Assessment of the left ventricular outflow tract during cardiac anaesthesia with biplane transoesophageal echocardiography An observational study

BACKGROUND Assessment of left ventricular outflow tract (LVOT) area is a key component of quantification of aortic stenosis and stroke volume. Current international guidelines recommend measurement of the LVOT diameter with two-dimensional (2D) echocardiography and assume a circle. This may lead to erroneous measures of aortic valve area and adversely affect pen-operative decision making. Multiplane orthogonal (biplane) and three-dimensional (3D) echocardiography imaging may allow more accurate calculation of LVOT, aortic valve area and stroke volume. OBJECTIVE To evaluate the shape and area of the LVOT with conventional 2D diameter, short axis cross-sectional planimetry with biplane imaging and 3D multiplane reconstruction in patients undergoing cardiac surgery with transoesophageal echocardiography (TOE). DESIGN A retrospective observational study. SETTING A single centre university hospital. PATIENTS 119 patients undergoing cardiac surgery with TOE. INTERVENTIONS None. MAIN OUTCOME MEASURES Measurements of the shape and area of the LVOT with standard 2D TOE, short axis biplane imaging and 3D TOE. RESULTS The LVOT shape is elliptical in 70% of patients. The (mean +/- SD, [range]) LVOT cross-sectional area with 2D TOE was 4.29 cm(2) +/- 0.98, [2.46 to 6.70], with biplane was 4.68 cm(2) +/- 1.03, [2.92 to 7.30] and with 3D was 4.59 cm(2) +/- 0.99, [2.78 to 7.10]. There was a statistically significant difference (P < 0.001) in the three pairwise comparisons. 2D LVOT area had large bias (7 to 9%) and wider limits of agreement (LOA) with both biplane and 3D LVOT area (-17 to 36%). Biplane and 3D LVOT areas had small bias (1.8%) with relatively narrow LOA (-8 to 11%). CONCLUSIONS 2D diameter measures of the LVOT assuming a circle underestimate LVOT area, underestimate aortic valve area and increase the apparent severity of aortic stenosis. This may lead to inappropriate aortic valve intervention. In a busy operating room environment, we suggest that for the calculation of stroke volume and aortic valve area, LVOT area is measured with biplane imaging.