Transcatheter Aortic Valve Replacement Technique and Current Approaches

Abstract

Aortic stenosis (AS) is a chronic, progressive disease. The most common cause of aortic stenosis etiology in advanced age is calcific, degenerative aortic stenosis. Once patients become symptomatic, the disease progresses rapidly. Treatment is surgical aortic replacement. Advanced age and the presence of comorbid conditions increase the risk of surgery. Therefore, a significant number of patients cannot be treated. For this purpose, transcatheter aortic valve interventions were developed and started to be used all over the world. In this article, we discussed the technical features of the transcatheter aortic valve replacement (TAVR) procedure, the types of valves used and the complications of the procedure. Clinical results of the procedure and comparisons with other treatment methods will not be included in our article.

1. Introduction

Aortic stenosis (AS) is the most common type of valvular heart disease in developed countries. Incidence of AS increases due to the prolongation of life expectancy. Until the 2000s, surgical aortic valve replacement (SAVR) was the unique treatment for symptomatic AS. In 2002, Cribier et al. [1] performed a transcatheter aortic valve replacement (TAVR) procedure with a balloon-expandable valve in an inoperable patient and a new era began.

First, TAVR was approved for patients with high surgical risk but currently as more data gleaned, the focus expanded to the intermediate- and low-risk patients as well [2]. All the available transcatheter heart valves belong to one of the following categories: balloon-expandable valves (BEVs) or self-expandable valves (SEVs). BEV expands using the radial strength of the balloon, in contrast, SEV is deployed until it faces the resistance of the annular wall, adapting to anatomy of aortic annulus [3]. Another classification is according to leaflets mounted within the stented frame to native aortic annulus. Based on this grouping, valves can be classified as supra-annular and intra-annular. Supra-annular valves are designed to avoid interaction with native annulus. This prevents blood flow obstruction. Also, supra-annular valves lead to lower transvalvular gradients and higher effective orifice area [4]. On the other hand, intra-annular valves lead to less interaction with coronary ostia, thereby minimizing the risk of obstruction [5].

2. Transcatheter aortic valve types

2.1 Self-expandable valves

Self-expandable valve family includes Evolut R, Evolut Pro, Evolut Pro+, *Evolut FX (Medtronic, Minneapolis, MN, USA), Portico, Navitor (Abbott Vascular, Santa Clara, CA, USA), Acurate Neo (Boston Scientific, Marlborough MA, USA), Allegra (Biosensors, Singapore, Singapore, and New Valve Technology, Hechingen, Germany) and Biovalve (Biotronik, Buelach, Switzerland).

2.1.1 CoreValve/evolut family

First, the SEV ‘CoreValve’ was initially presented by Medtronic. In CoreValve US Pivotal Trial, TAVR showed higher survival rates compared to SAVR at 1 year [6]. The main disadvantages of this system were large size of delivery system, increased postprocedure permanent pacing rate, increased rate of paravalvular leak (PVL) and relatively increased stroke rates [7, 8, 9, 10]. After the CoreValve system, Evolut R, Pro and Pro+ were designed by Medtronic (Figure 1). All models contain tri-leaflet porcine pericardial tissue on a Nitinol frame and work in a supra-annular position. Evolut R system has favorable outcomes compared to the CoreValve system, especially on paravalvular leak. Evolut Pro kept all features of Evolut R, is recapturable and repositionable to assist in optimal deployment. Also, this system has an extra porcine pericardial wrap over first 1.5 cells to reduce PVL [11, 12]. Evolut Pro+ platform can treat an even larger annulus range up to 30 mm diameter. Evolut FX valve was recently developed with enhanced visualization capabilities [13]. Platforms use transvascular ways. Evolut R and Evolut Pro+ have four annular diameter sizes. The size of 23 mm is suitable for 18–20 mm aortic valve annuli, 26 mm for annuli 20–23 mm, 29 mm for annuli 23–26 mm and 34 mm for annuli 26–29 mm. Evolut R platform uses 14 French (Fr) equivalent sheath. But 34 mm Evolut R and Evolut Pro platform use 16 Fr sheath. Evolut Pro+ platform uses 14 Fr sheath (18 Fr sheath is necessary for a 34 mm valve). Generally before implantation, predilatation is recommended. Usually rapid pacing is not necessary but in aortic regurgitation and high annuli diameter, controlled pacing (90–130 rates/min) can be used (Table 1).

Figure 1.

CoreValve/evolut valve design.

