What Are Possible Risks of a Bioprosthetic Valve?

Prosthetic heart valve is an interventional medical device for heart valve disease or defect [1]. The artificial heart was first applied to the clinic in 1960 [2], and then went through stages such as mechanical valves, biological tissue valves, and interventional valves, and has become a very important medical device in the field of cardiovascular therapy.

Chinese name: Artificial heart valve
Applied clinical time: 1960

Application area: Cardiovascular field
Category: medical instruments

[1,3] Development history of artificial heart valves [1,3]

1.1 Prosthetic heart valve 1.1 mechanical valve

Since its birth, mechanical flaps have undergone three major categories: ball cage flaps, cage disc flaps, oblique disc flaps, and bilobular flaps.

Ball cage petals and cage disc petals:

The typical ball cage flaps are Starr-Edwards flap, Smeloff-Cutter flap and Magovern flap. This mechanical valve uses a smaller ball cage to limit the position of the sphere's equatorial line in the suture ring. There is a small gap on the outer edge of the sphere to allow the sphere to pass through the valve hole. This tiny void can also cause a tiny reflux, which may play a role in inhibiting thrombosis. Ball cage flaps have a large volume, which limits their use to a certain extent. As a result, more compact cage disc petals came into being. The representative cage discs are Kay-Shiley and Beall. Mainly used for mitral valve replacement surgery. However, due to the poor hemodynamic characteristics of cage discs, they have been rarely used.

Oblique disc petals:

The emergence of Bjork-Shiley and Lillehei-Kaster oblique disc valves has become an important event in the history of mechanical valve development. Both heart valves use "living" floating disks. When the valve is opened, the disk is tilted to a pre-set angle under the constraints of the stent. Both mechanical flaps achieve a good fit of the disc and the circumference of the blood flow inlet in the closed state, with almost no overlap. Therefore, mechanical damage to red blood cells is reduced. A small amount of blood backflow during use can have a "scouring" effect on residual blood and platelets, which can theoretically reduce the incidence of thrombosis. Although the later emergence of the Medtronic Hall valve further improved its performance, the hemodynamic characteristics were significantly better than those of the ball cage and cage discs.

Double leaflet:

The double leaflet valve is the latest mechanical valve design, which is mainly based on the double leaflet full PYC valve developed by St. Jude Medical, Inc in 1978. The bilobal valve has two leaves. The leaflets open reasonably, the opening area is large, and the central blood flow pattern is the most widely used mechanical valve. Due to the different designs of different companies, the material selection and structural design of the double leaflet are slightly different. Some are metal valve rings with pyrolytic carbon leaflets, some ring petals are all pyrolytic carbon coating, and some are ring petals. The leaves are fully pyrolytic carbon, and some are leaflets are tungsten-containing pyrolytic carbon. Representative bilobal valves include St. Jude valve, CrboMedics valve, Sorin Bicarbon valve, ATS Open Pivot valve, On-X valve, etc.

1.2 Prosthetic heart valve 1.2 biological tissue valve

Biological tissue flaps are divided into two types: the same kind of biological flaps and the heterogeneous biological flaps. Biological tissue flaps usually have good biocompatibility and hemodynamic properties, and are widely used in clinical practice.

The first allograft operation was completed by Ross in 1962, with good clinical results. The whole-body biological valve transplantation can use the valve of the patient's other parts (such as the pulmonary valve to the aorta), or it can use other tissues of its own (such as the broad fascia removed from the body).

Xenograft heart valves are mostly removed from bovine pericardium or porcine pericardium tissue. Chemical treatment can prevent allogeneic rejection and increase tissue strength. With the continuous improvement of treatment technology, fixation technology and anti-calcification treatment technology, xenograft valves continue to emerge [5,6]. The representative are: Hancock porcine xenograft biological flap and Carpentier-Edwards biological flap.

1.3 Prosthetic Heart Valve 1.3 Interventional Valve

Interventional valve, also called stent valve, is a minimally invasive interventional heart valve with the rapid development of interventional cardiology. Compared to surgery, interventional therapy has minimal trauma to the human body, rapid recovery after surgery, no scarring, and no labor damage, which relieves the suffering of many patients. In the 1990s, people tried to apply catheterization to valve replacement. Especially in 2000, Bonhoeffer et al. First reported the clinical application of successful pulmonary valve replacement with a valve stent; in 2002, Cribier et al The first case of human percutaneous aortic valve replacement was reported. The emergence of transcatheter valve interventional therapy has created a new era of transcatheter valve replacement and achieved satisfactory clinical results [7,8].

2. [3] Artificial heart valves 2. Artificial heart valves currently in use [3]

Currently, more than 180,000 artificial heart valves are implanted into patients around the world every year. The stents currently used in clinic are mainly divided into 5 basic categories:

Ball cage flap
Oblique disc flap
Double leaflet
Bioprosthetic valve
Stentless biological valve

Heart valve manufacturers are constantly designing new mechanical and tissue valves. But the "ideal" heart valve has not yet appeared, and it will not be possible in the future. It is generally believed that "ideal" heart valves should have the following characteristics:

Non-toxic, completely sterile when implanted
Easy surgical placement into the normal position of the heart
Adapt to the structure of the heart, rather than the structure of the heart to adapt the valve (eg, the size and shape of the artificial heart valve cannot interfere with the normal function of the heart)
Minimal blood flow resistance, avoiding a significant pressure drop after blood flow
Under the premise of ensuring that the heart valve is closed and preventing valve insufficiency, the reflux effect is minimal
Resistant to mechanical and structural damage
Keep functioning for a long time (25 years) (eg: it cannot deteriorate over time)
Minimal damage to blood components and epithelial tissue around valves in the cardiovascular system
Thromboembolic syndrome is unlikely to occur without the use of anticoagulants
Quiet and low noise at work without disturbing patients
Visibility under radiation
Reasonable price

