**2. The development history of TAVI techniques**

Aortic valve stenosis is a common cardiovascular disease. In western countries, the incidence is about 2.0% in people aged ≥65 and 4.0% in people aged ≥85, which is second only to hypertension and coronary heart disease [1–3]. As early as the 1960s, researchers imitated vascular stents to treat aortic insufficiency by placing metal stents, but these designs stopped after animal trials because of many problems in hemodynamics, postoperative anticoagulation, and so on. Among the nonoperative interventional techniques for early aortic stenosis, only balloon dilatation (balloon aortic valvuloplasty, BAV) can be approved for clinical use. The technique, pioneered by Alain Cribier in 1985, is mainly used in patients with severe aortic stenosis who cannot be operated by routine open heart surgery. Many patients can improve short- and medium-term results, but the 1-year recurrence rate can be as high as 80% [4, 5]. However, due to the urgent need for high-risk patients undergoing thoracotomy, more than 1500 patients with severe aortic stenosis have received this treatment.

In the course of development since then, the stent interventional therapy of coronary artery disease has given a lot of revelation to the interventional therapy of valvular disease. In February 1989, at a medical conference in Phoenix City, USA, after listening to an academic report on coronary intervention stents, Sweden doctor Henning R. Andersen had a whim: if calcified coronary artery stenosis can be solved with metal stents, can aortic valve stenosis be done in a similar way? The first metal stent material that Andersen tried was the most commonly used sternal fixation wire in cardiac surgery, which was molded into a U-shaped structure in order to achieve a telescopic purpose. In May 1989, the prototype conceptual system of TAVI surgery emerged. From idea to feasibility verification, it took Andersen only two and a half months to revolutionize the diagnosis and treatment of aortic valve disease in the twenty-first century. The technology of transcatheter aortic valve implantation was born. Finally, in 1995, the famous patent for Andersen interventional valve was approved in the United States [6].

In the early stage after the feasibility verification of TAVI technology, it went through a long and difficult road of not being recognized. Andersen submitted the completed paper to the *Journal of the American College of Cardiology* (in 1990, when the influence factor of JACC was 5.9), but the reply was that "there is no advantage of this study to be published in JACC magazine." (It has too low priority for publication in JACC). Subsequently, the improved article in 1991 was submitted to Circulation (then impact factor 9.0), and the reply was still rejected. In 1992, at the European Heart annual meeting and the American Heart Association (AHA) annual meeting, the TAVI technology research report submitted by Andersen was arranged to be presented in a poster, and no one paid attention to it.

After that, the first TAVI animal experimental operation was successful, which confirmed the feasibility of the design concept. The article on animal experiments was published in European Heart Journal in 1992 [6]. TAVI technology has finally begun to attract attention, and other similar stent valve designs with animal studies have also begun to emerge. Alain Cribier's team also conducted in-depth research on this technology in 1993 and 1994, including the research and development of balloon-dilated valve stents, selection of stent materials, length and shape design considerations, and so on. However, throughout the 1990s, there was still no breakthrough in TAVI technology due to the high failure rate in animal experiments and the engineering and technical bottleneck in the manufacture of stent valves.

In 2000, Philipp Bonhoeffer and others first tried to use bovine jugular vein to make valve into platinum metal stent and then loaded it on the balloon delivery system to carry out sheep pulmonary valve replacement. The valve also successfully completed the first human pulmonary valve implantation in the same year [7]. However, there are great defects in the follow-up funding and design, which leads to the gradual cessation of the technology research.

**83**

*Transcatheter Treatment of Aortic Stenosis and Regurgitation*

PVT for \$150 million after an initial investment in 2003.

way to implant the valve [12].

effectiveness of TAVI technology.

of his research.

