Patients and methods: Thirty-one patients (16 females, 15 males; mean age: 42.3±15.0 years; range, 21 to 71 years) were enrolled in this cross-sectional study between June 2013 and January 2014. Transthoracic echocardiography and right and left heart catheterization were performed. B-type natriuretic peptide (BNP) and uric acid levels were evaluated. Patients were evaluated in two groups regarding the requirement of hospitalization in the one-year period, tricuspid annular plane systolic excursion (TAPSE) values, and right ventricle lateral wall tissue Doppler systolic velocity (St) values. A TAPSE <1.6 cm and an St <10 cm/sec were considered worse outcomes. Groups were compared in terms of hemodynamic, neurohormonal, and echocardiographic data.

Results: Hospitalized patients had lower 6-min walk test values (332.80±135.46 vs. 449.75±73.49, p=0.01) compared to those who were not hospitalized. Hospitalized patients had higher BNP levels [145.85 (11.82-688.66) vs. 36.62 (8.76-880.88), p=0.02]. The 6-min walk distance had a significant effect on predicting hospitalization (p<0.05; CI: 0.64-0.99). Considering the odds ratio, it was illustrated that the 6-min walk distance had a 0.96-fold effect in hospitalized patients compared to patients who were not hospitalized. Patients with lower TAPSE values had a lower left atrial end-systolic volume (15.98±7.40 vs. 25.48±12.31, p=0.01) and a lower left atrial expansion index (58.88±42.1 vs. 142.14±73.38, p=0.01). Left atrial ejection fraction was significantly lower in patients with lower St values (0.37±0.13 vs. 0.54±0.13, p=0.001).

Conclusion: Pulmonary arterial hypertension patients with lower TAPSE values tended to have a lower left atrial volume and left atrial volume index. The traditional parameters, such as BNP and 6-min walk test, were predictors of hospitalization in patients with pulmonary arterial hypertension.

There are several radiologic implications, such as cardiac magnetic resonance imaging and three-dimensional (3D) echocardiography, to evaluate both right and left cardiac functions and performance. Although cardiac magnetic resonance imaging is a preferred method in evaluating ventricular function,[3] there are certain limitations, namely financial cost, time, and requirement of general anesthesia in certain populations.[3,4] Transthoracic echocardiography plays a key role in the diagnosis and follow-up of patients with PAH. These parameters, including tricuspid annular plane systolic excursion (TAPSE), are related to a worse survival rate in this patient group.[5] Three-dimensional echocardiography has an incremental value to evaluate both right and left ventricular function and volumes.[6,7] This method does not require general anesthesia and is not time-consuming and cost-effective, thus it is a favorable method in such patient groups.

Due to the mechanical effect of right heart dilatation,[8] left atrium and ventricle volumetric and strain changes can also occur in patients with PAH. These changes may include worsening of the left ventricle systolic function, decrease in left ventricular volumes, left ventricle wall strain, and left atrial contraction abnormalities. As a result, left atrial and ventricular changes in severe PAH may contribute to clinical worsening, hospitalization, and mortality and may increase the necessity to use diuretics. Regarding neurohormonal biomarkers, B-type natriuretic peptide (BNP) and N-terminal (NT) pro-BNP have been found to be related to the severity of PAH, right ventricular failure, and mortality.[9]

Changes in the right ventricle and atrium in the course of pulmonary hypertension are well-defined. However, the left ventricle and left atrium response to the right ventricular overload on the disease course is not clearly shown yet. Hence, this study aimed to demonstrate left atrial and left ventricular 3D volumes and two-dimensional (2D) strain characteristics and their relationship with clinical status, neurohormonal markers (brain natriuretic peptide values), and invasive parameters measured by right heart catheterization in patients with different types of pulmonary arterial hypertension.

Transthoracic echocardiography was performed in patients with severe pulmonary hypertension using Philips IE33 equipment (Philips Electronics Ireland Ltd., Dublin, Ireland). For each patient, the pulmonary artery systolic pressure estimated by tricuspid regurgitation, right ventricle systolic function parameters, including TAPSE, peak systolic velocity of the tricuspid annulus by tissue Doppler imaging (TDI) (right ventricle [RV]- TDI-right ventricle lateral wall tissue Doppler systolic velocity [St]) were assessed. The eccentricity index in diastole and systole were recorded by using 2D echocardiography.

