Reentry in a morphologically realistic atrial model

Introduction: Atrial fibrillation is the most common cardiac arrhythmia. In ablation procedures, identification of the reentrant pathways is vital. Th is has proven difficult because of the complex morphology of the atria. The purpose of this study was to ascertain the role of specific anatomic struc tures on reentry induction and maintenance. Method and Results: A computationally efficient, morphologically realistic, computer model of the atria was developed that incorporates its major stru ctural features, including discrete electrical connections between the righ t and left atria, physiologic fiber orientation in three dimensions, muscle structures representing the crista terminalis (CT) and pectinate muscles, and openings for the veins and AV valves. Reentries were induced near the v enous openings in the left and right atria, the mouth of the coronary sinus , and the free wall of the right atrium. The roles of certain muscular stru ctures were ascertained by selectively removing the structures and observin g how the propagation of activity was affected. Conclusion: (1) The muscular sheath of the coronary sinus acts as a pathway for a reentrant circuit and stabilizes any circuits that utilize the isthm us near the inferior vena cava. (2) Poor trans-CT coupling serves to stabil ize flutter circuits. (3) Wall thickness is an important factor in the prop agation of electrical activity, especially in the left atrium. (4) The open ings of the inferior and superior venae cavae form natural anatomic anchors that make reentry easier to initiate by allowing for smaller ectopic beats to induce reentry.