DISCUSSION
The present study analysed the impact of a mechanical or biological prosthesis with PPM on survival and QoL after AVR. The significant findings include: (1) AVR with a mechanical prosthesis had markedly less risk of PPM than AVR with a biological prosthesis; (ii) patients with moderate to severe PPM and an implanted biological prosthesis are at the highest risk of long-term mortality; and (iii) patients with biological prosthesis and PPM had impaired QoL up to 6 years of follow-up.
PPM is associated with a higher risk of poor outcomes after AVR, and its prevention is of paramount importance when selecting a surgical heart valve for implantation.(14) Valve manufacturers provide iEOA values as the most appropriate for predicting PPM after implantation.(15) A cut-off level of iEOA < 0,85 cm2/m2 has been introduced to define moderate-to-severe PPM. In our study population, PPM was found in 21.5% of all patients who underwent AVR. However, when analysed separately, 69.8% of patients with biological valves implanted had PPM, while just 3.7% of patients with mechanical valves implanted had PPM (p < 0,001).
The Quebec group brought PPM into the spotlight, publishing several studies that showed significantly reduced long-term survival in those patients with PPM.(15, 16) The Toronto group confirmed their findings.(17) In a large study that enrolled 1856 patients with mechanical prostheses and 2275 patients with biological prostheses implanted after AVR, the presence of PPM significantly reduced both short-term and long-term survival. Our study supports these findings, showing lower survival in prostheses with PPM than those without PPM. However, none of these studies distinguished outcomes by the presence of a biological or mechanical prosthesis. Our study revealed lower survival with PPM remains for biological prostheses, while PPM for mechanical prostheses did not affect survival or the physical component of QoL.
Hoffmann et al. analysed 632 patients with consecutive AVR procedures with only Hancock II biological prostheses. PPM was present in 93.8% of patients, whereas 71% of patients had moderate and 22.8% of patients had severe PPM.(12) The authors found no difference in 5-year survival within the groups with and without PPM. Our study found a similar distribution of moderate PPM in the biological prosthesis group, while severe PPM was found in only 5.1% of patients. Besides, patients with a biological prosthesis and PPM had significantly lower survival after 6 years of follow-up than those without PPM. One potential explanation for the observed differences is that our study included several biological prosthesis types and complete follow-up. Sportelli et al. conducted an observational study that included 152 patients with both mechanical and biological prostheses used for AVR.(4) The overall PPM rate was 53.%, while 11.7% of patients had severe PPM. They reported no influence of the presence of PPM on survival after long-term follow-up. However, no separate analyses for the biological and mechanical prostheses were reported. Finally, Weber et al. revealed more frequent PPM in the biological prosthesis group than in the mechanical prosthesis group. Still, they did not perform a survival analysis for this group.(11) Severe PPM was a rare occurrence in our study, so it was not suitable for the subanalysis of this population. It should also be mentioned that none of the listed studies included patients with the sutureless biological prosthesis as in our study.
Also, it should be mentioned that nearly 37% of the biological valves implanted in our study population were Trifecta valves that had an issue of frequent SVD raised in a few previously published studies. However, the prosthesis used in these studies was a previous Trifecta model, while in our study the new Trifecta GT model was used. The clinical importance of this fact is yet to be determined.(18, 19)
Some studies that enrolled a small cohort have warned about the negative impact of PPM on QoL, especially on the physical component.(9, 20) As it is shown that PPM is associated with higher transprosthetic gradients, it can be expected that, with physical exercise, a rise in the gradient can come close to the values in mild and moderate native valve aortic stenosis.(21) The median values of the QoL measurements in the present study were close to the normal values. The values of the QoL mental component did not show a significant difference in both groups in patients with and without PPM. However, the physical component of the questionnaire revealed significantly lower scores in patients with a biological prosthesis and PPM than in those without PPM. In the mechanical prosthesis group, this difference was not observed. The freedom from angina on follow-up also did not differ in the groups. These results are similar to those published by Hoffman et al., who also found the difference only in the physical component of QoL, and Urso et al. (163 patients enrolled), who found lower physical scores in elderly patients.(12, 22) Sportelli et al. (152 patients enrolled) and Reskovic Luksic et al. (46 patients included) failed to demonstrate the difference in the QoL in patients that have PPM. Once again, neither of these studies performed subanalyses for biological and mechanical prostheses.
As it is well known that perioperative results are affected mainly by the type of valve implanted, the haemodynamic properties of each valve type can also influence the outcome. It is well known that, in every biological prosthesis, structural valve degeneration (SVD) will happen to some extent over time. SVD in prostheses with PPM with higher transprosthetic gradients could lead to further augmentation of gradients, especially during exercise. On the other hand, the transprosthetic gradients remain the same over time in a mechanical prosthesis.(23) Although the surgeon must strive to implant the largest valve possible if PPM is suspected in a biological prosthesis, if it is not possible, then a mechanical valve, sutureless valve implantation or the root enlargement procedure should be considered. The root enlargement procedure is also a debated and contemporary issue. It can be safely performed but requires advanced experience of both the surgeon and the centre. However, according to available publications, the volume of the procedures does not add to the operative risk. (24) Also, as the valve in valve TAVR clinical use expands its indications rapidly, the size of the implanted biological prosthesis should be carefully planned.