Predictors of work inability after acute myocardial infarction in Switzerland

This study aimed to examine whether acute myocardial infarction (AMI) patients in Switzerland return to work and identify factors associated therewith. Data of 4315 working-age AMI patients enrolled in the Swiss AMIS Plus registry between 01/2006 and 09/2021 with 1-year follow-up and self-reported work status were analyzed. Patient characteristics were compared between those who did not reduce their work hours, those who reduced, and those who were no longer working 1 year after AMI. Multinomial logistic regression was used to analyze independent predictors of working ability. Of the patients, 3204 (74.3%) did not reduce their work hours, 592 (13.7%) reduced and 519 (12.0%) were no longer working 1 year after AMI. Women were more likely to reduce or stop working. Patients who did not reduce were more frequently young and male. Multinomial logistic regression showed that work reduction was associated with female sex and a Killip class > 2 at admission whereas stopping work was associated with female sex and comorbidities. A high rate of AMI patients in Switzerland (88%) return to work 1 year after AMI. Approximately 1 in 8 did not return to work and approximately 1 in 7 reduced their work hours. Important factors associated with reducing or no longer working after AMI were female sex, older age and a higher proportion of comorbidities.


Methods
AMIS Plus is a large, prospective national registry in Switzerland that has been collecting hospital data on the whole spectrum of patients with acute coronary syndrome (ACS), including AMI and unstable angina.It was founded in 1997 by the Swiss Societies of Cardiology, Internal Medicine and Intensive Care 8 .Since 1997, 84 of 104 hospitals of all sizes have continuously or temporarily collected data for AMIS Plus using a standardized questionnaire filled out by the treating physician or a trained study nurse in the treating hospital.Since 2006, patients were additionally contacted by phone 1 year after the ACS for a follow-up if they gave their informed consent.This study is in accordance with the Declaration of Helsinki regarding investigations on humans and was approved by the Swiss National Ethical Committee for Clinical Studies, the Board for Data Security and all cantonal ethic committees approved the registry (NCT 01,305,785).
Data on self-reported work status before and 1 year after AMI of working-age AMI patients who were contacted by the AMIS Plus registry between 01/2006 and 09/2021 for the follow-up 1 year after hospital admission were analyzed.In Switzerland, the retirement age is 64 years for women and 65 years for men, therefore only data of women < 64 and men < 65 years of age at the time-point of follow-up were selected.Patients not working before and after AMI were excluded from data analysis.
Follow-up was carried out 1 year after discharge by telephone interview by trained AMIS Plus data center staff.Patients were asked about their employment status before and 1 year after the AMI and in case of employment, they were asked the percentage they worked at the respective time points.In Switzerland, a full-time (100%) workload refers to 42 h per week.For this study, work was defined as paid work excluding, for example, informal caregiving or housework.
According to the self-reported work hours before and 1 year after AMI, the patients were divided into 3 groups: patients who did not reduce their work hours; those who reduced their work hours; and patients no longer working 1-year after AMI.Additionally, patients were asked during the follow-up interview about rehospitalizations, complications, rehabilitation participation, newly diagnosed illnesses, complications due to medications and also about their subjective health status compared to the time before AMI.
Information on the clinical status at admission, diagnosis, comorbidities and risk factors was obtained from the main questionnaire filled out by the treating hospitals after the index event according to the following definitions: AMI was defined according to The Fourth Universal Definition of Myocardial Infarction 9 and patients were further categorized as having ST-segment elevation MI (STEMI) if the initial ECG showed an ST-segment elevation and/or new left bundle branch block.Non-STEMI (NSTEMI) included patients with ST-segment depression or T-wave abnormalities in the absence of ST-elevation on the initial ECG.Killip classification was used to describe the clinical status at admission ranging from a Killip class 1 describing patients with no clinical signs of heart failure to a Killip class 4 describing patients with cardiogenic shock 10 .Dyslipidemia, arterial hypertension and diabetes were considered if the patient was previously treated for such a condition and/or diagnosed by a physician.Patients were defined as smokers if the patients were smokers at the time of the cardiovascular event.

Statistical analysis
Using the Kruskal-Wallis rank sum test, the Chi-square test or the Fisher's exact test we compared patient characteristics between the three groups.Multinomial logistic regression with the reference group "no reduction" was used to analyze the independent impact of comorbidities and cardiac function on work stop or work reduction, respectively.All comorbidities or cardiac function variables with a significant group difference in the descriptive statistics were included in the model.Temporal trends of employment changes were depicted using smoothed line plots with mean estimates and 95% confidence intervals (CIs).Statistical analyses were performed with R version 4.0.5 (The R Foundation for Statistical Computing, 2021) and a P-value < 0.05 was considered statistically significant.