Speckle tracking and 3D echocardiography evaluations were performed during a brief breath hold and with a stable electrocardiogram recording. Two-dimensional speckle tracking echocardiography was performed to derive left ventricle longitudinal strain and left atrial reservoir strain and strain rate, conduit strain rate, and contraction strain rate. Left atrial apical four- and two-chamber view images were taken using conventional 2D grayscale echocardiography. The recommended frame rate was set between 60 and 80 frames per second during the processing. Left atrial endocardium surface was semiautomatically traced in both two- and four-chamber views by a point-and-click approach. The epicardial surface tracing was done automatically.[10]

During atrial reservoir phase, the left atrium fills and stretches so its strain curve increases, reaching a positive peak at the end of atrial filling before the opening of the mitral valve. After mitral opening, the left atrium empties quickly, and its volume reduces, so the strain initially decreases up to a plateau corresponding to the phase of diastasis. In patients that are in sinus rhythm, normally the plateau is followed by a second positive peak, smaller than the first, which corresponds to the period preceding atrial contraction, and finally by a negative peak after the atrial contraction[11]

Left ventricle four-, three-, and two-chamber images were recorded. During the processing, left ventricle peak longitudinal strain was recorded. To simplify our strain examination, we only used longitudinal systolic strain since it appears to be highly sensitive for myocardial disorders and more reproducible than either circumferential or radial strain. Because the left ventricle shortens from base to apex with systole, the fixed short-axis tracking that is required for radial and circumferential strain is more difficult than longitudinal tracking, which moves with the base-to-apex motion.[12]

Next, to obtain real-time 3D volumetric data of the left atrium and left ventricle, a matrix array transducer (X5-1; Philips Ultrasound Ltd, Bothell, WA, USA) was used. Electrocardiogram-gated multiple beats were recorded to achieve higher resolution. Full-volume mod was chosen for image acquisition according to current guidelines.[6]

The real-time three-dimensional echocardiography (RT3DE) was used to obtain fullvolume, real-time pyramidal volumetric data sets along four consecutive cardiac cycles. The RT3DE data sets were then digitally stored for analysis using the QLab-Philips version 9.1 software (Philips Ultrasound Ltd, Bothell, WA, USA). Manually marked anatomical points used to calculate left atrium volumes were defined as follows: lateral, septal, anterior, and inferior points of the mitral annulus and a fifth point at the left atrium apex. The points determined to represent the pulmonary vein ostium or the left atrium appendix were removed from the measurement. All stored digital data were analyzed by a blind observer to calculate the following volumes: (i) left atrium maximum volume (LAVmax), at the end of systole, when the atrial volume was greatest just before the mitral valve opening; (ii) left atrium minimal volume (LAVmin), at the end of the diastole, when the atrial volume was lowest just before the mitral valve closure; (iii) before atrial contraction volume, the time corresponding to the P wave in electrocardiogram or the last frame before the mitral valve opens. The obtained LAVmax index (LAVI) was calculated by dividing the LAVmax by the body surface area. The volumes calculated with the following formulas were chosen as parameters of left atrial function and were calculated using three different RT3DE left atrium volumes according to previous studies:[13] (i) left atrium total emptying volume= LAVmax - LAVmin; (ii) left atrium total emptying fraction= (LAVmax - LAVmin)/LAVmax. ¥100; (iii) LAVI=left atrial volume/body surface area. The left ventricle volume was measured using an apical approach with transthoracic echocardiography. Full-volume 3D echocardiography method was performed. This approach has an important advantage over the 3D-guided biplane and the triplane methods by not relying on geometric modeling. The calculated volume was obtained by directly counting the voxels inside the endocardial surface.[14]

