Over the past decade, biological prostheses have become increasingly used in the mitral and especially the aortic positions. Selecting the type of prosthesis is not a trivial decision and requires a calm discussion with the patient regarding the advantages and disadvantages. During this conversation, it is crucial to mention the shorter durability compared to mechanical prostheses and the benefits related to fewer bleeding and/or thromboembolic events. Indicating a bioprosthesis should not be based solely on the patient’s age, as various clinical factors like comorbidities, life expectancy, frailty, and preoperative treatment should also be considered. Likewise, assessing personal aspects is equally essential, such as quality of life, reproductive desires, occupation, and treatment adherence, among many other factors. Considering these elements, it is vital to recognize the inevitability of bioprosthetic degeneration and to develop a future management plan (reintervention and/or potential solutions via percutaneous intervention).
Clinical guidelines differentiate two age thresholds based on the position of bioprosthesis implantation. They recommend bioprostheses for mitral valve replacement (MVR) in patients over 65 years of age and for aortic valve replacement (AVR) in those over 50 years (ACC/AHA guidelines). However, as stated previously, age is merely one factor in the decision-making algorithm, and these guidelines, as their name suggests, are meant to guide rather than dictate. The choice of prosthesis type will always be an individualized and shared decision.
The current study aims to assess, on a population level, the long-term durability of bioprostheses in the aortic, mitral, and mitro-aortic positions. The Taiwanese national health insurance database was utilized to evaluate all cases of MVR, AVR, and mitro-aortic valve replacement (MAVR) from 2001 to 2017, with reoperation as the primary event. Two experimental designs were employed: a between-subject design and a within-subject design (for MAVR cases). For the former, a propensity score-matched analysis was performed to compare AVR with MVR.
A total of 10,308 patients were analyzed; 5,462 underwent AVR, 3,901 underwent MVR, and the remaining 945 received MAVR. After applying the propensity analysis, 2,259 patients were matched for AVR and MVR comparison. With a mean follow-up of 4.2 years (range from 1 day to 17.9 years), they found a reoperation rate of 3.5% for MVR compared to 2.6% for AVR (HR 1.41; p<.05). Similarly, MVR was associated with higher all-cause mortality (36.5% vs. 32.6% for AVR) with an HR of 1.21 (p<.05). In patients with MAVR using the same type of bioprosthesis, aortic-positioned prostheses showed a lower reoperation incidence.
The authors concluded that aortic-positioned bioprostheses present better outcomes in terms of durability, long-term mortality, and perioperative morbidity compared to those implanted in the mitral position. They foresee expanded indications for these prostheses due to enhanced durability resulting from advancements in anticalcification treatment for valve leaflets and the evolution of percutaneous interventions, which may delay/avoid future reinterventions.
COMMENTARY:
The results of this study, at first glance, do not seem to offer new insights beyond what we already know about bioprostheses. We know that aortic-positioned bioprostheses last longer than those in the mitral position, leading to more frequent reinterventions for mitral valves. It is also known that mitral valve surgery and re-surgery are more complex, with a more fragile patient profile, contributing to the higher morbidity and mortality of these procedures. This background knowledge aligns with the recommendations of clinical practice guidelines in developed countries, which suggest delaying biological mitral valve replacement until 65 years of age. However, this knowledge is based on personal and collective experiences from peers, societies, and the few published studies that directly compare bioprostheses in these two positions. Available studies are generally small, single-center, and limited in the range of models studied, often lacking sufficient statistical power and riddled with various biases. Despite the limitations of the current study, as discussed later, an analysis of a national database encompassing over 10,000 patients with various types of bioprostheses is a gem.
Like any gem, it must be polished to reveal its brilliance rather than be mistaken for an ordinary stone. The general data on reoperation and mortality consolidate and validate our experience regarding bioprostheses. The most interesting findings lie in the various subanalyses. When evaluated globally and independently of implantation position, no differences were found regarding the different models available on the market. However, for aortic-positioned bioprostheses, the Carpentier-Edwards Perimount/Magna® valves showed fewer reoperations—a finding not observed in the mitral position. Additionally, no differences in durability and reoperations were found between porcine and bovine bioprostheses. There were also no differences in infectious endocarditis rates based on the position of the bioprosthesis. Finally, none of the usual comorbidities (renal failure, prior heart failure admission, etc.) correlated with an increased reintervention risk, except for age.
The limitations of this type of study have been mentioned in various blog entries. As it is an administrative database of the national health insurance system, we lack access to laboratory or echocardiographic data. This study only considers reoperations and not prosthetic degenerations that would require echocardiographic data for diagnosis. This limitation may introduce bias, potentially overestimating the actual durability of the prostheses, as some patients may be indicated for reoperation but are inoperable due to age or comorbidities. Additionally, case identification relied on ICD-9 classification codes, with inherent coding errors. Lastly, an average follow-up of 4.3 years warrants caution with such low reintervention data.
In conclusion, the article by Chen et al., based on a valuable database, provides a contemporary view on the use of bioprostheses in aortic and mitral positions, offering a snapshot that confirms our perception of these outcomes.
REFERENCE:
Chen CY, Lin CP, Hung KC, Chan YH, Wu VC, Cheng YT, et al. Durability of Biological Valves Implanted in Aortic or Mitral Positions: A Nationwide Cohort Study. Ann Thorac Surg. 2023 Oct;116(4):751-757. doi: 10.1016/j.athoracsur.2023.05.038
