Characteristics and selection of transcatheter aortic valve prostheses

Key features of transcatheter valves

In transcatheter aortic valve implantation (TAVI), the selection of the best suited transcatheter aortic valve (TAV) for each individual patient remains a challenge. The ideal bioprosthetic transcatheter valve would have all of the following features:

Easy deliverability and placement in the aortic valve position
Wide sizing range fitting all annular sizes, even when calcified or asymmetric
Secure anchoring mechanism regardless of cause and type of valve dysfunction
Avoid interference with coronary ostia or coronary blood flow
Optimal valve hemodynamics with no paravalvular leak
Long durability (>15 years)

To date there is no perfect “one-size-fits-all” bioprosthetic TAV and the task of the heart valve team is to select the valve best suited for the individual patient—a process that has been termed patient-tailored TAVI therapy ( Table 6.1 ).

Apart from anatomic considerations such as sizing, complex considerations with regard to patient-specific criteria need to be taken into account in order to achieve the best possible implantation result.
Further, with the shift of treatment to the lower risk spectrum, future treatment considerations play an increasingly important role in the selection of the TAV.
In this setting the focus of attention additionally shifts toward possibilities for redo procedures in case of future degeneration and on maintaining coronary access.
In addition to the TAV as such, the delivery system with all its features also needs to be taken into account as there are important differences with regard to sheath sizes and deliverability.
Finally, access strategy also plays an important role, as ease of delivery may vary in different accesses such as subclavian, carotid, or direct aortic.

TABLE 6.1

Key Factors in Selection of a Bioprosthetic Transcatheter Aortic Valve

Transcatheter aortic valve factors	Anchoring mechanism Valve height/supraannular extension Available sizes Repositionability/retrievability Pacemaker rate
Delivery system	Sheath size Deliverability/flexibility
Patient factors	Age Annulus size Annular calcification Coronary height Vascular access
Operator and medical center preference/experience	Operator experience

In this chapter the respective strengths and weaknesses of the major available TAVI platforms are discussed, with a recommendation as to which TAV may be best suited in classic scenarios that are encountered frequently in daily TAVI practice. The available TAV can be grouped into the technology used for deployment and by valve position relative to the annulus:

Balloon-expandable TAVI valves versus self-expanding TAVI valves
Intraannular versus supraannular

Most devices make use of nitinol, which is suitable for the vast majority of patients, for the self-expanding properties. Examples of balloon-expandable valves include the Edwards SAPIEN 3 and Edwards SAPIEN 3 Ultra (Edwards Lifesciences) valves. Examples of self-expanding valves include the Evolut R, PRO, and PRO+ (Medtronic), Portico (Abbott), ACURATE neo2 (Boston Scientific), and Allegra (New Valve Technology or NVT) valves. Several other devices such as the Centera, the DirectFlow, the JenaValve, or Lotus are not discussed in this chapter as they have been discontinued or are currently under investigation for routine clinical use. Technical specifications of each device are summarized in Fig. 6.1 and detailed next.

Fig. 6.1, Technical Specifications and Features of Transcatheter Aortic Valves (TAVs).

Technical descriptions of specific transcatheter aortic valves

Balloon-expandable valves

The SAPIEN 3 (S3) TAV represents the fourth generation of balloon-expandable valves of Edwards Lifesciences. The device features a cobalt chromium alloy frame, bovine pericardium leaflets, and an outer polyethylene terephthalate skirt. Four different sizes are available, ranging from 20 to 23, 26, and 29 mm. The latest iteration of the device family, the SAPIEN 3 Ultra, is based on the SAPIEN 3 and features further enhancements to avoid paravalvular leak with an increased height of the outer skirt and is currently available in all sizes except for 29 mm.

Being one of the first and one of the most widely available devices in the field, clinical data and evidence of the SAPIEN family are ample, and it has been studied in the entire risk spectrum of patients in the PARTNER trial program. The SAPIEN XT and S3 devices have shown equivalence or superiority over surgical aortic valve replacement throughout the entire surgical risk spectrum.

The S3 is the only balloon-expandable device available for routine clinical use that by design is not repositionable, allows intraannular placement, and requires rapid pacing during implantation. Advantages of the S3 balloon-expandable valve include the following:

Flexible sheath facilitating implantation even with tortuous anatomy
A wide range of sizing options
A short device height without supraannular material (providing access to coronary ostiae)

Retrieval of the device once the expandable sheath has been passed may be difficult and is not recommended. High radial force of the device has led a high percentage of operators to successfully omit routine predilation and postdilation, further streamlining the TAVI procedure. A balloon-expandable valve is a good choice for bail-out procedures in case of severe complications such as device failure or dislocation of any other TAV.