	Evolut r	Evolut pro	Portico	Acurate neo
Approval	FDA, CE	FDA, CE	CE	CE
Leaflet position	Supra-annular	Supra-annular	Intra-annular	Supra-annular
Leaflet structure	Porcine	Porcine	Bovine	Porcine
Valve sizes	23,26,29,34	23,26,29 (pro+34 also)	23,25,27,29	23,25,27
Resheathability	Yes	Yes	Yes	No
Self-positioning	No	No	No	Yes

Table 1.

Comparison of self-expandable valves’ basic features.

2.1.2 Portico and Navitor

Portico is the first resheathable and repositionable SEV. Its intra-annular design provides early valve function and reduces hemodynamic interaction during the procedure. Portico has large frame cells that enhance coronary access. Available sizes are 23 mm, 25 mm, 27 mm and 29 mm. Both platforms use transvascular ways. The 14 Fr sheath is suitable for 23–25 mm valves and the 15 Fr sheath is suitable for 27–29 mm valves [14, 15]. Navitor is a new generation of Portico valves (Figure 2). It has an external cuff to reduce PVL. Abbott published 30-day results. All-cause mortality 0%, permanent pacemaker 15%, major vascular complications 0.8% and mean gradient 7.4 mmHg, higher than minimal PVL 0%, were observed. Highlighted potential risk is associated with increased rates of permanent pacemaker implantation [16].

Figure 2.

Portico/Navitor valve design.

2.1.3 Acurate TA and Acurate NEO

Acurate TA is used for transapical access and Acurate Neo is used for transvascular access. Unlike other SEVs, Acurate cannot be repositioned. It has a supra-annular design with three stabilization arches that help bioprosthetic valve alignment. Implantation has two steps from ‘up to down’. First aortic side releases then subannular side releases. Because of this unique opening style, the platform protects hemodynamics, allows blood flow and decreases embolization risk. Acurate Neo is especially suitable for low coronary distances and horizontal aorta (Figure 3). Acurate Neo has the lowest permanent pace ratio in all SEVs. This is a consequence of lower radial force. Due to lower radial force, conduction system trauma reduces. But this low radial force makes necessary predilatation and postdilatation. Acurate Neo has three sizes (23 mm, 25 mm and 27 mm) [17].

Figure 3.

Acurate neo design.

2.1.4 Allegra valve

Allegra (Biosensors, Singapore, Singapore, and New Valve Technology, Hechingen, Germany) has a tri-leaflet Nitinol stent roof made of bovine pericardium in the supra-annular position (Figure 4). The access way is transvascular. The delivery system includes three-stage release technology for implantation. Unlike other valves, the delivery system and valve are first placed toward the left ventricle. Then the valve starts to open from the middle part (Permaflow position). Because of low radial force, predilatation is recommended. In 2016 after the first results of the Allegra valve were positive, it received European Conformity, i.e., Conformité Européene (CE) approval in March 2017 [18, 19].

Figure 4.

Allegra valve design.

2.1.5 Biovalve

Biovalve (Biotronic, Buelach, Switzerland) is a new-generation valve with supra-annular structure, consisting of a skirt on a Nitinol roof and three leaflets made from porcine pericardium. This platform presents a large orifice area. The delivery system has a diameter of 18 Fr, suitable for transfemoral access, 360 degree flexible structure and ergonomic design. The valve can be resheathed up to 80% of implantation [20].

2.2 Balloon-expandable valves

Implantation of a transcatheter heart valve (THV) via a balloon-expandable system played an important role in the early stages of TAVR. The first clinical experience started with the Cribier-Edwards valve. After the technological developments, new-generation devices are made available. BEVs are Saphien family (Edwards Lifesciences Corporation, Irvine, CA, USA), Myval (Meril Life Sciences Pvt. Ltd., Vapi, Gujarat, India), Inovare (Braile Biomedical, São José do Rio Preto, Brazil) and Colibri (Colibri Heart Valve, Broomfield, USA). All BEVs are placed in an intra-annular position.

2.2.1 Saphien BEV family

Saphien is the first BEV. This family includes Saphien XT, Saphien 3 and Saphien 3 Ultra. The valves are made of tri-leaflet bovine pericardium mounted on a cobalt-chromium stent frame (Figure 5). Saphien XT valves are available in 20, 23, 26 and 29 mm sizes. This platform uses a 16 F sheath for 20 and 23 mm valves, 18 F sheath for a 26 mm valve and 20 F sheath for a 29 mm valve. Saphien 3 platform is compatible with the 14 F sheath for the 20 mm, 23 mm, and 26 mm valves and with the 16 F sheath for the 29 mm valve. All these sheaths are expandable and called ‘eSheath’. Sapien 3 and Sapien 3 Ultra valves are suitable for transfemoral processing up to 5.5 mm femoral artery diameter. The major improvement in Sapien 3 is polyethylene terephthalate (PET) outer skirt to reduce PVL and an open cell upper frame geometry to avoid obstruction and allow access to coronary arteries [21]. The last generation of Saphien family is Saphien 3 Ultra. This valve is based on Saphien 3 platform but has 40% taller skirt design to avoid PVL better. The 20, 23 and 26 mm valves feature a new skirt design, while the 29 mm valve remains in the existing Saphien 3 platform [22].

