The choice of valve prosthesis for patients requires an in-depth discussion of the risks and benefits of the different heart valves available today, and this choice is no longer limited to surgically implanted valves. Transcatheter aortic valve replacement (TAVR) has emerged as a reasonable alternative to surgical aortic valve replacement (AVR) in patients with severe aortic stenosis who are at high and intermediate surgical risk, and myriad transcatheter mitral valve replacement (MVR) devices are under investigation.^1-4 With new surgical innovation, advances in device technology, and evolving guidelines, patients and surgeons will have to choose among biologic, mechanical, and transcatheter biologic valves.

Among surgical valves, there are mechanical and biologic valve prostheses. Mechanical valve prostheses have evolved from the original ball-in-valve and tilting disk designs to the current generation of bileaflet valves constructed from pyrolytic carbon with excellent long-term durability. Given the risk for thromboembolic complications, these valves require lifelong anticoagulation with the associated risk of bleeding. Biologic valves do not require anticoagulation but are at risk for structural valve deterioration, which increases the risk for reoperation. Current options for biologic valve prostheses include homografts and xenografts (porcine, bovine pericardial, and equine). Xenograft valves can be further grouped into stented and stentless designs. Stentless valves have improved hemodynamic profiles, but they have not been shown to confer long-term survival benefits or improved durability over stented valves.⁵ New sutureless biologic valves allow for rapid deployment without the need for fixation of a sewing cuff.

The two most widely studied transcatheter valves utilize either bovine pericardium mounted on a balloon expandable stainless steel stent (Edwards SAPIEN valve [Edwards Lifesciences; Irvine, CA]) or porcine pericardium anchored onto a self-expanding Nitinol frame (Medtronic CoreValve [Medtronic, Dublin, Ireland]). Data regarding the intermediate-term outcomes of transcatheter valves have recently emerged, with the 5-year follow-up results of the PARTNER 1 (Placement of Aortic Transcatheter Valve) trial showing no difference in mortality among high-risk surgical patients receiving TAVR versus surgical AVR.⁶ Some concerns about TAVR resulting from these randomized control trials include higher rates of paravalvular aortic regurgitation noted in TAVR recipients at 5 years and higher rates of permanent pacemaker implantation in those receiving self-expanding TAVR.³ Currently, no data are available regarding long-term durability of these biologic devices, and this will be followed with much interest and scrutiny as more data become available.

Between 1998 and 2017, the American College of Cardiology and American Heart Association guidelines for valvular heart disease have continuously reduced the age after which implantation of a biologic prosthesis is acceptable. The lower limit was 65 years of age in 2006. In 2014, the guideline was updated to state that either a biologic or mechanical valve was acceptable starting at age 60. Current 2017 American College of Cardiology and American Heart Association guidelines recommend mechanical prosthesis for patients younger than 50 years of age, biologic prosthesis for patients older than 70 years of age, and either mechanical or biologic prostheses for patients between 50 and 70 years of age (Class IIa recommendation). These guidelines also do not distinguish between the aortic or mitral valve position.⁷

The appropriate type of prosthesis for patients between 50 and 70 years of age remains uncertain because the data on long-term survival have been equivocal.^8,9 The European Society of Cardiology and the European Association for Cardiothoracic Surgery continue to recommend age cutoffs for mechanical prosthesis that vary by valve location. Mechanical prostheses are recommended for patients younger than 60 years of age in the aortic position and younger than 65 years of age in the mitral position (Class IIa recommendation).¹⁰

We recently published in The New England Journal of Medicine a retrospective cohort study comparing the long-term mortality between patients who underwent AVR or MVR with a mechanical or biologic prosthesis between 1996 and 2013.¹¹ Our study used data from 142 non-federal cardiac surgery centers in the state of California and included 9,942 patients undergoing isolated AVR and 15,503 patients undergoing MVR.

Notably, the use of biologic valve prostheses increased dramatically, from 11.5 to 51.6% for aortic valves and from 16.8 to 53.7% for mitral valves. In our analysis, patients 45-54 years of age receiving a biologic prosthesis for AVR had significantly higher 15-year mortality when compared with those who received a mechanical prosthesis (30.6 vs. 26.4%, p = 0.03). Similarly, younger patients receiving a biologic prosthesis for MVR had significantly higher 15-year mortality when compared with those who received a mechanical prosthesis (40-49 years of age, 44.1 vs. 27.1%, p < 0.001; 50-69 years of age, 50.0 vs. 45.3%, p = 0.01). Furthermore, the incidence of reoperation was higher among those who received a biologic prosthesis, and those who received mechanical valves had a higher incidence of bleeding and, in some age groups, stroke. On the basis of these findings, we concluded that the long-term benefit of a mechanical prosthesis depended on the valve in question: the long-term mortality benefit of mechanical valve prostheses persisted until 70 years of age for patients undergoing MVR and 55 years of age for those undergoing AVR.

Our findings suggest that the current trend toward the use of biologic valves in young patients may need to be reexamined. Regardless of age, the choice of prosthetic heart valve requires a shared decision-making process that includes discussion of the risks associated with lifelong anticoagulant therapy, the potential need for reoperation, and the differences in long-term mortality between the two surgical valve types. Whether transcatheter valves readily substitute for surgical biologic valves in the general population—as opposed to the intermediate- and high-risk surgical populations studied—remains unknown, and the potential for expanded use of transcatheter valves will need to be approached with caution.

