In left atrial appendage closure using WATCHMAN FLX, accurate device measurement by transesophageal echocardiography (TEE) is important. We aimed to experimentally validate appropriate methods of device measurement with two-dimensional (2D) and three-dimensional (3D) TEE compared with actual size.

We prepared a full range of device sizes (20, 24, 27, 31, 35 mm), each with five different compression rates. Each device was measured by 2D and 3D TEE at depths of 2, 4, and 6 cm in vitro using inner, outer, and middle line methods. We compared the difference between the actual size by caliper and measurements at each compression rate and depth by the three methods in 2D and 3D TEE.

A total of 450 patterns of measurements were analyzed. The differences using the middle line method were much less than those using the inner and outer line methods in 2D and 3D TEE (2D TEE: 0.45 ± 0.36 vs. 2.55 ± 0.99 vs. 2.59 ± 0.72 mm, p < 0.01; 3D TEE: 0.34 ± 0.27 vs. 2.38 ± 0.69 vs. 1.86 ± 0.77 mm, p < 0.01). Moreover, the differences in measurements by 3D TEE were more accurate than those of 2D TEE in the inner (2.47 ± 1.86 vs. 1.86 ± 0.77 mm, p < 0.01) and middle (0.58 ± 0.37 vs. 0.34 ± 0.27 mm, p < 0.01) line methods.

Middle line method by 3D TEE is the most reliable approach for device measurement at left atrial appendage closure using WATCHMAN FLX device.