Figure 5.

Saphien BEV family.

Saphien 3 and Saphien 3 Ultra have some unique indications for use. The Food Drug and Administration (FDA) has approved them for mitral and pulmonary procedures. But this issue is beyond the scope of this article (Table 2).

Special condition	First choice
Small annulus (<23 mm)	Evolut R/Pro
Large annulus (>27 mm)	Evolut R/Pro
Low coronary distance	Acurate Neo
Small vascular diameter	Evolut R/Pro, Portico
Valve in valve	Evolut R/Pro, Acurate Neo
Concomitant coronary artery disease	Acurate Neo, Portico
Easy to use	Acurate Neo, Portico

Table 2.

Recommendations for [all conditions].

2.2.2 Myval BEV

Myval’s design is created with hexagons. Its special design has large open cells toward the aortic end, while it has closed cells toward ventricular end to maintain higher radial force (Figure 6). Unlike other valves, Myval has a large number of sizes, such as conventional (20, 23, 26 and 29 mm), medium (21.5, 24.5 and 27.5 mm) and extra large (30.5 and 32 mm). Myval THV of size 32 mm got CDSCO (Central Drugs Standard Control Organization, India) approval and 30.5 mm is pending CDSCO approval. Medium sizes are for avoiding a serious complication of BEV, annular rupture. The platform uses 14 F delivery system [23].

Figure 6.

Myval design.

2.2.3 Inovare BEV

Inovare BEV consists of tri-leaflet bovine pericardial valves mounted in a cobalt-chromium stent frame and is available in four sizes of 20, 22, 24 and 26 mm (Figure 7). The valve is implanted using the transapical and transaortic approach [24].

Figure 7.

Inovare design.

2.2.4 Colibri BEV

There are limited clinical data and Colbri BEV is a prefabricated TAVR system. The valve has a unique folding technique and is made of three independent porcine pericardium pieces. The first implantation was performed in November 2012 [24].

Table 3 summarizes general recommendations for choosing a proper valve; however, the most important recommendation is to use the platform that the operator is experienced to handle.

Scenario	Favor BEV	Favor SEV
Severely calcified annulus		+
Small annulus		+
Large annulus	+
Bicuspid aortic valve	+	+
Small femoral arteries		+
Concomitant coronary artery disease	+
Preexisting conduction abnormalities	+
Reduced ejection fraction		+

Table 3.

General recommendations for choosing a proper valve.

3. Accesses in TAVR procedure

Over the past 20 years, TAVR has become an alternative treatment for severe aortic stenosis. For this treatment, operators need a suitable access. According to the current guidelines, femoral approach is the first choice [25, 26].

3.1 Transfemoral approach

Transfemoral access is the first choice in TAVR procedures. This is because operators are experienced in handling femoral access and possible complications can be managed easily. Despite technical improvement in vascular sheath diameters, 10–20% of all patients are not suitable for undergoing transfemoral access due to advanced peripheral arterial disease [27]. So for these unsuitable patients, alternative access sites have been searched. TAVR can be performed alternatively via transapical, transaortic, transsubclavian/transaxillary, transcarotid, transcaval and suprasternal approaches. But before searching for an alternative site, it is very important to evaluate iliofemoral anatomy. First of all starting from the carotid arteries, subclavian-axillary arteries, aorta and iliofemoral arteries are evaluated with multidetector computed tomography (CT). Minimal lumen diameter is determined. It is very important to evaluate iliofemoral arteries and aortic tortuosity and calcification. Circumferential calcifications, calcification protruding into the vessel lumen and anteriorly located calcifications mostly interfere with femoral access. If problems can be solved, femoral access should be used. Balloon angioplasty and lithotripsy, e.g., can be used to modify calcification and/or stenosis. Such Lunderquist and Back-up Mayer guidewires can be used to handle iliofemoral and aorta tortuosity. The plaques in aortic arch, porcelain aorta and thoracoabdominal aneurysms should be evaluated. After all if femoral access is not suitable, alternative sites should be detected. The most important criterion is operator’s experience.

