2.1 Patient Population and Study Design
The inclusion criteria were: 1) according to the 2015 European Society of Cardiology/European Respiratory Society (ESC/ERS) guidelines, the haemodynamic definition of PAH relies on a mPAP≥25 mmHg at rest, PAWP≤15 mm Hg and PVR >3 Woods[2]; 2) patients with congenital heart disease(CHD) associated with PAH and idiopathic PAH(IPAH). The exclusion criteria were: 1) PAH except CHD-PAH and IPAH; 2) combined with hypertension, coronary artery disease, hypertrophic cardiomyopathy, rheumatic mitral stenosis, renal failure, hyperthyroidism, obstructive sleep apnea syndrome and other diseases; 3) combined with obvious arrhythmias: including atrial fibrillation, preexcitation syndrome, supraventricular tachycardia, atrioventricular block, left bundle branch block and pacemaker rhythm; 4) patients with serum electrolyte imbalance and receiving antiarrhythmic medications.
From January 2016 to October 2019, a total of 103 patients fulfilling the inclusion criteria were evaluated; 59 patients as PAH-CHD group and 44 patients as IPAH Group. 30 patients with CHD but no PAH(nPAH-CHD group) and 30 healthy control groups(HCG) were enrolled as a Control group. They were selected from The Second Xiangya Hospital of Central South University.
All patients signed informed consent to the study according to a protocol approved by the Ethical Committee of The Second Xiangya Hospital of Central South University.
We collected the basic clinical information of these patients, including sex, age, physical examination, echocardiography, six-minute walk test distance (6MWD), hemodynamic parameters, and blood tests for biochemical markers associated with clinical severity.
2.2 Echocardiographic evaluation
Echocardiography was performed by two experienced cardiologists at rest. The patient was in the left lying position, using commercial echocardiography equipment (video 7, General Electric, Milwaukee, WI, USA) and 3-MHz transducers. Transesophageal and transthoracic echocardiography was performed within 24 hours before operation. The pulmonary artery systolic pressure (SPAP) was calculated from the tricuspid regurgitation velocity of parasternal short axis and apical four chamber view using Bernoulli equation, and statistical analysis was performed. A SPAP< below 30 mm Hg is defined as normal. PAH was divided into mild (SPAP=30-44 mmHg), moderate (SPAP=45-59 mmHg), and severe (SPAP≥60 mmHg) based on SPAP. All parameters were measured separately for three times and averaged. The coefficients of intra-observer and inter-observer variation of echocardiographic parameters were less than 5% and were not significant.
2.3 Right heart catheterization
Patients were diagnosed by RHC according to criteria: mPAP≥25 mmHg and PVR>3 WU at rest in the presence of a normal PCWP (≤15 mmHg). Heart rate and systemic blood pressure were measured just before RHC. The catheter was passed through the femoral vein sheath and RA, RV, pulmonary artery, and PCWP were measured. Cardiac output (CO) was measured by Fick method, using oxygen consumption. Cardiac index (CI) was calculated as follows:
PVR was calculated as:
All parameters are calculated as the average of three different measurements. After obtaining baseline hemodynamics, acute vascular response tests were performed with inhaled nitric oxide or iloprost.
2.4 ECG measurements
The 12-lead synchronous electrocardiogram recording method was adopted. The paper walking speed was 25mm/s and the amplitude was 10mm/mV. Use Cardio Calipers version 3.3 software to measure PWD of electrocardiogram. The intersection of the starting point of P wave and equipotential line is taken as the starting point of P wave, the intersection of the ending point of P wave and equipotential line is taken as the ending point of P wave.The maximum value is the maximum P-wave time limit (Pmax), the minimum is the minimum P-wave time limit (Pmin), and the difference between them is p-wave dispersion (PWD). Each lead continuously measured three P wave time limits and took the average value. 30 patients were randomly selected for the PWD repeatability study. The same measurer measured PWD with the same method at different times to test the repeatability of this method. PWD measured separately for three times and averaged. The coefficients of intra-observer and inter-observer variation of echocardiographic parameters were less than 5% and were not significant.
2.5 Risk assessment of PAH
Patients were categorized as ‘Low risk’, ‘Intermediate risk’, or ‘High risk’ on the basis of cut-off values for NT-proBNP, mean right atrial pressure, pericardial effusion, right atrial area, cardiac index, 6 minutes walking distance, mixed venous oxygen saturation, cardiac function, and defined in the risk assessment instrument from the 2015 ESC/ERS guidelines (Table 1).[2] Each variable was graded from 1 to 3 where 1 =‘Low risk’, 2=‘Intermediate risk’, and 3=‘High risk’. Divide the sum of all grades by the number of variables available per patient to get the average grade. The average score was rounded to an integer to define the risk group of the patient[6]. In addition, according to the 2015 ESC/ERS guidelines, patients with PAH(CHD-PAH and IPAH) are divided into low-risk groups(30 patients), medium-risk groups(53 patients), and high-risk groups(20 patients). Risk stratification was assessed at baseline and at follow-up.
Table 1 Variables and their thresholds in the risk assessment tool included in the ESC/ERS 2015 Guidelines for the Diagnosis and Treatment of pulmonary hypertension
Determinants of prognosis
|
Low risk
|
Intermediate risk
|
High risk
|
WHO functional class
|
Ⅰ、Ⅱ
|
Ⅲ
|
Ⅳ
|
6MWD(m)
|
>440
|
165~440
|
<165
|
NT-proBNP(ng/L)
|
<300
|
300~1400
|
>1400
|
pericardial effusion
|
No
|
No or minimal
|
exist
|
right atrium area(cm2)
|
<18
|
18~26
|
>26
|
RAP(mmHg)
|
<8
|
8~14
|
>14
|
SvO2(%)
|
>65
|
60~65
|
<60
|
CI(L/min/m2)
|
≥2.5
|
2.1~2.4
|
≤2.0
|
Use the risk assessment tools in the 2015 ESC/ERS pH diagnosis and treatment guidelines. It is recommended to achieve a low-risk level as the treatment goal.[2]
6MWD, 6-minute walking distance; CI, cardiac index; NT-proBNP, N-terminal prohormone of brain natriuretic peptide; RA, right atrium; RAP, right atrial pressure; SvO2, mixedvenous oxygen saturation; WHO, World Health Organization.
2.6 Statistical Analysis
The SPSS 19.0 computer program (SPSS, Chicago, IL, USA) was used for the statistical analysis. The data is shown as the mean ± standard deviation of normally distributed variables, while the variables without a normal distribution are shown as the median, minimum, and maximum. The repeatability of the two groups of data with normal distribution is studied by paired sample t-test, and the comparison between the two sample groups is conducted by independent sample t-test. The nonparametric rank sum test (Mann Whitney U method) is used for the comparison between groups with nonnormal distribution. The adoption rate or constituent ratio (%) of counting data is expressed, and the comparison of rates is adopted χ2 test, Pearson correlation coefficient is used for correlation analysis between variables that conform to normal distribution, and Spearman correlation coefficient is used for correlation analysis between variables that do not conform to normal distribution.
A p value lower than 0.05 was considered to be statistically significant. The receiver operating characteristic curve (ROC curve) was used to evaluate the diagnostic efficacy of PWD for the occurrence of PAH-CHD and IPAH (including sensitivity, specificity, positive predictive value, negative predictive value, Youden index, accuracy), and the test level α=0.05.
2.7. Ethical considerations
The study protocol was approved by the Ethics Committee for Human Study, The Second Xiangya Hospital, Central South University. The study was performed in accordance with the Declaration of Helsinki.