Biological versus Mechanical Heart Valve Prostheses. Has the Paradigm Shifted Definitively?

Trends in Surgical Aortic Valve Replacement in More Than 3,000 Consecutive Cases in the Era of Transcatheter Aortic Valve Implantations

Editor's Commentary

In this article of the Thoracic and Cardiovascular Surgeon, Silaschi et al analyze the trends in surgical aortic valve replacement (sAVR) over the last decade in their institution, which is a high-volume center in both surgical and percutaneous intervention on the aortic valve.[1] In the background of this study is the fact that they are increasingly considering biological prostheses for sAVR in patients ≤60 years of age, based on the premise that this practice will preserve the option of performing a transcatheter valve-in-valve (ViV) procedure in case of structural valve deterioration.

During an 11-year period, from 2002 to 2012, over 3,000 patients with a mean age of ∼70 years underwent sAVR at their center. Use of mechanical valves decreased from 10.9 to 1.8% and the mean age of the patients decreased from ∼53 to 41 years in the same time period. According to the authors, the “indication for biological prostheses became more liberal” as a result of the perspective option for subsequent ViV procedures.

There are two aspects of this work that deserve careful reflection. First, this “liberal” use of bioprostheses, reaching patients in their 40s, is well out of the recommendations of current guidelines from both sides of the Atlantic, which clearly recommend the use of mechanical prostheses in the aortic position in patients below 60 years of age, unless contraindicated.[2] [3] Use of bioprostheses is recommended above 65 years by the ESC/EACTS and above 70 years by the AHA/ACC. Either a bioprosthetic or mechanical valve is reasonable in patients between 60 and 70 years of age (Class IIa indication).

Guidelines are based on best current scientific evidence, and since their recent publication, there has been no new evidence that could lead to substantial modification of these recommendations. Naturally, guidelines are not commandments and need not be rigorously followed, but the advice coming from them should seriously be considered. Conversely, significant deviation cannot be condoned.[4]

Second, the authors' main argument for preference of bioprostheses is that, in the near future, ViV will become common practice; hence, degeneration of surgically implanted bioprostheses will be less of a problem. Although this trend is followed by many other teams, in my view the current series has gone to an extreme, perhaps a dangerous one. Let us see. Assuming a mean durability of 15 years, and we are not sure if all bioprostheses will last that long, a 40-year-old patient with a life expectancy of 85 years would have to undergo at least three ViV procedures, assuming a similar durability of 15 years, which is even less probable. In any case, this is technically impossible, as, with an initial 23-mm bioprosthesis, the valve would become unacceptably stenotic. Besides, as the authors also point out, current mortality of ViV is 7%, far in excess of that of repeat surgery for young, low-risk patients, in whom the mortality of reoperation should not exceed 3%, and there are reports with even lower mortality.

Hence, in my opinion, this paper gives the wrong message to the surgical community, especially to young surgeons. The future may prove them right, but it is far too soon to enter it.

During the process of revision of this manuscript, which resulted in some substantial modifications of the original text, the authors admitted that “there is no evidence of a survival advantage for the practice of implanting biological valves into very young patients when structural valve deterioration has to be expected” and emphasized “the need for evidence as in current practice the ‘borderline’ group of patients aged between 50 and 60 years is significantly increasing.” But these statements are clearly not in tune with their real practice, as described. Not even the claim that “patients with heart valve diseases have a reduced life expectancy compared to the average population, therefore making it unlikely that these patients experience SVD of three generations of biological prostheses” can be considered an attenuating factor.

The authors suggest that “as performing a ViV will not complicate possible subsequent open reoperative AVR, it may be justified even in younger patients aged between 50 and 60 years who are more likely to experience structural deterioration of the transcatheter heart valve used for ViV.” But it then means pushing a second surgery to a much older age, which, naturally, is not desirable. On the contrary, I see it more appropriate to start by reoperation and leave the eventual ViV procedure for later.

Evidently, I agree with the authors' statement that “until scientific evidence proves superiority of the above-described concept, international guidelines should be followed and biological prostheses should only be implanted in patients ≤60 years if indicated either by patients' choice or by contraindication to life-long anticoagulation.” I can only suggest that they follow their own advice.

To solve this difficult equation, they propose that “further studies comparing two strategies—biological sAVR at an age of 50–60 years using subsequent ViV versus mechanical sAVR—are needed to determine advantages of either strategy and to evaluate long-term outcomes.” However, although improved durability of biological prostheses has often been suggested, it has not been proven. In fact, in the experience of Chan et al, the median interval to reoperation of contemporary, stented aortic bioprostheses was 7.74 years in patients less than 40 years and 12.93 years in patients between 40 and 60 years of age.[5] The authors confirm that in their experience the mean time to reoperation did not increase from 2002 to 2012.

