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Both, European and North American guidelines for the treatment of valvular heart disease1–3 define severe aortic stenosis (AS) primarily by transvalvular velocity, mean gradient and valve area. In agreement, cut-offs have been set at 4 m/s for peak velocity, 40 mm Hg for mean gradient and 1.0 cm2 for aortic valve area. These cut-offs have remained unchanged now for many years and have been used in clinical practice as well as in research studies of AS.
Assessment of AS severity requires quite a number of considerations. Transvalvular pressure gradients are well known to be flow dependent with the clinically most important consequence that patients with severe AS may present with velocities below 4 m/s and mean gradients less than 40 mm Hg when transvalvular flow is reduced. This highlights the importance of estimating the valve area when evaluating AS and is the reason why AS by definition can be classified severe if only the valve area is smaller than 1.0 cm2, while velocity and gradient remain below the recommended cut-offs (ie, ‘low gradient severe AS’).1–3 Although valve area may from a theoretical point of view indeed be the ideal measure to quantify AS, its assessment remains operator dependent and less robust than gradient estimates in clinical practice. Thus, current guidelines recommend that valve area alone with absolute cut-off points should not be relied on for clinical decision-making but should always be considered in combination with flow rate, pressure gradients, ventricular function, size and wall thickness, degree of valve calcification and blood pressure, as well as functional status.1 3
The subgroup of ‘low-gradient AS’ and the decision whether AS is indeed severe in these patients has become particularly challenging in clinical practice. This prompted a detailed recommendation paper by the European Association of Cardiovascular Imaging joint with the American Society of Echocardiography …
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