Transcatheter aortic valve replacement
Synonyms and keywords: TAVI; Edward's valve; Edward's SAPIEN transcatheter heart valve; CoreValve; percutaneous aortic valve replacement; PAVR; SAVR; Surgical aortic valve replacement

# Overview
TAVI is a safe and effective procedure for the treatment of severe symptomatic AS in all adults regardless of estimated surgical risk.
In patients considering a bioprosthetic AVR, the next step is the choice between SAVR and TAVI. When the surgery is high risk or prohibitive, TAVI or palliative care would be focused. If both SAVR and TAVI are options, TAVI durability and life expectancy should be considered. Data about the durability of SAVR is for more than 50 years, but it limited to 5 years for TAVI. SAVR valve deteriorates typically after >10 years, so longer-term is needed for evaluation of TAVI durability. Earlier RCTs comparing SAVR and TAVI in patients with a higher surgical risk included only older patients, with a mean age in the mid-80s. However, more recent RCTs that included patients at low to intermediate surgical risk had a mean age in the mid-70s. There is no data about the use of TAVI in patients younger than 65 years of age. Some younger patients with comorbid conditions have a limited life expectancy, whereas some older patients have a longer-than-average life expectancy. Comorbid cardiac and noncardiac conditions, frailty, dementia, and other factors that affect longevity or quality of life should be individualized for making decision the type of approach. Mortality rate  in TAVI is lower than SAVR and is associated with a shorter hospital length of stay, more rapid return to normal activities, lower risk of transient or permanent atrial fibrillation, lower risk of stroke, less bleeding, and less pain than SAVR. On the other hand, SAVR is associated with a lower risk of paravalvular leak, less need for valve intervention, and less need for a permanent pacemaker.

# Comparing transcatheter aortic valve replacement (TAVR) and surgical aortic valve replacement (SAVR)
Abbreviations:
MR: Mitral regurgitation;
AVA: Aortic valve area;
LVOT: Left ventricular outflow tract ;
SAVR: Surgical aortic valve replacement;
TAVI: Transcatheter aortic valve implantation;
AF: Atrial fibrillation;
CAD: Coronary artery disease;
AS: Aortic stenosis
Abbreviations:
AV: Aortic valve;
AVA: Aortic valve area;
LVOT: Left ventricular outflow tract ;
SAVR: Surgical aortic valve replacement;
TAVI: Transcatheter aortic valve implantation;
BSA: Body surface area;
CAD: Coronary artery disease
Abbreviations:
SAVR: Surgical aortic valve replacement;
TAVI: Transcutaneous aortic valve implantation;
AS: Aortic stenosis;
LVEF:Left ventricular ejection fraction ;