Considering specific valve tissue characteristics, the heart valve design needs to consider the following three engineering issues:

Hydrodynamic characteristics
Durability (Structural Mechanics and Materials Science)
Human biological response to implants

3.[3] Prosthetic heart valve 3.The development trend of current valve design [3]

Initially, the hemodynamic properties of the prosthetic heart valve were the primary concern of the designer. Later, the clinical appearance of porcine pericardial flaps solved this problem, and its hemodynamic characteristics were equal to or better than some mechanical flaps. At present, the long-term durability data of heart valves have been accumulated in the clinic, and it has been found that the long-term clinical durability of biological valves has become the biggest obstacle to its clinical application. For biological heart valves derived from pigs and cattle, the stress concentration can be reduced through the innovative support bracket design, as well as improved fixation and installation methods, and the introduction of more flexible tissue materials.

If the aforementioned challenges in the design can be solved, then the bioprosthesis will be able to have both good durability and antithrombotic ability (which is why patients no longer need antithrombotic treatment), which will inevitably bring the bioprosthesis Clinical use of counterattack.

Interventional heart valves are widely accepted by doctors and patients because of their minimally invasive implantation methods that reduce the risk of surgery. Interventional heart valve technology has been used not only for the treatment of critically ill patients, but also as an alternative to surgical treatment for the treatment of ordinary patients. In order to better achieve this goal, people have begun to pay attention to some shortcomings and deficiencies of the interventional valve itself, such as valve leakage and image guidance during implantation.

4.[3] Prosthetic heart valve 4. Summary [3]

It is very difficult, if not impossible, to compare the "comprehensive" characteristics and performance of different artificial heart valves. Different studies have different evaluation criteria for artificial heart valves. If long-term characteristics of artificial heart valves are to be studied, long-term observations of large sample patients are also needed. At the current stage, we need to improve and innovate in many aspects such as heart valve materials, design, and treatment methods. The age of patients with heart valve implants and people with potential heart valve disease is a very important data for the estimation of valve selection and service life. Prosthetic heart valves suitable for aortic valve replacement may not be suitable for mitral valve replacement. Therefore, it is impossible to determine a standard to determine which design is the "best" prosthetic heart valve. Artificial heart valves currently in use, whether mechanical or biological, produce relatively large turbulent stresses (which can cause fatal or semi-lethal damage to red blood cells and platelets) and greater pressure gradients and countercurrents than normal heart valves volume.

Therefore, we can summarize three possible development directions of artificial heart valves (also the three challenges for artificial heart valve design):

Improve the antithrombotic ability of new artificial materials.
Improve the durability of new biological tissue flaps. This can be achieved through the use of stent-free tissue flaps, new anticalcification treatments, better fixation techniques, and more.
Improve the blood flow characteristics of heart valves. In particular, reduce or eliminate areas of low shear force on the surface of the valve and blood vessels, as well as peripheral high turbulent shear forces caused by the jet at the valve exit or side leak.

Although there is still much room for improvement in the existing artificial heart valves. However, for the majority of patients, more advanced and advanced artificial heart valves are still worth looking forward to in the near future.

: Prosthetic heart valve references:

1. Cui Kai, Zhang Zhengcai, Han Qiaohui. Status and development of artificial heart valves. New Materials Industry. 2009, 5: 39-42.

2.Turpie AG, Gent M, Laupacis A, Latour Y, Gunstensen J, Basile F, Klimek M, Hirsh J. A comparison of aspirin with placebo in patients treated with warfarin after heart-valve replacement. N Engl J Med. 1993.19; 329 (8): 524-9.

3. Krishnan B. Chandran, Stanley E. Rittgers, Ajit P. Yoganathan. Biofluid mechanics- the human circulation. (2rd edition) CRC Press 2012

4. Izzat MB, Birdi I, Wilde P, Bryan AJ, Angelini GD. Comparison of hemodynamic performances of St. Jude Medical and CarboMedics 21 mm aortic prostheses by means of dobutamine stress echocardiography. J Thorac Cardiovasc Surg. 1996; 111 (2) : 408-15.

5. Golomb G, Schoen FJ, Smith MS, Linden J, Dixon M, Levy RJ. The role of glutaraldehyde-induced cross-links in calcification of bovine pericardium used in cardiac valve bioprostheses. Am J Pathol. 1987; 127 (1) : 122-30.

6. Chambers J, Coppack F, Deverall P, Jackson G, Sowton E. The continuity equation tested in a bileaflet aortic prosthesis. Int J Cardiol. 1991; 31 (2): 149-54.

7. Bleiziffer, S., Ruge, H., Mazzitelli, D., Schreiber, C., Hutter, A., Laborde, J. c., Bauemschmitt, R., and Lange, R. (2009) Results of percutaneous and transapical transcatheter aortic valve implantation performed by a surgical team. Eur. J. Cardiothorac. Surg. 35 (4): 615-620.

8. Webb, JG, Altwegg, L., Boone, RH, Cheung, A., Ye, J., Lichtenstein, S., Lee, M., Masson, JB, Thompson, C., Moss, R., Carere , R., Munt, B., Niet1ispach, F., and Humphries, K. (2009) Transcatheter aortic valve implantation: Impact on clinical and valve-related outcomes. Circulation 119 (23): 3009-3016.