Right and left heart catheterization were performed by two experienced cardiologists without any sedation. 7F femoral sheaths were inserted to left and right femoral veins. Pig-tail catheter was used for both right and left heart pressure recordings. Simultaneous measurement of the systemic arterial and pulmonary artery pressure were marked. Pulmonary capillary wedge pressure was obtained by using a Swan-Ganz catheter (Swan-Ganz thermodilution catheter, 7F 110 cm; Edwards Lifesciences, Irvine, CA, USA) instead of a pig-tail catheter to avoid misinterpretations. The Fick method was used to obtain cardiac output using a direct measure of the oxygen uptake (mL/min). The pulmonary vascular resistance was calculated based on the following formula: (mean pulmonary artery pressure [mPAP]-pulmonary capillar wedge pressure [PCWP]/cardiac output [CO]). Pulmonary arterial hypertension was defined as a pulmonary arterial mean pressure >20 mmHg according to the current European Society of Cardiology guidelines.[15,16]

B-type natriuretic peptide and uric acid levels were used as neurohormonal markers in this study. B-type natriuretic peptide is highly related to clinical worsening, hospitalization, cardiovascular events, and death in patients with PAH.[9] Uric acid levels are also higher in patients who are worsening.[17] Blood samples were obtained from a forearm vein after a 12-h fast. A Cobas 8000 c502 (Roche Holding AG, Basel, Switzerland) analyzer was used to assess uric acid levels.

The main characteristics of patients were analyzed. A TAPSE <1.6 cm and an St <10 cm/sec were considered worse outcomes. Patients were divided into two groups with regard to TAPSE and St values and the requirement of hospitalization in the one-year period. The groups were compared in terms of clinical setting, echocardiographic findings, and neurohormonal parameters.

Statistical analysis
Data were analyzed with the IBM SPSS version 25.0 software (IBM Corp., Armonk, NY, USA). In this study, data were expressed as mean ± standard deviation (SD) for normally distributed variables and as median (25^th-75^th percentiles) for nonnormally distributed variables. Categorical variables were expressed as frequency and percentage. The Kolmogorov-Smirnov test was used to evaluate the normality of the data, kurtosis, and skewness. Parametric tests were used when the values of kurtosis and skewness were between ±2.0 in the data with a significance level <0.05 obtained from the Kolmogorov-Smirnov test, considering that the values did not deviate excessively from the normal distribution. To compare two independent groups, the independent sample t-test and the Mann-Whitney U test were used. The relationship between categorical variables was examined with the chi-square and Fisher exact tests. In the analysis of the effect of independent variables on the two-category dependent variable, the effect was examined with binary logistic regression analysis. A p-value <0.05 was considered statistically significant.

Table 1 Main characteristics of patients

Hospitalized patients had lower values in the 6-min walk test (332.80±135.46 vs. 449.75±73.49, p=0.01) compared to those who were not hospitalized. Furthermore, hospitalized patients had higher levels of BNP (145.85 [11.82;688.66] vs. 36.62 [8.76;880.88], p=0.02) compared to non-hospitalized patients. Regarding hemodynamic markers, hospitalized patients had higher right ventricular systolic pressures ([19.79±7.24] vs. [14.50±6.11], p=0.04) compared to non-hospitalized patients. Other hemodynamic, echocardiographic, and clinical characteristics were comparable.

The characteristics of patients with regard to hospitalization values are summarized in Table 2. The 6-min walk distance had a significant effect on predicting hospitalization (p<0.05; CI: 0.64-0.99). Considering the odds ratio, it was determined that the 6-min walk distance had a 0.96-fold effect in hospitalized patients compared to patients who were not hospitalized (Table 3).

Table 2 The main characteristics of patients

Table 3 Comparison of variables in terms of hospitalization

Regarding echocardiographic parameters, patients with low TAPSE values had lower St values as well (9.84±1.55 vs. 12.62±2.94, p=0.02). In addition, patients with lower TAPSE values had a lower left atrial endsystolic volume (15.98±7.40 vs. 25.48±12.31, p=0.01) and lower left atrial expansion index (58.88±42.1 vs. 142.14±73.38, p=0.01). The other echocardiographic parameters were comparable between the two groups. Regarding invasive parameters, only right atrial pressure was statistically higher in patients with lower TAPSE values (14.38±7.23 vs. 9.96±3.55, p=0.03).

There was no significant difference between the two groups in BNP and uric acid levels. The evaluation of patients in terms of TAPSE levels is summarized in Table 4.

