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Low-flow, low-gradient (LFLG) AoS may occur in patients with preserved LVEF. This “Paradoxal” LFLG AoS entity is defined by an AVA < 1.0 cm2 and/or < 0.6cm2/m2 when indexed for body surface area and mean transvalvular gradient
This entity occurs in about 10-15% of patients with severe AS and it is more prevalent in patients of older age, in women, and in patients with concomitant systemic arterial hypertension.1 In patients with paradoxical LFLG AoS, the LVEF is typically within normal range (Figure 1). However, the LVEF grossly underestimates the extent of myocardial systolic dysfunction in presence of LV concentric remodeling. Indeed, when more sensitive parameters such as global longitudinal strain are utilized, it becomes evident that myocardial systolic function is significantly impaired in these patients.
It has been shown that these patients have a reduced survival compared with patients with normal-flow and high gradient AoS and those with moderate AoS patients. Furthermore, other studies have shown that AVR improves outcomes in these patients. Recent data suggest that TAVR may provide a valuable alternative to surgical AVR in these patients.
The main pitfall associated with the echocardiographic diagnosis of paradoxical LFLG AoS is an error in the calculation of the stroke volume due to inaccurate measurement of LV outflow tract diameter and/or misplacement of pulsed-wave Doppler sample volume. Indeed, an underestimation of stroke volume may lead to the erroneous conclusion that the patient has paradoxical LFLG severe AoS, whereas, in fact, he or she has a moderate AS with normal flow. Hence, when paradoxical LFLG AoS is suspected, measurements of LV geometry and function should first be reviewed with the expectation of finding typical echocardiographic features characterizing this entity (i.e. pronounced concentric remodeling, small LV cavity size, moderate-to-severe diastolic dysfunction, and reduced global longitudinal strain etc.). Second, the measurement of LV outflow tract stroke volume by the Doppler method should be systematically corroborated by other means such as 2D or 3D volumetric methods.
If the existence of paradoxical low flow AS is confirmed, it is then important to rule out the presence of a pseudo-severe stenosis. It has indeed been shown that about one third of these patients have pseudo-severe AS. Exercise-stress echocardiography can be useful in patients with no or equivocal symptoms to differentiate true- vs. pseudo- severe AS by assessing the response of AVA and gradient with increasing flow rate and by calculating calculate the projected AVA (Figure 2).(1) A low dose DSE may also be used in symptomatic patients but it should be used with caution and close monitoring of blood pressure and LV outflow tract velocity. The measurement of aortic valve calcification load by multislice CT may also be used to corroborate stenosis severity in patients with paradoxical LFLG (Figure 2).
In this context, Dobutamine stress echocardiography may be particularly useful to differentiate between true severe and pseudo severe AS]. And this is the algorithm that can be used for the interpretation of the DES data. The first step is to determine the presence of contractile reserve, which is generally defined as a relative increase in SV > 20%. If there is contractile reserve, you have a substantial increase in stroke volume and you can thus re-assess the indices of stenosis severity at higher flow rate. If the peak EOA achieved during dobutamine stress remains lower than 1 cm2 and mean gradient rises above 30 mmHg, the stenosis is considered severe and AVR is recommended. If not, conservative treatment may be advised. [If there is no contractile reserve, it is difficult to get a definitive answer with regard to stenosis severity. In this case, the therapeutic management remains unclear].If there is no contractile reserve, first this is a marker for poor prognosis. Second, given that there is no signficant change in flow rate, the stenosis severity remains indeterminate and the therapeutic management remains unclear.
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