Action potential characteristics in the sinus venosa of patients with and without atrial flutter

Background: A functional line of conduction block is often observed in the sinus venosa (SV) during typical atrial flutter (AFL). Little information, however, is available as to the action potential characteristics in the SV with respect to the functional block. Methods and Results: Monophasic action potentials (MAPs) from the SV and lateral wall of the right atrium were recorded in 7 patients with paroxysmal AFL and 11 control patients. For both the control and AFL patients, the MAP duration at 90% repolarization (MAPD₉₀) in the SV was longer, and the MAPD⁹⁰ restitution slope was less steep than in the lateral wall. The MAPD₉₀ in the SV in the AFL patients was slightly longer than that in the controls at the shortest cycle length (CL) tested (300 ms). However, the MAPD_90s at longer CLs (350-700 ms), as well as the MAPD₉₀ restitution slopes in the SV were comparable between the 2 groups. Conclusions: The MAPs in the SV are characterized by a long duration and flat restitution kinetics in humans. MAP properties to facilitate the development of conduction block in the SV are not appreciable in patients with paroxysmal typical AFL.