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Publication:

Surgical Technology International XV - Cardiovascular Surgery

Article title:

Advanced Technologies for Cardiac Valvular Replacement, Transcatheter Innovations and Reconstructive Surgery

Contents:

 

 

 

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1. Article Information, Introduction, Background

2. Current Bioprostheses

3. Mechanical Prostheses

4. Transcatheter Heart Valve Therapies, Aortic Valve Replacement

5. Mitral Valve Reconstruction

6. Annuloplasty Prostheses For Valvular Reconstructive Surgery

7. Technological Advances, Clinical Performance, Summary of Experience

8. Indications for Prostheses Choice, Conclusion

9. References

 

 

Transcatheter Heart Valve Therapies

 

 

Severe aortic and mitral valve disease has been in the therapeutic domain of cardiac surgery. The only significant exceptions have been balloon dilation of congenital aortic or pulmonary stenosis, and percutaneous balloon mitral valvuloplasty of rheumatic mitral stenosis (Fig. 61). Balloon aortic valvuloplasty was evaluated 20 years ago and was determined to be less effective than aortic valve replacement. The procedure is currently reserved for palliative care in non-surgical patients, or as a bridge to surgery in hemodynamically unstable patients.
Currently, there exists an emergence of catheter-based therapies for management of aortic stenosis and mitral regurgitation(Table III).4 A decade of experience comes from Great Ormond Street Hospital for Children–London with implantation of percutaneous stented bovine jugular valves in the pulmonary position.
There exists a considerable population with critical aortic stenosis who are very high operative risk or considered inoperable due to co-morbid disease. Also, a considerable population who have lesser degrees of mitral regurgitation in terms of congestive heart failure (NYHA functional class I-II) are considered candidates for mitral valve surgery—repair in preference to mitral valve replacement. There also is an opinion that quality of life could be enhanced substantially for aortic valve disease and quality and quantity of life for mitral valve disease. The devices in development are investigational, but are deemed promising. The regulatory and clinical trial strategies are under consideration. The major valve manufacturers are all in the process of bringing forward transcatheter devices for investigational evaluation, which provide extensive consideration to this area of endeavour or have devices in development yet to be introduced (ie, The Sorin Group; St Jude Medical Inc.).

 

Aortic Valve Replacement

The Edwards Lifesciences percutaneous aortic heart valve (Edwards Lifesciences, Irvine, CA, USA) is the Cribier-Edwards percutaneous aortic bioprosthesis. The prosthesis is an equine pericardium tricuspid valve mounted on a stainless steel stent (Figs. 62a & 62b). The original 23-mm prosthesis is crimped with the crimper device and advanced following a 22-mm Numed balloon catheter compatible with a 24F sheath. The device can be advanced retrogradely from the femoral vein with a transseptal approach across the mitral valve to the left ventricle or antegradely from the femoral/iliac or subclavian artery to the ascending aorta. The positioning and delivery are supported by angiography and echocardiography and a short interval of rapid pacing at 220 bpm to produce transient blood-flow reduction. The postoperative gradients and aortic valve areas of this investigational prosthesis in high-risk/non-operative patient candidates have been reported by Dr. Alain Cribier (Paris), and Dr. John Webb (Vancouver). The Paris series was conducted with 23-mm prostheses, whereas the Vancouver series was conducted with 26-mm prostheses. The first human implant was performed in Paris in April of 2002 in a feasibility study of compassionate patients. The potential complications are paravalvular leak following native calcific valve dilatation and prosthesis placement, cerebrovascular accident, and cardiac tamponade.

The CoreValve percutaneous pericardial aortic valve (CoreValve, Irvine, CA, USA) is a bovine pericardial valve mounted on a self-expanding nitinol stent (Fig. 63). The prosthesis is implanted via the retrograde approach. The prosthetic frame (stent) is manufactured by laser cutting of a nitinol metal tube with a length of 50 mm. The lower part has a high radial force to push aside the calcified leaflets and avoid recoil, the middle part is constrained to avoid coronaries and carries the valve, whereas the upper part expands for fixation in the ascending aorta and exits the system. The actual valve inner diameter is 21 mm to 22 mm. The valve is delivered via a 25F catheter, which houses the stent in the distal part. The stent deployment is retrograde via a surgical cut-down of the common iliac artery. The procedure is performed currently under general anaesthesia with transesophageal echocardiography (TEE) guidance and femoral-femoral partial cardiopulmonary bypass.

