This single centre study provides a contemporary picture of the safety and effectiveness of the two valve concepts. Event rates at 30 days may appear slightly high and we consider this the result of our clinic getting referrals of very complex cases that may result in longer procedural times and hazards. Furthermore our clinic is frequently chosen for re-interventions after failed procedures. Our study revealed a success rate of MVR that is quite comparable between valves, but confirmed that biological valves were used in older patients, while mechanical valves were used in younger patients and associated with an increased risk of bleeding.
Both types of valves have advantages and disadvantages, but also specific patient factors need to be taken into consideration when making the decision on which valve type to use [9, 10]. Historically, biological MVs were generally considered to have superior antithrombotic properties but lacked durability, while mechanical valves were thought to be more durable but were associated with thromboembolism and bleeding events [2, 5, 6, 9]. The data from our study confirm the observation that the use of anticoagulation along with mechanical valve implantation is associated with an increased risk of bleeding and that there is a potential survival benefit for patients receiving a biological MV.
Earlier studies report that mechanical valves were associated with increased durability [2, 5, 6]. The KM data confirm that at 10 years patient survival is higher with the mechanical valve than the biological valve (77.1% vs. 62.4%, respectively), despite survival being nominally higher with the biological valve within the first years of follow-up. Our Cox regression analysis revealed that after adjustment for key baseline variables there was no significant difference between the two valve types (HR 0.833; 95% CI 0.430–1.615; p = 0.589). Further information is needed to determine if the durability of the mechanical and biological valve affects patient survival because the biological valve recipients were 15 years older in our dataset. In addition, biological valves have been associated with an increased risk of re-operation and structural valve deterioration, which may start to occur at 3 years but, on the other hand, a durability of 12-plus years has also been reported [11,12,13,14,15].
Patient-specific factors, including age, surgical factors, comorbidities and patient preference, also influence the choice of valve type [9, 16]. With respect to the patient’s age, the general recommendations are that patients younger than 65 years should receive a mechanical valve because of their increased durability, while patients older than 65 years should be considered for a biological valve, as they are less likely to outlive the valve’s life expectancy [9, 17, 18]. Our study mirrors this approach, with the median age of patients in the mechanical valve group being 15 years lower. Comorbidities, such as atrial fibrillation, renal failure and diabetes, and surgical factors, such as the need for concurrent aortic root replacement, also affect valve selection [9, 19], although we did not observe any statistically significant difference in the rate of these comorbidities.
In the future, improvements in mechanical valve structure may lower the risk of thromboembolism thus potentially reducing the intensity of lifelong anticoagulation, which may result in a preference for these valve types . Furthermore, newer oral anticoagulants may also make mechanical valves more attractive from both the patient’s perspective and from a medical standpoint .
Overall, 324 patients were included in this study. The majority of these study patients received a biological valve (n = 265) and only 59 patients received a mechanical valve. Furthermore, patients receiving mechanical valve were typically younger than those receiving biological valve. Finally, there is an evolution of surgical techniques over time. As such, we adjusted the outcomes for differences in baseline variables to overcome this limitation. Data on major complications and echo data, collected at the patient’s last follow-up visit, were not available for some patients as they only recently received their implant. The data, however, provide a useful insight into post-procedural major complications and echocardiographic data.