Effect of weekend admission for acute myocardial infarction on in-hospital mortality: a retrospective cohort study

Background: No previous nationwide study has examined whether there is a 'weekend effect' of higher mortality after admission for acute myocardial infarction (AMI) when percutaneous coronary intervention (PCI) is easily accessible.

Methods: Using the Diagnosis Procedure Combination inpatient database in Japan, we identified AMI patients aged ≥20 years who were admitted to acute care hospitals between July 1, 2010 and March 31, 2013. Multivariable regression models fitted with generalized estimating equations were used to determine the association between weekend admission and in-hospital mortality. Eligible patients were also classified into subgroups according to Killip class at admission.

Results: Of 111,200 eligible patients, 30,847 patients were admitted on weekends and 80,353 patients on weekdays. Overall, the in-hospital mortality was significantly higher for weekend admission than for weekday admission (13.6% versus 11.4%; P<0.001; unadjusted odds ratio [OR] 1.222; 95% confidence interval [CI] 1.172 to 1.274), despite the higher rate of PCI performed on the day of admission (68.9% versus 64.8%; P<0.001). The association remained significant after adjusting for baseline characteristics, invasive procedures, and medications (adjusted OR 1.144, 95% CI 1.079 to 1.214). In subgroup analyses, the effect of weekend admission remained significant in the Killip II to IV subgroups, but became insignificant in the Killip I subgroup (adjusted OR 1.002, 95% CI 0.828 to 1.213).

Conclusions: This study showed that weekend admission for AMI was significantly associated with higher in-hospital mortality even in a setting where PCI was highly available.