Depression as a predictor of work resumption following myocardial infarction (MI): a review of recent research evidence

Initial searches were conducted independently by AO and CR, yielding 1231 results; 309 of these articles were considered for inclusion from an initial review, and their abstracts obtained. After screening using the inclusion criteria, the full text of 31 articles were obtained and details of those appearing to meet criteria were recorded in extraction tables. The first author and reviewer convened to compare the results of their respective searches. After excluding 19 of the 31 studies initially considered to meet criteria, 12 articles were finally agreed upon by the two assessors for inclusion (initial assessor consensus was 93%; where consensus was not reached, the second author was consulted). Reasons for exclusion were: duplicate articles of the same study (n = 8), follow up period not long enough (n = 2), did not record depression using appropriate assessment techniques (n = 2), and did not analyse/present data on predictors of work outcomes (n = 7). Figure 1 displays the results of the search strategy, in alignment with PRISMA guidelines. Papers included in the review were those published in English between 1994 and July 2009. Each article for final inclusion in the review was subject to assessment using a quality assessment inventory (Additional file 1). Quality assessment ratings are displayed in Table 2, where each article was graded using these criteria. Seven of the 12 articles were considered high quality, four moderate quality and one low quality. Collectively, the most common features of the articles were: well defined inclusion criteria, measurement selection and baseline data collection point, and use of multivariate techniques for data analysis. The least common feature of the articles was the reporting of a representative sample (four articles reported recruiting samples with males only). While measurements used for data collection were clearly documented, in most instances a justification for selection was not given.

The aim of the paper was to review whether depression remains a predictor of poorer work outcomes following MI, by reviewing the literature from the past 15 years. Our findings suggest that depression recorded between admission and up to two months post discharge can significantly predict poorer RTW outcomes 6 to 12 months after a cardiac event. There is also some evidence to suggest that increases in severity of depression can reduce likelihood of RTW. Age and patient perceptions of their illness or work performance were also shown to significantly predict RTW in these populations.

Our first finding is consistent with earlier studies conducted in the 1980 s [11, 12], which found depression to be a strong determinant of work outcomes. Hlatky et al (1986)[12] found depression to predict work disability outcomes (χ² = 20, p < 0.00001), and loss of employment in the year following CAD (p = 0.006). More specifically, MÆland and others (1987)[11] found that RTW rates were strongly related to level of depression reported by MI patients at hospitalization (χ2 = 20.74, p < 0.05, G = -0.49) and 6 week follow-up (χ2 = 11.30 p < 0.05), and that this relationship was linear. Although this result appears in alignment with our second finding, it should be noted that a combined depression and anxiety measure was used in the MÆland study. The confounding effects of measuring these conditions using a composite instrument need to be considered.

Interestingly, both studies also found that alongside depression, patient perception was an important determinant of work status after a cardiac event. This was a finding observed in the current review, and elsewhere (Petrie et al, 1996)[36]. This raises questions about the role of cognition as a mediating factor in the relationship between depression and work.

Overall, commonalities between past and present studies may suggest that while the management of cardiac patients has changed in recent years, the factors influencing recovery and RTW identified over 15 years ago remain relevant. Determining the extent to which depression can predict major QOL outcomes post MI is important due to its clinical applications to rehabilitation. Modern rehabilitation programs should not only ascertain participant intent to resume work, but assess and treat depression in order to facilitate recovery. In depressed populations, patients receiving depression treatment such as anti-depressants or psychotherapy are significantly more likely to maintain paid employment over a 12-month period than those who do not [37]. Workplace initiatives targeting depression could potentially improve retention rates for employees exhibiting depression after returning to work post MI. These findings are of further value as it has been argued that identifying depression as a predictor of RTW could "give insight into mechanisms underlying an association between depression and cardiac mortality and morbidity" [9].

The review methods that we report on have two significant shortcomings. First, several articles in the review included samples comprising participants either recruited from cardiac rehabilitation or who had received a surgical intervention, post infarct. While it is acknowledged that this reflects modern management of cardiac patients, this may have confounded the representativeness of these samples. Those experiencing co-morbid depression are often less likely to attend rehabilitation programs, and report higher withdrawal rates [38]. As a result, depression may have been underrepresented in these samples. The inclusion of samples using participants who underwent surgical procedures may also have confounded results. These patients may experience added complications in the post operative period which prevent work resumption, or conversely, these procedures may promote better work outcomes, a finding which has been reported previously [39]. A further issue related to sampling was the lack of representativeness of female participants (one third of the studies had all male participants). For example, after a cardiac event, men have been found to have a greater likelihood of returning to work in a full time capacity and are less likely to report depression than females [40]. The inclusion of samples with only male participants may have both overrepresented RTW rates, and underrepresented the presence of depression. Female representation in this area of study is important when considering the proportion of those in paid employment at the time of MI has increased for both genders in recent times. For example in 1985, studies showed 34% of males and 18% of females were employed at the time of MI [41] compared with 65% and 32% respectively in 1999 [42], which may reflect demographic changes of workforce participation, or a decrease in the average age of a cardiac event.

If we compare the studies that did and did not find an association between depression and RTW post-MI, while no clear methodological differences were observed, failure to control for gender may have been a potential issue. Of the seven studies reporting depression as a predictor of RTW, one included males only, compared with three of the studies not reporting significant results. In fact, of the studies which failed to show depression as a significant predictor of RTW post-MI, only one controlled for gender (Mayou [9]), which may have had an impact upon results.

Second, the wide variation between definitions of RTW and depression measures may have undermined comparability of the studies included in the review. It should be noted that the variance in depression assessment instruments used in these studies also meant inconsistencies in time frames over which participants were asked to report their depression symptoms (for example, the MMPI assesses depression over a 12 month preceding period, while HADS assesses depression over a four week period), which has implications on results. Although not the focus of the review, there is evidence to suggest that depression assessment tools vary in their sensitivity to detect depression as a predictor of RTW [39]. Future studies in this area should consider this. Despite these limitations, our findings suggest that the majority of articles included in this review remained of moderate to high quality. In order to overcome the methodological limitations observed, we recommend the development and use of a brief, validated work measurement to capture employment outcomes, in order to enhance comparability of studies and allow for appropriate analyses of work outcomes. While depression was found to be a significant factor influencing RTW at both 6 and 12 months post MI, further research is required to determine the long lasting effects of cardiac depression on job retention. As the studies included in the review did not report assessing clinical depression using diagnostic instruments but rather self-report inventories, it remains unclear whether treating depression would improve vocational outcomes. While there is evidence that treating depression symptoms can improve vocational outcomes in primary care attendees (e.g. Lo Sasso et al [43]), this is yet to be demonstrated in CVD populations.

Therefore, we recommend that future clinical trials evaluating the effectiveness of post MI depression treatment use RTW as an endpoint. Furthermore, only two of the studies included in this review examined the impact of pre-existing depression on RTW rates. With evidence suggesting that depression outcomes (persistent major depression, subthreshold depression, or remission) are strongly associated with the probability of maintaining paid employment in depressed populations [44], further research is required into how work outcomes may differ according to types of depression in cardiac populations. Distinguishing between transient depressive symptoms following a life threatening cardiac event, (which, in many cases are only captured by self-report inventories), and more stable clinical depression may be useful for anticipating longer term effects on functioning.