3.2 Transapical approach

The first transapical TAVR implantation was performed in 2005 [28]. During first years of TAVR, transapical approach was considered as the first alternative if femoral approach were not feasible. Transapical approach is more invasive than other concepts. Only BEVs are suitable for a transapical approach. Compared to the transfemoral approach, the advantages of the transapical approach are that valve alignment is easier, there are no vascular complications, less fluoroscopy time is required, and less contrast is used. Receiving general anesthesia, postoperative pain and bleeding from left ventricle (results in tamponade) are important limitations.

3.3 Transaortic approach

Transaortic approach is a highly invasive procedure compared to other vascular approaches. Transaortic intervention is performed through a right anterior mini-thoracotomy through an incision in the second intercostal space or mini-sternotomy puncture into the ascending aorta. BE and SE valves are suitable for this approach. Major advantages of this concept are less vascular complications, no necessity for left ventricular puncture and good contractility of valve. Major limitations are the need for general anesthesia, previous cardiac surgery (especially beware of left internal mammary artery (LIMA) and bypass grafts) and porcelain aorta. The distance from cannulation to annulus should be ideally 6–8 cm.

3.4 Subclavian/axillary approach

Subclavian/axillary approach is a useful alternative when transfemoral approach is not feasible. The procedure can be performed under general anesthesia or sedation and local anesthesia. Transsubclavian access is mainly via surgical approach but percutaneous access is possible too [29]. Right subclavian/axillary artery is rarely used for TAVR because of anatomical limitations. The main disadvantage of subclavian access is vascular complications. This artery is frailer than femoral artery. Because of subclavian anatomy, a manual compression might not be feasible. In subclavian access, calcification, stenosis, tortuosity, mammarian and vertebral artery relationship and during surgical cut-down brachial plexus should be evaluated carefully. Minimal subclavian artery diameter should be 5.5 cm. If there is a patent LIMA graft, subclavian access is relatively contraindicated [30].

Transaxillary approach was previously performed by surgical cut-down, nowadays this approach is done completely percutaneously. So that makes this approach first choice alternative way when transfemoral access is not feasible. Axillary artery is outside of thorax so manual compression is possible. The most ideal vascular entry point is between the medial of the pectoralis minor muscle and the outer side of the first rib, and puncture can be performed more easily when the arm is opened to the side [31]. Left axillary is generally preferred because of similarity between femoral artery exit angle. The ideal puncture site is the deltopectoral sulcus. Laterally puncture can cause brachial plexus injury, medially puncture can cause hemo−/pneumothorax and difficulty in compression. Major limitations are nearly same as transsubclavian approach but manual compression and completely percutaneous intervention are advantages.

3.5 Transcarotid approach

The first successful transcarotid approach was performed by Modine et al. in 2010 [32]. The procedure can be performed by a surgical cut-down or percutaneously. It is a safe procedure but we need to be aware of some special conditions. Carotid artery system should be carefully examined. Stenosis >50% or atheromatous plaques have higher risks for embolization. Contralateral carotid artery, vertebral arteries and posterior cerebral circulation, status of communicant arteries should be examined. Both carotid arteries can be used but the left carotid approach should be preferred because of its angulation with aorta. While performing the procedure, operators should be aware of vagus nerve, laryngeal nerve and respiratory tract.

One of the most important concerns of this procedure is periprocedural stroke. According to a study, comparing transfemoral approach with transcarotid/transsubclavian TAVR, after propensity-score matching, no significant differences in early and long-term outcomes were observed [33].

3.6 Suprasternal approach

Brachiocephalic artery is a new alternative site for TAVR when transfemoral approach is not feasible. The first suprasternal TAVI procedure was performed in 2015 [34]. This approach does not require sternotomy. Advantage of this access is short distance improving catheter stability. Tortuosity, vessel size, calcification and cervical neck anatomy should be evaluated carefully. Eudailey et al. presented a retrospective study from three centers in the USA of those patients who underwent suprasternal TAVR. A total of 84 patients were included in the study. Thirty-day survival was 98.8% and 0% transischemic attack or stroke was observed [35].

3.7 Transcaval approach

Because of increased stroke risk during carotid and subclavian approach and alternative sites are not feasible, a new intervention site should be searched. After understanding that caval-aortic truck physiology and detection of retroperitoneal pressure are always higher than those of vena cava inferior, in 2014 Greenbaum et al. performed the first transcaval TAVR [36]. This procedure, is extraordinary as it contains coronary, peripheral, congenital techniques and instruments. Before starting the procedure, aorta, vena cava inferior and adjacent structures should be evaluated carefully. The procedure starts with femoral vein puncture. After arriving at the suitable site, an aortacaval fistula is created with chronic total occlusion guidewire (e.g., Conquest or Astato). After passing the aorta valve, the delivery system is advanced via fistula. After the valve is deployed, fistula is closed with an Amplatzer device. In some cases, adjunctive aortic balloon inflations or covered stent implantation might be necessary. Follow-up CT angiography should be obtained at first and twelfth month after the procedure. This procedure is completely percutaneous and can be used when femoral approach is not feasible.

