Right atrial function assessed by volume-derived values and speckle tracking echocardiography in patients with hypertrophic cardiomyopathy

Background To detect the right atrial (RA) functions in hypertrophic cardiomyopathy (HCM) patients by using volume-derived values and two-dimensional strain. Methods Thirty-two HCM patients and 34 age and gender matched normal controls were enrolled for this study. RA volume-derived values were measured by using 2D ultrasonic images. RA strain (S-reservoir, S-conduit, S-booster pump) and strain rate (SR-reservoir, SR-conduit, SR-booster pump), representing the reservoir, conduit and booster pump functions, respectively, were measured by EchoPAC. Results Total RA emptying fraction (RAEF) and RA expansion index in HCM patients were significantly lower than normal controls (p < 0.05). The values of S-reservoir, S-conduit, Sr-reservoir and Sr-conduit in HCM patients were significantly lower than normal controls (p < 0.001). Although there were no significant differences in S-booster pump and Sr-booster pump between HCM patients and normal controls, the absolute values in HCM patients were lower than normal controls. Conclusions In this study, we concluded that RA dysfunctions, including the reservoir and conduit functions were impaired in HCM patients.

embolism and tricuspid regurgitation severity [11][12][13]. These studies were necessary to demonstrate that the technique could detect the RA functions flexibility and accuracy.
The mechanism of the association between RA function and HCM is unknown. Biagini et al. [14] found complex genotypes with double or triple mutations in end-stage HCM patients. Progressive diastolic dysfunction and atrial fibrillation may represent adequate substrates for RA remodeling [15]. A progressive "atrial myopathy" has been also suggested in patients with HCM [16].
Doesch C, et al. [17] found that RA and RV involvement could predict atrial fibrillation (AF) in patients with HCM evaluated by cardiac MRI, reduced tricuspid annular plane systolic excursion (TAPSE) and RA dilatation could serve as determinable markers of AF in patients with HCM. McCullough SA, et al. [18] also elevated RA pressure in HCM patients was associated with left-sided heart failure and was an independent predictor of all-cause mortality and new-onset AF. Limongelli G, et al. [15] demonstrated that RA enlargement may serve as a very useful marker of disease progression and adverse outcome in patients with sarcomeric hypertrophic cardiomyopathy. From these previous studies, we conclude that RA dysfunctions detection in HCM patients are very important.
In the study, we combined volume-derived values and two-dimensional strain, strain rate to assess RA functions in HCM patients. To our knowledge, this is the first research to detect the RA functions by volume-and strain-derived values in HCM patients.

Methods
All HCM patients and normal controls had completed the consent forms for participation in the study. This study was subjected to approval by the ethics committee of "the Affiliated Changzhou No.2 People′s Hospital with Nanjing Medical University".

Study samples
Thirty-two HCM patients and 34 age and gender matched normal controls were enrolled for the research. The inclusion criteria for HCM patients were: ① Mmode and 2D echocardiographic evidence of wall thickness ≥ 15 mm in one or more LV myocardial segments and non-dilated LV. ② Absence of another cardiac or systemic disease capable of producing the magnitude of hypertrophy evident in patients with HCM, such as valvular heart disease, hypertension, hyperthyroidism heart disease, uremic cardiomyopathy and coronary heart disease. ③ All enrolled HCM patients were nonobstructive, excluded the apical HCM, there was no obstruction at rest or provocation (peak gradient < 30 mmHg) based on the degree of LV outflow tract obstruction by continuous wave Doppler.
The normal controls had no evidence of hypertension and any other cardiovascular diseases. All of the physical examination, electrocardiogram, and echocardiography were showed normal.

Two-dimensional doppler echocardiography
All HCM patients and normal controls underwent conventional 2D echocardiography (Vivid E9, GE Healthcare, Horten, Norway), and left atrial diameter (LAd), interventricular septal thickness at the end-diastolic period (IVSd) and LV posterior wall thickness at the end-diastolic period (LVPWd) were measured in the parasternal long-axis view of the LV using M-mode. RV diameter at the middle level (RVd middle), RV diameter at the longitudinal (RVd longitudinal), RV diameter at the base level (RVd basal), RA diameter at the middle level (RAd middle), RA diameter at the longitudinal (RAd longitudinal), and tricuspid annular plane systolic excursion (TAPSE) were measured in the apical fourchamber view. Systolic pulmonary arterial pressure (sPAP) was measured in the parasternal 4-chamber view, if the tricuspid valve regurgitation was absence, sPAP was measured by the regurgitation of pulmonary valve in the parasternal short-axis view at the level of aortic valve or right ventricular outflow view. RV free wall thickness (RVWd) was measured in the subcostal 4-chamber view.
Peak early and late diastolic velocities of tricuspid valve (E and A, respectively) were measured by pulsedwave Doppler, and the ratio of E/A was then calculated.
The peak systolic (S′), early (E′) and late (A′) diastolic tricuspid annular velocities were obtained at the RV lateral wall using TDI, and the ratio of E′/A′ was then calculated.
ECG leads were connected to all the participants. The standard high frame rate (40-90 /s) of the apical 4chamber views (all contained the RA) of three consecutive cycles were stored for off-line analysis.

Data analysis for RA function
The apical 4-chamber views were analysed using the EchoPAC software (EchoPAC Version: 203, GE Vingmed Ultrasound, Norway). Using the button A4C to sketch the endocardial of the RA. The software automatically created a region of interest (ROI) that matched the RA walls. Once the ROI was approved, The RA strain (S-reservoir, S-conduit and S-booster pump) and strain rate (Sr-reservoir, Sr-conduit and Sr-booster pump) were measured (Fig. 1).

