Characterization and Normal Measurements of the Left Ventricular Outflow Tract by ECG-gated Cardiac CT: Implications for Disorders of the Outflow Tract and Aortic Valve

Rationale and Objectives: Studies suggest that electrocardiographically gated coronary computed tomographic angiography provides a clear definition of the left ventricular outflow tract (LVOT), and normal LVOT morphology may not be round, as assumed when the continuity equation is applied during echocardiography. The aims of this study were to demonstrate the morphology of the LVOT on coronary computed tomographic angiography and to establish normal values for LVOT measurements. Materials and Methods: Two independent readers retrospectively measured anterior-posterior (AP) and transverse diameters of the LVOT and performed LVOT planimetry on coronary computed tomographic angiographic studies of 106 consecutive patients with normal aortic valves. Results: Excellent interobserver agreement was observed for all measurements (r = 0.78-0.94). The LVOT was ovoid, with a larger transverse diameter than AP diameter during diastole and systole (P < .001). However, the ratio of AP diameter to transverse diameter was closer to 1.0 during systole (P < .001). Mean indexed LVOT area was minimally larger in systole than in diastole (P = .01-.04) and was larger in men than in women during diastole (P <= .001) and systole (P <= .01). Mean LVOT area indexed to body surface area was 2.3 +/- 0.5 cm(2)/m(2) in women and 2.6 +/- 0.7 cm(2)/m(2) in men. LVOT area demonstrated significant correlation with aortic root diameter. Conclusions: The normal LVOT is ovoid in shape. LVOT is more circular during systole, but the AP diameter remains smaller than the transverse diameter throughout the cardiac cycle. The oval shape of the LVOT has important implications when LVOT area is calculated from LVOT diameters. Normal LVOT area values established in this study should facilitate diagnosis of the fixed component of LVOT obstruction.