943-9 Is Atrial Flutter a Circus Movement Around the Tricuspid Ring? Observations in the Transplanted Heart

Abstract

Atrial incision in the right atrium of transplanted heart may create a similar anatomical obstacle to the “Y” lesion model of atrial flutter. In 8 patients with atrial flutter in the donor heart we studied the right atrial activation sequence using the local electrograms recorded at three points as close as possible to the tricuspid ring, 1) the lateral right atrium (LRA), 2) interatrial septum (IS) and 3) high right atrium (HRA). We also determined the conduction times between LRA and IS during Entrainment from LRA, LRA-IS(E), and between IS and LRA during entrainment from IS, IS-LRA(E). They were compared with the interval LRA-IS and IS-LRA measured during flutter. The electrogram activation sequence was clockwise in all cases LRA-ISHRA. Entrainment from LRA and IS reproduced exactly the flutter activation sequence and the local electrogram morphology. During entrainment from LRA, LRA-IS(E) was similar to LRA-IS (155 ± 34 vs 146 ± 33 msec, r = 0.94; P < 0.0001), the return cycle at the stimulation point was 210 ± 16 msec. During entrainment from IS the conduction time IS-LRA(E) and the interval IS-LRA were almost equal (59 ± 43 vs 53 ± 40 msec, r = 0.98; P < 0.0001), the return cycle at the stimulation point was 207 ± 21 msec. LRA-IS(E) plus IS-LRA(E) was similar to the flutter cycle length (215 ± 15 vs 200 ± 19, r = 0.93, P < 0.0001. The similarity between the conduction times from LRA to IS and from IS to LRA and the flutter intervals LRA-IS and IS-LRA suggest that these points belong to the flutter circuit. Also the return cycle at the stimulation point during entrainment from both sites, LRA and IS, was similar to the flutter cycle length. These observations may best be explained by a macroreentry around the tricuspid ring.