“Surgical bioprostheses are no longer the reference for long-term durability.” This statement has been repeated by some interventional cardiologists at meetings over the past year. One of these instances occurred at the annual EACTS Congress in Vienna, sparking murmurs of disapproval with no significant repercussions. Although this argument has been applied primarily to bioprostheses in the aortic position, it is likely to extend to bioprostheses in any position with the evolution of transcatheter mitral valve implants.

Beyond competition with the transcatheter field, understanding the real outcomes of surgical bioprostheses is essential, considering the progressively growing trend favoring bioprostheses over mechanical ones. We have moved from an era where a commitment to implant a prosthesis “that would outlast the patient” was expected (with structural degeneration viewed as a true failure) to one where only early failure is considered adverse. This shift allows patients to avoid long-term oral anticoagulation with dicoumarin if a mechanical prosthesis were implanted. Additionally, simply reinstating oral anticoagulation with direct oral anticoagulants (DOACs) in patients with atrial fibrillation has become a strong enough reason to promote the implantation of mitral bioprostheses. When combined with the positive outcomes of TAVI-in-mitral-bioprosthesis implants that avoid reoperation, the potential disadvantage of structural degeneration is more tolerable.

Surgical bioprostheses have undergone multiple designs and evolutionary generations, with porcine valves being more prevalent than in the aortic position. The lack of data on some aortic bioprostheses (e.g., St. Jude Trifecta® and Sorin Mitroflow®/Livanova Crown®) led to the well-known poor outcomes that affected many surgical cohorts in studies, both intentionally and retrospectively, focusing on durability, while also providing cases for TAVI-in-aortic-bioprosthesis procedures worldwide.

For this reason, the authors conducted a comprehensive review of all published literature from the past 20 years to determine the true durability of mitral bioprostheses. While much has been written about their durability in the aortic position, there are hardly any studies for the mitral position. This study is aligned with the PROSPERO registry. The authors included studies with at least 50 patients who underwent isolated or concomitant mitral valve replacement with bioprosthesis, published between 2003 and 2023, and with at least 5 years of follow-up, reporting on survival and freedom from reintervention and/or structural degeneration.

A total of 21 studies encompassing 15,833 patients from 11 countries, with surgeries performed between 1984 and 2018, were identified. Therefore, this is considered the largest study published to date on this topic.

The etiologies of the mitral pathology treated included rheumatic (32%), degenerative (25%), functional (13%), and endocarditis (8%). The most commonly implanted bioprostheses were bovine pericardium (Balmedic® and Carpentier-Edwards®) and porcine (Biocor®/St. Jude Epic®, Hancock II®, and Medtronic Mosaic®). The most frequently implanted prosthesis was the Medtronic Mosaic® (n = 1825), followed by the Carpentier-Edwards® (n = 1397), with St. Jude Epic® in third place. The most common size implanted was 29 mm. Up to two-thirds of the patients underwent concomitant procedures, especially coronary revascularization (28.8%) and tricuspid valve repair (24.4%). Comorbidities were appropriately documented, with atrial fibrillation (AF) in 35% of patients and diabetes mellitus in 15.4%. Regarding hemodynamic performance, mean gradients were favorable, ranging from 4 to 6.3 mmHg.

Structural degeneration was defined by the criteria proposed by Atkins et al. in most studies. In others, severe dysfunction was indicated by transprosthetic gradients >8 mmHg and/or a regurgitant orifice >40 mm². In less frequent cases, pathological criteria based on findings from surgical explants or autopsies were applied without hemodynamic data. The freedom from structural degeneration at 15 years was 58.3% to 93% for porcine bioprostheses and 61.6% to 86.7% for pericardial prostheses. The outcomes for porcine prostheses were primarily attributed to the Medtronic Mosaic®, with structural degeneration rates of 5.8% and reoperation rates of 4.8% at 10 years. For other porcine bioprostheses, like St. Jude Epic®, structural degeneration occurred in 7 cases, with a reoperation rate of 4.3% at 10 years. The best-performing pericardial bioprosthesis was the Carpentier-Edwards, with 20-year structural degeneration rates of 23.7% and a reoperation rate of 40.5% as reported in Bourghignon et al., estimating a “lifespan” of the bioprosthesis at 16.6 years. Similar results were reported by Beute et al., with a reoperation rate of 13.2% at 15 years.

