TAVR is recommended for patients with severe symptomatic aortic stenosis (AS) who are not suitable to undergo conventional AVR as assessed by a heart team, who are likely to gain improvement in their quality of life, and who have a life expectancy of more than 1 year after consideration of their comorbidities.

Transcatheter aortic valve implantation (TAVI) should also be considered for high-risk patients with severe symptomatic AS who are suitable for surgery, but for whom TAVI is favored by a heart team as a COR IIa, level of evidence (LOE) B recommendation.

Various risk scores have been used to aid in decision making by the heart team. Among these, the logistic EuroScore (ES) is known to overestimate the effective mortality; a logistic ES of 20% or more has been suggested as an indication for TAVI. Its successor, the ES II, has been shown to correlate better between the anticipated and observed survival. Currently the most reliable score is the Society of Thoracic Surgeons (STS) predicted risk of mortality (STS-PROM) score, with a value of more than 8% to 10% indicating high risk. However, none of these risk scores were designed for TAVR. The STS/American College of Cardiology (ACC) TAVR In-Hospital Mortality Risk score was recently published and combines easy calculation and good correlation with the real in-hospital mortality.

Regardless of risk scores, other factors include status post–coronary artery bypass grafting with a patent graft, porcelain aorta, severe chronic obstructive pulmonary disease (COPD), status postradiation therapy, renal failure, low ejection fraction, and significant frailty, among others. These may be clear indicators leading to a heart team decision in favor of performing TAVR.

Thus, TAVR is already widely performed in intermediate-risk patients. The transcatheter valve therapy registry (TVT registry) has reported a median STS risk score of approximately 7% in patients treated with TAVI from November 2011 to March 2013. During the same period, the median STS score in the German aortic valve registry (GARY) was 5.0, indicating an intermediate-risk profile. The trend to expand the indications for TAVR to intermediate-risk and eventually low-risk patients has been gaining momentum after recent studies demonstrated the noninferiority of TAVR compared to SAVR in intermediate-risk patients.

Despite this trend, it has to be considered that comprehensive long-term follow-up for TAVR prostheses is not available yet. However, long-term durability will be a prerequisite for further expansion of the procedure, especially to younger patients.

Aortic regurgitation (AR) causes about 11% of all native valve disease. However, because calcification is usually absent in isolated AR, anchoring of a TAVR valve is more challenging and thus a relative contraindication for TAVR. Various devices have been used off-label for successful implantation in patients with AR, but only small series have been reported.

Up to now, the Jenavalve prosthesis (Jenavalve Technology, Munich), which clips on to the aortic valve leaflets, was the first CE mark–approved device for the treatment of isolated AR and has shown a high success rate in a multicenter study. (CE marking is a certification mark indicating conformity with health, safety, and environmental protection standards for products sold within the European Economic Area.)

However, despite proven feasibility, neither European nor US guidelines recommend TAVR for pure AR.

Because TAVR is performed without direct vision of the operating field, preoperative planning and imaging are essential.

After assessment of the perioperative risk and the heart team’s decision that TAVR might be a treatment option, some anatomic characteristics have to be determined to evaluate if TAVR is feasible and to estimate the technical risk of the procedure.

With the currently available devices, TAVR can only be performed in patients with an aortic annulus between 18 and 29 mm ( Table 16.1 ). This, however, applies to more than 95% of potential patients.

The distance between the annulus and coronary ostia should be more than 10 mm, and/or the aortic sinus needs to be sufficiently large to prevent occlusion of the coronary ostia by calcifications or by native valve leaflets.

Ideally, annulus measurements are performed by TEE in two-dimensional and three-dimensional views, as well as by CT. In recent years, specific CT software tools have been developed that allow for precise and automated measurement of the aortic root, including the effective aortic annulus, based on its area and/or perimeter (e.g., 3mensio Structural Heart, Pie Medical Imaging, Maastricht, The Netherlands).

The improved preoperative planning and imaging techniques have been an important contributing factor to decrease the incidence of severe paravalvular regurgitation and annulus rupture after TAVR. Thus, careful screening cannot just stratify the risk more precisely than a risk score, but is required for assessment of the feasibility of TAVR and for selection of the most appropriate access and valve.

Current devices for performing TAVR are mostly second- or third-generation valves that have shown improved patient outcomes and enhanced safety compared to the first-generation devices. These include specific features to minimize paravalvular leakage, reduction in delivery system and sheath diameter to allow TF access, despite smaller access vessels, options to retrieve the device partly or completely after implantation (if possible, after it is already fully functional), and the possibility of commissural orientation with exact anatomic positioning.

TAVR devices consist of a specifically designed valve and application system, which is usually inserted over a guidewire by means of a sheath or in a sheathless manner. The valve consists of a thin stent, which is balloon-expandable (stainless steel or cobalt-chromium) or self-expanding (usually nitinol). Valve leaflets consist of bovine pericardium, porcine pericardium, or porcine leaflets. Some of these valves have an additional anticalcification treatment similar to that of conventional surgical xenografts to protect against tissue degeneration and thus achieve optimal valve durability.

