Depression and mortality following myocardial infarction: the issue of disease severity

Associations of mood symptoms with NYHA functional classes in angina pectoris patients: a cross-sectional study

BACKGROUND

Depression and anxiety are prevalent and associated with a worse prognosis in coronary heart disease (CHD) patients. However, the influence of disease severity on mood symptoms is unknown. The specific associations of mood symptoms with NYHA classes remain unexplored.

METHODS

In this cross-sectional study, 443 consecutive inpatients with angina pectoris (AP) confirmed by angiography were included into analysis. Somatic and cognitive symptom scores derived from Patient Health Questionnaire (PHQ-9) and Generalized Anxiety Disorder Scale (GAD-7) were used to assess mood symptoms. Predictors for depression and anxiety with strict and lax standards were compared. We hypothesized NYHA classification to be an indicator of disease severity through analyses with clinical features using ordinal logistic model. Applying both binary and ordinal logistic models, we evaluated the associations of mood symptoms with NYHA classes.

RESULTS

Discrepancy of disease severity existed between the depressed and nondepressed. NYHA classification was proved to be an integrated index under influence of age, coronary stenosis, heart failure and diabetes. NYHA class I and II individuals with AP were at equivalent risk for depression (NYHA II vs I: binary model OR 1.32 (0.59,2.96), p = 0.50; ordinal model OR 1.17 (0.73,1.88), p = 0.52), however NYHA class III/IV patients shared a sharply higher risk (NYHA III/IV vs I: binary model OR 3.32 (1.28,8.61), p = .013; ordinal model OR 3.94 (2.11,7.36), p < .001). Analyses on somatic and cognitive depressive symptoms confirmed this finding and hinted a greater impact of education background on mood when patient's condition is unstable. Anxiety seemed in the whole picture irrelevant with NYHA classes. Comparing with NYHA class I/II, AP patients in NYHA class III/IV tended to be less anxious. However, when CHD became unstable, the calmness may immediately be broken up. A great distinction of the ratio of anxiety and depression symptom scores between NYHA class III/IV stable and unstable AP patients (p = .018) was observed.

CONCLUSIONS

Mood symptoms in CHD patients are to a great extend derived from disease itself. Only for patients with relatively serious physical condition, unexpected discomforts caused by disease notably impact the emotions. Education background tends to influence the mood especially when disease is still unstable.

Risk factors, confounding, and the illusion of statistical control

When experimental designs are premature, impractical, or impossible, researchers must rely on statistical methods to adjust for potentially confounding effects. Such procedures, however, are quite fallible. We examine several errors that often follow the use of statistical adjustment. The first is inferring a factor is causal because it predicts an outcome even after "statistical control" for other factors. This inference is fallacious when (as usual) such control involves removing the linear contribution of imperfectly measured variables, or when some confounders remain unmeasured. The converse fallacy is inferring a factor is not causally important because its association with the outcome is attenuated or eliminated by the inclusion of covariates in the adjustment process. This attenuation may only reflect that the covariates treated as confounders are actually mediators (intermediates) and critical to the causal chain from the study factor to the study outcome. Other problems arise due to mismeasurement of the study factor or outcome, or because these study variables are only proxies for underlying constructs. Statistical adjustment serves a useful function, but it cannot transform observational studies into natural experiments, and involves far more subjective judgment than many users realize.

Epidemiology of comorbid coronary artery disease and depression

This article reviews the epidemiology of comorbid coronary artery disease and unipolar depression. Both major depression and subsyndromal depressive symptoms will be considered; unless otherwise specified, the term depression will be used to designate all depressive states, including major depressive disorder, minor depression, dysthymia, and other subsyndromal forms of depression. While 17% to 27% of patients with coronary artery disease have major depression, a significantly larger percentage has subsyndromal symptoms of depression. Patients with coronary artery disease and depression have a twofold to threefold increased risk of future cardiac events compared to patients without depression, independent of baseline cardiac dysfunction. The relative risk for the development of coronary artery disease conferred by depression in patients initially free of clinical cardiac disease is approximately 1.5, independent of other known risk factors for coronary disease. In the discussion, special attention will be paid to the interactions of both gender and age with depression and coronary artery disease risk. Scrutiny of the role of confounding risk factors is presented, such as global burden of comorbid medical illness and modification of traditional risk factors, which may, in part, mediate the effect of depression on coronary artery disease.