On the other hand, and in opposition to what the authors state, newer generation of mechanical valves have shown remarkable performance with regard to freedom from serious complications, including thromboembolism, so much so that lowering the dosage of anticoagulation, and hence of INR levels, has been recommended.[6]

The question of the patients' choice also deserves some discussion. This concept has become fashionable. Indeed, the ESC/EACTS guidelines include, as class I indication, “the desire of the informed patient.” Naturally, the patient has to be included in the decision process, but what is an “informed patient” if we, the “experts” in the matter, most often fail to reach consensus? Should we peacefully accept a young patient's choice of a bioprosthesis just because he does not “feel like” taking anticoagulants? I do not think so! Fortunately, in my country, and I suppose in most others, the patients most often follow our advice.

There is, however, one important message to be learnt from this paper: surgeons must do everything in their power to increase the size of prostheses implanted, not just to avoid patient–prosthesis mismatch, but to prepare for the future, if and when bioprostheses degenerate and ViV may be indicated. This can also be done by adequate choice of more hemodynamically efficient prostheses. From this point of view, the authors' experience has been positive, as the use of valve sizes < 25 mm decreased significantly and the mean size of the prostheses implanted has increased by ∼1 mm during the study period. This may require a wider use of annular enlargement procedures, which are simple to perform and efficacious.

In the authors' institution, there has been a decline in sAVR numbers after introduction of transcatheter aortic valve implantation (TAVI), which they say “may be explained by a substantial amount of patients eligible for both types of procedures and the consequence that in a center with a large interventional program this leads to a reduction of those patients treated surgically.” Although this appears to be a trend in Germany, where more than 40% of the isolated aortic valves are now treated percutaneously (although with stable sAVR numbers),[7] it is by no means a universal experience, most reports showing exactly the inverse, that is, an increase in surgical numbers, probably resulting from a much greater referral of patients with aortic stenosis for evaluation of the heart teams, the majority still ending in surgery.

The authors state that because theirs is a “center with a large interventional program” there is a more liberal switch to TAVI, although the indication for it remains “high-risk” patients. One cannot avoid feeling that “difficult” patients are increasingly included in that classification. Naturally, a better selection has resulted in improved outcomes, as happened in their experience where the 30-day mortality of isolated sAVR was 0% in 2012, which is certainly a goal but remains elusive for most surgical groups.

Concluding, the new technologies in valve substitution are certainly poised to take an increased, perhaps preponderant, role in the future, but the progress in this regard must take into account lessons learned in the past with surgical procedures. And surgeons need not necessarily take “steps longer than their legs.” Rather, we should be aware that our surgical results can still be significantly improved and keep working toward that goal.

• References

• 1 Silaschi M, Conradi L, Treede H , et al. Trends in surgical aortic valve replacement in more than 3000 consecutive cases in the era of transcatheter aortic valve implantations. Thorac Cardiovasc Surg 2015; ; this issue
• 2 Vahanian A, Alfieri O, Andreotti F , et al; Joint Task Force on the Management of Valvular Heart Disease of the European Society of Cardiology (ESC); European Association for Cardio-Thoracic Surgery (EACTS). Guidelines on the management of valvular heart disease (version 2012). Eur Heart J 2012; 33 (19) 2451-2496
• 3 Nishimura RA, Otto CM, Bonow RO , et al; American College of Cardiology; American College of Cardiology/American Heart Association; American Heart Association. 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 Practice Guidelines. J Thorac Cardiovasc Surg 2014; 148 (1) e1-e132
• 4 Antunes MJ. Guidelines in real life. Why are they not always enforced?. Eur J Cardiothorac Surg 2008; 34 (5) 935-936
• 5 Chan V, Malas T, Lapierre H , et al. Reoperation of left heart valve bioprostheses according to age at implantation. Circulation 2011; 124 (11, Suppl): S75-S80
• 6 Kaneko T, Aranki SF. Anticoagulation for prosthetic valves. Thrombosis 2013; 2013: 346752
• 7 Beckmann A, Funkat AK, Lewandowski J , et al. Cardiac Surgery in Germany during 2014: A Report on Behalf of the German Society for Thoracic and Cardiovascular Surgery. Thorac Cardiovasc Surg 2015; 63 (4) 258-269