3.5. LACV measurement
Left atrial conduction distance and conduction time were calculated from the start to the end of the propagation wave front in the left atrium. LACV was calculated as conduction distance divided by conduction time. An example LACV measurement is presented in Figure 1. Conduction time was the difference in activation time between the start (septum) and end of the propagation wave front (lateral wall) in the left atrium. Conduction distance was measured manually by tracing the pathway of the propagation wave front from the start point to the end point in the left atrium. The pathways of the propagation wave front were classified into anterior and posterior routes. The anterior route originates at the septum, crosses the anterior wall toward the appendage, passes over the left atrial appendage orifice, and finally reaches the lateral mitral annulus, where superior- and inferior-direction propagation waves collide and disappear. The posterior route goes toward the superior left atrium (roof) from the septal propagation origin, then goes downward on the posterior wall, turns below the left inferior pulmonary vein, and reaches the lateral mitral annulus.
Reproducibility of the LACV was assessed. Interobserver variability for anterior and posterior LACV was 0.025 m/s, calculated in 10 randomly selected patients as the difference in 2 measurements in the same patient by 2 different observers. There was no difference in anterior (0.88 [0.81, 1.06] vs. 0.88 [0.80, 1.06] p=0.86) or posterior LACV values (1.08 [0.86, 1.23] vs. 1.07 [0.85, 1.23], p = 0.55) between 2 examiners.