Modeling Mother Rotor Anchoring in Branching Atrial Tissue*

Background: It has been hypothesized that stable mother rotors may increase the stability of atrial fibrillation. Local shortening of action potential duration due to vagotonic activity may promote the formation of mother rotors. However, prior studies have shown that meandering rotors typically drift out of the region of short action potential duration (APD), making the formation of stable rotors unlikely. Thus, for the formation of mother rotors in vagotonic AF a mechanism must be involved which increases rotor stability. Hypothesis: Local variation of electrotonic load due to branching muscle sleeves in the atrial tissue may avoid rotor drift and ease the formation of stable vagotonic AF. In this chapter the underlying mechanisms are illustrated by means of computer modeling. Model formulation: Anchoring is illustrated in a square patch of tissue and a monolayer model of the atria. Vagotonic activity was modeled by increasing ACh-concentration in the vicinity of the pulmonary veins (PVs). Close to the right lower PV, a muscle sleeve branching into the vein was included in the model. A model of canine atrial membrane kinetics was used providing detailed data on electrical remodeling and vagal activity. AF was analyzed computing dominant frequency (DF) maps and phase singularities (PSs). Model predictions: In the case of a missing anchor site AF was self terminating within 2 s of simulated activity. The rotor drifted out of the short APD region. After including a branching tissue structure, mother rotor formation was observed (anchoring and almost periodic activity over the entire simulated interval of 4.2 s). Pull and push currents were identified as the mechanism stabilizing the rotor trajectory. Push currents in the bundle reduced the DF at the branching by about 10%with respect to the highest DF (15 Hz). The computed DFmapmainly reflected the underlying ACh concentration (correlation 0.9). Summary: Branching tissue structures in regions of high ACh-concentration may constitute the substrate underlying vagotonic AF. Future experimental studies are needed to further confirm motor rotor anchoring in branching tissue.