Effect of weekend admission for acute myocardial infarction on in-hospital mortality: A retrospective cohort study
Introduction
A ‘weekend effect’ of hospital admission has been reported, whereby there is higher mortality in patients admitted on a weekend compared with admission on a weekday [1], [2], [3]. Hospitals generally provide comprehensive care on weekdays but have decreased staffing levels on weekends, with possible reductions in the quality of care [4], [5], [6]. The differences in the level of care between weekdays and weekends may cause ‘weekend effect’ in several diseases [1], [2], [3].
The management of acute myocardial infarction (AMI) generally requires emergency invasive cardiac procedures, such as percutaneous coronary intervention (PCI) [7], [8], which are often less available during off-hours (weekends and nights) than during regular hours because of limited staff availability [4], [5], [9]. The effect of off-hour admission for AMI on mortality has been controversial because previous studies have shown inconsistent results [1], [3], [4], [5], [9], [10], [11], [12], [13], [14], [15]. Recently, a study using data from an administrative database in New Jersey reported that 30-day mortality for AMI was higher in patients admitted on weekends than on weekdays [10]. On the other hand, a study from an American Heart Association database reported no significant difference in in-hospital mortality between off-hour and regular hour admissions for AMI [9]. Most recently, a meta-analysis of 48 related studies suggested that patients with AMI admitted during off-hours had higher short-term mortality, and patients with ST-elevation myocardial infarction (STEMI) had longer door-to-balloon times [16]. Off-hour admission for AMI, therefore, could affect the performance of invasive procedures and short-term mortality. In studies from Western countries, however, less than 50% of patients with AMI and less than 60% of patients with STEMI underwent PCI during hospitalization [4], [5], [9], [10], [11], [12].
In the above-mentioned study from New Jersey, the difference in 30-day mortality between weekend and weekday admissions became insignificant after adjustment for invasive cardiac procedures [10]. Thus, the higher mortality for weekend admissions could partially be a result of the decreased availability of PCI [4], [10]. In Japan, many hospitals are equipped to perform PCI [17], [18], [19], and previous studies revealed that the proportion of patients undergoing primary PCI for AMI was much higher in Japan (75–97%) than in Western countries (6–60%) [4], [5], [6], [9], [10], [11], [12], [14], [19], [20]. It remains unclear whether weekend admission for AMI is associated with higher mortality when there are many hospitals equipped to perform PCI.
It also remains unknown whether the effect of weekend admission for AMI is different according to the severity of AMI at admission. To our knowledge, no study has examined the effect of weekend admission in patients with different severities of AMI. The Killip classification is a classical but still useful predictor of short-term mortality in patients with AMI [21], [22], [23]. A higher Killip class is associated with a greater need for mechanical circulatory support such as intra-aortic balloon pumping (IABP) and extracorporeal membrane oxygenation (ECMO), which require high staff input for prompt administration in the acute phase.
The present study therefore had two objectives: to determine whether weekend admission for AMI was associated with higher in-hospital mortality compared with weekday admission in a nationwide setting in Japan, where PCI is easily accessible; and to assess whether the effect of weekend admission for AMI was different according to the Killip class at admission.
Section snippets
Data source
Data for this study were extracted from the Diagnosis Procedure Combination (DPC) database in Japan, which includes hospital administrative claims data and discharge abstracts, and is described in detail elsewhere [24]. Since July 1, 2010, data have been continuously collected by the DPC Study Group, and in 2012 the database included data of approximately 7 million inpatients from over 1000 hospitals, representing approximately 50% of all inpatient admissions during the year to acute care
Study population
Among approximately 18 million inpatients in the database between July 2010 and March 2013, 111,885 patients aged ≥ 20 years were admitted with AMI. After exclusion of 685 patients who were discharged alive on the day of admission, there were 111,200 patients eligible for inclusion in the study, 30,847 admitted during weekends and 80,353 admitted during weekdays.
Patient characteristics
Table 1 shows the baseline characteristics of the study population. Fewer hospitals were available on weekends than weekdays. Patients
Discussion
This study showed that in-hospital mortality of AMI patients was significantly higher for weekend admission than weekday admission, despite the higher rate of PCI performed on the day of admission. In multivariable analysis, weekend admission was significantly associated with higher in-hospital mortality, even after adjustment for confounding factors. In subgroup analyses, weekend admission was associated with higher mortality in the Killip II to IV subgroups, but not in the Killip I subgroup.
Conclusions
The present study showed that weekend admission for AMI was significantly associated with higher in-hospital mortality even in a setting where PCI was readily available. The effect of weekend admission on in-hospital mortality remained significant after adjusting for baseline characteristics, invasive procedures, and medication. In a subgroup analysis, the effect of weekend admission remained significant in the Killip II to IV subgroups, but was not significant in the Killip I subgroup.
Funding sources
This work was supported by grants from the Ministry of Health, Labour and Welfare, Japan (Research on Policy Planning and Evaluation grant number: H25-Policy-010), and the Council for Science and Technology Policy, Japan (Funding Program for World-Leading Innovative R&D on Science and Technology, FIRST program grant number: 0301002001001).
Conflict of interest
The authors report no relationships that could be construed as a conflict of interest.
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All authors take responsibility for all aspects of the reliability and freedom from bias of the data presented and their discussed interpretation.