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.