Results
For the period 2006 to 2021, 14,033 AMI patients had consented to the 1-year follow up, and of these, 12,885 were reachable (Fig. 1).Among these 12,885 AMI patients, 5663 (44.0%) were of working age.For 627 patients, information on working status was incomplete and 721 patients did not work before and after AMI, therefore 4315 AMI patients could be included in this analysis.The follow-up was performed after a median (IQR) time of 400 (375; 441) days.The median (IQR) age was 54.4y (49.3y, 58.6y) and 3772 (87.4%) were males.The median (IQR) age of men was 54.4y (49.2y, 58.7y) and 54.4y (50.1y, 58.1y) for women.
The 1-year follow-up showed that 3204 (74.3%) patients did not reduce their work hours, 592 (13.7%) reduced and 519 (12.0%) stopped working (Fig. 1).Patients who did not reduce their work hours, were younger (median age (IQR): 53.8y (48.7y, 58.0y)) than those who reduced and who stopped work (56.5y (51.0y, 60.3y) and 56.5y  (51.3y, 60.6y) respectively), and p < 0.001 over all groups (Table 1).There was a statistically significant association between sex and the three groups, p < 0.001 (Table 1).Men were more likely to not reduce work, and women were more likely to reduce or stop working after 1 year (Table 1).Figure 2 shows the distribution of men and women in the three groups.
Over time (2006-2020), the rate of patients not reducing work after AMI remained stable, whereas the rate of patients stopping work tended to decrease and the rate of patients reducing work tended to increase in the years between 2018 and 2020 (Fig. 3).