# Notes
- Outcomes and durability after SAVR were excellent for both mechanical and bioprosthetic valves.
- Earlier RCTs compared SAVR and TAVI in higher surgical risk patients including only older patients, with a mean age in the mid-80s. However, more recent RCTs included patients at low to intermediate surgical risk with a mean age in the mid-70s, but there were very few patients <65 years of age, so the evidence base cannot be extrapolated to these patients.
- Valve durability should be considered in younger patients with longer life expectancy and lower surgical risk. 
- SAVR  is recommended for adults <65 years of age unless life expectancy is limited by comorbid cardiac or noncardiac conditions.
- Patients values and preferences and risks associated with valve intervention should be considered for choosing the approach.
- There are no data for the use of TAVI in patients <65 years of age.
- Both SAVR and TAVI are effective approaches to AVR in adults 65 to 80 years of age.
- Selected patients in TAVI compared SAVR had high-velocity severe AS (Stage D1).
- TAVI  is not encouraged for symptomatic patients with low-flow, low-gradient severe AS (Stages D2 and D3).
- Risk of mortality is slightly lower in TAVI and is associated with a shorter hospital length of stay, more rapid return to normal activities, lower risk of transient or permanent atrial fibrillation, less bleeding, and less pain than SAVR.
- SAVR is associated with a lower risk of paravalvular leak, less need for valve intervention, and less need for a permanent pacemaker.
- Factors related to approach to TAVI or SAVR include vascular access, comorbid cardiac, and noncardiac conditions, functional status and survival after AVR, and patient values and preferences.
- TAVI is a safe and effective procedure for the treatment of severe symptomatic AS in all adults regardless of estimated surgical risk.
- The mortality rate for transfemoral TAVI is lower than that for SAVR
- TAVI also is associated with a lower risk of stroke,  major bleeding, and AF, shorter hospital length of stay, less pain, and more rapid return to normal activities.
- In comparison with SAVR, TAVI results in higher rates of vascular complications, paravalvular regurgitation, permanent pacemaker implantation, and valve intervention.
- Durability of TAVI valves is at least 5 years.
- Valve-in-valve TAVI is a second TAVI within the first prosthesis when significant valve deterioration does occur.
- When a transfemoral approach is not possible, other factors, such as alternative vascular access, comorbid cardiac and noncardiac conditions, expected functional status and survival after AVR, and patient values and preferences, must be considered.
- Choosing a balloon-expandable valve or self-expanding valve depends on patient anatomy and other considerations.
- In patients with LVEF <50%, the choice of TAVI versus SAVR is likely in patients with symptomatic severe AS.
- SAVR is recommended in preference to TAVI in asymptomatic patients with abnormal exercise blood pressure response, an elevated serum BNP level, rapid hemodynamic progression, or very severe AS with a velocity of 5 m/s.
- When transfemoral TAVI is not feasible, SAVR or palliative care are options that should be included in the shared decision-making discussion.
- TAVI was compared with standard medical therapy in severe symptomatic inoperable AS .
- In comparison with medical therapy, TAVI patients demonstrated lower rate of all-cause death and  hospitalization and improvement in NYHA class. However, the rate of major stroke and major vascular complications was higher with TAVI than with standard therapy.
- Factors associated with a poor outcome after TAVI include advanced age, frailty, smoking or chronic obstructive pulmonary disease, pulmonary hypertension, liver disease, prior stroke, anemia, and other systemic conditions.
- Patients with a mechanical impediment to SAVR, such as a porcelain aorta or prior chest radiation damage, may have better outcomes after TAVI than do frail patients or those with moderate to severe disease in more than one other organ system.
- TAVI is not recommended in patients with 1) a life expectancy of <1 year even with a successful procedure or 2) those with a chance of survival with benefit of <25% at 2 years.
- Percutaneous aortic balloon dilation has a limited role in treating older patients. However, the role in treating children, adolescents, and young adults with AS has been shown.
- The mechanism of balloon dilation is a modest reduction in the severity of stenosis in older patients and fracture of calcific deposits within the valve leaflets and, to a minor degree, stretching of the annulus and separation of the calcified or fused commissures.
- Immediate hemodynamic results include a moderate reduction in the transvalvular pressure gradient, but the post-dilation valve area rarely exceeds 1.0 cm2.
- An early symptomatic improvement usually occurs, despite the modest change in valve area. However, serious acute complications, including acute severe AR, restenosis, and clinical deterioration, occur within 6 to 12 months in most patients.
- Therefore, in patients with AS, percutaneous aortic balloon dilation is not a substitute for AVR and can be planned as a bridge to TAVI or SAVR in symptomatic severe AS and refractory pulmonary edema or cardiogenic shock.

# Valve Types
- There are currently 8 prosthetic transcatheter valve types which are available. Two of these are FDA approved in the United States.
- The CHOICE trial is a small study which compared the most prominent two valves (CORE and SAPIEN) and no major significant differences were found in primary clinical endpoints between both valves. Nevertheless, there are situations, anatomical variability, and operator preferences that continue to make one valve more preferable to the other, depending on the situation. There are currently three ongoing major trials comparing newer generation valves to the aforementioned devices.

