?” and “During the past month, have you often been bothered by having little interest or pleasure in doing things?”) and a brief follow-up interview if one of the questions is answered affirmatively.39,40
For maximal benefit, detection and treatment of depression should be combined with patient-support programs, such as frequent nursing follow-up and close monitoring of adherence to therapy.41,42
Our findings demonstrate that depressive symptoms are at least as important as cardiac function in the health-related quality of life of patients with coronary disease. Indeed, “low-tech” measures of health, including depressive symptoms and exercise capacity, were more strongly associated with health status outcomes than “high-tech” measures of cardiac disease severity, including ejection fraction and ischemia. These results are consistent with a large body of literature demonstrating poor correlation between “high-tech” physiological measures and health-related quality of life in patients with other chronic diseases such as asthma,43
chronic obstructive pulmonary disease,44,45
peptic ulcer disease,46
and musculoskeletal disorders.49,50
Health status measures are increasingly used to assess the benefits of the rapies in clinical trials.51
Since many cardiac interventions can alter both physiology and mood,2,52
it is plausible that some quality-of-life improvements found in these trials may be due to noncardiac factors. Our results suggest that studies measuring quality-of-life outcomes should attempt to determine whether changes are due to cardiac or to noncardiac factors.
If improvements in depressive symptoms are responsible for changes in quality of life, then future efforts to enhance the health status of cardiac patients could focus on modifying depressive symptoms.30
Such efforts would have substantial implications for care in patients with coronary disease, where the traditional focus has been on cardiac physiology and psychosocial factors such as depression are often overlooked.53,54
Several limitations must be considered in interpreting our results. First, we chose to focus on depressive symptoms and coronary disease because they are the most common chronic mental and physical disorders and the 2 leading causes of disability in the world.55
However, only 7% of eligible patients actually enrolled in the study, and the majority of participants were men, so our results may not generalize to other groups of patients. Second, our study population was recruited based on the presence of coronary disease and did not require a diagnosis of heart failure. Thus, the prevalence of systolic dysfunction was low (12%). However, the prevalence of other cardiac conditions was relatively high in our sample, including a history of myocardial infarction in over half of the participants, a history of revascularization in over half of the participants, inducible ischemia in a third of the participants, and a wide range of exercise capacity. Thus, we believe our sample represents an appropriate population in which to examine the contributions of depressive symptoms and cardiac function to health status.
Third, since the PHQ does not assess duration or recurrence of depressive symptoms, we were not able to explore potential differences in the association between depressive symptoms and health status by duration of depression or number of recurrences. Finally, our cross-sectional design precludes determination of the direction of causality between depressive symptoms and health status. However, since health status is by definition a subjective internal experience, a cross-sectional measurement of its association with psychological and cardiac function provides insight that would not be achieved by assessing health status at a subsequent time point when the patient's physiologic or psychological state could have changed.