**4.1 Balloon-expandable valves**

The SAPIEN platform (Edwards Lifesciences, Irvine, USA) is one of the most diffuse BEVs. It is an intra-annular device, with bovine pericardial leaflets mounted on a *Transcatheter Treatment of Aortic Valve Disease Clinical and Technical Aspects DOI: http://dx.doi.org/10.5772/intechopen.105860*


#### **Figure 5.**

*Principal TAVI platforms and technical characteristics.*

cobalt-chromium balloon-expandable frame. SAPIEN valves have a flexible delivery system that allows adapting the implantation in angulated aorta; the balloon expansion allows volumetric modification according to annular sizes, although it is not recapturable during the implantation. The fourth-generation SAPIEN 3 Ultra features an increased outer seal cuff to reduce paravalvular leak (PVL). There are 4 currently available sizes: 20, 23, 26, and 29 mm. The SAPIEN family valves have a lower stent frame profile, which makes easier the coronary catheterization after TAVI [52].

#### **4.2 Self-expanding valves**

The Evolut PRO+ (Medtronic, Minneapolis, USA) is the last generation prosthesis of the Evolut family of SEV. They have a supra-annular design and consists of three porcine pericardial leaflets attached to a self-expanding nitinol stent. The stent is a diamond-shaped cell and the valve has an hourglass shape, with a larger circumference at the proximal and distal anchoring points. The delivery system allows the device to recapture after partial deployment and repositioning. Four valve sizes are available (23, 26, 29 and 34 mm) [52].

The ACURATE Neo 2 valve (Boston Scientific, MA, USA) is a SEV with supraannular design and porcine pericardial leaflets. Its design includes stabilizing arches to facilitate correct positioning. Its top-down deployment, with or without the need for ventricular pacing, does not allow any recapture. It has less radial force, so predilatation is mandatory. The open-cell design and the short-stent body should ease coronary access after implantation. Furthermore, it has a superior crown designed to keep the native cusps away from the coronary ostia [53].

The Portico valve (Abbott Vascular, Santa Clara, CA, USA) comprises a bioprosthetic bovine pericardial aortic valve mounted upon a self-expandable nonflared nitinol frame. The leaflets are located at the annular level, ensuring valve function immediately upon deployment.

Allegra (Biosensors International, Morges, Switzerland) and HYDRA (SMT, Wakhariawadi, India) are two self-expanding nitinol frame valves with bovine pericardial leaflets. Their use is limited to high surgical risk patients and the evidence of safety and efficacy are quietly poor.

#### **4.3 Device choice**

So far, there is insufficient evidence to claim the superiority of a prosthesis or another. Each TAVI device has a unique design, and certain elements may slightly favor one or another prosthesis. Among the factors to consider when choosing a valve for TAVI, those that may favor BEV are short or narrow sinus of Valsalva, the presence of conduction disturbances (right bundle branch block or 1st degree AV block), and the anticipated need for future coronary re-access and a horizontal aorta. In small annuli and in case of severe LV outflow tract calcification, SEV may be preferred [52, 54].

The intra-annular design is associated with higher trans-prosthetic gradients and more frequent patient-prosthesis mismatch (an effective orifice area too small in comparison to patient's body surface area) [55]. Patient-prosthesis mismatch is associated with a worse prognosis in surgical prosthesis; however, the clinical relevance of TAVI remains uncertain [56].

Only few randomized trials directly compared different TAVI devices. Direct comparisons are difficult because the small number of events makes necessary the use of composite endpoints. Furthermore, data from early generations TAVI devices cannot be automatically extrapolated to current-generation prosthesis. The Comparison of Transcatheter Heart Valves in High-Risk Patients With Severe Aortic Stenosis (CHOICE; NCT01645202) trial, which randomized high-risk patients to receive a BEV (Sapien XT) or a SEV (Core Valve), showed a greater rate of device success with early generation BEV. The greater device success of BEV in comparison to SEV (95.9% vs. 77.5%; relative risk, 1.24; 95% CI, 1.12–1-37; p < 0.001) was driven by a significantly lower frequency of significant aortic regurgitation and less frequent need for the implant of a second valve. Placement of a new permanent pacemaker was less frequent in the BEV group (17.3% vs. 37.6%, P = 0.001). A randomized trial compared the SAPIEN 3 valve with the ACURATE Neo valve (Safety and efficacy of the Symetis ACURATE Neo/TF Compared to the Edwards SAPIEN 3 Bioprosthesis - SCOPE 1; NCT03011346) [57]. The non-inferiority of the ACURATE Neo was not met in a composite endpoint. In the SCOPE 2 trial (NCT03192813), the ACURATE Neo valve did not meet the non-inferiority criteria in comparison with Core Valve Evolut prosthesis. Nevertheless, the ACURATE neo showed a significative reduction in permanent pacemaker implantation (PPI) (10.5% vs. 18%) [58]. Data from observational analysis seem to favor BEV [59, 60], but should be interpreted with caution.

