Non-invasive, Robust Estimation of Refractory Period of Atrioventricular Node during Atrial Fibrillation

During atrial fibrillation (AF), the atrioventricular (AV) node is continuously bombarded with atrial impulses. The AV nodal properties, and in particular the refractoriness, play an important role in determining the ventricular response during AF. Therefore, it is very useful to determine the refractory period of the AV node non-invasively. The lower envelope of the Poincarè plot (a plot representing the dependence of i-th RR over (i-1)-th RR) has been shown to represent a measure of the refractory period of the AV node. In this study we compare different techniques to estimate the lower envelope: i) a linear fitting (LF), ii) a modified LF, and iii) an image-based method using the Hough transform. The simulation results suggest that the refractory period of the slow pathway can be accurately estimated even in the presence of many artifacts by the image-based technique. Without artifacts, the modified LF provides the best estimates (normalized absolute error: LF 0.15 ± 0.04; modified LF 0.04 ± 0.03; image-based 0.13 ± 0.12). Increasing the percentage of artifacts, LF methods perform worse, while the performance of the Hough-based technique is largely unaffected (normalized absolute error for 1.5% of artifacts: LF 0.19±0.09; modified LF 0.43±0.15; image-based 0.13±0.10).