Pathways and Induction of Intranodal Reentry

curves on atrial extrastimulus testing. Stimulation was performed from the right atrium in all cases. The left atrium was stimulated from the coronary sinus in 13 patients and directly through a patent foramen ovale in two patients. Baseline fast-AVN-pathway AH intervals were significantly shorter with left atrial stimulation. Maximum AH intervals for conduction over the fast or slow AVN pathways were also significantly shorter with left atrial stimulation. Refractory periods of the fast or slow AVN pathways were not significantly altered by the site of stimulation. Although failure to induce dual AVN pathways or AVN reentry could occur with use of only one site of atrial stimulation, this was uncommon (four of 15 patients); the ineffective site was usually the left atrium, and the reason was generally a prolonged atrial functional refractory period at that site. Provided the atrial functional refractory period was not prolonged compared with other sites and several basic cycle lengths were used, the site of atrial stimulation did not significantly affect demonstration of dual AVN pathways and induction of AVN reentry. Variability of most measurements ofAVN function and reentry were common. A critical AH interval did not appear to be necessary for induction of AVN reentry in four cases. We conclude that site of atrial stimulation influences AH conduction times over both fast and slow AVN pathways without altering refractoriness. The site of stimulation does not significantly affect ease of demonstration of dual AVN pathways or induction of AVN reentry.