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Atrial Fibrillation (Af)


Atrial fibrillation (AF) is the most common persistent cardiac arrhythmia in clinical practice.(1) Patients with AF hospitalized on weekends were previously reported to have higher mortality and increased length of hospital stay.(2) A subsequent analysis reported improved mortality,(3) but the results were not replicated in a national database. We sought to investigate the outcomes in the year 2014 through publically available nationwide inpatient sample database (NIS).


The NIS is a part of the Healthcare Cost and Utilization Project (HCUP) which is sponsored by the Agency for Healthcare Research and Quality (AHRQ).(4) Each year of the NIS records over 7 million inpatient hospitalizations. The NIS is one of the largest all-payer databases of hospital inpatient stays available in the United States of America (USA). The 2014 NIS sampling frame is comprised of 44 States and the District of Columbia, covering more than 96 percent of the U.S.A population and including more than 94 percent of discharges from U.S.A community hospitals.

Our main interest group were the hospitalizations who had a primary diagnosis (dx1) of atrial fibrillation or flutter. All patients with international classification of diseases, 9th revision, code 427.31 or 427.32 as the principal diagnosis (dx1) were included. Per AHRQ-HCUP, the weekend admissions were defined as admissions on Saturday-Sunday.(5) The use of cardioversion (rhythm control procedures denoted by the presence of ≥ 1 of the following procedural codes in any position: 99.61, 99.62 and 99.69). We also examined regional cost differences for AF admissions. Our primary outcomes were in-hospital mortality, utilization of cardioversion procedures, length of hospital stay (LOS), time to cardioversion procedure and total hospitalization charges.

The study protocol was reviewed by the University of Iowa Hospitals and Clinics, Iowa City, institutional review board, and the study was exempt from human subject research as it includes only de-identified, publically available data. All analyses were performed using SAS, version 9.4 (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. Descriptive statistics 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 motioned outcomes between the weekday and weekend admissions, which consisted of the Rao-Scott chi-square test for categorical outcomes and t-tests for continuous outcomes. Finally, multivariate models were applied to test the adjusted associations between the outcomes of weekend versus weekday admissions. For in-hospital mortality, a logistic regression model was used. The level of significance (α) was chosen as 5%.


There were 90,701 hospitalizations with AF as the primary diagnosis. It yielded a national estimate of 453,505 hospitalizations. Of these, 92,220 were characterized as weekend hospitalizations and 361,285 as weekday hospitalizations. The baseline characteristics of the patients are listed in Table 1.

Comparing the in-hospital mortality in two groups, we have identified that the mortality for patients admitted on weekends did not significantly vary from those admitted on the weekdays (0.94% vs 0.93%). The difference in mortality did not differ after the data was adjusted for patient’s characteristics, co-morbidities, and hospital characteristics.

Secondary outcomes were the number of inpatient cardioversion procedures, interval to procedure, length of stay and the cost of hospitalization. These characteristics are listed in Table 2. We discovered that the patients admitted on the weekend for AF underwent fewer cardioversion procedures than those hospitalized on a weekday (2.90% vs 14.83%, p< 0.0001). The average time to cardioversion was not significantly different among both groups (0.89 days on a weekend vs 0.71 days on a weekday). The weekend AF admission was associated with a lower cost of hospitalization. On multivariate logistic regression analysis, we observed that patients with higher number of co-morbidities (greater than or equal to 5) had the most significant association with in-hospital mortality compared to all other parameters OR= 1.342 (95% CI 1.014-1.776).


The main outcome of our analysis on the NIS 2014 data are 1) AF hospitalizations on a weekend showed no significant differences in mortality, length of stay, time to cardioversion 2) We also found that patients admitted on the weekend were less likely to undergo cardioversion and 3) they had overall lower mean cost of hospitalization.

Prior publication on AF weekend hospitalization by Deskhmukh et al(2) reported the adjusted in-hospital mortality to be higher for weekend admissions (OR 1.23, CI 1.03-1.51), longer weekend length of hospitalization and lower rates of utilization of cardioversion (7.92% weekend vs 16.2% weekday). Similarly, another publication by Weeda et al(3) has reported that there were no differences in the adjusted in-hospital mortality rate (OR 1.02; 95 % CI 0.94 to 1.11) and the length of hospitalization. However, they were found to have longer time-to-procedure and lesser treatment costs with weekend admissions. In patients with AF, the higher mortality, length of stay and lower utilization of cardioversion procedures were thought to be secondary to limited availability of services on the weekends. It was proposed that the subtle primary signs of acute problems go unnoticed until later on a weekend. Studies focused on the weekend effects in general have emphasized for a better organized model of care which could help in bridging the gap of the weekend effect.

In comparison to the prior studies (Table 3), our results match Deshmukh et al where the utilization of cardioversion and cost of hospitalization was lower in patients admitted during the weekends with AF. On the other hand, our analysis also matches Weeda et al in demonstrating a lack of difference in mortality and the length of hospitalization stay among both groups comparing weekend and weekday admissions. The outcomes on the weekend are informally referred as the ‘weekend effect’. It is a phenomenon which is often highlighted to associate poor outcomes in patients hospitalized over the weekends. It has been proposed that it might be a result of lack of healthcare management organizations to improve practices of care, which includes ensuring round the clock accessibility to life-saving procedures.(6) Also, published meta-analysis have associated poor outcomes in patients admitted with myocardial infarction and other medical conditions.(7)

We notice a trend in improvement of outcomes in patients with AF over a period of 6 years (Table 3). The difference in-hospital mortality, length of hospitalization, and time to cardioversion has been gradually decreasing since Deshmukh et al’s publication. These changes might due to implementation of a robust patient care across the hospitals in the United States to provide 24/7 accessibility to life saving procedures.(8, 9) However, utilization rates of cardioversion continue to be low among the patients admitted over the weekend. One of the reasons might be due to delay in identifying subtle signs of acute problems, such as hypotension, may go unnoticed until later.

Though our study had essential strengths of including a large sample, our study is subject to a number of limitations. First, the NIS relies on claims data which can incur inaccurate billing and underestimation of covariates of interest, thus leading to coding bias.(10) Missing values in our data prevented us from including certain variables in the multivariate analysis. 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).

Future directions should be focused on improving the utilization rates of cardioversion procedures and assessing the reasons for disparity within the hospitalization costs associated with weekend hospitalizations. Our study findings provide valuable data demonstrating the improved mortality outcomes and length of hospitalization. Understanding the reasons behind decreased cost of admission on weekends and decreased utilization of cardioversion procedures might help to bridge the gap difference.


In the nationwide US practice, the weekend AF hospitalizations appear to have improving rates of in-hospital mortality, rates of cardioversion utilization and improved utilization of anticoagulation. However, the overall rates of utilization of cardioversion continue to be less when compared to the weekday. Further studies are required to identify the differences and explore the opportunities to improve AF weekend care.