Depression following myocardial infarction--an overseen complication with prognostic importance

Myocardial infarction (MI) is a severe life event that is accompanied by an increased risk of depression. Mounting evidence suggests that post-MI depression is associated with adverse outcomes, but the underlying mechanisms of this association remain unclear, and no previous studies have examined whether the mental burden of MI is so heavy that it increases the risk of suicide. Although post-MI depression is common and burdensome, the condition remains under-recognised and under-treated. The development of new strategies to improve the quality of care for people with post-MI depression requires thorough understanding of the mechanisms that influence the prognosis as well as knowledge of the present care provided. The purpose of this PhD thesis is accordingly subdivided into four specific aims: 1. To estimate the prevalence of depression in people with MI after three months, and to estimate the provided hospital-based psychosocial rehabilitation (Paper I); 2. To examine GPs' practice of screening for depression in people with MI, and to analyse whether the screening rate varied among subgroups of people with a particularly high risk of post-MI depression (Paper II); 3. To examine the association between post-MI depression and new cardiovascular events or death, taking potential mediators into account (Paper III); 4. To examine the association between MI and suicide (Paper IV).

Two different study designs were employed: a population-based cohort study using data obtained from registers and questionnaires sent to MI patients and their GPs (Paper I-III); a nationwide population-based matched case-control study using data obtained from registers (Paper IV).

Three months after having suffered MI, about one fifth of the patients in our study had depression according to the Hospital Anxiety and Depression Scale (HADS). Upwards of half of the patients had participated in some rehabilitation, thirty per cent had participated in psychosocial support and three per cent reported that they had been examined for depression by questionnaire during the hospital-based rehabilitation. The rate of participation in psychosocial support and examination for depression was the same for patients with or without depression at three months following MI. A good fourth of the patients' GPs stated that they had screened the patient for depression within the first year after the patient suffered an MI. Three months after the MI, the screening rate was higher among patients with a history of mental illness and among patients with anxiety or depression than among patients without these conditions. Most of the GPs who performed screening followed guidelines by asking about specific depressive symptoms. According to the HADS, depression three months after MI was associated with an increased risk of a new cardiovascular event or death. This association was partly explained by the underlying cardiac disease severity and physical inactivity, but depression remained an independent prognostic risk factor after adjusting for these potential confounders. We found a tendency towards a weaker association with increasing physical activity and among users of antidepressants. MI was strongly associated with an increased risk of suicide. This risk was particularly high immediately after the MI, but remained high for more than five years after the MI. The association between MI and suicide remained stable throughout the study period (1981-2006), although many other factors changed (e.g. suicide rate, treatment of MI).

This thesis demonstrated that post-MI depression is common, under-recognized and has a strong prognostic impact. About one in five patients have depression three months after MI. Guidelines recommend screening for depression, but the guidelines have not been systematically implemented either in the hospital-based rehabilitation or in Danish general practice. In the absence of systematic screening, we found that a significant part of those who had depression were not recognized. MI increases the risk of suicide, and depression following MI impairs the overall prognosis. The thesis indicates that physical activity and antidepressants modify the adverse prognosis in patients with post-MI depression, but larger studies are needed to clarify the impact of these potential modifiers and to evaluate how they may be catered for in the treatment of post-MI patients with depression.