The fibrillatory frequency trend and the time-dependent spectral characteristics can be investigated using a spectral profile technique in patients with atrial fibrillation (AF). The aim of this study is to develop model-based means for stricter control on the update of the spectral profile. A spectral model defined by Gaussian functions is suggested for describing the fundamental and harmonics of the atrial waves during AF, thereby accounting for basic characteristics of the typical AF spectrum. The model parameters are obtained from weighted least squares fitting of the model to the observed spectrum. The method was tested on simulated signals with two different frequency trends. A marked improvement was observed when tracking the main fibrillatory frequency as the error was reduced by more than 50% in comparison with the original method.