Atrial fibrillation as an acute severity amplifier during cancer hospitalizations: A National Inpatient Sample analysis, 2018–2022.

e23098 Background: Atrial fibrillation (AF) is highly prevalent among patients with cancer and is frequently treated as a chronic comorbidity during hospitalization. Whether the presence of AF during cancer hospitalizations independently amplifies acute inpatient severity, critical care utilization, and mortality at a national level remains incompletely defined. Methods: A serial cross-sectional analysis was performed using adult hospitalizations with a principal diagnosis of malignancy in the 2018–2022 Healthcare Cost and Utilization Project National Inpatient Sample. AF/atrial flutter was identified using any-diagnosis ICD-10-CM code I48*. Outcomes included All Patient Refined Diagnosis Related Group (APR-DRG) severity of illness, extreme severity (APR-DRG level 4), in-hospital mortality, shock (R57*), mechanical ventilation, length of stay (LOS), and hospitalization cost. National estimates accounted for survey stratification, clustering, and discharge-level weighting. Survey-weighted multivariable regression adjusted for demographics, payer, ZIP-code income quartile, admission characteristics, cancer type, hospital characteristics, and year. Results: Among 961,848 unweighted cancer hospitalizations, representing 4,809,239 admissions nationally, AF was present in 11.9%. Hospitalizations with AF demonstrated substantially higher acuity compared with those without AF. Mean APR-DRG severity was higher (2.99 vs 2.50), and extreme severity occurred more frequently (5.19% vs 3.22%). In-hospital mortality was nearly doubled among AF-associated admissions (7.75% vs 3.93%). AF was also associated with higher rates of shock (2.83% vs 1.19%) and mechanical ventilation (4.97% vs 2.26%), longer LOS (8.23 vs 6.44 days), and greater hospitalization costs ($26,265 vs $22,365). After multivariable adjustment, AF remained independently associated with increased inpatient severity (APR-DRG severity β 0.38, 95% CI 0.36–0.39), extreme severity (odds ratio [OR] 1.79, 95% CI 1.72–1.86), in-hospital mortality (OR 1.75, 95% CI 1.70–1.80), shock (OR 2.34, 95% CI 2.23–2.44), and mechanical ventilation (OR 2.36, 95% CI 2.28–2.44). Conclusions: Atrial fibrillation occurring during cancer-related hospitalizations functions as an acute inpatient severity amplifier. The presence of AF as a comorbidity was independently associated with higher illness severity, ICU-level care, and mortality. These findings support reframing and prioritizing AF as a clinically actionable marker of inpatient decompensation rather than a chronic comorbidity, with implications for early risk stratification and escalation strategies in hospitalized oncology populations.