Discussion
The data from the AMIS Plus database in Switzerland showed a RTW rate of 88% 1 year after AMI, which means that approximately 1 in 8 did not return to work 1 year after AMI.Patients with comorbidities were more likely to stop working whereas worse cardiac function was associated with a work reduction.Furthermore, our data showed that women were more likely to reduce or stop working after AMI, whereas men were more likely not to reduce working.Multinomial regression showed that both work reduction and stopping work were significantly associated with female sex.To our knowledge, no similar data was published before for Switzerland.
Several studies from different countries reported that male gender was associated with a greater RTW rate after AMI as described in a systematic review from the year 2021 13 where various reasons have been suggested   www.nature.com/scientificreports/ to explain this observation.For example, men may feel pressured to resume work after AMI in order to support their family financially, and women might have greater responsibilities for provision of family care and undertake more domestic work 13 .With respect to RTW after AMI, similar RTW rates as found in our data were reported in studies from other countries.In a study conducted in the USA, Spain and Australia with 1680 participants published in the year 2016, a RTW rate of 86% at 12-month follow-up was described 14 .In a nationwide retrospective cohort study conducted in Denmark with 22,394 participants, published in the year 2017, a RTW rate of 91.1% at 12 months post-AMI was found 5 .A prospective cohort study conducted in Italy with 102 participants published in the year 2018 showed a RTW rate of 92.7% 1 year post-AMI 6 .Warraich et al. used data from a registry to assess the Table 2. Follow-up data of acute myocardial infarction patients 1 year after discharge. 1n (%).www.nature.com/scientificreports/It should be emphasized that RTW rates among studies may not be comparable due to different inclusion criteria, outcome definition or study design.Also, different publication timepoints may have an impact on the reported RTW rate.For example, it may be possible that advancements in AMI care, e.g.improvement of treatments and reduction of complications, have an influence on RTW rates over time.Our analysis showed that the rate of those not reducing work remained stable over time.On the other hand, the rates of those reducing work and those stopping work were almost identical for the years 2006 until 2018, and afterwards a trend of decreasing rate in those stopping work was recognizable while the rate of those reducing work was increasing.
Our data showed that a higher proportion of comorbidities, such as past AMI, hypertension, diabetes mellitus and cerebrovascular diseases as well as rehospitalization or reinfarction after the initial event was more likely associated with stopping work.Similar findings were described in other studies 5,15,19 .
Further factors inhibiting RTW after AMI described in other publications were for example: depression, lower education, cancer, use of antidepressants or anxiolytics, a history of sickness absence, a physically demanding occupation and being a blue collar worker 13,16,20,21 .
The data from the AMIS Plus database showed that approximately 1 in 7 reduced professional activity 1 year after AMI.Work reduction was significantly related to worse cardiac function.Warraich et al. described 3% of patients working less at 1 year post-AMI 15 .This is in stark contrast to our finding of approximately 14% of individuals reducing work after AMI.In a qualitative study conducted in Turkey with 12 male AMI patients and published in the year 2016, it was described that "many of the participants continued to work at the same job by working less" after AMI 22 .In a study conducted in Italy with 253 angioplasty or heart surgery patients it was described that work hours decreased in 57% of the patients 23 , which is a clearly higher rate than what we found.
The observations described here may not be comparable due to different patient collectives and different types of analyzed outcomes.In addition, socio-political and cultural differences in different countries may also influence a patient's decision to reduce work, making comparisons difficult.
Further, the data from the AMIS Plus database showed that 74.3% did not reduce work 1 year after AMI.Patients not reducing work after AMI were younger than those reducing or stopping work.Other studies reported similar findings 16,17,19,24,25 .As described elsewhere 13 , older patients may opt for an early retirement after experiencing AMI, which may partially explain why older age results as a factor inhibiting RTW.However, Warraich et al. found in their study that only 27 in 492 individuals who reported an adverse change in employment 1 year post-AMI reported retirement 15 .
Our data showed that patients reporting a better subjective health status at the 1-year follow-up were more likely to RTW.This is in line with other studies 25,26 .Further factors facilitating RTW after AMI reported in other studies were for example: high educational level, self-employment status, higher job satisfaction, higher salary, clerical type of work and being married 5,6,14,16,19,27 .In our study, patients not reducing work had the highest rate of semiprivate/private insurance coverage which might, similar to these studies, reflect a better socio-economic status compared to patients reducing or stopping work.
In our study, rehabilitation after the initial event showed no association with the RTW rate.Maybe an association was not detectable because only data of patients who were contacted for follow-up were used and therefore data of other AMI patients undergoing rehabilitation is not present in this analysis.With respect to RTW, the role of rehabilitation in patients with cardiovascular disease seems to be inconclusive.A systematic review and meta-analysis about RTW in cardiovascular patients after cardiac rehabilitation showed in subgroup analyses that the proportion of RTW was higher in white-collar compared to blue-collar workers and that cardiac rehabilitation in out-patients was more effective compared to cardiac rehabilitation in in-patient and usual care 28 .
Lastly, our data showed that 5663 (44.0%) of 12,885 patients with AMI were of working age.This is in line with a previous study describing a rate of approximately 45% 4 , but is slightly lower when compared to the rate of approximately 50% given by a follow-up study conducted in Iran on 200 patients suffering from first AMI attack 27 .It must be considered that the rate of patients of working age in different studies may not be comparable due to different inclusion criteria of patients across different studies and different definitions of working age across different countries.

Strengths and limitations
For the first time it was possible to analyze the association between several patient characteristics and RTW after AMI for a large number of AMI patients in Switzerland.
However, it must be noted that the focus of the AMIS Plus registry is not on researching RTW issues.Some important data, for example, educational level, professional activity before and after AMI, time until returning to work after AMI, job satisfaction, symptoms of anxiety/depression or the exact reasons for reducing or stopping work are missing in the AMIS Plus database.

Conclusion
The analysis of the data in the AMIS Plus registry showed that a high rate of patients (88%) return to work 1 year after AMI.Females were more likely to reduce or stop working after AMI, whereas males were more likely not to reduce work.Younger age was an important factor associated with RTW after AMI.Work reduction was significantly associated with worse cardiac function whereas stopping work was associated with comorbidities.Over the observed time period (2006-2021), the rate of patients not reducing work after AMI remained stable.However, since 2018 a trend can be seen in a decreasing rate of patients stopping work after AMI and at the same time an increasing rate of patients reducing work after AMI.Knowledge of factors facilitating or inhibiting RTW after AMI is important in order to adapt healthcare measures, work conditions and policies with the aim to improve the RTW rate after AMI.

Figure 1 .
Figure 1.Overview of AMI patients with regard of working status (FU=Follow up).

Figure 2 .
Figure 2. Distribution of men and women in the three groups (in percent with respect to the total of men and women respectively).

Table 1 .
Baseline characteristics of AMI patients according to working status 1 year after acute myocardial infarction.