Table 4 Comparison of variables in terms of TAPSE

Regarding echocardiographic parameters, patients with higher St values had increased TAPSE values (2.02±0.43 vs. 1.54±0.17, p=0.01). Patients with low St values had increased peak atrial strain conduit rate (–0.76 [–1.23;-0.50] vs. –1.09 [–3.19;-0.40], p=0.01). In addition, patients with lower TAPSE values had a lower left atrial expansion index (66.25±40.28 vs. 139.57±76.52, p=0.02). Left atrial ejection fraction was significantly lower in patients with lower St values (0.37±0.13 vs. 0.54±0.13, p=0.001). Other clinical, laboratory, and hemodynamic parameters were comparable in these groups. The comparison of patients in regard to St parameters is summarized in Table 5.

Table 5 Comparison of variables in terms of St

Pulmonary arterial hypertension is a significant and rare disease, characterized by right ventricular overload and dysfunction and these consequences can be clearly detected by transthoracic echocardiography. While right atrial and ventricular functions were altered in severe PAH, the function of the changes in left atrial and ventricular dynamics are not clear during disease course and progression. A recent trial showed that showed the impact of right ventricular volumes, ejection fraction, and free wall strain on disease progression.[8] Vitarelli et al.[18] demonstrated that right ventricular ejection fraction was lower in patients with precapillary and postcapillary PAH in their study on 73 patients. Left ventricular global strain is an important marker to detect early left ventricular systolic function in certain patient groups; however, left ventricular global strain was not found to be lowered in patients who were under dialysis treatment due to chronic renal failure.[19] Thus, the role of left systolic ventricular function in certain patient groups is crucial. As expected, it is recommended to monitor right ventricle end-systolic and end-diastolic volumes in patients with PAH, as these parameters can have additional impact on disease course.[20]

Neurohormonal parameters, namely NT BNP and BNP, are markers of disease progression. Since patients with high NT-BNP levels have worse outcomes, NT-BNP levels have become a treatment goal.[21] Levels of BNP are related to right ventricular fractional area change and ejection fraction.[9] Changes in right ventricle deformation characteristics are also associated with the World Health Organization functional class.[10]

In patients with PAH, not only right heart dynamics but also left atrial and ventricular volumes are affected. Strain changes may occur despite normal left ventricle ejection fraction, as well as flattening of the interventricular septum, which may contribute to global worsening of the left ventricle longitudinal strain, left ventricular stroke volume, and ejection fraction. However, the impact of change in the left heart on disease prognosis is not well-defined.

It is quite intelligible to detect alterations in right ventricular function in patients with a worse prognosis. On the other hand, the impact of left ventricular and atrial conditions on PAH is negligible unless it is not due to group 2 PAH. According to our data, patients with lower TAPSE values tended to have a lower left atrial systolic volume index as well as left atrial volume. In addition, the hospitalization rate was higher in patients with high BNP values. The 6-min walk test was demonstrated as a predictor of future worsening in this patient group.

There are some limitations to this study. The number of participants was limited on the grounds that pulmonary hypertension is a highly rare disease. In addition, due to the flattening of the interventricular septum in both systole and diastole, it is problematic to evaluate the left atrium and left ventricle. Patients with arrhythmia could not be included in this study. Finally, magnetic resonance imaging, a gold standard procedure to detect volumes in this patient group, was not applied due to cost and eligibility. Further trials are needed.

In conclusion, PAH patients with lower TAPSE values tended to have lower left atrial volume and left atrial volume index. The traditional parameters, such as BNP and 6-min walking test, were predictors of hospitalization in patients with PAH.

Ethics Committee Approval: The study protocol was approved by the Koşuyolu Yüksek İhtisas Training and Research Hospital Ethics Committee (date: 12.07.2013, no: 2013.3/4). The study was conducted in accordance with the principles of the Declaration of Helsinki.

Patient Consent for Publication: A written informed consent was obtained from each patient.

Data Sharing Statement: The data that support the findings of this study are available from the corresponding author upon reasonable request.

Author Contributions: Idea/concept, critical review: C.K., T.A.; Design: T.A., N.P.; Control/supervision: C.K.; Data collection and/or processing, analysis and/or interpretation: T.A., N.P.; Literature review, writing the article, references and fundings: T.A.; Materials: N.P., C.K.

Conflict of Interest: The authors declared no conflicts of interest with respect to the authorship and/or publication of this article.

Funding: The authors received no financial support for the research and/or authorship of this article.

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