An overview of the most common prostheses is shown in Fig. 16.1 .

Overview of the most common TAVR prostheses. (A) Balloon expandable bovine pericardial tissue transcatheter bioprosthesis. (B) Self-expanding porcine pericardial tissue transcatheter bioprosthesis. (C) Self-expanding bovine pericardial tissue transcatheter bioprosthesis. (D) Self-expanding native porcine leaflets transcatheter bioprosthesis. (E) Alternative expansion design bovine pericardial tissue transcatheter bioprosthesis.

From Arsalan M, Walther T: Durability of prostheses for transcatheter aortic valve implantation. Nat Rev Cardiol . 2016;13(6):360-7. B3, ACURATE neo™ Aortic Valve. Image provided courtesy of Boston Scientific. © 2017 Boston Scientific Corporation or its affiliates. All rights reserved. C1, Portico™ valve. Reproduced with permission of St. Jude Medical, © 2017. All rights reserved. D1, ACURATE TA™ Valve. Image provided courtesy of Boston Scientific. © 2017 Boston Scientific Corporation or its affiliates. All rights reserved. D2, *This product is no longer available in the market and Jena Valve now develops a transfemoral pericardial TAVR Valve (JenaValve Everdur). Used with the permission of Jena Valve. All rights reserved. E2, LOTUS™ Valve. Image provided courtesy of Boston Scientific. © 2017 Boston Scientific Corporation or its affiliates. All rights reserved.

The balloon-expandable Edwards SAPIEN valve (Edwards Lifesciences, Irvine, CA) is available for retrograde (TF, TAo, TS) and antegrade (TA) access and is currently available in its third generation, the SAPIEN 3. It is a rather short device designed for subcoronary implantation, with the leaflets located in an intraannular position.

The self-expanding Medtronic CoreValve (Medtronic, Minneapolis) is available for retrograde implantation only. The device stent is longer and thus requires an implantation that surpasses the coronary ostia while obtaining additional aortic stabilization. The leaflets are attached in a supraannular position.

In addition to these two most frequently implanted prostheses, several other devices have been developed:

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  The Acurate neo system (Symetis, Dusseldorf, Germany) has gained the largest clinical following after the previously mentioned valves and is available for TF-TAVR and TA-TAVR. The Acurate valve has a self-expanding nitinol stent that can be placed in an anatomically correct position, matching the commissures to the native ones quite easily (with the TA approach), and that allows for partial repositioning.

  
  
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  The Portico device (St. Jude Medical, St. Paul, MN) consists of a nitinol stent that extends from the aortic annulus to the ascending aorta. It allows for retrieval after up to 80% of deployment, for which valve functionality can be assessed.

  
  
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  The Lotus valve (Boston Scientific, Marlborough, MA) consists of a nitinol mesh, which is quite long in the crimped position and foreshortens during deployment. Complete retrieval of the device is possible, allowing for complete assessment of valve function before final detachment of the delivery system.

  
  
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  The Direct Flow valve (Direct Flow Medical, Santa Rosa, CA) is unique in design. It consists of two nonmetallic, inflatable, double-ring structures that are interconnected by a tubular bridging system. Initially, the valve is filled with a radiopaque exchange solution that is replaced with a polymer once the correct position in the native aortic annulus has been achieved.

  
  
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  The Jenavalve TA system (Jenavalve Technology, Munich) is a unique self-expandable stent with additional feelers to guide positioning at the annular level together with commissural alignment and safe anchoring. It is the only device approved for the treatment of AR (CE mark–approved device).

  
  
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  The Venus A-Valve (Venus MedTech, Hangzhou, China) is the only TAVR device meeting China Food and Drug Administration clinical requirements. It is a self-expanding nitinol stent frame that carries porcine pericardial leaflets and can be delivered via TF, TA, TSc, and TAo approaches.

  
  
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  The Braile Inovare prosthesis (Braile Biomédica, São José do Rio Preto, Brazil) is a balloon-expandable device with a cobalt-chromium frame and a single sheet of bovine pericardium comprising the leaflets. It is already commercially available in Brazil, but currently only suitable for TA access.

  
  
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  Other devices are in clinical trials or are currently still under development.

TAVR procedures will usually be performed in a hybrid operating suite. Because intraoperative imaging plays a major role in TAVR, a high-quality angiography system is favored over a mobile, C arm–based system.

Furthermore, in case general anesthesia is needed, TEE should be used for periprocedural guidance and assessment. Because a fast connection to a heart-lung machine might be needed in case of hemodynamic instability, an already primed heart-lung machine should therefore be available.

Furthermore, conversion to conventional surgery via sternotomy should be possible in a timely manner. All these features, including adequate hygienic standards, can best be realized in a hybrid operating suite. A well-equipped cardiac catheterization laboratory may be the next best alternative. Positioning of the patient, together with hardware setup and operator and assistant positioning, are shown in Fig. 16.2 .

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