Statistical analysis
All data analyses were performed using SPSS 24.0 software (SPSS, Chicago, IL, USA). Shapiro-Wilk′s test was used to detect the normality of all the values. Differences between HCM patients and normal controls were compared with independent Student′s t-test for the data distribution was normal. For variables with a non-normal distribution, the nonparametric Mann-Whitney test was used. Data are presented as the mean ± standard deviation (mean ± SD). Difference was considered statistically significant in all tests when the p-value was < 0.05.

Intra-and interobserver variability
Twenty patients were randomly selected for intra-and interobserver variability. RA strain and strain rate were measured by two experienced cardiologists who were blinded to patients′ clinical data results. Intraobserver variability was measured at different time. Interobserver variability was determined by repeating measurements from the same off-line images. Intra-and interobserver variability was calculated using intraclass correlation coefficients (ICCs).

Results
Clinical baseline parameters and 2D echocardiographic characteristics between HCM patients and normal controls were shown in the Table 1.
There were significant differences in LAd, IVSd, LVPWd and RAd longitudinal, E, E/A, E′ and E′/A′ between HCM patients and normal controls (p < 0.05). LAd, IVSd, LVPWd and RAd longitudinal were significantly larger than normal controls, while E, E/A, E′ and E′/A′ were significantly lower than normal controls. No significant differences were found in LVEF, RVWd, RVd middle, RVd basal, RAd middle, TAPSE, A, S′ and A′ (p > 0.05).
2D echocardiographic RA volume and volume-derived values between HCM patients and normal controls were shown in Table 2, Fig. 2a.
There were significant differences in Total RASV, Passive RASV, Total RAEF and RA expansion index (p < 0.05), and all the values were significantly lower than normal controls. Although there were no significant differences in RAVmax, RAVpre, RAVmin, Active RASV, Passive RASV and Active RAEF (p > 0.05), the absolute RA reservoir, conduit and booster pump functions between HCM patients and normal controls by detecting the RA Strain and strain rate were shown in Table 3, Fig. 2b, c There were significant differences in S-reservoir, Sconduit, Sr-reservoir and Sr-conduit between HCM patients and normal controls (p < 0.001). All the values were significantly lower than normal controls. Although there were no significant differences in S-booster pump and Sr-booster pump between HCM patients and normal controls, the absolute values in HCM patients were lower than normal controls.

Intra-and interobserver variability
The results for the intraobserver and interobserver variability for the RA strain and strain rate upon repeated measurements in 20 random patients were shown in Table 4. ICC values were higher for intraobserver and interobserver variability when the same images were analyzed by the two different cardiologists. What′s more, the results also demonstrated that the analysis of the  software had the well repeatability and reliability in this study.

Discussion
The main findings of the research were: RA reservoir and conduit functions were impaired in HCM patients when compared with normal controls. 2D-STE is a new echocardiographic technique that has been validated for the assessment of LV, LA, RV and RA functions in HCM patients by previous studies [19]. Also, our group had been done some researches in LA and LV function of HCM. Huang J, et al. [20,21] detected the longitudinal and circumferential strain of different myocardium layers, radial strain, and longitudinal rotation by using 2D-STE, and demonstrated that the long-axis and short-axis LV functions in HCM patients were impaired. Huang J, et al. [22] also detected the LA dysfunction in HCM patients by 2D-STE and volume- RA functions play an important role in the cardiac and 2D-STE is a feasible, angle-independent method for the evaluation of RA function [24]. Researchers mainly focused RA functions on pulmonary artery hypertension, acute pulmonary embolism, hypertension, the influence of severity tricuspid regurgitation, right ventricular myocardial infarction, tetralogy of Fallot, and so on [11,12,[25][26][27]. However, till now, we have not found a research about RA functions in HCM patients by using 2D-STE and RA volume-derived values.
Recently, some researchers have found RV functions were impaired in HCM patients by 2D-STE. Cincin A, et al. [28] explored RV mechanical function in HCM patients by demonstrated 2D-STE-derived RV systolic function was impaired in HCM patients when compared with healthy subjects. D'Andrea A, et al. [29] analyzed RV systolic function in patients with HCM at rest and during exercise, and found that RV contractile reserve for HCM was impaired. This study demonstrates for the first time that 2D-STE algorithm applied to routine grey-scale 2D images represents a promising and feasible non-invasive technique to assess RA functions in HCM patients.
From basic 2D echocardiographic characteristics between HCM patients and normal controls, we found RA and LA diameters were dilated in HCM patients. From the volume-derived values, total RAEV, total RAEF and RA expansion index represented the reservoir function, passive RAEV represented the conduit function were significantly lower than normal subjects, the results indicated that RA reservoir and conduit functions were impaired. Strain and strain rate analysis also demonstrated that reservoir and conduit functions were impaired. Although the booster pump function of volume and strain derived-values had no significant differences between HCM patients and normal controls, the absolute values in HCM patients were lower than normal controls. HCM is a progressive disease characterized by LV hypertrophy and fibrosis. LA, LV and RV dysfunctions were observed and demonstrated that the functions were damaged. Our findings may stress the significance of the evaluation of RA dysfunction because it permits us to evaluate RV function on the other hand.

Conclusion
From the study, we concluded that RA dysfunctions, including the reservoir and conduit functions were impaired in HCM patients.   the included findings, Changzhou Science and Technique Program major helps in the design of the study and collection of patients; Changzhou "Qingmiao talents" Project major helps in the analysis and interpretation of the data, revision of the manuscript.

Availability of data and materials
The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Ethics approval and consent to participate
The study complied with the Declaration of Helsinki and was reviewed and approved by the Human Subjects Committee of Changzhou No.2 People's Hospital approved this study. Written informed consent was obtained from each couple enrolled in the study.

Consent for publication
This manuscript does not include any individual person's data.