Conduction Velocity Around the Tricuspid Valve Annulus During Type 1 Atrial Flutter: Defining the Location of Areas of Slow Conduction by Three-Dimensional Electroanatomical Mapping

Background: Conduction velocity (CV) around the tricuspid valve annulus (TVA) during type 1 atrial flutter (AFL) has been shown to be slowest in the tricuspid valve-inferior vena cava (TV-IVC) isthmus, compared to the septal or free wall segments of the TVA. However, fiber orientation in the triangle-of-Koch suggests that the inferior septum and medial TV -IVC isthmus should be the most slowly conducting segments around the TVA. Methods: To test this hypothesis we evaluated CV around the TVA during type 1 atrial flutter in 11 patients, using an electro-anatomical mapping system (Carto). CV was first calculated in 4 segments around the TVA including the TV-IVC isthmus, lateral free wall, superior free wall and septum, and then calculated in 8 segments around the TVA including medial (MI) and lateral isthmus (LI), inferior (IL) and superior lateral (SL) free wall, lateral (LS) and medial superior (MS) free wall, and superior (SS) and inferior septum (IS). Statistical comparison of CV from these multiple segments was made by one-way analysis of variance. Results: Measured in 4 segments around the TVA, mean CV (m/sec) in the TV-IVC isthmus (0.81 ± 0.23) and the septum (0.93 ± 0.18) was significantly slower than CV in the lateral free wall (1.16 ± 0.23) and superior free wall (1.10 ± 0.20), and CV in the TV-IVC isthmus was significantly slower than in the septum (p < 0.05). However, when analyzed in 8 segments, mean CV in the MI (0.56 ± 0.16) and IS (0.59 ± 0.24) was significantly (p < 0.05) slower than in all other segments including the LI (1.06 ± 0.46), IL (1.17 ± 0.40), SL (1.15 ± 0.40), LS (1.04 ± 0.25), MS (1.15 ± 0.28), and SS (1.26 ± 0.36) segments. Conclusions: Consistent with previous reports, CV around the TVA during type 1 AFL was slowest in the TV-IVC isthmus, compared to the septum, superior and lateral free wall regions. However, when the TVA was further subdivided into 8 segments, CV in the MI and IS segments was significantly slower than in all other segments around the TVA. These observations more precisely define the regions of slow conduction in human type 1 AFL, and are consistent with the known anisotropy and slow conduction in the Triangle of Koch.