Alain Cribier's team continued the study of balloon dilatation of the stent valve, testing the stainless steel stent in 12 aortic valve stenosis specimens obtained from human surgery, confirming that the stent could open the natural valve repeatedly, regardless of the valve's calcification. And they concluded the ideal height of the stent may be 14–16 mm, which can avoid blocking the coronary opening and interventricular septum or affecting the anterior leaflet of the mitral valve. Then Percutaneous Valve Technologies, a PVT company led by Alain Cribier, was founded in 1999 with the help of investors and medical valve companies. The engineer R&D team of the Israeli subsidiary officially began the design and development of the interventional valve. After a great deal of laboratory work, the first TAVI valve model (balloon dilatation) was born soon [8]. On April 16, 2002, Alain Cribier successfully completed the world's first TAVI operation with Cribier-Edwards interventional valve in Lyon, France, which opened the prelude to the development of TAVI technology. Since then, 40 operations have been completed [9]. Edwards acquired

Alain Cribier used the transfemoral vein method to enter the aortic valve for TAVI. John Webb of Canada collaborated with Edwards to develop retrograde arterial implantation. The technique has a deflectable sheath that can easily pass through the aortic arch and the narrowed valve orifice [10]. John Webb and his colleagues also performed the first transapical valve implantation [11]. Walther et al. promoted the number of cases of TAVI via Edwards' apical approach as an easier

After Jacques Seguin founded CoreValve in the United States in 2001, Eberhard Grube carried out the first clinical implantation of CoreValve valve in 2005 after previous animal experiments [13]. The results proved the feasibility of using selfexpanding valve for TAVI. At the ACC meeting in 2006, Grube reported the first group of 14 patients who underwent TAVI with self-expanding CoreValve valves. At that time, only nine of these patients had no adverse cardiac events in the first 2 weeks. The device can be implanted via femoral artery approach. The CoreValve valve has been continuously improved since then, and the company was acquired by Medtronic in February 2009. Since then, the CoreValve valve has been replaced by a series of Evolut valves. In 2007, the Edwards SAPIEN valve and CoreValve valve first entered the European market and obtained CE approval. Since 2012, they have been approved by the FDA in the United States for surgical high-risk patients with aortic valve stenosis. Since then, the technology has developed by leaps and bounds, and research centers in Europe and the United States have successfully carried out more than 20 clinical multicenter randomized controlled trials, proving the safety and

This is an epoch-making minimally invasive surgical technique that does not require thoracotomy and extracorporeal circulation or cardiac arrest. A large number of expert consensus and guidelines have been issued, and the recommendation level of TAVI has been gradually improved. Andersen successfully performed TAVI surgery on his father in 2011, and he defined this time as the end of a perfect cycle

In the European 2012 guidelines, TAVI candidates are limited to surgical highrisk patients and require the presence of surgeons and the heart team (heart team) to make decisions [14]. Through the safety and effectiveness of TAVI technology with the rapid development of the new generation of valve and technical experience, many clinical research results continue to get good results, and the recommendation level of TAVI in European and American valvular disease guidelines is getting higher and higher. In 2010, the PARTNER 1B study pointed out that although TAVI has incidence of massive hemorrhage and vascular complications in patients with inoperable aortic valve stenosis, the incidence of all-cause mortality,

*DOI: http://dx.doi.org/10.5772/intechopen.92997*

*Advances in Complex Valvular Disease*

this treatment.

States [6].

is second only to hypertension and coronary heart disease [1–3]. As early as the 1960s, researchers imitated vascular stents to treat aortic insufficiency by placing metal stents, but these designs stopped after animal trials because of many problems in hemodynamics, postoperative anticoagulation, and so on. Among the nonoperative interventional techniques for early aortic stenosis, only balloon dilatation (balloon aortic valvuloplasty, BAV) can be approved for clinical use. The technique, pioneered by Alain Cribier in 1985, is mainly used in patients with severe aortic stenosis who cannot be operated by routine open heart surgery. Many patients can improve short- and medium-term results, but the 1-year recurrence rate can be as high as 80% [4, 5]. However, due to the urgent need for high-risk patients undergoing thoracotomy, more than 1500 patients with severe aortic stenosis have received

In the course of development since then, the stent interventional therapy of coronary artery disease has given a lot of revelation to the interventional therapy of valvular disease. In February 1989, at a medical conference in Phoenix City, USA, after listening to an academic report on coronary intervention stents, Sweden doctor Henning R. Andersen had a whim: if calcified coronary artery stenosis can be solved with metal stents, can aortic valve stenosis be done in a similar way? The first metal stent material that Andersen tried was the most commonly used sternal fixation wire in cardiac surgery, which was molded into a U-shaped structure in order to achieve a telescopic purpose. In May 1989, the prototype conceptual system of TAVI surgery emerged. From idea to feasibility verification, it took Andersen only two and a half months to revolutionize the diagnosis and treatment of aortic valve disease in the twenty-first century. The technology of transcatheter aortic valve implantation was born. Finally, in 1995, the famous patent for Andersen interventional valve was approved in the United

