Background. General anaesthesia and surgically induced changes in cardiac loading conditions may alter flow across the aortic valve. This study examined how echocardiographic assessment of the severity of aortic stenosis (AS) changes during surgery.Methods. Patients who underwent aortic valve replacement for any severity of AS between July 2007 and June 2015 were identified. Peak velocities, mean gradients, and dimensionless indices (DI) measured with preoperative transthoracic echocardiography (TTE) were compared with those measured with intraoperative transoesophageal echocardiography (TOE). Additionally, agreement of preoperative and intraoperative grading of AS based on these measurements was assessed.Results. Data from 319 patients were analysed. On average, intraoperative TOE peak velocity and mean gradient were lower by 0.59 m s−1 and 12.5 mm Hg, respectively (P<0.0001), compared with preoperative TTE measurements, whereas the difference in mean DI was minimal at 0.008. Preoperative and intraoperative grades of AS severity (mild, moderate, and severe) by peak velocity, mean gradient, and DI agreed in 53.3, 53.7, and 83.3% of patients, respectively. The TOE grade of AS severity by peak velocity and mean gradient was at least one lower than the TTE grade in 45.1 and 42.7% of patients, respectively. Significantly fewer patients had their severity of AS reclassified based on DI (P<0.0001).Conclusions. Intraoperative TOE peak velocities and mean gradients are often significantly lower than preoperative TTE measurements, leading to underestimation of AS severity in nearly half of our study patients. The DI is a more reliable measurement of AS severity in the intraoperative setting.
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