**6. Conclusions**

*Aortic Stenosis - Current Perspectives*

severity [56].

moderate AS [59].

*5.2.3 Normal flow/low gradient*

AVA cutoff value for severe AS closer to ≤0.8 cm<sup>2</sup>

This AS pattern is defined as AVA < 1.0 cm<sup>2</sup>

compared to conservative management [60].

Projected AVA **<sup>=</sup>** AVArest **<sup>+</sup>** (

**Projected AVA calculation**

MG < 40 mmHg, and LVEF ≥ 50% with SVI ≥ 35 ml/m<sup>2</sup>

to be present in about one third of AS patients [30], and some studies have suggested that this AS pattern may be due to marked reduction in transaortic gradient from systemic hypertension and decreased aortic compliance [57, 58]. Patients with NL/LG AS are reported to have less severe disease than the other AS categories with lower BNP and preserved LV longitudinal function [35]. In terms of diagnosis, technical measurement errors need to be excluded, and aortic valve calcium scoring using MDCT may be beneficial to further determine the AS severity [38]. According to the 2017 European Association of Cardiovascular Imaging and the American Society of Echocardiography Recommendations, however, this entity is considered to be due to measurement errors or the consequence of inconsistent cutoff values for transaortic velocity/ gradient and AVA [35]. Some studies have supported this thought as patients in the NF/LG AS subgroup demonstrated the same outcome as patients with

There are no particular recommendations for this subgroup in the current guidelines, and AVR should only be considered in symptomatic patients with confirmed severe AS. One study showed survival benefit in these patients [43], while another study showed no difference in survival in patients who underwent early AVR

∆ AVA **=** AVApeak **−** AVArest **=** Change in AVA at rest and at peak DSE

Projected AVA at a normal flow rate (250 ml/s) <1.0 cm<sup>2</sup>

∆ Q **=** Qpeak **−** Qrest **=** Change in *Q* at rest and at peak DSE (1)

AVArest, aortic valve area at rest; DSE, dobutamine stress echocardiography; AVApeak, aortic valve area at peak; *Q*rest, stroke volume at rest; *Q*peak, stroke

\_\_\_\_\_\_\_\_\_\_\_ **∆** AVA

**<sup>∆</sup>** *<sup>Q</sup>* ) **<sup>∗</sup>** (**<sup>250</sup> <sup>−</sup>** *<sup>Q</sup>*rest)

suggests severe AS.

Another large study demonstrated that patients with LF/LG AS with preserved LVEF had better spontaneous survival than the patients with HG severe AS, and the results are unaffected by flow states. Furthermore, the patients with LF/LG AS with preserved LVEF progressed to develop HG AS over time, and in all patients who showed a reduction in transvalvular gradients over time, this decrease was associated with reduction in LVEF [54]. Another study showed that patients with severe LF/LG AS with preserved LVEF had similar outcomes as patients with mild to moderate AS, and there was no significant benefit of AVR in this group [55]. However, a comparison of two studies by Hachicha et al. [31] and Jander et al. [53] showed that there were some differences between the study group findings which may, at least in part, have contributed to the differing outcomes. Some investigators have proposed for reducing the

to avoid overestimation of AS

,

. NF/LG AS has shown

, AVA indexed < 0.6 cm<sup>2</sup>

**106**

volume at peak DSE.

The different hemodynamic categories of severe AS have shown to have varying clinical outcomes. Low flow state has exhibited the worst prognosis due to intrinsic myocardial dysfunction and/or under-recognition of the disease severity resulting in inappropriate delay in AVR. Low-gradient AS with low flow state is of particular challenge for clinical decision-making, especially when differentiating true-severe AS (where AVR may be beneficial) vs. pseudo-severe AS (where conservative medical management is appropriate). In LF/LG AS with reduced LVEF, DSE is beneficial for the confirmation of AS severity and risk stratification. In the setting of partial or no flow reserve, projected AVA and/or calcium scoring with MDCT may be useful to guide management. LF/LG AS with preserved LVEF is an entity where the natural history and the pathophysiology are not well understood. There has been much controversy and differing schools of thought around this AS subgroup. Numerous studies have shown that LF/LG AS with preserved LVEF is associated with poor prognosis, and therefore, careful evaluation and identification of these patients are necessary to ensure proper management. Calcium quantification using MDCT has shown to be the preferred technique for confirming AS severity with this subgroup. However, other investigators have reported that this AS entity represents moderate AS with no significant difference in outcomes between the groups. These discrepant findings may be resolved based on more randomized studies with large cohorts and with the application of more advanced diagnostic imaging techniques capable of overcoming the limitations of the currently available technology to better assess AS severity. In symptomatic high-gradient severe AS, regardless of the flow state, AVR is the only treatment option that has demonstrated to improve symptoms and survival. In asymptomatic high-gradient severe AS, regardless of the flow state, the current guidelines recommend watchful waiting and conservative management, although controversy exists about the optimal timing of intervention.

Over the years, the operative risk for SAVR for severe AS has significantly decreased, and TAVR has emerged as a promising alternative treatment for these patients with different operative risk profiles—high, intermediate, and more recently low risk. Recent data have supported that TAVR is superior or noninferior to SAVR in the treatment of severe AS and long-term follow-up assessment will better validate the true comparison between the two approaches and determine the optimal treatment strategy. As the TAVR technology continues to advance, the next generations of bioprostheses will be introduced which may further improve outcomes. Therefore, it is vital to accurately diagnose AS severity and identify those individuals who may benefit from AVR in a timely manner to optimize patient care and clinical outcomes.

#### **Conflict of interest**

None.

*Aortic Stenosis - Current Perspectives*