In the early stage after the feasibility verification of TAVI technology, it went through a long and difficult road of not being recognized. Andersen submitted the completed paper to the *Journal of the American College of Cardiology* (in 1990, when the influence factor of JACC was 5.9), but the reply was that "there is no advantage of this study to be published in JACC magazine." (It has too low priority for publication in JACC). Subsequently, the improved article in 1991 was submitted to Circulation (then impact factor 9.0), and the reply was still rejected. In 1992, at the European Heart annual meeting and the American Heart Association (AHA) annual meeting, the TAVI technology research report submitted by Andersen was

After that, the first TAVI animal experimental operation was successful, which confirmed the feasibility of the design concept. The article on animal experiments was published in European Heart Journal in 1992 [6]. TAVI technology has finally begun to attract attention, and other similar stent valve designs with animal studies have also begun to emerge. Alain Cribier's team also conducted in-depth research on this technology in 1993 and 1994, including the research and development of balloon-dilated valve stents, selection of stent materials, length and shape design considerations, and so on. However, throughout the 1990s, there was still no breakthrough in TAVI technology due to the high failure rate in animal experiments and the engineering and technical bottleneck in the manufacture of stent valves.

In 2000, Philipp Bonhoeffer and others first tried to use bovine jugular vein to make valve into platinum metal stent and then loaded it on the balloon delivery system to carry out sheep pulmonary valve replacement. The valve also successfully completed the first human pulmonary valve implantation in the same year [7]. However, there are great defects in the follow-up funding and design, which leads to

arranged to be presented in a poster, and no one paid attention to it.

the gradual cessation of the technology research.

**82**

Alain Cribier's team continued the study of balloon dilatation of the stent valve, testing the stainless steel stent in 12 aortic valve stenosis specimens obtained from human surgery, confirming that the stent could open the natural valve repeatedly, regardless of the valve's calcification. And they concluded the ideal height of the stent may be 14–16 mm, which can avoid blocking the coronary opening and interventricular septum or affecting the anterior leaflet of the mitral valve. Then Percutaneous Valve Technologies, a PVT company led by Alain Cribier, was founded in 1999 with the help of investors and medical valve companies. The engineer R&D team of the Israeli subsidiary officially began the design and development of the interventional valve. After a great deal of laboratory work, the first TAVI valve model (balloon dilatation) was born soon [8]. On April 16, 2002, Alain Cribier successfully completed the world's first TAVI operation with Cribier-Edwards interventional valve in Lyon, France, which opened the prelude to the development of TAVI technology. Since then, 40 operations have been completed [9]. Edwards acquired PVT for \$150 million after an initial investment in 2003.

Alain Cribier used the transfemoral vein method to enter the aortic valve for TAVI. John Webb of Canada collaborated with Edwards to develop retrograde arterial implantation. The technique has a deflectable sheath that can easily pass through the aortic arch and the narrowed valve orifice [10]. John Webb and his colleagues also performed the first transapical valve implantation [11]. Walther et al. promoted the number of cases of TAVI via Edwards' apical approach as an easier way to implant the valve [12].

After Jacques Seguin founded CoreValve in the United States in 2001, Eberhard Grube carried out the first clinical implantation of CoreValve valve in 2005 after previous animal experiments [13]. The results proved the feasibility of using selfexpanding valve for TAVI. At the ACC meeting in 2006, Grube reported the first group of 14 patients who underwent TAVI with self-expanding CoreValve valves. At that time, only nine of these patients had no adverse cardiac events in the first 2 weeks. The device can be implanted via femoral artery approach. The CoreValve valve has been continuously improved since then, and the company was acquired by Medtronic in February 2009. Since then, the CoreValve valve has been replaced by a series of Evolut valves. In 2007, the Edwards SAPIEN valve and CoreValve valve first entered the European market and obtained CE approval. Since 2012, they have been approved by the FDA in the United States for surgical high-risk patients with aortic valve stenosis. Since then, the technology has developed by leaps and bounds, and research centers in Europe and the United States have successfully carried out more than 20 clinical multicenter randomized controlled trials, proving the safety and effectiveness of TAVI technology.

