In-hospital symptoms of depression do not predict mortality 3 years after myocardial infarction

Deirdre Lanea, Douglas Carrollb, Christopher Ringb, D Gareth Beeversa and Gregory Y H Lipa

a University Department of Medicine, City Hospital NHS Trust, Dudley Road, Birmingham, B18 7QH, UK.
b School of Sport and Exercise Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.

Correspondence: Douglas Carroll, School of Sport and Exercise Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT. E-mail: carrolld{at}bham.ac.uk

Abstract

Background The main aim of this study was to examine the relationship between symptoms of depression following myocardial infarction (MI) and 3-year survival status.

Methods The Beck Depression Inventory was completed by 288 patients hospitalized for MI. Patients’ cardiological status, including indices of disease severity, were recorded or derived from hospital notes. Three-year survival status was determined using patient information systems and cause of death ascertained from death certificates.

Results During the 3 years of follow-up, 38 patients (13%) died, 33 (11%) from cardiac causes. Symptoms of depression did not predict either cardiac-specific or all-cause mortality. Similarly, in-hospital levels of anxiety were not associated with prognosis. In contrast, measures of disease severity and discharge medication status were strong prognostic indicators. Depression was not related to measures of disease severity at entry to the study.

Conclusions Symptoms of depression following MI do not predict longer-term survival, although measures of disease severity and discharge medication status do. Previous positive results for depression and cardiac mortality in MI patients could reflect the occasional confounding of depression with disease severity.

Keywords Depression, disease severity, myocardial infarction, mortality

Accepted 9 July 2002

Symptoms of depression are particularly prevalent and persistent following myocardial infarction (MI)1 and have been reported to predict subsequent short-term (<=18-months), cardiac mortality.2–7 Such findings have helped inspire a large-scale, multi-site intervention trial in the US, aimed at reducing such mortality by enhancing the psychological status of MI patients through cognitive behavioural therapy, and, if necessary, pharmacological treatment.8 However, at least two recent prospective observational studies have failed to detect associations between in-hospital symptoms of depression and short-term cardiac mortality in such patients.9–11 As yet, only two studies have reported longer-term mortality data in MI patients; whereas one found an association between in-hospital depression and mortality 5 years later,12 the other observed no association at 3-year follow-up.13 Below we report the findings from a long-term follow-up of the MI patients from our previous study.9,10

Participants and Methods

The in-hospital characteristics of the 288 patients with a definite diagnosis of MI have been described previously.9,10 Their mean (SD) age was 62.7 (11.5) years, men constituted 75% of the sample, and the majority were Caucasian (93%). In addition, 52% had evidence of heart failure (Killip class II–IV), and the mean (SD) Peel Index score, a prognosis indicator based largely on the severity of the MI, was 10.4 (5.0). Killip class is a widely used measure of the degree of left ventricular dysfunction.14 It is a four-point clinical assessment based on chest X-ray, heart and lung sounds, and signs of cardiac shock. The Peel Index is a prognostic device, and includes, in arriving at a score, consideration of age, sex, previous cardiological history, degree of severity of cardiac shock, presence and severity of heart failure, cardiac rhythm, and the nature and extent of ECG abnormalities.15 Peel Index scores >=17 are considered to indicate a poor prognosis. Also from patients’ medical notes, medication status (warfarin, beta-blockers) at discharge was recorded. Depressive symptomatology was measured in-hospital using the 21-item self-report Beck Depression Inventory (BDI). Scores >=10 are considered to indicate the presence of mild to severe symptoms of depression. Anxiety status following MI has also been linked to short-term prognosis.16 Thus, state anxiety was also measured in these patients, by the commonly used Spielberger inventory; scores >=40 were considered high.16 Both the BDI and the Spielberger have very good psychometric properties.17,18 For example, a meta-analysis of the BDI’s internal consistency revealed a mean Cronbach’s alpha coefficient of 0.86 for psychiatric patients and 0.81 for non-psychiatric patients, as well as test-retest correlation coefficients as high as 0.86 and 0.83, respectively, in these populations.17 The Speilberger state anxiety scale has also been shown to have good internal reliability, with Cronbach’s alpha of 0.92 reported.18 The 3-year survival status of the patients was established using comprehensive hospital patient information systems and cause of death was determined from death certificates. Data were analysed by logistic regression. The slight variation in N for some of the variables reflects occasional data unavailability. While analyses using the maximum data available for each variable are reported, analyses confined to those participants with complete data on all measures yielded similar outcomes.

Results

In the 3 years following MI, 38 patients (13%) died, 33 (11%) from cardiac causes. Of the latter group, 20 died from recurrent MI or ischaemic heart disease, 10 from heart failure, and three from arrhythmias. The key characteristics of survivors and those who died from cardiac causes are summarized in Table 1Go. As can be seen, both of the main indices of disease severity, Killip class and Peel Index score, predicted the 3-year outcome. The association between Killip class survived adjustment for age, in years (OR = 5.61; 95% CI: 1.86–16.91). Since age informs the Peel Index, no statistical adjustment for age was undertaken. In a multiple logistic regression model in which both Killip class and Peel Index status were entered, both emerged as significant predictors of cardiac mortality (OR = 5.91; 95% CI: 1.96–17.86 and OR = 2.76; 95% CI: 1.13–6.78, respectively). Those on warfarin at discharge were more likely to have died from cardiac causes in the ensuing 3 years and those on beta-blockers less likely.