Self-expanding valves

The Medtronic Evolut R, PRO, and PRO+ are characterized by the following:

Supraannular device with porcine pericardial leaflets
A self-expanding nitinol frame
No requirement for rapid pacing during implantation
A sheathless delivery system allowing repositioning and retrieval of the TAV

The Evolut PRO features an additional external porcine pericardial sealing wrap over the first 1.5 cells. The Evolut PRO valve has 3 sizes: 23, 26, and 29 mm. The 34-mm Evolut PRO is not yet available and the Evolut R 34-mm can be used. Iterations of the Medtronic Evolut TAV have been extensively studied in a large number of registries and randomized controlled trials. Recently in low-risk patients, using mainly Evolut R, TAVI was noninferior to conventional surgery in a composite endpoint of death or disabling stroke at 24 months.

The Evolut features a proprietary delivery system, the Enveo InLine Sheath, which allows for a sheathless implantation (i.e., omitting the need for an introducer sheath for the delivery system). The Evolut devices allow for the possibility to resheath (i.e., refold the device into the delivery capsule) and reposition and even retrieve entirely from the body after insertion. During implantation, the device is momentarily occlusive and does not require rapid pacing, though many operators prefer fast ventricular pacing in order to limit the occurrence of extrasystole.

The Abbott Portico is characterized by the following:

A self-expanding nitinol stent valve
Intraannular bovine leaflets
A porcine sealing cuff at the landing zone to prevent paravalvular leakage (PVL)
A larger cell opening aims to facilitate coronary access
Treatment with an anticalcification technology

The Portico is available in four sizes (23, 25, 27, and 29 mm) that cover 19- to 27-mm diameter annuli. The Portico is fully resheathable and repositionable and can be completely retrieved from the body until up to approximately 80% of its deployment.

During implantation, the device is momentarily occlusive and does not require rapid pacing. The valve is prepared and loaded at room temperature instead of ice water. Recently the delivery system has undergone an update and is now referred to as the FlexNav system allowing for a “sheathless” delivery via an integrated sheath. The FlexNav features an additional layer to offer more stability during deployment compared with previous iterations.

The Portico TAV has been studied in small registries and has yielded promising results ; randomized trials on the device are not available. A larger postmarket registry (CONFIDENCE, NCT03752866) is currently underway. Recently the successor of the Portico TAV, the Navitor has entered the market featuring an enhanced PVL sealing mechanism.

The ACURATE neo (Boston Scientific) is a self-expanding nitinol frame with a supraannular porcine pericardial leaflet valve featuring three stabilization arches and a stent frame with an upper crown and a lower crown that anchors within the native aortic annulus. There are three available sizes, small (S or 23 mm), medium (M or 25 mm), and large (L or 27 mm).

The ACURATE neo TAV has been extensively studied in clinical registries showing promising clinical results, and registry data suggest good comparative effectiveness to other TAVI. A first, smaller randomized controlled trial versus the SAPIEN 3 has shown inferiority with regard to a composite endpoint and with low radial force, the rate of PVL has been found higher compared with the SAPIEN 3, albeit counterbalanced by lower transvalvular gradients.

The ACURATE neo, as a self-expanding device, uses a different implantation technique than the other self-expanding devices. The implantation is performed in a forward motion with a top-down deployment with first opening of the upper crown and subsequent release of the lower crown.

Implantation of the ACURATE neo is nonocclusive and requires no rapid left ventricular pacing. During implantation a certain degree of position correction is possible. The device is not resheathable and once it has exited the sheath, retrieval from the body may be difficult by design and is impossible after the upper crown has been liberated. Recently, the ACURATE neo2 has entered the market featuring enhanced sealing skirts to minimize PVL.

The Allegra valve is a self-expanding concave-shaped nitinol stent frame valve, carrying a supraannular bovine pericardial valve, with a sealing skirt of 12 mm that minimizes the risk of paravalvular leaks. According to the manufacturer, tip deflection during diastole aims at potentially enhancing durability by reducing leaflet stress. The device is available in three different sizes (23, 27, and 31 mm), which are all delivered through an 18-French sheath.

During delivery and release the device is nonocclusive. The so-called Permaflow allows for the leaflets to move within the stent frame. No rapid pacing is required during deployment. To date, few clinical data on the Allegra TAVI are available. One small study in 59 patients, however, has shown promising results.

Anatomic considerations

Several important scenarios in TAVI are listed, and the usefulness of the different TAV in each is discussed. It is important to note that many of the considerations in TAV selection discussed here are not always based on scientific evidence but on individual experience, as randomized controlled trials performing a head-to-head comparison of different TAVs are scarce. Moreover, data on the performance of each TAV in challenging anatomic scenarios are also limited. An experienced operator might well be able to treat demanding anatomies with any valve. However, we believe that there are certain scenarios and considerations that merit sharing with the community, but it is important to note that recommendations made in this chapter reflect the authors’ personal experience ( Fig. 6.2 ).

Fig. 6.2, Advantages and Disadvantages of Different TAVs in Different Scenarios.

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