An integrate-and-fire based model of PP and PR variability in the human electrocardiogram

The autonomic nervous system (ANS) plays a central role in modulating cardiac electrical activity at the sino-atrial (SA) node, and hence has a direct influence on the overall interbeat variability of heart rate, as assessed by surface PP or RR measurements. However, the ANS also influences intra-beat variability through its innervation of the atrio-ventricular (AV) node. This affects the conduction time through the AV node, which can be assessed through surface PR recordings. Conduction time through the AV node is also strongly influenced by refractory effects, so that the overall dynamics of the PR interval are complex. We present a novel integral pulse frequency modulation model to account for both PP and PR interval. The model output compares favorably with experimental data, and is supportive of a hypothesis that independent ANS modulation of the AV and SA node occurs.