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Table 1 Key in-hospital characteristics of patients who survived to 3-years and those who died of cardiac causes
 
In stark contrast, symptoms of depression were not associated with cardiac mortality 3 years after the index MI. State anxiety also failed to predict mortality. Of the psychological and socioeconomic variables measured, only years in education predicted cardiac mortality, although this association did not withstand adjustment for age (OR = 0.94; 95% CI: 0.66–1.35). Largely similar outcomes emerged from analyses of all-cause mortality. For example, neither symptoms of depression (OR = 1.04; 95% CI: 0.50–2.16) nor anxiety (OR = 0.91; 95% CI: 0.39–2.12) significantly predicted all-cause mortality.

Table 2Go presents the baseline data for participants who had relatively high levels of depressive symptomatology (BDI scores >=10) and for those with relatively low levels of depression (BDI scores <10). Aside from a substantial association with state anxiety, BDI status was linked only to sex and diabetes; women and patients with diabetes were more likely to register BDI scores >=10.


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Table 2 Baseline data for participants with and without elevated Beck Depression Inventory (BDI) scores
 
Discussion

Our main measures of disease severity, Killip class and Peel Index scores, predicted 3-year mortality following MI. Medication status at discharge was also associated with mortality. The finding that patients on warfarin were much more likely to die during follow-up undoubtedly reflects their poorer prognosis; warfarin prescription correlated positively with our other measures of disease severity. In contrast, symptoms of depression and anxiety measured in-hospital failed to predict 3-year survival status. The present null finding for depression is similar to the results of one study,13 although at odds with those of the other study,12 for reporting long-term mortality in MI patients. It is also in line with the outcome of the recent large-scale intervention trial that was targeted at MI patients with major or minor depression. While the intervention was successful in alleviating symptoms of depression, it did not reduce mortality or the recurrence of MI over the average follow-up period of 41 months.19

In general, since correlational studies with positive and null outcomes have had similar levels of power to detect effects, have used the same or highly correlated measures of depressive symptomatology, and have recruited patients with similar socio-demographic profiles, it is difficult to account for the variations in results among studies from obvious differences in design and patient characteristics. Further, although there was a relatively high prevalence of patients with Killip classes II–IV in the present cohort compared to some other studies reporting positive outcomes, death rates were not dissimilar.2,3,13

It seems more likely that discrepancies in results for depression and mortality in MI patients hinge on the issue of the association between depression and disease severity. As a recent editorial in the journal Psychosomatic Medicine commented: ‘One of the main issues regarding the role of depression is the potential confounding with severity of disease.’20 It should be pointed out here that some of the more somatic symptoms of depression may also characterize increased disease severity. However, in the present study, in contrast to others reporting positive associations between short-term mortality and depression,2–7 depressive symptomatology was not related to indices of cardiac disease severity. Further, depression was also not correlated with medication status on discharge, nor, with the exception of diabetes, any of the conventional cardiac disease risk factors (such as blood pressure status, smoking, and hyperlipidaemia).9 Thus, it remains possible that where positive associations between depression and mortality following MI have been observed, they arise largely as a function of the confounding of depression and cardiac disease severity. It is worth noting that in a number of studies in which symptoms of depression were associated with both short-term mortality following MI and disease severity, statistical adjustment for disease severity abolished the significant association between depression and mortality.4–7

This explanation, however, raises the question of why depression is correlated with disease severity in some studies but not others. It is perhaps worth noting that, unlike studies with positive outcomes, the present study and two other null studies, one of short-term11 and the other of longer-term13 mortality, were conducted in England in large state hospitals. If it is assumed that symptoms of depression are a cause rather than an effect in MI patients, it is interesting to speculate that the accuracy of patients’ perceptions about the severity of their condition might explain whether or not depression and disease severity are linked statistically. By an effect, we mean that depression would be regarded as a consequence of the patient’s encounter with a life-threatening event. As a corollary of this view, the extent of depressive symptoms would, among other things, reflect patients’ perceptions of just how serious the event was and the likely prognosis. Where physicians provide only scant and general prognostic information or, at least, patients perceive this to be the case, then one would expect symptoms of depression to be largely independent of objective disease severity and likely prognosis. Conversely, if physicians’ communications make explicit just how ill patients are, the extent of depressive symptoms might be presumed to follow the patient’s reasonably accurate appreciation of the severity of their condition and the prognosis. We acknowledge that this is highly speculative, but, at the very least, it does generate a testable hypothesis: that a positive association between depression and disease severity will appear where there are positive associations between objective measures of disease severity and patients’ perceptions of how sick they are.


KEY MESSAGES

  • Symptoms of depression and anxiety following a heart attack did not predict mortality over the proceeding 3 years.
  • In contrast, measures of cardiac disease severity following the target heart attack were highly predictive of subsequent prognosis.
  • In this study, symptoms of depression were not associated with cardiac disease severity.
  • Previous positive results relating depression to subsequent death in heart attack patients could reflect the occasional confounding of depression with disease severity.

 

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