A subgroup analysis based on age groups revealed that the freedom from structural degeneration at 10 years improved as patient age increased, ranging from 58% in patients <55 years to >90% in those >65 years. Particularly in this age group, all bioprostheses demonstrated excellent survival outcomes, with >95% freedom from structural degeneration at 5 years and 78% at 10 years.

The authors concluded that despite considerable variability in study reporting, follow-up duration, structural degeneration criteria, and disease phenotypes, this study provides the most significant reference for the durability of bioprostheses in the mitral position.

COMMENTARY:

This is undoubtedly a landmark article that establishes long-term durability benchmarks for currently available mitral bioprostheses. The primary findings from the data presented are as follows:

The performance of porcine and pericardial bioprostheses is nearly comparable, with porcine valves possibly showing slightly better durability, keeping them relevant in clinical practice. This may be because mitral bioprostheses experience greater hemodynamic stress than their aortic counterparts due to higher closure pressures. However, given the larger size of mitral bioprostheses, prosthesis-patient mismatch is rare (moderate mismatch <1.2 cm²/m² and severe <0.9 cm²/m²), thus not allowing pericardial bioprostheses to demonstrate a true design advantage. Conversely, the fact that porcine prostheses are actual cardiac valves grants them a definitive performance advantage. The performance of newer platforms such as Edwards Mitris® with Resilia® pericardial tissue remains to be seen, as they are currently in the early stages of the COMMENCE durability registry follow-up.

The disadvantage of implanting mitral bioprostheses at a younger age is greater than for aortic bioprostheses. Although clinical guidelines recommend bioprosthesis implantation starting at age 70, this study shows positive outcomes from age 65, which seems reasonable to extend this strategy. Beyond this, it is unadvisable, especially for patients without significant life expectancy limitations or contraindications to oral anticoagulation with dicoumarin.

Altogether, structural degeneration rates ranging from zero to 41% at 10 years, and from 7% to 41.3% at 15 years, with freedom from reoperation rates of 65% to 98.7% at 10 years and 78.5% to 91% at 15 years, represent the benchmarks to beat. However, it should be noted that this information may reflect publication biases. The authors identified only 2 studies (of 21) with severe biases, while the others showed lesser biases. Data come from independent studies, such as national registries or single-center experiences, with minimal conflicts of interest. This aspect does not eliminate the bias of positive result selection, but since these studies come from periods without as much industry pressure, they may even appear more reliable and closer to real-world performance. None of the studies were randomized, and thus the inherent heterogeneity in design, associated procedures, and patient characteristics is extensive. Lastly, structural degeneration criteria have also varied, with many studies not following the standardized criteria proposed by Atkins et al. in EACTS guidelines for reporting mortality and morbidity in valvular surgery, introduced in 2008. Consequently, even if considered inappropriate, reoperation rates take on added value in assessing the “clinical” durability of bioprostheses. Notably, this field lacks VARC-defined criteria, which were only developed for mitral valve repair procedures, especially for percutaneous edge-to-edge repair.

Until percutaneous mitral valve implants become widespread and compete with surgical prostheses, patients who are not candidates for mitral valve repair (surgical or percutaneous) will continue to rely on these devices to address their cardiac condition. Long-term outcomes are generally favorable, though predictably inferior to aortic bioprostheses. Therefore, more than ever, it is crucial to engage in shared decision-making with the patient, considering potential longevity, comorbidities, anticoagulation needs, and individual preferences in choosing between a “mechanical or bioprosthetic” path, as a fully biocompatible permanent solution does not yet exist.

REFERENCE:

Koulouroudias M, Di Mauro M, Lorusso R. Long-term outcomes of bioprosthetic valves in the mitral position: a systematic review of studies published over the last 20 years. Eur J Cardiothorac Surg. 2023 Nov 1;64(5). doi: 10.1093/ejcts/ezad384.