Review looks at TAVI device selection and concludes head-to-head studies needed

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Transcatheter aortic valve implantation (TAVI) device selection should be guided by patient, anatomic, and device-specific factors, a review of the considerations for optimal device choice in aortic valve stenosis has concluded. Key factors to be considered include the likelihood of paravalvular leak (PVL), conduction abnormalities, coronary reaccess, long-term durability, and valve reintervention.

The review, which was carried out by Bimmer E Claessen (Division of Cardiology, Mount Sinai Medical Center, Icahn School of Medicine at Mount Sinai, New York, USA), was published in JAMA Cardiology and considered the currently available data and factors influencing device choice. Head-to-head trials directly comparing TAVI devices will be necessary to make adequate recommendations regarding potential advantages of one device over another, as TAVI technologies continue to evolve, the study’s authors recommend, noting that to date, only three such studies have taken place.

Claessen and colleagues note that currently three commercially available TAVI device-types are approved by the US Food and Drug Administration (FDA), namely a balloon-expandable valve, a self-expanding valve, and most recently a mechanically-expandable valve. Other TAVI devices are currently undergoing early feasibility studies or investigational device exemption trials. Outside of the USA a growing number of TAVI devices are approved for clinical use or are undergoing investigation, the study notes.

Looking at balloon-expandable devices, the review notes that at present, the only US FDA-approved devices are the Sapien 3 and Sapien 3 Ultra (Edwards Lifesciences), intra-annular valves which may result in higher residual gradients compared with supra-annular designs, particularly in patients with smaller annuli. Claessen and colleagues add that the Sapien valve is non-repositionable, meaning that the operator has only a single chance to properly implant the valve. However, it is noted that in clinical practice, implantation of a second valve is rarely needed. “The lower stent frame profile of the Sapien valve means coronary reaccess after TAVR [transcatheter aortic valve replacement] is generally straightforward and uncomplicated,” Claessen and colleagues note.

“The field of self-expanding valves is more diverse,” the review goes on to state. The Evolut Pro+, part of the CoreValve family of valves (Medtronic), is the only available US FDA-approved self-expanding valve to date. These feature a supra-annular design, which may have increased effective orifice area (EOA) and lower gradients than intra-annular TAVI devices, Cleassen and colleagues report. The current systems allow for device recapture and repositioning to optimise valve implantation, they add. Compared with balloon-expandable TAVI systems, the Evolut delivery system is not steerable, and the increased frame height (approximately 46 mm) and diamond frame lattice may make coronary reaccess more challenging, they suggest, noting that future iterations of this device will include a delivery system with enhanced steerability and a smaller stent frame.

Several other self-expanding valves are currently undergoing clinical studies in the USA, such as the Acurate neo2 valve (Boston Scientific) and Portico valve (Abbott Structural Heart). The ACURATE neo 2 valve has a supra-annular design and is deployed top down, allowing for control of implant depth, Claessen and colleagues note. However, it is non-repositionable, and predilation of the aortic valve is mandatory. The Portico valve is repositionable and retrievable with an intra- annular design and tall stent frame.

Turning to mechanically-expandable valves, the review describes the Lotus Edge (Boston Scientific) as “fully repositionable and retrievable”. The device recently received US FDA approval in patients at high and extreme surgical risk, and consists of a bovine trileaflet valve in a braided nitinol frame and a polycarbonate-based skirt to reduce PVL. The valve is deployed by shortening the nitinol frame in both directions followed by locking the frame in place for the valve to function.

The review then goes on to consider the long-term clinical outcomes for the various TAVI devices, but discourages direct comparison of event rates between different device types due to differences in baseline risk profiles of the patient populations between the various studies. “Given the lack of large-scale head-to-head comparisons of various TAVR devices and the rapid development of new device iterations, there is insufficient evidence to claim superiority of one device type over another,” the study notes, adding that “as each TAVR device has unique design characteristics, certain patient-related and anatomy-related factors may slightly favour one or several particular designs”.

The first factor outlined as an important consideration in TAVI device selection is valve function and unknown long-term durability. “Haemodynamic parameters to evaluate TAVR prosthesis function include mean aortic valve gradient, EOA [effective orifice area] and PVL,” the study details, adding that current literature has shown lower mean gradients and larger EOAs in supra-annular, self-expanding valves vs balloon-expandable valves, although the short-term and long-term effect of this difference remains unclear.

On annular size, the second factor listed for consideration in the review, Claessen and colleagues note that device sizing is guided by annular diameter, perimeter, or area on multislice computed tomography imaging. “Most TAVR devices are available in a comprehensive range of sizes allowing for their applicability in most patients,” the study team suggests, noting that in small annuli, a supra-annular valve design may result in superior haemodynamics and avoid severe prosthesis-patient mismatch. In very large annuli, TAVI devices have been successfully used in anatomy beyond manufacturer recommendations, the study adds.

Turning to aortic valve and aortic root calcification, the study notes that most TAVI decives require leaflet calcification to achieve adequate anchoring and sealing. However, it adds, in patients with significant annular or left ventricular outflow tract calcification, significant PVL may result despite using current-generation TAVI devices. Covering the next criteria, bleeding and vascular complications, the review states that prior research has shown a clear association between smaller sheath size and a reduction in the occurrence of such complications. “This association is enhanced in patients with a small femoral artery diameter,” it is noted.

Discussing the risk of new persistent conduction abnormalities, Claessen et al note that the need for new permanent pacemaker implantation (PPI) is dependent on patient characteristics, valve type and valve deployment technique. The study notes: “It appears there is a trade-off between the degree of PVL and need for new PPI. Mechanistically, PVL may be reduced by a greater radial force of the TAVR device exerted on the aortic annulus, left ventricular outflow tract, and the membranous septum where the conduction system is situated. Nonetheless, higher radial forcemay exert external pressure on the conduction system, especially in self-expanding and mechanically expandable devices where radial force is applied continuously after valve implantation.”

A further consideration is coronary reaccess and risk of coronary occlusion, on which Claessen and colleagues note: “TAVR valves incorporating a taller frame design generally complicate coronary reaccess 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. Therefore, selective coronary angiography after TAVR with the CoreValve family of self-expanding valves could be more challenging than with the SAPIEN family of balloon-expandable valves, although the success rates of percutaneous coronary intervention remained similar.”

Considering future directions of TAVI devices, Claessen and colleagues note that as technologies to evolve, adequate evaluation of postmarket data of TAVI devices should be performed. “Head-to-head trials directly comparing TAVR devices are necessary to make adequate recommendations regarding potential advantages of one device over another.

In conclusion, the review suggests that a “multitude of factors should be considered when selecting a TAVR device in patients with symptomatic severe AS being evaluated for therapy. Optimal device selection should be guided by patient-specific, anatomic-specific, and device-specific factors, including likelihood of PVL, conduction abnormalities, coronary reaccess, long-term durability, and valve reintervention”.


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