CORRESPONDENCE: LETTER TO THE EDITOR
Reply
Chris Dickens, PhD*,
Barbara Tomenson, MSc and
Francis Creed, MD
* Department of Psychiatry, Rawnsley Building, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL, United Kingdom (Email: chris.dickens{at}manchester.ac.uk).
We are grateful for the comments of Dr. Thombs and colleagues.
In our recent study we set out to examine the effects of the timing of assessment of depression on mortality after myocardial infarction (MI) (1). We showed that depression before MI, whether chronic or not, does not increase cardiac mortality. This was a surprise to us because we anticipated that pre-MI depression, which was associated with chronic social difficulties (2) and likely to be persistent (3), would be related to increased mortality after MI. We have published this paper to make it clear that this is not the case. Furthermore, we found that depression present 12 months after MI did not predict subsequent mortality.
We acknowledge that our study alone does not provide direct evidence for a window of effect for depression predicting increased mortality. However, if we contrast our findings with those studies showing an association of depression in the days or weeks after MI with post-MI mortality, it seems likely that it is those people who develop depression in the period immediately after MI that are at increased risk of cardiac mortality. Patients developing depression after an acute cardiac event have been shown to be at increased risk of dying in previous studies (4,5), and we are now looking at this particular question in our own data.
Our negative findings for depression cannot be dismissed as resulting from our statistical methods. We accept the point that the number of independent variables included was large, but our finding was the same in the uncontrolled (univariate) comparison. Furthermore, our findings remained stable if we used backward elimination of variables, so that the number of independent variables in the final model was few (hazard ratio [HR] for depression = 0.86, p = 0.60) or if we performed our analyses using fewer variables (e.g., age, gender, educational level, degree of cardiac dysfunction, and revascularization procedures (4), HR for depression = 1.02, p = 0.94). Our findings also remained negative when we did not control for medications at discharge (HR for depression = 0.87, p = 0.62).
Our finding that subjects with depression at both baseline and 12 months had an apparent survival advantage is confusing and counterintuitive. We can clarify here that, compared with the remainder, this group was more likely to be female gender (49% vs. 28%) and younger (mean age 45.3 vs. 60.8 years). Controlling for age and gender alone eliminated the association between persistent depression and subsequent mortality (p = 0.97).
The fact that depression that predates the MI and persists through the post-MI period does not predict mortality is extremely important. It supports the suggestion that it is not depression alone that is having the adverse impact on survival but that some additional factor interacts with depression to create this effect (6,7). Rather than ignoring the heterogeneity in previous findings, future research should continue to examine possible reasons for this heterogeneity as it may identify vulnerable subgroups and explain how and why depression has this effect on survival.
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References
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1. Dickens C, McGowan L, Percival C, et al. Depression is a risk factor for mortality after myocardial infarction: fact or artifact? J Am Coll Cardiol 2007;49:1834-1840.[Abstract/Free Full Text]2. Dickens CM, Percival C, McGowan L, et al. The risk factors for depression in first myocardial infarction patients Psychol Med 2004;34:1083-1092.[CrossRef][Web of Science][Medline] 3. Lloyd GG, Cawley RH. Psychiatric morbidity after myocardial infarction QJ Med 1982;51:33-42.[Abstract/Free Full Text] 4. de Jonge P, van den Brink RH, Spijkerman TA, Ormel J. Only incident depressive episodes after myocardial infarction are associated with new cardiovascular events J Am Coll Cardiol 2006;48:2204-2208.[Abstract/Free Full Text] 5. Grace SL, Abbey SE, Kapral MK, Fang J, Nolan RP, Stewart DE. Effect of depression on five-year mortality after an acute coronary syndrome Am J Cardiol 2005;96:1179-1185.[CrossRef][Web of Science][Medline] 6. Frasure-Smith N, Lesperance F, Talajic M. Depression and 18-month prognosis after myocardial infarction Circulation 1995;91:999-1005.[Abstract/Free Full Text] 7. Frasure-Smith N, Lesperance F, Gravel G, et al. Social support, depression, and mortality during the first year after myocardial infarction Circulation 2000;101:1919-1924.[Abstract/Free Full Text]
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