## 2 Computed Tomography and Aortic Valve
### CT Assessment of the Aortic Valve for Transcatheter Procedures  
Multidetector computed tomography (MDCT) is considered crucial for the assessment of aortic valve defects (stenosis and regurgitation) and the preprocedural planning of TAVI [23].  
On the technical side, TAVI CT assessment comprises two scans: an EKG-synchronized computed tomographic angiography (CTA) of the heart and aortic root, followed by a high-pitch non-EKG-synchronized CT multislice (CTM) for the evaluation of the access vessels. The two scans are combined into a complete protocol with a single contrast bolus through a peripheral vein. The amount of contrast medium should be calibrated to its concentration, patient's BMI, and kidney function (three thresholds should be considered: \(\geq\)60 mL/min/body surface area (BSA), 30-59 mL/min/BSA and \(<\)30 mL/min/BSA). Furthermore, for high-quality studies, according to the Cardiovascular Computed Tomography Society (SCCT), imaging should cover the entire cardiac cycle, and ALARA principles (as low as reasonably achievable) should be followed [24]. This means that the radiation dose that a patient could receive will vary depending on their weight or body mass index (BMI): 100 kV for patients with a BMI of 30 or less (or weight of 90 kg or less) to 120 kV for patients with a BMI of more than 30 kg (or weight more than 90 kg). Three scans are necessary to obtain useful parameters: the first is a basal one without contrast employed to calculate calcium scoring; a second one is used for cardiac evaluation with the administration of iodine contrast agent (after retrospective ECG synchronization); the last one should be extended from clavicles to the thigh's proximal portion in order to evaluate femoral and axillary accesses [24; 25].  
CT is almost universally accepted as a standard of care since its use has demonstrated a positive impact on clinical decision-making, favoring better post-TAVI clinical outcomes (Table 1) [26]. Therefore, [PERSON] et al. proposed a CT-based score called TAVI CT score, including the presence of nodular subvalvular calcium, the elliptical index (defined as the ratio of minimum aortic valve annulus diameter to maximum aortic valve annulus diameter), the aortic isthmus angle, the aorta ventricle angle, the presence of bicuspid valve, the coronary height, the detection of lilofemoral calcification, the access size, and the type of planned access, to predict outcomes. Notably, an increased risk of vascular complications was associated with higher scores [27]. Additionally, in a subanalysis of the WIN-TAVI registry, [PERSON] et al. found that moderate or severe left ventricle outflow tract (LVOT) calcification detected by CT scan was an independent predictor of 1-year mortality or stroke [28]. The authors also reported that new pacemaker implantation (PMI) was independently associated with calcium volume of the right coronary cusp. In contrast, a protective effect on the same outcome was observed with the calcium volume of the noncoronary cusp. Lastly, according to this study, severe calcification of the noncoronary/right-coronary commissure can independently predict new atrial fibrillation onset [28]. In a study by [PERSON] et al., it was demonstrated that membranous septum length measured at CT showed strong discriminatory ability for PMI [29]. Furthermore, [PERSON] et al. highlighted that MDCT-derived global left ventricular longitudinal strain was a powerful predictor of all-cause mortality. As shown with the Kaplan-Meier curves, MDCT-derived LV GLS \(>-14\%\) was related to higher cumulative rates of all-cause mortality than MDCT-derived LV GLS \(\leq-14\%\)[30]. In the following paragraphs, we discuss all specific parameters obtained using CT that are considered of interest in the preprocedural planning for aortic valve replacement.