RESULTS
General clinical characteristics
According to the estimated PAWP, forty-one patients had pre-capillary PH, and fifty-seven patients had post-capillary PH. Clinical characteristics of the patients were detailed in Table 1 . In line with the NICE classification[1], most of patients with pre-capillary PH belonged to group 1, 3, and 4, while patients with post-capillary PH could be predominantly classified into group 2. There were significantly higher with NT-Pro BNP, hemoglobin and HbA1c in post-capillary PH group comparing with pre-capillary PH group (p <0.05). However, BMI, BSA, heart rate, systemic blood pressure and serum Hb did not differ between the two groups (p >0.05).
Echocardiographic analysis (Table 2 )
Although the diameter of pulmonary artery (PA) and the areas of right atrial (RA) were enlarged in both groups, there were no significantly differences in structure and function of the right heart chamber between the two groups, including PA, RA areas, RVFAC, S’, TAPSE and TAPSE/PASP (p >0.05). For the left ventricular, the LVEDI, LVESI, LVMI and E/e’ were obvious higher in patients with post-capillary PH, while the LVEF was lower than pre-capillary PH (p <0.001).
LA volume indices were significantly increased in post-capillary PH compared to pre-capillary PH (LAVImax: 54.89±22.04 vs. 29.54±13.06 mL/m2, LAVImin: 36.75±17.65 vs. 16.26±8.57 mL/m2, LAVIpreA: 46.55±20.49 vs. 23.25±11.48 mL/m2, p < 0.0001), while DEI (0.34±0.12 vs. 0.45±0.11, P < 0.001), PEI (0.15±0.10 vs. 0.22±0.11, P = 0.0001) and AEI (0.21±0.11 vs. 0.30±0.12,P = 0.05) were decreased (Figure 2) . LASr (11.30±6.92 % vs. 17.50±6.70 %, P < 0.001) and LAScd (-6.45±3.75 % vs. -11.38±5.78 %, P < 0.001) obviously reduced in post-capillary PH group compared with pre-capillary PH group. Besides, there were obvious decreased with LA strain in patients of post-capillary PH, as a result, the post-capillary PH group had higher ePALGS. (Figure 3 )
Regression analysis
Logistic regression analysis was used to determine which of the parameters of echocardiography could be used to distinguish pre- from post-capillary PH. The parameters would be put into multivariate analysis if p <0.10 in univariate analysis. Thus, the volume and the function of LA in different phases, LASr, LAScd, LVEDi and LVEF were chosen as inputs for multivariate logistic regression model. However, only LAVImax (OR: 1.40; 95% CI, 1.05–1.87; P = 0.021) and LAScd (OR: 1.76; 95% CI, 1.18–2.49; P = 0.004) were considered as the most powerful independent predictors for detecting post-capillary PH (Table 3 ). ROC analysis showed that LAVImax (AUC=0.82, p < 0.001) and LAScd (AUC=0.78, p<0.001) had a high discriminating power in distinguishing between pre-capillary and post-capillary PH groups, and their cutoff values were 35.69ml/m2 (sensitivity 86%, specificity74%) and -9% (sensitivity 80%, specificity70%) (Figure 4A ). Considering LAVImin and ePLAGS were useful to discriminate between pre- and post-capillary PH in previous studies, both the parameters were also taken into ROC analysis in our studies. It was demonstrated that they had high differentiation capability (LAVImin: AUC=0.84, p<0.001; ePLAGS: AUC=0.72, p <0.001) as well (Figure 4B ).
Observer variability Intra-observer variability for LAVImax, LAVImin, LAVIpreA, LASr, LAScd and LASct by inter-class correlation were 0.992 (p < 0.001), 0.983 (p < 0.001), 0.994 (p < 0.001) and 0.960 (p < 0.001), 0.901 (p< 0.001),0.878 (p = 0.001) respectively. Inter-observer variability for LAVImax, LAVImin, LAVIpreA, LASr, LAScd and LASct by inter-class correlation were 0.985 (p < 0.001), 0.991 (p < 0.001), 0.935 (p < 0.001) and 0.963 (p = 0.001), 0.848 (p = 0.001); 0.802 (p= 0.001) respectively.