Discussion
We have evaluated the long-term effect of pregnancy on structural and
functional echocardiographic measurements of RV and their association
with the number of parity. Although the parameters used for evaluation
of RV function had never been measured under the lower reference limit
in the study population, these parameters have reduced in some extent.
On the other hand, the structural changes of RV were more evident owing
to the findings about RV dilation and RV hypertrophy meaning RV basal
diameter and free wall thickness were above the upper reference limit.
While the number of parities had a significant effect on these
functional and structural changes of RV, giving a birth was found as
independent risk factor for RV dilation.
The cardiovascular system undergoes several changes during pregnancy in
order to supply metabolic demands for both mother and fetus (6).
However, the interesting data demonstrated in our study, was the
persistency of some of these physiological changes seen in RV after
pregnancy and their relationship with the number of parity. The
situation can be explained by cardiac remodeling which is defined as
basic changes in geometry, wall thickness, size, and ventricular
function by means of complex process including a group of molecular,
cellular, and interstitial changes (7-10). Although the exact mechanism
of cardiac remodeling is poorly understood, the renin-angiotensin system
(RAS) is a key mediator involved in the pathogenesis of cardiac
remodeling. Activation of RAS is essential for normal pregnancy in order
to be able to cope with the increased demand for salt and water during
pregnancy. Many studies have shown that in normal pregnancy there is an
increase in almost all the components of the RAS. Therefore,
irreversible changes in RV dimensions can be seen by means of remodeling
related to activation of RAS in pregnancy (11-13). On the other hand, it
should be kept in mind that RAS is activated in pregnancy because of
maternal physiological demands and in healthy pregnancy it does not
result in pathologic processes such as intrauterine growth restriction,
preeclampsia etc. This data also can explain why RV dilation and
hypertrophy have found in this study without RV dysfunction which are
distinct components of RV remodeling (14-16).
The inflammatory process is also responsible for cardiac remodeling
(17). While both pro-inflammatory and anti-inflammatory markers increase
in pregnancy, a prospective study comparing the inflammatory mediators
between late pregnancy and early postpartum, has showed that markers
that have predominantly anti-inflammatory effect were higher in
pregnancy (18). In addition, some of the autoimmune diseases such as
rheumatoid arthritis can ameliorate during pregnancy in line with this
prospective study. On the other hand, most of the physiologic changes
resolve during the postpartum period in which pro-inflammatory markers
are high. Each pregnancy means exposure of this pro-inflammatory
postpartum period that may influence RV remodeling and this situation
can be the reason of our finding about significant relation between
number of parity and RV dilation and RV hypertrophy. Hormonal
alterations have important roles in many physiological changes during
pregnancy. Estrogen levels gradually increase and reach highest value in
late pregnancy. Eghbali et al demonsrated the association between
estrogen level and pregnancy-related heart hypertrophy in pregnant rats
(19). Indeed this study is very supportive for our finding about
association between RV hypertrophy and parity. Whatever the mechanism of
cardiac changes during pregnancy, it is obvious that dilation and
hypertrophy of cardiac chambers are compensatory alterations against
increased plasma volume and cardiac output. Therefore, these changes are
necessary for completion of normal pregnancy and the more pregnancy the
woman has, the more she will be exposed to this condition. Thus,
association between parity and structural changes of RV is reasonable.
According to our study the other independent risk factors for RV
dilation were smoking, age and BMI. Indeed, systemic disease especially
HT, DM, smoking, increasing age and obesity have negative effect on
cardiac remodeling (20-21). In our study population there were neither
resistant HT (HT controlled via ≥ 4 antihypertensive drugs) nor
complicated DM. This can be the reason why we did not found relation
between such diseases and RV dilation. Smoking has structural and
functional cardiac effects related to tremendous mechanisms such as
hemodynamic and neurohormonal changes, oxidative stress, inflammation
etc. Although structural and functional effects of smoking on LV were
more studied and well known, in a population-based cohort study, smoking
was found independently related to worse RV outcomes (22). From this
aspect, our study may give a little contribution to literature even
though it was not the main purpose of study. Similarly, obesity has such
cardiac alterations either by itself or high incidence of relation with
comorbidities such as coronary artery disease, HT, DM. World Health
Organization defines overweight and obesity as a BMI over 25 and BMI
over 30 respectively. We did not use this classification in study but
increasing BMI itself was found as independent risk factor for RV
dilation. Again, in line with our study, it has shown in many studies
that several structural and functional cardiac alterations are
age-related irrespective of comorbidities (23-24).
Although relation between the number of parity and estimated PAP was
found statistically significant, there was not any value exceeding 35
mmHg. In fact, transthoracic echocardiography is unreliable method for
PAP and overestimates it (25-26). On the other hand, our study may point
a linear increase in PAP with increasing number of parity other than
causing clinically important outcomes. RA dimensions were also found
higher in parous women and it was related to the number of parity.
Scarcity of studies about RA and pregnancy makes it difficult to
compare, but it can be handled with RV and commentions about RV can be
applied to alterations about RA.
Echocardiography is method of choice for assessment of RV. It is widely
available and provides useful information about the right heart chambers
(27). We have assessed the right heart especially focusing on RV via
echocardiography and evaluated the long-term effects of parity on RV and
its relation of the number of parities. The studies about the right
heart are very few when compared to the left heart and the number of
studies declines when it is applied to pregnancy. What makes this study
important is its uniqueness indicating the parity had long-term effects
on RV and this association has increased in a number-related manner.