Novel method to evaluate the conduction velocity and conducting area during isthmus-dependent atrial flutter

Objective: The difference of the conduction velocity (CV) around the tricuspid valve annulus between the counter-clockwise (CCW) atrial flutter and the clockwise (CW) atrial flutter has not been well clarified. This study was undertaken to evaluate the CV and the conducting area (CA) per millisecond around the tricuspid valve annulus using the electroanatomical mapping. Methods: The electroanatomical mapping was performed during the tachycardia for 30 consecutive patients (mean age: 61±16 years) with isthmusdependent atrial flutter (CCW, 25; CW, 5). We measured the CV and the CA of five divided areas of the right atrium, that is, upper septum (US), lower septum (LS), isthmus (I), upper lateral wall (UL) and lower lateral wall (LL) using the novel measurement method in the isochronal map. Statistical differences of these data between the two groups were assessed by the Student’s t-test and one-way analysis of variance methods. Results: In total, the CV of the LS was significantly slower than other areas (m/sec: US, 0.57±0.18; LS, 0.43±0.18; UL, 0.60±0.26; LL, 0.53±0.20; I, 0.50±0.17; p 0.05) and the CA of the US and UL were significantly larger than other areas (mm2/sec: US, 34.5±16.2; LS, 16.2±9.5; UL, 40.0±14.1; LL, 27.0±17.0; I, 16.8±8.5; p 0.0001). There was no significant difference between the CCW and the CW atrial flutters in terms of the CV and the CA of equally divided five areas. Conclusion: In both of the CCW and the CW atrial flutters, the CV of the LS was significantly slower than other areas and the CA of the lower atrium was significantly smaller than the upper atrium.