Discussion
Operations in the setting of extended ascending aortic replacement can
range in complexity from hemiarch to total arch replacement. The
proponents of the hemiarch repair cite its technical simplicity,
perceived durability, shorter circulatory arrest times, and potential
for lower morbidity11,12. Those who prefer the total
arch repair believe that the reintervention rate should be lower with
complete replacement leading to improved long-term
survival13-15.
There are two principle findings of this study. The first is that, total
arch replacement at the time of extended ascending aortic replacement is
associated with increased mortality and reintervention rates when
compared with hemiarch replacement. Second, age is associated with
increasing mortality regardless of the extent of repair. Collectively,
our data suggests that mortality and reintervention rates are higher in
the total arch group, making the hemiarch procedure the preferred
procedure as long as it adequately addresses the aortic pathology,
especially in those of advanced age.
The baseline characteristics of those undergoing hemiarch and total arch
replacement were somewhat different in this series. Those undergoing
hemiarch replacement were more commonly male, hypertensive, diabetic,
had peripheral arterial disease and a prior myocardial infarction. In
addition, those undergoing hemiarch repair were more likely to have been
done emergently and have an aortic dissection as opposed to an aortic
aneurysm as the operative indication. Our assessment is that the
hemiarch group in this study appeared somewhat “sicker” than the total
arch group, and that would be consistent with our philosophy of only
performing a total arch replacement during extended ascending aortic
replacement when clinically indicated.
Our in-hospital and 30 day mortality was 5.4 and 4.7% in the hemiarch
group and 13.4 and 14.3% in the total arch groups. These results, as
well as our overall survival at 1, 3, and 5 years of 83.6, 76.2, and
68.2% are comparable to previously published
studies12,16-18. While our study did not
focus on perioperative outcomes, we had relatively low stroke rates (3.4
vs 5.4%, hemiarch vs total arch, p=0.43), as well as similar rates of
paraplegia, need for postoperative extracorporeal membrane oxygenation,
and reoperations for bleeding between groups. These results are similar
to others reported in the literature as well as rates of
paraplegia12,19-23.
The primary objective of this study was to analyze preoperative and
intraoperative factors which may be associated with survival in the
setting of aortic arch surgery at the time of extended ascending aortic
replacement. By Kaplan-Meier estimates, there was a clear difference in
survival between those undergoing a hemiarch versus a total arch repair
(log-rank p=0.012). To examine this relationship further, a
multivariable Cox proportional hazard model was created which adjusted
for baseline characteristics between groups. In this analysis, the
presence of a total arch repair was associated with a 2.5 time increase
in the likelihood of death during the follow up period as compared to
the hemiarch group (HR 2.53, 95% CI 1.38-4.62, p=0.003). In addition to
type of aortic repair, increasing age was also shown to be highly
associated with mortality during the follow up period – with a 1.8 time
increase per 10-year increase in age (HR 1.76 per 10 years of age, 95%
CI 1.37-2.28, p<0.001). Other factors of significance or
borderline significance on univariable modeling were not associated with
mortality on multivariable modeling (gender, use of antegrade cerebral
perfusion, previous myocardial infarction, renal failure, chronic lung
disease, peripheral arterial disease, hyperlipidemia, hypertension, and
concomitant coronary artery bypass grafting). It is also notable that
the effect of age was constant in both the hemiarch and total arch
groups, as assessment of an interaction term was not significant.
The central figure of this manuscript (Figure 3) demonstrates the
powerful effect of type of repair and age. This figure puts the impact
of the age and type of aortic repair estimates on mortality in
perspective based on our multivariable model. The predicted hazard for
mortality for a 50-year-old undergoing a hemiarch repair is 17.1 (HR
17.1, 95% CI 4.8 – 61.5), while the predicted hazard for mortality for
a 70-year-old undergoing the same repair is 53.3 (HR 53.3, 95% CI 18.9
– 319.4). Similarly, the predicted hazard for mortality for a
50-year-old undergoing a total arch repair is 43.4 (HR 43.3, 95% CI
10-181), while the predicted hazard for mortality for a 70-year-old
undergoing the same repair is 134.9 (HR 134.9, 95% CI 20-909). One can
also compare across repair types – in a 50-year-old the hazard was 17.1
for a hemiarch and 43.4 for a total arch, and in a 70-year-old, the
hazard was 53.3 with a hemiarch and 134.9 with a total arch.
