Low gradient aortic stenosis (LGAS) represents about 5% to 10% of all cases of severe AS and is the most challenging subgroup of patients with AS in terms of management. The term LGAS is usually applied to patients with a mean gradient < 30 mmHg (or 40 mmHg), an aortic valve area (AVA) < 1 cm2, and an ejection fraction (EF) < 35% (or 40%. Low EF in LGAS may be caused by severe low-flow AS with inadequate compensatory LV hypertrophy, called afterload mismatch, but also by another myocardial disease (such as extensive fibrosis, associated cardiomyopathy or myocardial infarction(MI), in which case, AS is not the primary problem. The essential problem for clinicians is to distinguish true severe low-flow AS, responsible for low EF, from pseudo-severe AS comprising mild-to-moderate AS associated with another cause of left ventricular dysfunction (LVD).Very low gradient may be observed in true severe low-flow AS, while the decreased AVA observed in pseudo-severe AS reflects poor opening of the aortic valve directly related to low transvalvular flow. For the clinician, the 2 main questions in LGAS are: -how severe is the AS? – which patients can benefit from surgery?
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