Aortic stenosis: flow matters.

The presence of a low transvalvular pressure gradient (<40 mmHg) in conjunction with a small aortic valve area (AVA ≤1 cm) is a challenging situation as it raises uncertainty about the actual severity of aortic stenosis (AS) and therefore about the indication of aortic valve replacement (AVR) if the patient is symptomatic. This lowgradient ‘severe’ (small AVA) AS entity may in fact be related to: (i) measurement errors: underestimation of stroke volume (SV), AVA and/or gradient; (ii) small body size: a small AVA in a small patient may correspond to moderate AS and low gradient; (iii) inherent discrepancies in the AVA (≤1 cm) gradient (≥40 mmHg) cut-off points proposed in the guidelines S3 to define severe AS; and (iv) a low-flow state. Among these four potential causes of low-gradient AS, only the last, that is, the low-flow state, would a priori have a negative impact on outcomes. It is well known that in patients with depressed LV systolic function (LVEF <50%), the SV and thus the transvalvular flow are often reduced. And in such conditions, the gradient, which is highly flow-dependent, may be low (<40 mmHg) despite the presence of a severe stenosis. Recent studies and guidelines have also emphasised that LV outflow is often reduced in patients with preserved LVEF and this entity has been named ‘paradoxical’ low flow. S2–S4 In these patients, the reduction of SV is related to pronounced concentric LV remodelling with small LV cavity, impaired diastolic filling and depressed LV longitudinal systolic function (although LVEF is still preserved). S4 S5 Furthermore, other factors frequently encountered in the elderly population with AS may contribute to the low flow including reduced arterial compliance, atrial fibrillation, mitral stenosis, mitral regurgitation and tricuspid regurgitation. In their Heart paper, Eleid et al present the results of an elegant study in which they examined the prognostic value of LV outflow, as expressed by SV index (SVI), in patients with low-gradient AS and preserved LVEF. They showed that lower SVI is incrementally associated with mortality and that the risk of mortality increases sharply when the SVI becomes lower than 35 mL/m.