It was not our intention in this study to examine indication in detail
as we wanted to look at a comprehensive aortic experience in the setting
of extended ascending aorta replacement. However, indication is known to
be a strong risk factor for mortality in other
studies17,22 and was included in our multivariable
modeling. While Indication was not associated with overall survival in
this analysis, this variable violated the proportionality assumptions of
Cox proportional hazard modeling. Therefore, our final multivariable
model referenced above was “stratified” by indication. However, to
confirm our primary findings that age and type of repair were highly
associated with mortality and that this was not influenced by
indication, three sensitivity analyses were performed (Supplemental
Table 4). As can be seen in Supplement Table 4, stratification by the
indication variable in the model resulted in an improvement in model fit
with a lower AIC and BIC as compared to the non-stratified model (AIC
562 to 448, BIC 608 to 487). The violation of proportionality occurred
in the “other” indication for surgery (infections, porcelain aortas,
and aorto-esophageal fistulas, n=16). As this group is admittedly a bit
“unique” we performed the analysis excluding these observations, with
similar finding for presence of a total arch repair and age per 10 years
(both remained highly significant, and this model had worse fit than the
indication stratified model). Finally, we fit our final model
separately, in the cohorts only with aortic dissections and only with
aneurysms, again with similar findings that total arch replacement and
age per 10 years were both associated with increased mortality. Our
findings on the effect of age on overall outcomes can be supported by
recent literature publications13,24.
Type of aortic arch repair at time of extended ascending aortic
replacement is thought to influence the need for subsequent aortic
reintervention5,13,14,24,25. In this study, we
utilized competing risk with death as a competing risk to determine
estimates of aortic reintervention rates. As one cannot definitively
determine that those who died would not have needed aortic
reintervention, considering death as a competing risk is appropriate.
However, analyses of these type are a bit difficult to interpret in the
context of the literature as the vast majority of studies have not
utilized this methodology.
Despite a more extensive aortic repair, those undergoing total arch
replacement at the time of extended ascending aorta replacement had
markedly higher reintervention rates (2.6, 2.6, and 4.4% at 1, 2, and 3
years in the hemiarch group and 5.0, 10.3, and 11.9% in the total arch
group). After adjustment for age (the other strong predictor in the
mortality model), those with a total arch repair were 3.2 times as
likely to need aortic reintervention as compared to the hemiarch group
(SHR 3.21, 95% CI 1.01 – 10.2, p=0.047). Age itself was not associated
with the need for aortic reintervention (SHR 0.90, 95% CI 0.65 – 1.23,
p=0.50).
There are numerous limitations to this study. First, this study is
subject to all the limitation of a retrospective, non-protocoled study.
Second, while presence of a total arch repair and age were variables of
significance, the lack of a factor as significant could be due to small
sample size and a type II error. Third, we lack power to examine
different types of aortic arch repair. Fourth, the lack of accurate
anatomic data from preoperative and postoperative computed tomography
imaging makes assessment of these variables as it relates to mortality
or need for aortic reintervention impossible. Fifth, there is a
potential third group of interest we did not include in this study –
those who had non-extended ascending aortic replacements with an aortic
cross clamp in place. Sixth, the difference in survival may be due to
higher perioperative mortality in the total arch group despite
appropriately modeling to assess the continued adjusted risk over time.
Seventh, surgeon bias and preference largely dictated when to intervene
on aortic arch in extended ascending aortic replacement and type of
aortic arch repair chosen. Last, the limited number of endovascular
interventions in this study make any assessment of this technology in
our practice difficult, although it is being increasingly utilized.
The optimal approach to aortic arch repair in the setting of ascending
aortic disease remains controversial and continues to evolve. While some
advocate for extensive replacement of the aortic arch during extended
replacement of the ascending aorta, others prefer a more tempered
approach absent true pathology. While this study cannot directly compare
the two philosophical approaches of aortic arch repair outlined above,
as aortic arch repair was only performed in this study when clinically
indicated, if addressing all aortic pathology present at the time of
operation is adequate, we have might expect to see similar survival and
reintervention rates between these two groups. On the other hand, if
more isolated pathology only requiring hemiarch replacement of the aorta
truly progresses, then one may see a higher reintervention and possibly
mortality rate in the less aggressively managed “hemiarch” group. The
fact we found higher rates of mortality and reintervention in the total
arch group, when we only addressed the aortic arch when pathology was
present suggests that this group represents a group of patients with
disease distinct from those with isolated ascending aortic pathology and
that those with arch pathology inherently have more advanced disease
which is likely to both decrease survival and increase the need for
further aortic reintervention. This effect was particularly prominent in
those of advanced age.
In conclusion, our data suggests that mortality and reintervention rates
are higher with total arch replacement in the setting of extended
ascending aortic replacement, making the hemiarch procedure the
preferred procedure as long as it adequately addresses the aortic
pathology, especially in those of advanced age. The rationale for
extending ascending aortic repair to include a total arch replacement in
order to decrease reintervention may not be valid.