Non-Circular Shape of Right Ventricular Outflow Tract

BACKGROUND: The shape of right ventricular outflow tract (RVOT) has been assumed to be circular. The aim of this study was to assess RVOT morphology using 3-dimensional transesophageal echocardiography (3D TEE). METHODS AND RESULTS: This prospective study included 114 patients who underwent 3D TEE. Two-dimensional (2D) TEE measured maximum and minimum RVOT diameters (RVOTD max and min) during a cardiac cycle. 3D TEE determined RVOT area (RVOTA) max and min, RVOT fractional area change, and RVOT shape index (RVOTSI; vertical/horizontal RVOTD). Cardiac output (CO) was calculated using 2D TEE, 3D TEE, and a Swan-Ganz catheter in 23 patients. All patients were classified into group 1 (RVOTSI ≤1) or group 2 (RVOTSI >1) based on the RVOT shapes. The mean RVOTSIs were 0.84±0.21(max) and 0.82±0.20 (min). Only 17 patients (14.9%) had circular RVOT (RVOTSI: 0.95-1.05); 82 patients (71.9%) were categorized into group 1 and 32 patients (28.1%) into group 2. 2D TEE, compared with 3D TEE, underestimated RVOTA max and min (both P<0.001). CO with 3D TEE had better agreement with CO with a catheter than CO with 2D TEE (r=0.83 and 0.53, respectively). CONCLUSIONS: 3D TEE revealed that RVOT geometry was not generally circular but oval with 2 different types. Because of the detailed morphological information of RVOT, 3D TEE could provide more accurate assessment of CO than 2D TEE.