Transcatheter aortic valve replacement

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Editors-in-Chief: Roger Laham, M.D., C. Michael Gibson, M.S., M.D.; Jeffrey J. Popma, M.D.

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Synonyms and keywords: TAVI, Edward's valve, Edward's SAPIEN transcatheter heart valve, CoreValve, percutaneous aortic valve replacement, PAVR

Overview

Untill recently, aortic valve replacement (AVR) was the only effective treatment to severe symptomatic aortic stenosis. However, over the past decade percutaneous treatment of aortic valve disease with implantation of a stent-based valve prosthesis has been introduced as a new treatment in patients considered inoperable because of severe co-morbidities. In Transcatheter Aortic Valve Implantation (TAVI) also known as Percutaneous Aortic Valve Replacement (PAVR), a synthetic valve is transported to the heart through a small hole made in groin. This procedure can be compared to that performed when placing a stent, or performing balloon angioplasty. Traditional aortic valve replacement is an invasive surgical procedure, with considerable mortality and morbidity, especially in more fragile patients. In the newly developed TAVI procedure, the dysfunctional aortic valve is replaced percutaneously, which removes the need for open heart surgery.

Valve types

CoreValve

The CoreValve device was first inserted in 2005.It consists of three leaflets of bioprosthetic pericardial tissue valve mounted on a self-expendable nitinol stent, which expands from the left ventricular outflow tract (LVOT) to the ascending aorta. The CoreValve frame is currently available in two sizes;a 26-mm design for aortic annular sizes between 20 and 23 mm and a 29-mm design for aortic annular sizes between 23 and 27-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 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 coronaries 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. Porcine pericardium was selected due to its lower profile(compared with bovine 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 valve

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 retrograde transfemoral approach. It is available in two sizes(23mm and 26 mm). In the first generation the leaflets were made of equine pericardium; in the second generation they are made of bovine pericardium with big improvements in the frame suture and an increase in the skirt length to decrease the risk of aortic regurgitation

Procedure

The diseased valve is moved aside by Aortic balloon valvuloplasty, than the Corevalve prosthesis is loaded in a specialized delivery catheter and advanced to the stenosed aortic valve. Once correctly positioned, the external part of the delivery system is progressively retracted, deploying the Corevalve Prosthesis. The delivery catheter is then closed and retrieved. <youtube v=7EhoUbWHW2A/>

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.

Complications

Following CoreValve implantation:

• QRS duration: In one observational study of 270 patients, the QRS duration increased from 105±23 milliseconds at baseline to 135±29 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:

1. Periprocedural atrioventricular block (odds ratio, 6.29; 95% confidence interval, 3.55 to 11.15)
2. Balloon pre-dilatation (odds ratio, 2.68; 95% confidence interval, 2.00 to 3.47)
3. Use of a larger 29 mm CoreValve prosthesis (odds ratio, 2.50; 95% confidence interval, 1.22 to 5.11)
4. The interventricular septum diameter (odds ratio, 1.18; 95% confidence interval, 1.10 to 3.06)
5. A prolonged QRS duration (odds ratio, 3.45; 95% confidence interval, 1.61 to 7.40)