Background-Recent studies and current clinical observations suggest that some patients with severe aortic stenosis on the basis of aortic valve area may paradoxically have a relatively low gradient despite the presence of a preserved left ventricular (LV) ejection fraction. The objective of the present study was to document the prevalence, potential mechanisms, and clinical relevance of this phenomenon. Methods and Results-We retrospectively studied the clinical and Doppler echocardiographic

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... a of 512 consecutive patients with severe aortic stenosis (indexed aortic valve area Յ0.6 cm 2 ⅐ m Ϫ2 ) and preserved LV ejection fraction (Ն50%). Of these patients, 331 (65%) had normal LV flow output defined as a stroke volume index Ͼ35 mL ⅐ m 2 , and 181 (35%) had paradoxically low-flow output defined as stroke volume index Յ35 mL ⅐ m Ϫ2 . When compared with normal flow patients, low-flow patients had a higher prevalence of female gender (PϽ0.05), a lower transvalvular gradient (32Ϯ17 versus 40Ϯ15 mm Hg; PϽ0.001), a lower LV diastolic volume index (52Ϯ12 versus 59Ϯ13 mL ⅐ m Ϫ2 ; PϽ0.001), lower LV ejection fraction (62Ϯ8% versus 68Ϯ7%; PϽ0.001), a higher level of LV global afterload reflected by a higher valvulo-arterial impedance (5.3Ϯ1.3 versus 4.1Ϯ0.7 mm Hg · mL Ϫ1 · m Ϫ2 ; PϽ0.001) and a lower overall 3-year survival (76% versus 86%; Pϭ0.006). Only age (hazard ratio, 1.04; 95% CI, 1.01 to 1.08; Pϭ0.025), valvulo-arterial impedance Ͼ5.5 mm Hg · mL Ϫ1 · m Ϫ2 (hazard ratio, 2.6; 95% CI, 1.2 to 5.7; Pϭ0.017), and medical treatment (hazard ratio, 3.3; 95% CI, 1.8 to 6.7; Pϭ0.0003) were independently associated with increased mortality. Conclusion-Patients with severe aortic stenosis may have low transvalvular flow and low gradients despite normal LV ejection fraction. A comprehensive evaluation shows that this pattern is in fact consistent with a more advanced stage of the disease and has a poorer prognosis. Such findings are clinically relevant because this condition may often be misdiagnosed, which leads to a neglect and/or an underestimation of symptoms and an inappropriate delay of aortic valve replacement surgery.