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Background: Paradoxical low gradient "severe" aortic stenosis (AS) (aortic valve area (AVA) < 1cm2, mean transvalvular gradient < 40 mmHg) despite preserved left ventricular ejection fraction (LVEF>50%) is a clinically challenging scenario observed in almost one third of unselected patients (pts) with AS. A few retrospective studies suggested these pts may have an advanced stage of AS and poor prognosis, although recently published data show they have an outcome similar to pts with moderate AS.Purpose. To comparatively assess the echocardiographic characteristics of pts with paradoxical low gradient "severe" AS versus pts with AS and high transvalvular gradient in a prospective study using speckle tracking echocardiography (STE).Methods: We prospectively enrolled 104 pts (68±11 yrs) with severe AS (AVA<1 cm2, 0.34–0.99 cm2) and preserved LVEF (63±7%). Thirty-one pts (32%) had a mean transvalvular gradient < 40 mmHg (18–39 mmHg, group 1) and 73 pts had a mean gradient ≥40 mmHg (40–105 mmHg, group 2). A comprehensive echocardiography was performed in all (including TDI derived myocardial velocities at septal and lateral sites). LV filling pressures were estimated using average E/E' ratio. Global LV longitudinal strain (GLS) by STE was available in 65 pts and LV torsional deformation parameters in 96 pts.Results: Patients in group 1 were older than pts in group 2 (72±8 vs 67±11 yrs, p=0.025). There were no differences regarding gender, body surface area and NYHA class between groups (p>0.08 for all). AVA was smaller in group 2 (0.6±0.2 vs 0.8±0.2 cm2, p<0.001). Pts with low transvalvular gradient had smaller end diastolic and systolic LV volumes (40±13 vs 48±16 ml/m2, p=0.02 and 15±6 vs 19±9 ml/m2, p=0.01) and lower indexed LV mass (135±28 vs 153±37 g/m2, p=0.01). Indexed left atrial volumes, E/E'ratios and peak systolic myocardial velocities were similar between groups (p>0.3). No significant differences were found between groups regarding LVEF (64±6 vs 63±7, p=0.4), indexed LV stroke volume (39±7 vs 41±7 ml/m2, p=0.3) and LV rotation/torsion parameters. Conversely, GLS was higher in group 1 (-17±3 vs -15±3%, p=0.02) indicating a better longitudinal LV function.Conclusions: Patients with low gradient “severe” AS and preserved LVEF are older, have smaller LV volumes and lower LV mass when compared to pts with severe AS and higher transvalvular gradients. In our study the echocardiographic characteristics associated with this state do not indicate an advanced stage of systolic or diastolic dysfunction in these pts. Further studies are needed to better characterize this group of pts and their prognosis.