This is an epoch-making minimally invasive surgical technique that does not require thoracotomy and extracorporeal circulation or cardiac arrest. A large number of expert consensus and guidelines have been issued, and the recommendation level of TAVI has been gradually improved. Andersen successfully performed TAVI surgery on his father in 2011, and he defined this time as the end of a perfect cycle of his research.

In the European 2012 guidelines, TAVI candidates are limited to surgical highrisk patients and require the presence of surgeons and the heart team (heart team) to make decisions [14]. Through the safety and effectiveness of TAVI technology with the rapid development of the new generation of valve and technical experience, many clinical research results continue to get good results, and the recommendation level of TAVI in European and American valvular disease guidelines is getting higher and higher. In 2010, the PARTNER 1B study pointed out that although TAVI has incidence of massive hemorrhage and vascular complications in patients with inoperable aortic valve stenosis, the incidence of all-cause mortality,

readmission and cardiac symptoms is significantly lower than that of standard treatment [15]. The results of 5-year follow-up of PARTNER IB (inoperable) were released at the 2014 Annual Meeting of Transcatheter Cardiovascular Therapeautics (TCT), suggesting that compared with standard treatment, TAVI had significant benefits in terms of all-cause death rate (71.8%: 93.6%), cardiovascular death (57.3%: 85.9%), readmission rate (47.6%: 87.3%), and improvement of cardiac function (III: IV = 14.3%: 40%). In 2016, the PARTNER 2 study turned to the mediumrisk population, confirming that the mortality, disability, and stroke incidence of TAVI and surgical surgery was similar [16]. The PARTNER III study and the EVOLUTE study published similar results in 2019. In these randomized controlled study of patients with low-risk aortic valve stenosis, whether it is balloon-expandable valve or self-expanding valve, the mortality and complication rate of TAVI group is better than that of conventional thoracotomy group. As a result, the United States and European Drug Regulatory agencies have extended the use of TAVI to patients with low-risk aortic stenosis since 2019 [17, 18].

In 2015, about 40,000 patients in Europe received TAVI treatment, and that number will rise to 60,000 in 2020. The number of patients with TAVI indications in Europe is expected to exceed 114,000/year, and if extended to low-risk patients, it can increase to 177,000/year. In France, 1600 and 8000 patients were treated with TAVI in 2010 and 2015, respectively, and the figure is expected to reach 10,000 in 2016. Germany receives TAVI treatment for every 1 million residents, which has the highest TAVI implementation rate in Europe. There were more than 15,000 cases in Germany in 2016, three times as many as in 2011. The number of valve replacement cases in routine surgery remained relatively stable, with no less than 10,000 cases per year. In developed countries such as Germany (2013) and the United States (2019), the number of TAVI surgeries has exceeded that of conventional thoracotomy aortic valve replacement, and the gap is still widening. A total of more than 400,000 TAVI operations have been completed worldwide.

In 2018, Durko et al. used Monte Carlo mathematical model combined with 37 clinical studies of 26,402 cases of severe aortic valve stenosis to predict the number of patients with TAVI indications each year in Europe and the United States. In patients over 65 years old, the incidence of severe aortic stenosis was 4.4‰ per year. 68.3% patients with severe aortic stenosis had related symptoms. Despite severe symptoms of aortic stenosis, 41.6% did not undergo surgical aortic valve replacement. Of the nonsurgical patients, 61.7% received TAVI treatment. This model predicts 114,757 European and 58,556 North American TAVI candidates each year. The conclusion is that there are currently about 180,000 patients a year in the European Union and North America who can be considered potential candidates for TAVI. If the indications for TAVI are extended to low-risk patients, this number may increase to 270,000. These findings have a significant impact on healthcare resource planning in 29 countries [19].

The European Valve observation registration study (EURObservational Research Programme VHD II) conducted a survey at 22 centers in 28 countries to show changes in the structure of heart valve patients and their impact on clinical treatment. 7247 patients with VHD (including 4483 inpatients and 2764 outpatients) were enrolled in the study. Compared with a similar survey conducted in 2005, the latest survey in 2019 showed that the actual treatment strategies of patients with aortic valve disease were more in-line with the guidelines and the proportion of transcatheter therapy was gradually increasing (39% of aortic stenosis and 17% of mitral regurgitation) [20].

