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Previous studies have identified a “weekend effect” in terms of a poor outcome for patients hospitalized with various acute medical conditions. The aim of our study was to investigate whether weekend admissions for atrial fibrillation (AF) result in worse outcomes than those admitted on weekdays. In the Nationwide Inpatient Sample 2008 database, we identified a total of 86,497 discharges with a primary discharge diagnosis of AF. The use of a cardioversion procedure for AF on weekends was lower than that on a weekday (7.9% vs 16.2%; p <0.0001; odds ratio 0.5, 95% confidence interval 0.45 to 0.55, p <0.0001). After adjusting for patient and hospital characteristics and disease severity, the adjusted in-hospital mortality odds were greater for weekend admissions (odds ratio 1.23, 95% confidence interval 1.03 to 1.51; p <0.0001). The length of stay was significantly longer for weekend admissions. In conclusion, patients admitted with AF on weekends had lower odds of undergoing a cardioversion procedure and greater odds of dying.
The outcome of conditions such as acute myocardial infarction is relatively poor when patients are hospitalized over a weekend versus a weekday.
A likely contributing factor to this observation is the limited number of hospital staff and availability of in-house expertise for invasive coronary procedures on the weekends. Data on the “weekend effect” for atrial fibrillation (AF)-related hospitalizations and their outcomes are not available. Because AF is the most common sustained cardiac rhythm disturbance, even a small difference in mortality between the weekday and weekend admissions of patients would result in a substantial number of increased deaths in the population by virtue of its high incidence. We investigated the differences in outcomes for AF-related hospitalization on the weekend versus weekdays using a large national hospitalization database.
The Nationwide Inpatient Sample (NIS) for 2008 is the largest all-payer database of hospital inpatient stays available in United States. Data from the NIS have been used to identify, track, and analyze national trends in healthcare usage, patterns of major procedures, access, disparity of care, trends in hospitalizations, charges, quality, and outcomes. The 2008 NIS contains all discharge data from 1,044 hospitals located in 40 States, approximating a 20% stratified sample of United States community hospitals. The sampling frame for the 2008 NIS is a sample of hospitals that comprises approximately 90% of all hospital discharges in the United States. Each individual hospitalization is de-identified and maintained in the NIS as a unique entry with 1 primary discharge diagnosis and ≤14 secondary diagnoses during that hospitalization. Each entry also carries information on demographic details, insurance status, co-morbidities, primary and secondary procedures, hospitalization outcome, and length of stay.
The NIS contains the clinical and resource use information included in a typical discharge abstract, with safeguards to protect the privacy of individual patients, physicians, and hospitals (as required by the data sources).
The 2008 database was the most recent release from the Healthcare Cost and Utilization Project. NIS data have been used to explore the outcomes for discharges for various medical and surgical diagnoses.
Our primary interest group was hospitalizations with a primary diagnosis of AF. All patients with International Classification of Diseases, 9th Revision, Clinical Modification, code 427.31 or 427.32 as the principal diagnosis were included. In alignment with previous studies, weekend admissions were defined as admissions between midnight on Friday through midnight on Sunday.
Our main outcomes were the use of cardioversion procedures, length of stay, hospital mortality, and total hospitalization charges.
All analyses were performed using SAS, version 9.2 (SAS Institute, Cary, North Carolina). Survey procedures available within the SAS were applied in the analysis to account for design features of the complex sample survey, such as clustering, stratification, and sampling weights. Therefore, the resulting estimates should be representative of the national hospital inpatient admissions. Descriptive statistics, including proportions, mean values, and standard errors, were generated for the individual and hospital characteristics for both weekend and weekday admissions. Univariate tests were applied to compare the equality of the mean or proportions for the mentioned outcomes between the weekday and weekend admissions. These tests consisted of the Rao-Scott chi-square test for categorical outcomes and simple linear regression analysis for continuous outcomes. Finally, multivariate models were applied to test the adjusted associations between the outcomes and weekend versus weekday admissions. For the number of procedures, days to the procedure, length of stay, and total charges, we applied multivariate linear regression models. Adjusted parameter estimates for weekend versus weekday admission were collected. For in-hospital mortality, a logistic regression model was used. The level of significance (α) was set at 5%.
There were 86,497 discharges with AF as the primary diagnosis, yielding a national estimate of 425,744 hospitalizations, with the number adjusted for the entire United States population. Of these, 16,949 were characterized as weekend admissions and 69,548 as weekday admissions. The baseline characteristics of the patients as a whole and in each group (weekday admission group and the weekend admission group) are listed in Table 1.
Table 1Baseline characteristics of atrial fibrillation (AF) hospitalizations
Weekday Hospitalizations (n = 69,548)
Weekend Hospitalizations (n = 16,949)
Total Hospitalizations (n = 86,497)
70.3 ± 0.1
70.5 ± 0.1
70.3 ± 0.1
Hospital teaching station
Hospital bed size
Data presented as mean ± standard error or percentages.