## **5. Minimizing complications**

#### **5.1 Paravalvular leaks**

Paravalvular leak (PVL) consists of a residual gap between the native calcified aortic valve, aortic annulus, and the prosthesis. PVL can be identified during the TAVI procedure using invasive hemodynamics and cine-angiography, while echocardiography is the most diffusely used technique to detect, grade, and follow PVL [61].

The hemodynamic effects of a significant residual regurgitation have a negative clinical impact. Moderate to severe PVL are independent predictors of short-term and long-term mortality, while the impact of mild PVL is unclear [62].

Calcification of the aortic valve, leaflet asymmetry, prosthesis malposition and under-sizing, and the use of SEV is associated with the development of PVL [63].

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

SEV is more influenced by the calcium burden, as they exert less radial force than BEV, therefore they are more often under-expended or eccentrically shaped. On the other side, the higher radial force exerted by BEV could lead to annular rupture [63, 64].

The first-generation devices had a 30-day incidence of moderate to severe PVL of 9.0% and 11.8% (respectively for SEV and BEV) in high-risk patients [65, 66]. Newer-generation devices were designed with features aimed to reduce PVL, such as external skirt of the SAPIEN 3 Valve and the external sealing system of the Evolut PRO Valve. In the more recent PARTNER III trial, the SAPIEN 3 valve had a decreased incidence of moderate to severe PVL in low-risk patients (0.6%) and of note that was similar to residual PVL of SAVR (0.5%) [8]. In the Evolut Low-Risk Trial, there was a greater incidence of moderate to severe PVL: 3,5% in TAVI vs. 0,5% in SAVR [10]. This discrepancy is consistent with the different designs of prosthesis.

A significant PVL may benefit from several treatment options, which includes balloon post-dilatation of the prosthesis, percutaneous closure with plugs, and TAVIin-TAVI to exert a superior radial force against the PVL, and surgical intervention.

#### **5.2 Coronary obstruction and coronary re-access**

Almost half of the patients undergoing TAVI have coronary artery disease, and about a third of the patients are in a low-risk population [8, 67]. TAVI may influence coronary in two ways: the prosthetic valve struts may prevent the selective catheterization of coronaries during PCI and the prosthesis or the dislodged native leaflets may cause acute coronary obstruction.

The coronary re-access following TAVI is influenced by several anatomical factors (sino-tubular junction dimensions, sinus height, leaflet length and bulkiness, sinus of Valsalva width, and coronary ostial height) and device-related and procedural factors (commissural tab orientation, sealing skirt height, and valve implantation depth) [68]. Prosthesis with higher frame design hinders coronary re-access more than those with a lower frame due to the barrier of the stent frame in allowing coronary catheters to directly engage the coronary ostia (**Figure 6**). Therefore, selective coronary angiography after TAVI with some SEV could be more challenging than with BEV [68].

Otherwise, some SEVs, such as ACURATE NEO (Boston Scientific, MA, USA), are characterized by lower stent frame, which could allow for easy coronary engagement.

The alignment of the TAVI valve commissures with the native aortic valve commissures is a promising modifiable factor to facilitate coronary re-access. TAVI differs from aortic valve replacement in the fact that the orientation of commissural posts relative to the coronary ostia is random. It has been shown that specific orientations of the Evolut and ACURATE neo at initial deployment could improve commissural alignment [69]. Of note, a commissural alignment is particularly helpful in highframe SEV in avoiding coronary artery overlap; this may be fundamental in coronary artery access and redo TAVR.

Acute or delayed coronary obstruction after TAVI is a rare but life-threatening complication, with an incidence inferior to 1% [70, 71]. Coronary obstruction is usually caused by the displacement of the calcified native valve leaflet over the coronary ostium or by the direct occlusion of the coronary ostium by the covered skirt of the transcatheter aortic prosthesis. Anatomical factors associated with coronary obstruction are low coronary ostia height and shallow sinuses of Valsalva. Procedural-related elements include BEV and valve-in-valve (VIV) for surgical bioprosthesis [70]. To prevent this complication some coronary protection techniques may be used, such

**Figure 6.**

*Difference between TAVI device profile in coronary re-engagement. Device with low profile could theoretically guarantee a easier coronary cannulation.*

as preventive coronary wiring or positioning of an undeployed stent in high-risk patients. If the coronary blood flow is compromised during or after TAVI release, the stent is retracted and deployed to create a channel for coronary perfusion between the displaced leaflets and the aortic wall (chimney technique) [72, 73].
