DISCUSSION
In this study, we have showed that BSA-index of left atrial maximum
volume (LAVImax) and left atrial conduit strain (LAScd) measured by 4D
auto LAQ were useful noninvasive parameters in distinguishing pre- and
post-capillary PH: LAVImax and LAScd were higher in post-capillary PH
group, and their cutoff values were 35.69ml/m2(sensitivity 86%, specificity74%) and -9% (sensitivity 80%,
specificity 70%).
In our studies, most patients in post-capillary PH group were belong to
group 2 PH according to the NICE classification, along with higher serum
NT-Pro BNP, hemoglobin and HbA1c, which were in line with previous
studies[1, 6-8, 18]. It was indicated that the clinical diagnosis
and grouping were reliable, although the PASP and PAWP were estimated by
echocardiography in our studies. Both groups had similarly structure and
function of right heart chamber, with enlarged PA and RA, right
ventricular-pulmonary artery uncoupling and decreasing RV systolic
function. However, the LVEF was lower, while LVMI and E/e’ were higher
in post-capillary PH group, which indicating that the LV systolic and
diastolic function were depressed. These findings supported that
post-capillary PH predominantly classified into group 2 PH in our study.
As we know, LA size is a maker of LV filling pressure and diastolic
function. The LA and the pulmonary veins and venules are the proximal
part of the pulmonary circulation. Therefore, regardless of any cause in
LA pressure rising, it would be reflected on the pulmonary venous
circulation pressure, and following on the PAWP. Continuous increasing
of LA pressure could cause LA and LV enlargement, myocardial stretch and
significant rise of stiffness[19, 20]. Consequently, LA volume and
strain were important in differentiating pre- and post-capillary PH
except for PAWP. Recent studies had showed that LA maximum area access
by CT, LA maximum volume index evaluated by MRI and echocardiography
were useful parameters for distinguishing pre- and post-capillary
PH[8, 21, 22]. These were consistent with our results, which
demonstrated that LAVImax measured by 4D auto LAQ was a valuable
indication. However, Csaba et al. showed that LAVImin measured by
transthoracic 3DE discriminated better than LAVImax between pre- and
post-capillary PH[6]. In that paper, the software of 3DE were not
specifically dedicated to 3D left atrial measurements, and the strain of
LA wasn’t taken into for analysis, which may explain the reason
inconsistency with our study. Besides, when analysing the ability of
LAVImin for differentiating pre- and post-capillary PH, the AUC was also
high by ROC analysis (AUC=0.844, P <0.001), yet LAVImin
wasn’t an independent factor for differentiating both groups when adding
the LA strain parameters into multivariate logistic regression analysis.
4D auto LAQ is specially designed for LA 3D analysis which could
determine the LA volume of different periods in diastole as well as LA
strains conveniently and highly reproducibly. In our study, it was
demonstrated that LAScd was lower, while ePLAGS were higher in
post-capillary PH, and they were also useful parameters for
distinguishing pre- and post-capillary PH. Ashwin et al. also found that
ePLAGS assessed by 2D echocardiography accurately differentiated
pre-capillary from post-capillary PH[7], and this was in line with
our study. On the basis of Frank Starling law, the enlargement of LA is
associated with myocardial thinning, restrained contraction function and
hence compromised deformation. We found that LASr and LAScd were
obviously decreased in patients of post-capillary PH in our study, which
could be seen as directly reflecting LA myocardial dysfunction, in
adhering with previous study that LA Strain was the strongest predictor
of cavity pressure.[23] Nevertheless, LAScd was one of the most
independent factors for differentiating pre- and post-capillary PH by
regress analysis. Maybe because the LA conduit strain connected
reservoir strain and LA contraction strain, and it can also be reflected
the LV filling pressure as well as LASr. In addition, LA storage and
channel function (DEI and PEI) were higher in post-capillary PH group,
but LA active systolic function (AEI) was not in this study, which could
be evidenced this suppose.
Nevertheless, there are a few limitations. Firstly, this was a
single-center study with a relatively small sample size. Secondly, the
PASP and PAWP were measured from echocardiography and not obtained by
invasively, while these noninvasive parameters were significantly
correlated with invasive measurements[2]. Finally, we didn’t analyse
the variability of parameters of LA structure, function and stain
between 4D auto LAQ and 2D echocardiography. LA myocardial function
assessed by 2D strain analysis is much more complex than that of the
thicker LV, so LA volume and function should be calculated with another
software.