## Synopsis
TF: Trasfemoral, TA: Transapical
 They claimed that can cover aortic annulus diameters from 21 to 27 mm.

## Description of Valves

### Core Valve
The Core-Valve device was first inserted in 2005.  It consists of three leaflets of bioprosthetic pericardial valve tissue mounted on a self-expendable nitinol stent, which expands from the left ventricular outflow tract (LVOT) to the ascending aorta.  The Core Valve frame is currently available in 3 sizes (23 mm, 26 mm and 29 mm). The multilevel nitinol frame was designed for optimal functionality,stability,and durability.  The inflow portion of the frame exerts high radial expansive force to provide proper support of the frame within the annular location. The design of this portion of the frame with its radial strength prevents annular recoil, allowing the frame to partially conform to the non circular shape of the aortic annulus.  The center portion of the frame has very high hoop strength that resists size and shape deformation which is a very important part of the device since it contains the valve leaflets, which are supra-annular.  This center portion of the frame is concave to allow normal flow of blood through the coronary arteries and coronary cannulation after implantation.  The largest part of the frame is the outflow portion that exerts low radial forces and allow optimal flow of blood through the valve.  For the tissue in the valves, porcine (pig) pericardium was selected due to its lower profile (compared with bovine (cow) pericardium) and its durability. The trileaflet valve is made of six individual pieces of porcine pericardium, with three pieces used to make a skirt at the inflow section of the valve thus preventing aortic regurgitation and three leaflet elements that are constructed with long commissures to distribute the aortic pressure load to the valve leaflets and the commissural posts.

### The Edwards SAPIEN Valves
This prosthesis is considered the second generation of the Cribier-Edwards valve. It is a balloon-expendable valve made of a stainless steel frame covered by a Dacron skirt where three leaflets of pericardium are sutured.  The device is placed in a subcoronary position during rapid ventricular pacing, via anterograde, transapical or a retrograde transfemoral approach. It is available in two sizes (23mm and 26 mm).  In the first generation the leaflets were made of equine (horse) pericardium; in the second generation they are made of bovine (cow) pericardium with  improvements made in the frame suture and an increase in the skirt length to decrease the risk of aortic regurgitation.
The Edwards SAPIEN 3 Transcatheter Heart Valve is comprised of a balloon-expandable, radiopaque, cobalt-chromium frame, trileaflet bovine pericardial tissue valve, and polyethylene terephthalate (PET) fabric skirt. The leaflets are treated according to the Carpentier-Edwards ThermaFix process. It is available in 4 sizes (20mm, 23mm, 26mm and 29mm).
- The Edwards SAPIEN XT
- The Edwards SAPIEN 3

### St. Jude Portico valve
The valve stent is made from nitinol, a nickel-titanium alloy that has self-expanding properties and is radiopaque. The valve cuff is made from porcine pericardium that is sutured to the stent frame. The cuff provides the sealing area for implantation. The valve orifice is made by suturing three valve leaflets, each made from a single layer of bovine pericardium, into a tri-leaflet configuration on the stent frame. It is available in 4 sizes (23mm, 25mm, 27mm and 29mm).

### Direct Flow Medical valve
It features a metal-free frame. The Direct Flow Medical System incorporates a polymer frame, which is expanded using pressurized saline and contrast for placement, assessment and repositioning. The saline/contrast solution is exchanged for a quick-curing polymer that solidifies and secures the valve in place once optimal positioning is reached. It is available in 4 sizes(23 mm, 25 mm, 27 mm, 29 mm).

### Symetis Acurate neo valve
Acurate neo is composed of a porcine pericardial tissue valve sutured within a self-expanding nitinol stent covered by a pericardial skirt on the outer and inner surface of the stent body.It is a nitinol-based valve that incorporate features that facilitate positioning and anatomic orientation in relation to the native valve commissures and coronaries. The valve is currently implanted only transapically.
It is available in three sizes (S, M, L) and its delivery system boasts an 18F outer diameter and it cover the aortic annulus diameters from 21 to 27 mm.

### Medtronic Engager valve
It has a self expanding nitinol frame and polyester skirt and bovine pericardial tissue. It is available in 2 sizes(23 mm, 26 mm)

### Lotus edge valve
Lotus valve consisting of a pre-attached, stent-mounted tissue valve prosthesis and catheter delivery system for guidance and percutaneous placement of the valve. It is the first device of its kind that offers controlled mechanical expansion, which allows the valve to be fully deployed, assessed and then released, providing unparalleled control during the procedure. It is available in 3 sizes (23 mm, 25 mm and 27 mm).

### Jena valve
The transapical JenaValve prosthesis consists of a natural aortic porcine root bioprosthesis fitted with an outer porcine pericardial patch, a so-called skirt. The JenaValve is available in 3 sizes, 23mm, 25mm and 27mm. It is not commercially available now and is waiting for approval.