The SAPIEN 3 valve is the third generation in the SAPIEN series of valves developed by Edwards. The valve stent contains an outward reflexed skirt, which can prevent perivalvular leakage. The delivery system as a whole becomes smaller,

**85**

*Transcatheter Treatment of Aortic Stenosis and Regurgitation*

shrinking to 14F (16F for 29 mm valves). At the same time, the conveying system has good controllability, so that the near-center section of the conveying system can be bent and maintain better coaxiality. The SAPIEN 3 Ultra is an improved and upgraded version of the SAPIEN 3 valve system, and a 14F sheath can be used for all sizes of valves [21]. Centera is a self-expanding valve developed by Edwards Corporation. This valve is quite different from Medtronic's self-expanding valve. Its nickel-titanium stent is short, similar to a balloon-expandable valve, using a bovine pericardial valve. There is a metal wire at the waist of the stent, which can be tightened to retract the valve so that it can be retrieved. The conveying system is 14F, which can be bent to ensure the release with good coaxiality. The electric release handle makes the release easier, and the valve can be released by a single operator. Centera valve design combines the characteristics of self-expandable stents (recyclable stents with good deformability) and ball-expanded stents (short

The Evolut R valve is an upgraded version of the Medtronic CoreValve valve. The valve enhances the radial force at the annulus level, and the lower end of the skirt extends downward to prevent perivalvular leakage. The valve stent is shorter, so that the coaxial line of the stent is better after release. The shape of the stent is more straight and cylindrical. More importantly, a nickel-titanium casing is arranged at the near end of the delivery system, and before the valve stent is completely released, the valve can be pulled back to the nickel-titanium casing to achieve retrieved; thus the position of the valve can be readjusted. On the basis of Evolut R, Evolut pro wrapped a pericardial patch around the lower segment of the stent to reduce the incidence of perivalvular leakage and pacemaker implantation [23–25]. The Lotus Edge valve is a product developed by Boston Science Co., Ltd., which is an upgraded version of the Lotus valve. The Lotus valve stent is made of Ni-Ti alloy. The diameter of the short axis of the stent can be shortened after lengthening longitudinally, so as to achieve the purpose of recycling. The lower part of the device has an adaptive sealing ring, which can reduce the incidence of perivalvular regurgitation. Lotus Edge retains the advantages of full retrieved valve of Lotus, prevention of perivalvular leakage, early valvular work, and so on. At the same time, the delivery system is improved to make it softer and more curved. More important is the implantation depth protection technology to prevent the valve from entering the outflow tract too deep, thus reducing the incidence of conduction block. In previous clinical trials, the implantation rate of Lotus pacemakers was as high as 35.5% and was later withdrawn from the market. Lotus Edge is expected to reduce the pacemaker implantation rate compared with Lotus. In April 2019, the Lotus Edge valve was approved for sale by the FDA in the United States [26].

ACCURATE neo is a self-expanding valve implanted via artery, and it is also a design of Ni-Ti alloy stent and supra-annular valve. Its unique design lies in that it contains an anchoring device and can be positioned automatically. The release of the valve is different from that of other self-expanding valves. Generally, the self-expanding valve first releases the proximal end and then releases the distal end. During the ACCURATE neo release procedure, the distal end is first released, the anchoring device exposed, and the valve stent is leaded down to the autologous aortic annulus level and then the proximal part is released. It also contains the outer edge of the skirt to prevent the valve from leaking. The distal stent grid has a large aperture and does not interfere with percutaneous coronary intervention after valve implantation. The lower part of the stent is covered by the inner layer and the outer layer of the pericardium to prevent perivalvular leakage. Its delivery system is equivalent to 15F. In the latest large randomized controlled study, 739 patients (mean age 82.8 years, STS score 3.5%) were randomly divided into two groups: ACCURATE neo valve 367 cases and SAPIEN 3 valve 364 cases. The main end point

*DOI: http://dx.doi.org/10.5772/intechopen.92997*

stents and low incidence of pacemakers) [22].

