NASPE YOUNG INVESTIGATOR AWARDEE-1993 Computer Model of the Atrioventricular Node Predicts Reentrant Arrhythmias CHRISTOPHER T. LEFFLER and J. PHILIP SAUL* From the Division of Health Sciences and Technology, Harvard Mfidical School-Massachusetts Institute of Technology, and the *Department of Pediatrics, Harvard Medical School, and Department of Cardiology, Children's Hospital, Boston, Massachusetts LEFFLER, C.T., ET AL.: Computer Model ofthe Atrioventricular Node Predicts Reentrant Arrhythmias. Introduction: Following atrial premature beats, the AV node may exhibit sustained reentrant tacbyarrhytb- mias, isolated ecbo beats, or discontinuities in tbe recovery curve (tbe plot of conduction time versus atrial cycle length). A computer model was used to examine the bypotbesis tbat spatial variation of AV nodal passive electrical resistance may account for these pbenomena. Metbods and Results: A computer model of a rectangular lattice of elecirotonically linked elements wbose ionic kinetics simulated nodal ionic flux was developed. Tbe model showed that there exists a resistance value that minimizes the effective refractory period, because high resistance prevents depolarization of distal elements, while low resistance allows leakage of depolarizing current by electrotonic transmission, preventing activation of proximal elements. Higb resistances stabilized reentry by slowing conduction. Simulations incorporating equal resistance values between elements predicted increased AV nodal conduction times with increasing prematurity of atrial impulses. A model with a gradual change in resistance between fibers produced discontinuities and tacbycardia, but not both simultaneously. Uniform anisotropy produced preferential transverse block, leading to ecbo beats and "fast-slow" tacbycardia, but not recovery curve discontinuities. Nonuniform anisotropy could produce reentry, but tachycardia often occurred without discontinuities. Dividing the lattice into two electrotonically linked parallel pathways witb different resistance values ("dual pathway model") predicted recovery curve discontinuities, echo beats, and tachycardia. At critical atrial cycle lengtbs, only the (bigh resistance) slow pathway conducted antegradely, wbile the fast pathway conducted retrogradely, to generate the typical "slow-fast" tacbycardia. Responses ofthe dual pathway model to ablation were consistent witb clinical data, including the previous observation ofa decrease in fast patbway effective refractory period after slow pathway ablation. Conclusion: Differences in passive electrical resistance of electrotonically linked dual pathways within tbe AV node may account for func- tional longitudinal dissociation, reentrant arrhythmias, and responses to catheter ablation therapy. (PACE, Vol. 17. fanuary 1994) atrioventricular node, electrophysiology, reentry, dual pathways, computer model, catbeter ablation This work was supported by a Biomedical Engineering Grant from the Whitaker Foundation. Dr. Saui is supported by a Clini- cal Investigator Award from the National Institutes of Healtli #K08-HL02380-03. This manuscript was presented at the North American Society of Pacing and Eleclrophysiology Conference, 1993, and was awarded first prize in the Young Investigator Awards Competi- tion for basic science. Address for reprints: ]. Philip Saul, M.D., Children's Hospital, 300 Longwood Ave., Boston, MA 02115. Fax: (fil7) 735-7513. Introduction Atrloventricular (AV) nodal reentrant tachy- cardia is one ofthe most Gommon forms of parox- ysmal supraventricular tachycardia in adults.^ TypiGally the tachycardia involves slow antegrade and fast retrograde AV conduction.' ' Microelec- trode studies in the isolated rahbit heart have shown that during this arrhythmia the AV node PACE. Vol. 17 January 1994 113