# Valve Sizing and Positioning
Valve sizing and positioning is of utmost importance in the success of the TAVR procedure and the risk of paraprocedural compications. The utilization of 2D echocardiography was initially used to estimate the annulus size. Currently, the gold standard for estimating the size of the aortic outlet is CT angiography focussing on the area of the valve or the perimeter of the annulus to estimate the required device size. Furthermore, the positioning of the valve must be estimated by an experienced operator as every valve type presents advantages and disadvantages according to the variability in the anatomy. Examining the left ventricular outflow tract, the origin of the coronary arteries, and the sinotubular junction constitute some of the considerations the operator must entertain. Additionally, the positioning of the aorta and the degree of calcification of the valve and the proximal aorta must be assessed in planning a successful procedure.

# Contraindications
General contraindications for transcatheter aortic valve implant (TAVI) through every approach include:
- Aortic annulus size 25 mm for balloon expandable devices and 27 mm for self expandable devices.
- Severe mitral regurgitation.
- Presence of apical left ventricle thrombus.
- Aortic root  dimension > 45 mm at the sino-tubular junction for self-expandable prostheses.
- Low position of the coronary ostia (<8 mm from the aortic annulus)
- Asymmetric heavy valvular calcification which may compress the coronary arteries during the procedure of TAVI.
- Bicuspid aortic valves - because of the risk of incomplete placement of the prosthesis
- Intracardiac mass, thrombosis, vegetation
- Severe aortic regurgitation
- Serum creatinine >3.0 mg/dL or patient on dialysis
- Left ventricular ejection fraction <20%
- Untreated coronary heart disease requiring revascularization
- Hemodynamic instability
- Upper gastrointestinal bleed within the past 3 months
- Cerebrovascular accident (CVA) or transient ischemic attack (TIA) within the last 6 months
- Aortic aneurysm or severe ilio-femoral insufficiency disease
- Hypertrophic cardiomyopathy
- Bleeding disorders
- Active infective endocarditis
- Life expectancy < 1 year
- Comorbidities suggesting no improvement of quality of life after procedure
The transfemoral approach has a few specific contraindications which include:
- Severe tortuosity, calcification and narrowing of the iliac arteries
- Previous aorta-femoral bypass
- Abdominal aortic aneurysm
- Severe angulation of the aorta
- Severe atherosclerosis of the ascending aorta and arch of the aorta.
Contraindications for transapical approach include:
- Previous surgery to the heart
- Severe respiratory insufficiency
- Chest deformity

# Procedure
The diseased valve is first moved aside by aortic balloon valvuloplasty.  The Corevalve prosthesis, which is loaded on a specialized delivery catheter, is advanced to the stenosed aortic valve.  Once correctly positioned, the external part of the delivery system (the sheath) is progressively retracted, deploying  the Corevalve Prosthesis. The delivery catheter is then closed and retrieved.

## Techniques
Two major catheter based techniques for replacing the aortic valve have been investigated:
retrograde percutaneous implantation and direct apical puncture. An antegrade transseptal approach has also been studied but not fully adopted.

### Retrograde Approach
After a routine aortic balloon valvuloplasty, a 22F or 24F sheath is advanced from the femoral artery to the aorta. The manipulation of the prosthesis around the aortic arch and through the stenotic valve is facilitated by a steerable, deflectable catheter. Rapid ventricular pacing is used to decrease cardiac output while the delivery balloon is inflated to deploy the prosthesis within the annulus.

### Transapical Antegrade Approach
An alternate catheter based method consists of a direct left ventricular apical puncture and antegrade aortic valve implantation via a small anterolateral thoracotomy without the need of cardiopulmonary bypass or sternotomy. This technique is used in patients with severe peripheral arterial disease and heavily calcified ascending aorta and arch (porcelain aorta) who have an increased risk of stroke and other embolic events using other approaches.

### Alternative Vascular Access
In some patients, the peripheral vascular anatomy is unsuitable for a transfemoral approach; for such reason a number of other vascular access have been suggested. The Subclavian (ie,axillary) or Transaortic access may be useful in solving such problems. In a series of 54 cases treated via the Subclavian approach in the Italian National Registry, procedural success was achieved in 100% of cases. No specific complications such as vessel rupture or vertebral or internal mammary ischemia associated with Subclavian access were found. No deaths at 30 days in this series, and the 6-month mortality rate was 9.4% and was no different from those who underwent a transfemoral approach.