In conclusion, access for TAVR is a crucial step in patient management. Transfemoral approach is the first choice but, if not feasible, alternative access sites should be discussed in a heart team.

4. Techniques of procedure

After vascular access, a venous access (generally femoral vein) is obtained for pacing during procedure. Nowadays, pacing over the wire technique, which consists of left ventricle (LV) stimulation through the stiff guidewire, is being used. Two arterial accesses are obtained. The main site is for the delivery system and second site is for pigtail. Pigtail is used for reference and aortography. For passing through the calcified aortic valve, generally an Amplatz left 1 (AL1) catheter is used with a soft straight guide wire. When AL1 catheter fails, Amplatz left 2 (AL-2), Judkins right 4 (JR-4) or Amplatz right 1 (AR-1) catheters can be tried in accordance with the anatomy of the ascending aorta and aortic annulus. Using the left anterior oblique (LAO) projection can be useful. After passing the valve, the catheter is advanced to the ventricle and a 300 cm J-tip guidewire is exchanged. A pigtail is advanced over this guidewire. J-tip guidewire is changed to a stiffer guidewire while pigtail is in left ventricle. Safari and Confida are first choices but according to tortuosity stiffer wires, such as Amplatz Super Stiff, Lunderquist Extra Stiff or Backup Maier, can be used. Operators should be aware that the stiff side of the wire must be away from ventricle wall and the position of the wire must be maintained during all manipulations. Patients have severe calcifications and for those who can tolerate rapid pacing, predilatation should be performed with a suitable balloon. The balloon size should not exceed minimal annulus diameter. During full balloon inflation, contrast application via a pigtail catheter can help estimate suitable valve size, interaction with coronaries and probable PVL. In case of severe aortic regurgitation and hemodynamic instability, the valve prosthesis should be ready for insertion before the balloon procedure is completed. Next is valve insertion. Platform should advance, beware of aortic wall interaction. Because of high stent frames, future coronary interventions can be challenging in SEV. With the developing technology, commissural alignment can be achieved using different markers [37]. These markers are different for each valve platform. Fluoroscopic imaging should be followed from the groin to the aortic root. In severe tortuosity and calcific anatomy, detachment may occur in the capsule where the valve is loaded. In such a case, a stiffer wire should be used.

The angle in which the aortic cusps are in the same plane on fluoroscopic imaging is called the coplanar angle (golden angle). Nowadays, a new term is created called the ‘Cusp overlap angle’. In this fluoroscopic image, the right and left cusps are superposed and the noncoronary cusp is separated. Compared to other angles, the cusp overlap angle shows more distance between basal annular plane and conduction system. Coplanar angle is the standard plane for many platforms. But SEV platforms use cusp overlap angle because of a high implantation plane for avoiding the need for a permanent pacemaker. According to the noncoronary cusp, >5 mm depth is related to the need for a permanent pacemaker and < 1 mm depth is related to migration. In these situations, SEV platforms allow resheathing.

At the end of the procedure after pulling back the platform, vascular closure is crucial. This is because access site complications are one of the most important mortality and morbidity causes during and postprocedure phase. Dedicated closure devices are used for these issues. But using these devices needs an expert. When closure is done, the patient is taken to the intensive care unit (ICU) for observation.

5. Summary and conclusions

Transcatheter aortic valve replacement (TAVR) is a minimally invasive treatment for those patients with severe aortic stenosis who cannot be treated surgically due to surgical risk. The first human experience was demonstrated in 2002 and after this date, it started to be performed all over the world. As the experience on this subject increases, TAVR has been brought to the agenda in patients with intermediate and low surgical risk, and studies on this subject are continuing. The procedure is generally performed by femoral approach. Different approaches (transapical, transaortic, subclavian/axillary, transcarotid, suprasternal and transcaval) can be used in patients who are not anatomically suitable for the femoral approach. Venous access was also obtained with two arterial access. A temporary pacemaker is placed via the venous route. Main arterial site is for delivery system and second site is for pigtail. Two types of valves can be used in the TAVR process: self-expandable (SE) and balloon-expandable (BE). In this chapter, we discuss valve types, which valve type will be preferred in which patient, the technical parts of different accesses and the specific complications of the procedures, and the points to be considered during the procedure.