Evolving "valve-in-valve" transcatheter procedures will inevitably add an additional layer of complexity to the choice of valve prosthesis. The use of TAVR within failed surgically implanted biologic valves represents an attractive and less invasive treatment approach over surgical reoperation.¹² However, valve-in-valve procedures are not without risk; the reintervention itself currently carries a 7-8% mortality risk.^13-15 Results from the global valve-in-valve registry highlight several safety and efficacy concerns that include device malposition, coronary ostium obstruction, and high valvular gradients.¹⁴ Additionally, the long-term durability of transcatheter valves implanted within surgical aortic valves is unknown. With advances in technology and technique, outcomes of these procedures will improve. However, whether valve-in-valve procedures will reduce the long-term mortality for recipients of biologic valve prostheses to achieve equivalence with mechanical valves remains to be determined.

In conclusion, surgical valve replacement has shifted considerably toward the use of biologic implants over mechanical valves for patients of increasingly younger age. Biologic prostheses are prone to degeneration, and although valve replacement is considered standard of care, reoperation carries significant risks of morbidity and mortality. We identified a long-term mortality benefit associated with mechanical prosthesis in patients undergoing AVR and MVR persisting until 55 and 70 years of age, respectively. Consequently, the choice of valve prosthesis may necessitate separate counsel for AVR and MVR.

References

1. Smith CR, Leon MB, Mack MJ, et al. Transcatheter versus surgical aortic-valve replacement in high-risk patients. N Engl J Med 2011;364:2187-98.
2. Leon MB, Smith CR, Mack MJ, et al. Transcatheter or Surgical Aortic-Valve Replacement in Intermediate-Risk Patients. N Engl J Med 2016;374:1609-20.
3. Reardon MJ, Van Mieghem NM, Popma JJ, et al. Surgical or Transcatheter Aortic-Valve Replacement in Intermediate-Risk Patients. N Engl J Med 2017;376:1321-31.
4. Adams DH, Popma JJ, Reardon MJ, et al. Transcatheter aortic-valve replacement with a self-expanding prosthesis. N Engl J Med 2014;370:1790-8.
5. Cohen G, Zagorski B, Christakis GT, et al. Are stentless valves hemodynamically superior to stented valves? Long-term follow-up of a randomized trial comparing Carpentier-Edwards pericardial valve with the Toronto Stentless Porcine Valve. J Thorac Cardiovasc Surg 2010;139:848-59.
6. Mack MJ, Leon MB, Smith CR, et al. 5-year outcomes of transcatheter aortic valve replacement or surgical aortic valve replacement for high surgical risk patients with aortic stenosis (PARTNER 1): a randomised controlled trial. Lancet 2015;385:2477-84.
7. Nishimura RA, Otto CM, Bonow RO, et al. 2017 AHA/ACC Focused Update of the 2014 AHA/ACC Guideline for the Management of Patients With Valvular Heart Disease: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. J Am Coll Cardiol 2017;70:252-89.
8. Chikwe J, Chiang YP, Egorova NN, Itagaki S, Adams DH. Survival and outcomes following bioprosthetic vs mechanical mitral valve replacement in patients aged 50 to 69 years. JAMA 2015;313:1435-42.
9. Stassano P, Di Tommaso L, Monaco M, et al. Aortic valve replacement: a prospective randomized evaluation of mechanical versus biological valves in patients ages 55 to 70 years. J Am Coll Cardiol 2009;54:1862-8.
10. Vahanian A, Alfieri O, Andreotti F, et al. Guidelines on the management of valvular heart disease (version 2012): the Joint Task Force on the Management of Valvular Heart Disease of the European Society of Cardiology (ESC) and the European Association for Cardio-Thoracic Surgery (EACTS). Eur J Cardiothorac Surg 2012;42:S1-44.
11. Goldstone AB, Chiu P, Baiocchi M, et al. Mechanical or Biologic Prostheses for Aortic-Valve and Mitral-Valve Replacement. N Engl J Med 2017;377:1847-57.
12. Webb JG, Dvir D. Transcatheter aortic valve replacement for bioprosthetic aortic valve failure: the valve-in-valve procedure. Circulation 2013;127:2542-50.
13. Dvir D, Webb JG, Bleiziffer S, et al. Transcatheter aortic valve implantation in failed bioprosthetic surgical valves. JAMA 2014;312:162-70.
14. Dvir D, Webb J, Brecker S, et al. Transcatheter aortic valve replacement for degenerative bioprosthetic surgical valves: results from the global valve-in-valve registry. Circulation 2012;126:2335-44.
15. Yoon SH, Whisenant BK, Bleiziffer S, et al. Transcatheter Mitral Valve Replacement for Degenerated Bioprosthetic Valves and Failed Annuloplasty Rings. J Am Coll Cardiol 2017;70:1121-31.

Keywords: Heart Valve Diseases, Aortic Valve, Aortic Valve Insufficiency, Mitral Valve, Transcatheter Aortic Valve Replacement, Stainless Steel, Heterografts, Reoperation, Retrospective Studies, Allografts, Heart Valve Prosthesis, Heart Valve Diseases, Alloys, Aortic Valve Stenosis, Stroke, Pericardium, Hemodynamics, Anticoagulants, Registries, Stents, Surgical Instruments, Risk Assessment, Pacemaker, Artificial, Biological Products

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