### *Transcatheter Treatment of Aortic Stenosis and Regurgitation DOI: http://dx.doi.org/10.5772/intechopen.92997*

*Advances in Complex Valvular Disease*

readmission and cardiac symptoms is significantly lower than that of standard treatment [15]. The results of 5-year follow-up of PARTNER IB (inoperable) were released at the 2014 Annual Meeting of Transcatheter Cardiovascular Therapeautics (TCT), suggesting that compared with standard treatment, TAVI had significant benefits in terms of all-cause death rate (71.8%: 93.6%), cardiovascular death (57.3%: 85.9%), readmission rate (47.6%: 87.3%), and improvement of cardiac function (III: IV = 14.3%: 40%). In 2016, the PARTNER 2 study turned to the mediumrisk population, confirming that the mortality, disability, and stroke incidence of TAVI and surgical surgery was similar [16]. The PARTNER III study and the EVOLUTE study published similar results in 2019. In these randomized controlled study of patients with low-risk aortic valve stenosis, whether it is balloon-expandable valve or self-expanding valve, the mortality and complication rate of TAVI group is better than that of conventional thoracotomy group. As a result, the United States and European Drug Regulatory agencies have extended the use of TAVI to

In 2015, about 40,000 patients in Europe received TAVI treatment, and that number will rise to 60,000 in 2020. The number of patients with TAVI indications in Europe is expected to exceed 114,000/year, and if extended to low-risk patients, it can increase to 177,000/year. In France, 1600 and 8000 patients were treated with TAVI in 2010 and 2015, respectively, and the figure is expected to reach 10,000 in 2016. Germany receives TAVI treatment for every 1 million residents, which has the highest TAVI implementation rate in Europe. There were more than 15,000 cases in Germany in 2016, three times as many as in 2011. The number of valve replacement cases in routine surgery remained relatively stable, with no less than 10,000 cases per year. In developed countries such as Germany (2013) and the United States (2019), the number of TAVI surgeries has exceeded that of conventional thoracotomy aortic valve replacement, and the gap is still widening. A total of more than

In 2018, Durko et al. used Monte Carlo mathematical model combined with 37 clinical studies of 26,402 cases of severe aortic valve stenosis to predict the number of patients with TAVI indications each year in Europe and the United States. In patients over 65 years old, the incidence of severe aortic stenosis was 4.4‰ per year. 68.3% patients with severe aortic stenosis had related symptoms. Despite severe symptoms of aortic stenosis, 41.6% did not undergo surgical aortic valve replacement. Of the nonsurgical patients, 61.7% received TAVI treatment. This model predicts 114,757 European and 58,556 North American TAVI candidates each year. The conclusion is that there are currently about 180,000 patients a year in the European Union and North America who can be considered potential candidates for TAVI. If the indications for TAVI are extended to low-risk patients, this number may increase to 270,000. These findings have a significant impact on healthcare resource

The European Valve observation registration study (EURObservational Research

Programme VHD II) conducted a survey at 22 centers in 28 countries to show changes in the structure of heart valve patients and their impact on clinical treatment. 7247 patients with VHD (including 4483 inpatients and 2764 outpatients) were enrolled in the study. Compared with a similar survey conducted in 2005, the latest survey in 2019 showed that the actual treatment strategies of patients with aortic valve disease were more in-line with the guidelines and the proportion of transcatheter therapy was gradually increasing (39% of aortic stenosis and 17% of

The SAPIEN 3 valve is the third generation in the SAPIEN series of valves developed by Edwards. The valve stent contains an outward reflexed skirt, which can prevent perivalvular leakage. The delivery system as a whole becomes smaller,

patients with low-risk aortic stenosis since 2019 [17, 18].

400,000 TAVI operations have been completed worldwide.

**84**

planning in 29 countries [19].

mitral regurgitation) [20].

shrinking to 14F (16F for 29 mm valves). At the same time, the conveying system has good controllability, so that the near-center section of the conveying system can be bent and maintain better coaxiality. The SAPIEN 3 Ultra is an improved and upgraded version of the SAPIEN 3 valve system, and a 14F sheath can be used for all sizes of valves [21]. Centera is a self-expanding valve developed by Edwards Corporation. This valve is quite different from Medtronic's self-expanding valve. Its nickel-titanium stent is short, similar to a balloon-expandable valve, using a bovine pericardial valve. There is a metal wire at the waist of the stent, which can be tightened to retract the valve so that it can be retrieved. The conveying system is 14F, which can be bent to ensure the release with good coaxiality. The electric release handle makes the release easier, and the valve can be released by a single operator. Centera valve design combines the characteristics of self-expandable stents (recyclable stents with good deformability) and ball-expanded stents (short stents and low incidence of pacemakers) [22].