# Complications

## Mortality
The 30-day all-cause mortality has been estimated at 2.2%.

## Strokes and Transient Ischemic Attacks
The etiology of cerebrovascular events after TAVI is thought to be related to the embolization of atherothrombotic material during advancement of the device to and across the aortic valve. Magnetic resonance imaging have shown that microembolization is common with both balloon-expandable and self-expanding percutaneous valves, as well with surgical aortic valve repair (SAVR), but the presence of clinical strokes are infrequent (2.9%-5.1%)
Silent strokes detected by MRI has been estimated at 76%.

## Aortic Regurgitation
Significant aortic regurgitation caused by paravalvular leak after CoreValve percutaneous implantation is usually an uncommon complication  that relates more frequently to low positioning of the CoreValve frame, incomplete expansion of the frame into the eccentrically shaped annulus, rigidity of the underlying aortic annulus due to calcium, or undersizing of the valve relative to the aortic annular size.

## Vascular Access Complications
The relatively large-caliber sheath (18F) required for placement of the percutaneous  valve  may be the cause of various vascular complications. One of the most common vascular events encountered are incomplete arteriotomy closure. Avoiding such complications is possible; preprocedural screening using computed tomographic angiography, vascular ultrasound guidance for arterial access, and alternative (eg, subclavian) access have allowed better selection to avoid those vascular complications.

## Coronary Artery Occlusion
Coronary occlusion after TAVI is usually rare but may occur in some cases due to expansion of the native aortic valve across the orifice of the coronary ostium. This complication can be prevented with careful preprocedural screening to ensure adequate sinus of valsava width (30 mm) and height (15 mm).

## Conduction Abnormalities
Worsening or new conduction abnormalities are frequently observed with TAVI; more often when self-expandable CoreValve device is used. Conduction abnormalities may be due to compression of superficially running left bundle branch (in the uppermost part of ventricular septum) by the lower one third of prosthesis which exerts radial forces for secure anchoring of the stent against the native annulus and outflow septum. Hence, deeper the implantation of the prosthesis into the left ventricular outflow tract, greater is the risk of development of severe conduction defect requiring pacemaker implantation.
A study in Italy reported that 77% of the patients post TAVI developed new onset or worsening of per-existing conduction abnormalities. 44% of the patients developed left bundle branch block (LBBB) and subsequently 39% of the patients underwent implantation of pacemaker. After TAVI, 6 (75%) of 8 patients with right bundle branch block (RBBB) at baseline required pacemaker implantation versus 19 (34%) of 56 patients, who had not had RBBB before TAVI. It was concluded that the RBBB was the only baseline conduction abnormality that significantly affected the occurrence of pacemaker implantation after TAVI because if patients already have a right bundle branch block, then a procedure-induced left bundle branch block will result in a complete atrioventricular block requiring a pacemaker.
Other CoreValve implantation complications are:
- QRS duration: In one observational study of 270 patients, the QRS duration increased from 10523 milliseconds at baseline to 13529 milliseconds following TAVI. (P<0.01).
- Left Bundle Branch Block (LBBB): The incidence of left bundle-branch block increased from 13% at baseline to 61% following TAVI (P<0.001).
- Permanent pacemaker implantation: Approximately one third of patients will require a permanent pacemaker be implanted by 30 days with a median time to insertion of 4 days (interquartile range, 2.0 to 7.75 days).
- Multivariate predictors of permanent pacemaker implantation included:
- Periprocedural atrioventricular block (odds ratio, 6.29; 95% confidence interval, 3.55 to 11.15)
- Balloon pre-dilatation (odds ratio, 2.68; 95% confidence interval, 2.00 to 3.47)
- Use of a larger 29 mm CoreValve prosthesis (odds ratio, 2.50; 95% confidence interval, 1.22 to 5.11)
- The interventricular septum diameter (odds ratio, 1.18; 95% confidence interval, 1.10 to 3.06)
- A prolonged QRS duration (odds ratio, 3.45; 95% confidence interval, 1.61 to 7.40)