We compared the in-hospital mortality among patients admitted on weekends and those admitted on a weekday. We found that the patients admitted on weekends experienced a greater proportion of in-hospital mortality than those admitted on weekdays (1.1% vs 0.9%; p = 0.01). Patients hospitalized on a weekend for AF were 1.24 times more likely to die compared to those hospitalized on weekdays (odds ratio 1.24, 95% confidence interval 1.02 to 1.51; p = 0.0029) after the data were adjusted for patient characteristics, co-morbidities, and hospital characteristics.
The number of inpatient cardioversion procedures, interval to procedure, length of stay, and cost of hospital stay before and after adjustment for patient characteristics are listed in Table 2, Table 3, respectively. We found that those admitted on the weekend for AF underwent fewer cardioversion procedures than those hospitalized on a weekday (7.9% vs 16.2%, p <0.0001). The time to cardioversion was significantly longer for patients with a weekend admission, and this resulted in a longer length of stay. The weekend AF admission was associated with a $2,500 lower total charge on average, after adjustment for other covariates. This difference remained significant after adjustment for patient characteristics, disease severity, and hospital characteristics (odds ratio 0.5, 95% confidence interval 0.45 to 0.55, p <0.0001).
Table 2Unadjusted estimates for atrial fibrillation (AF) hospitalizations on weekend versus weekdays
Weekend Admission (n = 16,949)
Weekday Admission (n = 69,548)
Length of stay (days)
3.6 ± 0.04
3.5 ± 0.03
Total charges (US$)
22,000 ± 500
26,000 ± 700
Data presented as mean ± standard error or percentages.
On multivariate regression analysis, we observed that patients with ≥3 co-morbidities had the greatest association with in-hospital mortality compared to all other parameters outlined in Figure 1. Although urban hospital admission patients had significantly lower mortality, the size of the hospital had no effect on in-hospital mortality. Finally, black American patients hospitalized with AF had a significantly greater chance of dying in-hospital than did white American patients hospitalized with AF (odds ratio 1.5, 95% confidence interval 1.2 to 1.9).
Our analysis of the NIS 2008 data on AF showed that mortality was greater among patients admitted on weekends than among those admitted on weekdays after adjustment for major covariates. We also found temporal changes in the length of stay, number of procedures, and interval to procedure time. More specifically, patients admitted on weekends were less likely to undergo cardioversion than those admitted on weekdays. Also, the interval between admission and performance of procedures was longer for patients admitted on weekends. These findings might explain, to some extent, the increased mortality among weekend admission patients hospitalized with AF. When cardioversion was added to the regression model, the difference in weekend and weekday mortality was not significant. Furthermore, delays in procedure time on weekends can, in part, explain the increased length of hospital stay for these patients. The lower cost of hospital care among weekend admission might be an indirect indicator of the decreased number of procedures, including cardioversion, among patients hospitalized with AF on a weekend.
One possible reason for such a “weekend effect” could be differences in staffing. During weekends, hospital staffing is reduced in overall quantity and in the number qualified to perform certain procedures.
It may be surmised that subtle early signs of acute problems will go unnoticed until later. In many hospital settings, a physician not entirely familiar with the patient's problem is likely to provide coverage on weekends; hence, the patient might not have access to a physician familiar with all the medical issues.
This also resulted in delay in the proper care for the patient. Another study found a lower cardiac arrest survival rate on nights and weekends, except in the emergency department and trauma service, for which the staffing is independent of time and day of the week.
Exploring methods to minimize such staffing differences and regionalization of care could potentially bridge the gap in mortality between weekend and weekday admissions observed in our study. The data examining the effect of weekend admissions on stroke outcomes have not been unanimous, and an organized systems-based approach has been recommended as a potential solution to counter the adverse outcomes observed on weekends.
An organized model of AF care could have a similar effect, and it could possibly facilitate bringing down the weekend effect on mortality and length of hospital stay among patients with AF. Additional investigation into weekend care quality problems and what might help to compensate for these differences, along with the progress in the understanding of AF and its management, is crucial to counter the adverse outcomes observed on weekends.
Just as with other data mining studies, our study had quite a few limitations. We could not eliminate the effect of unmeasured confounders that might have contributed to the reported differences in mortality between patients admitted on weekends and those admitted on weekdays. Some examples of such confounders include, but are not limited to, data on the time from the onset of symptoms to presentation, type of AF, hemodynamic status at presentation, and medications administered during or before hospitalization. Furthermore, we did not evaluate the causes that could have accounted for this difference that are not patient related but related to the hospital (e.g., staffing differences on weekends). Nonetheless, the present study had important strengths, including a large sample and the absence of patient selection, because all patients with AF in the NIS 2008 database were enrolled in the study. The observation of a significant and clinically relevant increase in mortality among patients with AF who were admitted on a weekend rather than a weekday has important implications for clinical care and is an significant issue that needs additional exploration sooner rather than later.
Myocardial Infarction Data Acquisition System (MIDAS 10) Study Group
Weekend vs weekday admission and mortality from myocardial infarction.