Medtronic Melody transcatheter pulmonary valve (Medtronic Inc., Minneapolis, MN, USA), originally developed by Bonhoeffer and colleagues, is a bovine jugular valve mounted within a platinum stent. The bioprosthesis is delivered via the femoral vein and deployed in the pulmonary outflow tract (Fig. 64). The experience over the past five years now numbers 100 cases at Great Ormond Street Hospital for Children in London and is slated for multi-centre trials within North America in 2006. The device can be deployed either in the native or prosthetic pulmonary outflow tract.
The ENABLE™ Aortic Bioprosthesis (3F Therapeutics, Lake Forest, CA, USA) consists of a 3F Aortic Bioprosthesis, Model 1000, that has been mounted into a self-expandable frame made from Nitinol temperature memory alloy (Fig. 65). It is malleable at 0°C to 5°C, which allows easy contraction of the diameter for quick insertion into the aortic root orifice that remains after resection of the diseased aortic valve on cardiopulmonary bypass. Above 20°C, the frame or stent expands to the given diameter of the valve size, the radial force being sufficient to maintain the position of the valve. Deployment times are less than 3 minutes, with the attendant decrease in ischemic and cardiopulmonary bypass times.

The ENTRATA™ transventricular aortic bioprosthesis (3F Therapeutics, Lake Forest, CA, USA) consists of a tubular structure assembled from three equal sections of equine pericardial material preserved in glutaraldehyde (Fig. 66). The structure incorporates commissural tabs made from sections of pericardium anchored to the posts of the stent. The stent is manufactured from SMLS 316L vacuum melted extruded stainless steel tubing. Annealing of this stent allows compression and subsequent dilatation when within the aortic root. The aortic valve is dilated by way of the apical transventricular delivery system. The bioprosthesis is delivered antegradely through the apical transventricular catheter system into the ventriculo-aortic junction. The bioprosthetic valve is formulated in sizes 19 mm to 29 mm in increments of 2-mm diameters.
The Edwards Ascendra™ valve replacement system (Edwards Lifesciences, Irvine, CA, USA) is a transapical placement (TAP) of a stented equine pericardial bioprosthesis preserved in glutaraldehyde. (Cribier-Edwards aortic bioprosthesis(Figs 62a & 62b).

The Sadra Percutaneous pericardial aortic valve (Sadra Medical, Campbell, CA, USA) is a self-expanding pericardial bioprosthesis on a nitinol stent. The prosthesis is designed for retrograde implantation and can be repositioned, as indicated. The bioprosthesis has an outer dynamic seal to prevent periprosthetic leak.

Prostheses based on nanotechnology are in the investigational stage. The AorTx (AorTx, Palo Alto, CA, USA) concept is one of these for percutaneous aortic valve replacement (Fig. 67). Another of these is the Palmaz-Bailey prosthesis composed completely of nitinol. These nitinol leaflets have the capacity for endothelial overgrowth.

The Corazón PAVR system (Corazón Technologies, Menlo Park, CA, USA) is designed for isolated demineralization of the aortic valve. The process incorporates gentle mechanical agitation and demineralization lavage at a low pH with hydrochloric acid and controlled pathways for simultaneous lavage of the aortic valve, solution neutralization, and aspiration. The percutaneous device consists of a flexible, multi-lumen catheter for percutaneous navigation, soft tip for placement into the left ventricle (LV), and a balloon for occluding the LV outflow tract below the aortic valve, an expandable central lumen with temporary aortic valve to enable beating heart aortic valve treatment, and aortic isolation of treatment using a compliant bell designed to conform to the shape of the aortic valve cusps.

The Corazón Surgical Aortic Valve Repair (SAVR) System (Corazón Technologies, Menlo Park, CA, USA) is designed for an open procedure. The system is similar to the percutaneous device with addition of a soft-tip catheter for LV venting; three foam elements to fit the aortic sinuses and contain the treatment solution in the aortic root; small pulsatile balloon for agitation of the solution; vacuum-activated coronary ostial occluder caps and locking cap to compress foam elements into the aortic root, which controls delivery, aspiration, and buffering of the lavage solutions (Fig. 68).