**3.1 Echocardiography**

Echocardiography is fundamental to diagnosis and to assess aortic stenosis severity, valve calcifications, LV systolic and diastolic function, and other cardiac pathologies. Current ESC guidelines underline the importance of echocardiographic evaluation when blood pressure is well controlled to reduce confounding flow effects of increased afterload [13].

Aortic stenosis severity assessment lies on the measurement of mean pressure transvalvular gradient, peak transvalvular velocity (Vmax), and aortic valve area (AVA). Based on these parameters, three categories of severe aortic stenosis may be identified and could benefit from aortic valve replacement [13]:


• "Paradoxical" low-flow, low-gradient AS: characterized by mean gradient <40 mmHg, AVA ≤ 1 cm2 (or AVAi ≤0.6 cm2/m2), LVEF ≥50% and SVi ≤ 35 ml/m2. This condition is typical of patients with profound concentric LV hypertrophy with small cavities that are not able to generate enough SV to effectively open the aortic valve [44]. In this context, a computerized tomography (CT) assessment of valve calcification's degree helps to define the probability of true severe AS (highly likely with Agatston units >3000 for men and > 1600 for women).

In peculiar cases, especially with patients with poor echocardiographic transthoracic windows, transesophageal echocardiography could be a valid alternative (**Figure 3**).

### **3.2 Cardiac catheterization**

Despite the evaluation of aortic valve stenosis is mainly based on echocardiography, there is a not negligible discrepancy between effective aortic valve area (AVA) derived from Doppler and from cardiac catheterization. According to Minners *et al.,* there are inconsistencies in grading aortic valve stenosis in patients with normal LV function, in particular with respect to AVA, while mean pressure gradient seems to be a more robust parameter [45]. In a prospective study on assessment of aortic stenosis severity between echocardiography and cardiac catheterization, AVA correlated poorly between the two techniques, with an average AVA difference of 0.25 cm2 (range 0–1.59) [46]. That is due to the fact transvalvular pressure gradient is maximal at the level of the vena contracta, the point in a fluid stream where the diameter of the stream is the least and fluid velocity is at its maximum, which occurs where all the layers of the stream converge, slightly downstream of anatomic aortic valve area. After the vena contracta, part of the jet kinetic energy is recovered in pressure but, during this process, there is some energetic dispersion as a result of flow separation and vortex formation. Echocardiography, measuring transvalvular pressure gradient at the vena contracta (where it is maximal), tends to overestimate pressure gradient and, therefore, underestimate aortic orifice area. Cardiac catheterization, instead, tends to measure a lower transvalvular pressure gradient because it samples it at some distance downstream to vena contracta, where conversely catheter would have trouble maintaining the position of the pressure sensor due to the instabilities secondary to flow-jet turbulence [46]. As assessed by Garcia *et al.*, effective orifice area calculated by catheterism (EOAcath) may therefore be larger than the one calculated by echocardiography (EOAecho). This overestimation becomes relevant as the ascending aorta diameter decreases, mostly when sino-tubular junction diameter is ≤30 mm [47]. Moreover, echocardiography could also overestimate EOA because of poor alignment of the ultrasound beam with the stenotic jet [48]. In the end, cardiac catheterization provides data about pulmonary pressures and resistances that, if elevated, could identify an advanced pathology grade that may not benefit from valve correction [37]. Nevertheless, current ESC/ EACTS Guidelines for the management of valvular heart disease recommend LV catheterization only when there is a severe aortic stenosis clinic and noninvasive assessment is inconclusive [13]. Criteria for defining aortic valve stenosis severity and its prognosis are derived from catheter measurements, and nowadays the invasive assessment could be a valid ally in an accurate definition of aortic stenosis severity, although a proper selection is mandatory to limit unavoidable complications related to its invasiveness.

*Transcatheter Treatment of Aortic Valve Disease Clinical and Technical Aspects DOI: http://dx.doi.org/10.5772/intechopen.105860*

**Figure 3.**

*Integrated assessment of patients with aortic valve stenosis [13].*

#### **3.3 Computerized tomography scan**

Electrocardiogram-gated CT scan has a central role in the pre-procedural planning for TAVI. First of all, it is fundamental to evaluate annular valvular area and perimeter (essential to guide the choice of prosthesis' size), extent and distribution of calcifications, aortic root anatomy, and height of coronary ostia from aortic annulus and LV outflow tract dimension (**Figure 4**). All this information is pivotal to define prosthesis implantation. For example, an overestimation of the aortic annulus dimensions

**Figure 4.**

*Computed tomography evaluation for TAVI procedural planning. Aortic annulus measure (A) and calcium distribution (B). Coronary distance from virtual basal ring (C, D). Aorta and peripheral artery evaluation for a transfemoral access (E-G).*

poses a significant risk for aortic root lesions or disruption during prosthesis release. On the other hand, underestimation increases the risk of paravalvular aortic regurgitation [49, 50]. Considering that aortic annulus dimensions vary throughout the cardiac cycle, they should be measured during systole, i.e., when they are larger.

Another main scope of CT scan concerns the planning of vascular access through imaging of aorta and iliofemoral vasculature. This assessment has become increasingly important and has led to a significant decrease of pre- and post-procedural major and minor vascular complications in TAVR patients [51].
