A Lumped-Parameter Cardiovascular Model for Investigating Hemodynamic Alterations During Atrial Fibrillation.

Atrial fibrillation (AF) is a major cardiac arrhythmia characterized by impaired hemodynamics caused by irregular ventricular activation and loss of coordinated atrial contraction. However, the coupled effects of rhythm irregularity and progressive atrial remodeling on cardiovascular hemodynamics have not been sufficiently quantified. In this study, a closed-loop lumped-parameter cardiovascular framework was developed to investigate hemodynamic alterations under normal sinus rhythm (NSR) and AF conditions. Time-varying elastance functions were used to represent cardiac chamber mechanics, while stochastic RR interval sequences reproduced the irregular ventricular response characteristic of AF. Progressive atrial remodeling was represented through systematic increases in atrial elastance to simulate increasing chamber stiffness. The results demonstrated that AF produced irregular left atrial pressure fluctuations and pronounced beat-to-beat variability in ventricular pressure and volume. Ventricular stroke volume decreased from 70-75 mL under NSR to 55-65 mL under AF conditions. With progressive remodeling, left atrial volume decreased by 36.4%, while ventricular end-diastolic volume increased from 130 to 134 mL, indicating compensatory ventricular adaptation. These findings suggested that atrial stiffening impaired atrial compliance and reservoir function, whereas ventricular adaptation partially compensated for the impairment in atrial mechanical function.