Early mortality
The observed pooled early mortality was 5.5%. This is in accordance
with an older review on aortic root replacement (4.5 to 5.3%) and with
the recent report of the Society of Thoracic Surgeons database from the
U.S. that estimates early mortality after bioprosthetic aortic root
replacement to be 6.2% (45,
46). However, these studies include also
acute and emergent operative indication like endocarditis and aortic
dissection.
Early mortality was mainly due to low cardiac output (22.7%) and
multi-organ failure (18.1%). Surgical indication was endocarditis in
9.2% of patients and type A aortic dissection in 7.2%. The high
mortality could (partly) be explained by operation in emergent setting
and partly by the additional procedures (e.g. arch replacement, CABG).
Nevertheless, overall early mortality seems not changed significantly
last 2 decades.
Late mortality and reintervention outcome There was a high mortality rate (4.8%/pt-year) for a pooled mean age
of 65.9 years, which is higher than the general population mortality.
Translated to our microsimulation-based life-expectancy, there is a
life-expectancy of 14.3 year for a 60 year old patient receiving a
bioprosthetic root replacement, while there is a life-expectancy of 22.5
years for the 60 year old U.S. “healthy” population
(12). From previous research there is
evidence of significant “excess mortality” in (elective) isolated
aortic valve replacement, compared to the age-matched general population
(47). Additionally, patients in this
study were diagnosed with a dilated aortic root as well, with about 13%
suffering from a dissection of the root and/or connective tissue
disease, which are conditions that may influence patient survival due to
complication other than valve-related events.
This microsimulation model shows a life-time reintervention risk of 9%
for patients older than 60 years, which is comparable to previous
predictions on biological aortic valve prostheses
(3). It is known that younger patients,
especially younger than 60 years, are more likely to have a
reintervention after biological aortic valve replacement, mainly due to
progressive SVD (3,
48). Of the 8 studies that explicitly
tested association between age and reintervention, 3 found indeed that
older age is associated with lower reintervention hazard.
Thromboembolic eventsWe found a high incidence of thromboembolic events, with a life-time
risk of more than 20% after bioprosthetic aortic root replacement. Data
on TE events are not comprehensive, thus discriminating between TIA and
disabling ischemic CVA is not possible. However, a previous systematic
review and microsimulation study on aortic valve replacement with
isolated biological stented valve, published by Puvimanasinghe et al.
(3), reports similar TE event rates
(1.4%/patient-year). Additionally, the incidence of thromboembolic
events is known to increase with age (49,
50) and might partly explain this high
incidence of thromboembolic events.
Subsequently the question arises whether there is a difference with
patients receiving a classical Bentall prosthesis. Although this
comparison is hampered by the differences in patient characteristics,
mainly due to the younger age in patient receiving mechanical valves; a
recently published meta-analysis on the Bentall procedure (mean age 50
years), shows lower thromboembolic event rates (0.77%/patient-year)
(51). Another study on mechanical valve
replacement in non-elderly showed suboptimal survival and considerable
lifetime risk of anticoagulation-related complications
(52).
However, the anticoagulation therapy after mechanical valve implantation
in these patients plays a protective role in prevention of
thromboembolic events, as it also occurs irrespective of the aortic
valve replacement due to the aging process
(50).
Additionally, TE hazard is less likely to occur during long-term
follow-up, suggesting a larger hazard in the early postoperative period,
which may be related to anticoagulation therapy. According to the
current US and European guidelines on the management of valvular heart
disease, antiplatelet therapy is reasonable and may be considered for
the first 3 months after biological valve replacement
(2, 53).
Additionally, the European guidelines state that the need for a 3 months
postoperative period of anticoagulation therapy has been challenged in
patients with bioprostheses, with low-dose aspirin being favored as an
alternative.
Hence, it is questionable whether the proposed anticoagulation therapy
is appropriate in patient receiving a bioprosthetic aortic root
replacement. Nevertheless, due to a lack of data on the exact
anticoagulation therapy and patient compliance, it is not possible to
make broad inference about this possible association. Further studies
are needed to determine the most optimal anticoagulation therapy after
biological aortic valve replacement.Endocarditis
and type of prosthesesAlthough the rate of endocarditis after bioprosthetic aortic root
replacement varies widely in the literature
(54), our findings are comparable to an
older study on biological aortic valve replacement [3].
Additionally, we found 3 large studies with an endocarditis rate of more
than 2.8%/patient-year (22,
26, 55),
all including stentless valve prostheses.
However, these studies included a
relatively high proportion of patients with active endocarditis which
may explain the higher re-endocarditis rate, although the severity of
endocarditis was not provided. Hence, the trend toward more endocarditis
in stentless valves could possibly be explained by the latter. Based on
these data it is reasonable to assume that stented bioprosthetic grafts
are at least not inferior to stentless bioprosthetic grafts to be used
in case of endocarditis, although the extent of endocarditis may allow
for different inference. Moreover, we found no difference in other
valve-related events between stentless and stented prosthesis. We
believe that both prostheses are safe to use in the average patient
undergoing aortic root replacement.