The Evolut R valve is an upgraded version of the Medtronic CoreValve valve. The valve enhances the radial force at the annulus level, and the lower end of the skirt extends downward to prevent perivalvular leakage. The valve stent is shorter, so that the coaxial line of the stent is better after release. The shape of the stent is more straight and cylindrical. More importantly, a nickel-titanium casing is arranged at the near end of the delivery system, and before the valve stent is completely released, the valve can be pulled back to the nickel-titanium casing to achieve retrieved; thus the position of the valve can be readjusted. On the basis of Evolut R, Evolut pro wrapped a pericardial patch around the lower segment of the stent to reduce the incidence of perivalvular leakage and pacemaker implantation [23–25].

The Lotus Edge valve is a product developed by Boston Science Co., Ltd., which is an upgraded version of the Lotus valve. The Lotus valve stent is made of Ni-Ti alloy. The diameter of the short axis of the stent can be shortened after lengthening longitudinally, so as to achieve the purpose of recycling. The lower part of the device has an adaptive sealing ring, which can reduce the incidence of perivalvular regurgitation. Lotus Edge retains the advantages of full retrieved valve of Lotus, prevention of perivalvular leakage, early valvular work, and so on. At the same time, the delivery system is improved to make it softer and more curved. More important is the implantation depth protection technology to prevent the valve from entering the outflow tract too deep, thus reducing the incidence of conduction block. In previous clinical trials, the implantation rate of Lotus pacemakers was as high as 35.5% and was later withdrawn from the market. Lotus Edge is expected to reduce the pacemaker implantation rate compared with Lotus. In April 2019, the Lotus Edge valve was approved for sale by the FDA in the United States [26].

ACCURATE neo is a self-expanding valve implanted via artery, and it is also a design of Ni-Ti alloy stent and supra-annular valve. Its unique design lies in that it contains an anchoring device and can be positioned automatically. The release of the valve is different from that of other self-expanding valves. Generally, the self-expanding valve first releases the proximal end and then releases the distal end. During the ACCURATE neo release procedure, the distal end is first released, the anchoring device exposed, and the valve stent is leaded down to the autologous aortic annulus level and then the proximal part is released. It also contains the outer edge of the skirt to prevent the valve from leaking. The distal stent grid has a large aperture and does not interfere with percutaneous coronary intervention after valve implantation. The lower part of the stent is covered by the inner layer and the outer layer of the pericardium to prevent perivalvular leakage. Its delivery system is equivalent to 15F. In the latest large randomized controlled study, 739 patients (mean age 82.8 years, STS score 3.5%) were randomly divided into two groups: ACCURATE neo valve 367 cases and SAPIEN 3 valve 364 cases. The main end point

of ACCURATE neo 30 days and SAPIEN 3 did not achieve non-inferiority (24% vs. 16% personality 0.42). Although there was no difference in 30-day mortality (2 vs. 1%) and stroke (2 vs. 3%) between the two groups, the incidence of acute renal injury (3% vs. 1%) and moderate perivalvular leakage (9 vs. 3%) was higher in the ACCURATE neo group [27].

The JenaValve valve is specially designed [28, 29]. The stent valve with three fixed keys is implanted through the apical approach. TF-JenaValve is the new version of JenaValve via the femoral artery. The JenaValve is a short stent with a large mesh hole at the upper end, which is beneficial to the introduction of the coronary artery. The outer edge of the stent contains three anchoring parts, which can prevent the stent from being fixed to the bottom of the three aortic sinuses. The artificial valve is designed for supra-annular valve. The JenaValve deployment first releases the proximal anchoring device, then pushes it to the autologous aortic valve annulus, automatically locates and gets stuck, then releases the proximal stent, and finally releases the distal connecting device. The delivery system of TF-JenaValve is 18F, which has a bending function to ensure the coaxiality of the release valve and the aortic valve annulus. The design of the JenaValve with a fixed key makes it possible to treat aortic regurgitation and patients with low coronary artery openings. This is similar to the Chinese domestic J-Valve.

The design of the Engager valve produced by Medtronic is similar to that of the JenaValve valve. It is also a valve implanted through the apical approach. By placing the control arm with anatomical positioning function at the root of the aortic sinus, the valve stent can be positioned accurately, and the complications can be reduced [30, 31].
