In-Hospital Mortality Rate and Predictors of 30-Day Readmission in Patients With Heart Failure Exacerbation and Atrial Fibrillation: A Cross-Sectional Study

Data from Framingham Heart Study participants showed that atrial fibrillation (AF) occurs in more than half of individuals with heart failure (HF), and HF occurs in more than one-third of individuals with AF.1) It is estimated that around 6.2 million people in the US have HF.2) Approximately 13.4% of deaths in 2018 have HF mentioned in the death certificate.2) HF exacerbation poses a major financial burden on society, and it was estimated to cost around $30.7 billion in 2012.3)

AF and HF share common risk factors.4) Prevalence of AF has been reported to range from 27% to 65% in HF patients with increasing rates in HF with preserved ejection fraction (HFpEF). AF is associated with increased long-term mortality and morbidity.5), 6), 7), 8) Data from the Swedish Heart Failure registry6) showed AF increased hazards of HF hospitalizations regardless of the ejection fraction over 12-year period, and the European Society of Cardiology-Heart Failure long-term registry7) showed an increased risk of hospitalizations in HF with mildly reduced ejection fraction and HFpEF. Data from US Medicare beneficiaries between 2006–2008 showed increased all-cause readmission at 1 year.9)

The data on the effect of AF on HF exacerbation over the short term is lacking. In 2014, Medicare and Medicaid shifted from fee-for-service to value-based reimbursement, leading to the increased focus on preventing 30-day readmissions. Currently, there is limited information on the predictors of these short-term outcomes and the utilization of resources in patients with HF and AF. This study, aimed to identify the 30-day readmission rate, causes, and impact on healthcare in HF exacerbation with a history of AF.

Our study has several important findings. Firstly, among patients admitted with HF exacerbation with AF, the all-cause readmission rate was 16.7% within the first 30 days of discharge from index hospitalization, and the leading cause of readmission was HF. Second, low socioeconomic status, Charlson comorbidity score, and lower median income, Medicare and Medicaid insurance were predictors for increased 30-day readmission. Third, the mortality rate during readmission was higher when compared to index admission (8.12% vs. 7.28%, p=0.05).

The 30-day readmission rate in the US is significantly higher at 16.7% compared to 9.9% from a similar population-based study in Australia.11) However, this is consistent with rates of HF readmission rate in the US, which was at 18.2% based on the national readmission database.12) Our study showed a similar rate of readmission in patients with HF with underlying AF. The data on the effect of AF on HF readmission is variable. A metanalysis by Saito et al.13) revealed that having AF did not increase the risk of HF short-term readmission. Similar results were found in smaller studies in the US population,14) the Japanese population,15), 16) and the Spanish population.17) Ahmed et al. showed similar findings in patients older than 65 years using Medicare data, that AF did not increase the 30 days readmission.18)

Having AF by itself did not increase the short-term readmission rate for HF. This might be due to advances in the management of AF in terms of ablation techniques,19) an increase in the use of antiarrhythmics, novel oral anticoagulants, improvements in cardiac resynchronization therapy, and permanent pacemakers.20) Patients with both HF and AF are likely to have well-established outpatient care, given the complexity of management which might help prevent short-term readmissions.

In contrast to our results, Eapen et al.21) showed a modest increase in the 30-day readmission rate with increased hazards of 1.09 using Medicare claims data. However, a larger study sample and an all-payer source database are some of the unique features of our study. The most common cause of readmission remains HF exacerbation, similar to previous studies.11), 12), 22)

Like prior evidence in HF,12), 23), 24), 25), 26) our study revealed low socioeconomic status, Charlson comorbidity score, and lower median income, Medicare and Medicaid insurance were predictors for increased 30-day readmission. Around 90% of patients included in the study either had Medicare or Medicaid, and they had a high chance of readmission (29% and 47%) compared to patients with private insurance. A likely explanation might be the lack of Medicare part B and D coverage, which provides outpatient services. At the same time, very sick patients with low socioeconomic status and no insurance are likely to apply for Medicaid and have poor access to health care. These findings stress the importance of policies specifically geared towards patients of low socioeconomic status and hospitals taking care of these populations.27) We did not find age and gender predictive of readmission rates consistent with previous evidence.13), 18), 23), 28), 29)

Although the rates of cardiogenic shock and mechanical ventilation were significantly higher with index admission, the mortality rate was slightly higher in readmitted patients (8.12% vs. 7.28%, p=0.05). The underlying severity of HF and ejection fraction might drive this, and although rates were adjusted with the Charlson comorbidity index, HF AF shares similar risk factors, which increases the chance of unmeasured confounders. Nevertheless, these findings emphasize the importance of preventing readmission. Length of stay and hospitalization charges are comparable to index admission (6.1 vs. 6.4 days, p<0.001) ($61,693 vs. $65,741, p=0.01). Total preventable days of hospitalization were 45,706 for 2018, which translates to a $461 million financial burden.

Subgroup analysis showed that the mortality rate was higher in HFpEF (6.47% vs. 8.88%), while in HFrEF, mortality did not differ. The difference in mortality in HFpEF is likely due to unmeasured confounders such as degree of kidney dysfunction or sepsis, which were among the top 3 causes of readmission. Further studies are warranted if medications with mortality benefit or ablation for AF had an impact on mortality during readmission in patients with HFrEF and AF.

As with any cross-sectional study, we cannot establish causality but only associations. Our study is based on a database based on ICD-10 CM coding, which can include possible coding errors/risk factors or diagnoses not entered into the database. We did not distinguish between different types of AF and lacked information on race, type of antiarrhythmics drugs used, laboratory data, imaging findings, baseline vital signs and if has had any outpatient ablation procedures for AF. We could not evaluate social barriers for discharge or readmission, outpatient resource accessibility, and medication compliance. NRD does not record out-of-state readmissions.

In conclusion, the 30-day readmission rate was 16.7% in HF patients with concurrent AF. Readmitted patients had a higher mortality rate when compared to the index admission. Low socioeconomic status, comorbidities, Medicare and Medicaid insurance, are independent predictors for 30-day readmission. Financial burden incurred from readmission was $461 million for the year 2018. Future studies directed with interventions to prevents readmissions are warranted.