Discussion
BAV related aortopathy has been a controversial issue in the past few
years. Most of the researches focused on BAV with dilated ascending
aorta, but there were limited documents of patients with normal-sized
proximal aorta. In this current study, the following main findings were
described: 1) ascending aortic dimensions at baseline were larger in BAV
patients than in TAV patients, but growth rates of aortic size in a
follow-up of 7 years were comparable between two groups after AVR ; 2)
the incidence of adverse aortic events were very low in BAV patients
with normal-sized proximal aorta after AVR, which was not different from
TAV patients; 3) ascending aortic dimension at baseline was a
significant predictor of progression of ascending aorta .
Although the exact pathogenesis of BAV related aortopathy is not yet
well elucidated, there were two main hypotheses being widely accepted:
hemodynamic and genetic causal factors. Robicsek and colleagues first
described the patterns of transvalvular flow in BAV
patients.10 After that, many clinical and basic
researches focused on the role of valve related hemodynamics and found
consistently eccentric turbulent transvalvular flow in non-stenotic or
regurgitated BAV patients.11-14 BAV related
hemodynamic factors, such as tensile and shear stresses, play an
important role in dilation of ascending aorta. In an ex-vivo model,
Juraszek and colleagues found significant pressure differences in
various locations of ascending aorta in BAV compared with TAV, which may
contribute to BAV related aortopathy.15 On the other
hand, some studies have found the ascending aortic wall of BAV patients
is intrinsically different from that of TAV
patients.16-19 Due to significant lack of fibrillin-1,
vascular smooth muscular cell would detach from elastin and collagen,
leading to apoptosis and loss of structural
integrity.3 Several genes mutations have been reported
in BAV patients, including that involved in cell growth,
differentiation, and matrix deposition and
apoptosis.20, 21 There is still no consensus on the
roles of these two factors. The two different hypothesis lead to
different surgical strategies for the ascending aorta in BAV patients:
the former may lead to a relatively conservative strategy, it’s believed
that the ascending aorta will not further progress after disappearance
of hemodynamic factors due to AVR; however, the latter may bring out a
more aggressive strategy.
In the present study, we found a larger ascending aorta at baseline in
BAV patients compared to TAV patients. However, there was a comparable
progression of ascending aortic dimension in both groups in a relatively
long term follow up period. Most of the patients in our study groups
didn’t experience severe ascending aortic dilatation. In accordance with
previous studies, there was a considerable low risk of adverse aortic
events in our population.9, 22, 23 Mayo published a
large series of cases with an average follow up of 12 years after AVR,
there was a very low rate (1.9%) of aortic events in BAV
patients.24 Meanwhile, many clinical basic studies
have found that the transvalvular flow patterns are significantly
abnormal in BAV patients, which is obviously related to ascending aortic
dilation.11-14 According to the present study and
other literatures, we thought that the hemodynamic factor may be the
main pathogenesis of BAV related aortopathy.
We didn’t evaluate per year growth rate of the ascending aorta in BAV
group, but it seems that there was no significant aortic dilation during
follow-up in patients with normal ascending aorta at baseline after AVR.
Valentina Agnese and colleagues found a growth rate of 0.5mm per year of
ascending aorta in BAV patients, and the growth rate per year was high
in the first two years then decreased steadily.22However, all included patients in their study didn’t undergo AVR. A
correlation between artery hypertension and aortic dilation was observed
in some research,9, 25 but the correlation was
insignificant in our study, that perhaps due to a more precise control
of artery hypertension after AVR in our patients. Notably, we found
ascending aortic dimension at baseline was a significant predictor of
progression in ascending aorta. Further prospective study should be
conducted to confirm this finding.