DISCUSSION
This single-center propensity-matched study of over 1,500 isolated
bioprosthetic surgical aortic valve replacements demonstrates comparable
short-term and long-term outcomes of bovine and porcine prostheses.
There were no significant differences in postoperative clinical
outcomes, echocardiographic data, readmission rates, reintervention
rates, or long-term survival between the propensity-matched groups.
Notable differences between bovine and porcine valves have been hitherto
established. Importantly, we know that the mode of structural valve
deterioration (SVD) differs between these two valve types; porcine
valves tend to fail via leaflet tears, while bovine pericardial valves
tend to degenerate via fibrosis/calcification.8Interestingly, despite these respective modes of SVD, previous
prospective and/or randomized studies have demonstrated higher
transprosthetic gradients for porcine valves, with smaller indexed
effective orifice areas (despite larger implanted valve sizes) when
compared to bovine prostheses.9,10,11 Bovine valves
have been found to have more favorable hemodynamics in general across
the majority of these studies. Our study, on the other hand, found
comparable gradients between the two xenograft materials, though this
finding may not have persisted at 5 or 10 years.
How bovine and porcine valves compare with one another regarding
short-term and long-term clinical outcomes remains unclear. In an effort
to answer these questions, several comparative studies have been
performed to-date, though most have included concomitant operations and
have not accounted for differences in baseline characteristics with
propensity matching. Moreover, data from these studies have yielded
conflicting results.
One such study, involving roughly 13,000 patients in Sweden, found a
long-term survival benefit with porcine prostheses, though with a higher
need for reoperation when compared to bovine
prostheses.6 A study of almost 40,000 patients in
England and Wales demonstrated no difference in long-term survival or
need for reintervention among patients who received bovine or porcine
aortic valves, as did another study from Duke.4,12Importantly, all of these studies included patients who received
concomitant CABG, and none of them utilized propensity matching to
account for baseline differences. A recent meta-analysis of studies
published from 2010-2015 also demonstrated no difference in long-term
survival in patients who underwent AVR with a bovine or porcine
prosthesis, though these studies also included patients who underwent
concomitant operations and did not match on baseline
characteristics.13 Our study, which included only
isolated AVRs and which incorporated propensity matching to adjust for
confounders, may help to clarify and adjudicate prior findings.
As valve-in-valve TAVR becomes more popular, suitability for this
subsequent intervention, should it be necessary, also becomes an
important consideration when choosing a surgical prosthesis. Prior
studies have not found specific differences in feasibility or outcomes
of valve-in-valve TAVR according to use of bovine or porcine surgical
valves, though it has been demonstrated that residual stenosis following
valve-in-valve TAVR is more common with surgical valves that have an
inner diameter of < 20 mm.14 Thus, it is not
so much the type of surgical valve, but rather the size of the implanted
valve, that seems to carry the most importance.
Another important question that has been investigated is the comparison
between stented and stentless bioprosthetic aortic
valves.15,16,17,18 A randomized controlled trial was
performed to compare clinical outcomes and hemodynamic performance
between these two valve types. In comparison to stented prostheses, this
trial found stentless valves to have greater effective orifice areas, as
well as greater improvement in postoperative left ventricular function
when used in patients with small annuli or left ventricular
dysfunction.19 A recent meta-analysis has adjudicated
this finding of superior short-term hemodynamic outcomes with stentless
valves in patients who have small annuli.20
Outcomes of valve-in-valve TAVR following stented versus stentless
prostheses have also been investigated. In a study using the
Valve-in-Valve International Data registry, stentless valve-in-valve
TAVR was associated with more periprocedural complications such as
device malposition, coronary obstruction, and paravalvular
leak.21 Thus, while long-term outcomes of stented
versus stentless AVR appear to be comparable, and stentless valves
confer better hemodynamics in patients with small annuli, these valves
may also complicate the performance of future valve-in-valve TAVR.
This study is inherently limited by its retrospective, observational
design. Moreover, multiple valve types were included, and the
performance of a particular valve model could have impacted outcomes. We
did not include data on indexed effective orifice area; however, we
matched on implanted aortic valve size to adjust for this potential
confounder. Serial, longitudinal echocardiographic data at set
time-points was not available but would have been very useful in
evaluating changes in hemodynamic performance of these two valves over
time. The study also incorporated longitudinal data with varying
follow-up times, with some patients being lost to follow-up. Finally,
the data is from a single high-volume center, which may limit
generalizability of the findings.
The use of either bovine or porcine bioprosthetic aortic valves yields
comparable postoperative outcomes, long-term survival, freedom from
reintervention, and freedom from readmission.