Hospitalizations of Patients with Atrial Fibrillation (AF) in Poland: A Nationwide Study Based on over One Million AF Hospitalizations in 2017–2021

<b>Background/Objectives:</b> Atrial fibrillation (AF) is one of the most common forms of persistent arrhythmia in adults worldwide. The aim of this study was to present recent data on the epidemiology of patients hospitalized with AF in Poland. <b>Methods:</b> This is a retrospective, population-based study conducted using hospital discharge records. The data covered 1,225,424 cases of AF hospitalization reported in 2017-2021. <b>Results:</b> The study group consisted of 51.36% men and 48.64% women. The mean and median ages were 73.6 and 74 years, respectively. Women were older than men (77 vs. 70 years, <i>p</i> < 0.001). The mean and median lengths of hospitalization were 6.9 and 4 days. The mean annual hospitalization rate was 640.0 per 100,000 person-years. In the group of patients aged ≥65 years, the hospitalization rate was 2870.4 per 100,000 person-years. Men were hospitalized more frequently than women (<i>p</i> < 0.001). The total in-hospital mortality rate was 37.7 per 100,000 person-years, and it was higher in women than in men (<i>p</i> < 0.001). There was a significant downward trend in first-time hospitalizations during the analyzed period and a significant downward trend in mortality rates with a marked increase in the years 2020-2021. <b>Conclusions:</b> Although women are less frequently hospitalized for AF, they show a higher risk of fatal hospitalizations. The pandemic may have reduced new AF diagnoses and increased mortality in this group of patients. The results of this study may be helpful in making comparative analyses in the European and global contexts and taking actions aimed at improving the health condition of the Polish population.