Background
The study was designed to compare RV morphological and functional parameters derived from conventional and myocardial deformation echocardiography in two instances of right heart pressure overload: pulmonary arterial hypertension (PAH) and pulmonary stenosis (PS).
Methods
Sixty-two individuals were included: 22 patients with pulmonary arterial hypertension (PAH), 19 patients with PS and 21 healthy individuals who served as a control group. All patients had clinical evaluation with 6-minute walking test, standard and two-dimensional strain echocardiography and B-type natriuretic peptide evaluation.
Results
At similar levels of pressure overload (RV systolic pressure, 88.2 ± 31.5 vs 73.4 ± 34.9 mm Hg; P = NS) the right ventricles of patients with PS were less dilated (RV end-diastolic diameter, 31.7 ± 3.7 vs 43.7 ± 10.5 mm; P < .001) and performed significantly better than those of patients with PAH (RV strain, −27.4 ± 5.8% vs 16.2 ± 7.9%; RV fractional area change, 51.1 ± 9.2% vs 29.1 ± 11.3%; P < .001). Although some of the RV functional parameters were comparable with those in healthy individuals, strain rate showed lower values, suggesting subclinical longitudinal dysfunction in patients with PS. Myocardial stress biomarkers were correlated with RV systolic pressure only in patients with PAH ( r = 0.64, P = .03), not in those with PS ( r = 0.22, P = .50).
Conclusions
At similar levels of pressure overload, the right ventricle is less dilated and performs better in patients with PS compared with those with PAH.
In recent years, evidence has accumulated that the right ventricle plays an important prognostic role in various cardiovascular pathologies. With its complex anatomy and heterogenous pattern of contraction, the assessment of the right ventricle is difficult and often requires the combination of data from several parameters and imaging techniques. Echocardiography is the main clinical tool for assessing right ventricular (RV) anatomy and function. Various indices of RV performance have been described and validated. In particular, echocardiographic deformation imaging has been shown to reliably describe global and regional RV function in normal and pathologic conditions.
Normally working in a low-impedance system after birth, the right ventricle has only limited reserves to adapt to chronic increase in afterload. RV function plays an important role in establishing longevity for patients with pulmonary artery hypertension (PAH), the classic condition leading to RV afterload increase. In the long run, the progressive dilation of the right ventricle will result in decreased systolic performance and reduced cardiac output, which will ultimately result in RV failure and death. The molecular mechanisms underlying this maladaptive response in PAH are not fully understood but appear to be related to dysfunctional cardiomyocytes, decreased angiogenesis, and fibrosis. Even though this model of adaptation was described in pressure overload associated with PAH, some reports suggest that in other situations, the right ventricle may have a different pattern of remodeling that will result in maintained systolic performance.
Congenital pulmonary stenosis (PS) accounts for 6% to 10% of all cardiac malformations. In this condition, the resistance to ejection is located proximal to the ventricle. Although RV pressures can exceed systemic pressures, maintained cardiac output and a better survival profile in patients with PS compared with other forms of RV pressure overload have been reported.
In the present study, we hypothesized that the different outcomes in the two conditions are related to differences in RV morphologic and functional adaptation in face of pressure overload.
Methods
Study Population
We analyzed data from 62 individuals: 22 patients with PAH, 19 patients with PS, and 21 healthy individuals who served as a control group. Patients with PAH were enrolled consecutively after the diagnosis of PAH was reached at our institution. Of the 22 patients with PAH, 16 had idiopathic PAH and six patients had PAH related to connective tissue disease (scleroderma). The etiologic diagnosis of PAH was reached using the stepwise approach suggested by the recent European Society of Cardiology guidelines, idiopathic PAH being a diagnosis of exclusion. Other etiologies of PAH were excluded to increase the homogeneity of our study group. All patients in the PS group had congenital valvular stenosis with negligible infundibular component. They were included consecutively when the diagnosis of PS was established at our clinic during the study period or were identified from our hospital’s database and informed about our study. Patients with PS and significant infundibular component ( n = 5) and patients with other congenital defects ( n = 1 [atrial septal defect]) were excluded. The control group consisted of healthy individuals with no histories of heart disease, diabetes, or hypertension; normal results on clinical examination; normal results on electrocardiography; and normal echocardiographic findings. Patients and controls were of similar ages and sex distribution.
All patients provided informed consent to take part in this study, on the basis of a protocol approved by the local ethics committee.
Clinical Evaluation
The functional capacity was quantified in patients using the 6-min walk test. The test was performed in an indoor 50-m corridor, according to current recommendations. All patients were informed in a standardized manner of the method of the test before it was performed. The 6-min walk test was not performed in the control group.
Echocardiography
Transthoracic echocardiography was performed using commercially available scanners (Vivid 7 and Vivid i; GE Vingmed Ultrasound AS, Horten, Norway) and a 2.5-MHz broadband transducer. The conventional echocardiographic examination was followed by the acquisition of Doppler tissue imaging data sets (for velocity measurements). Standard echocardiographic views used for two-dimensional strain analysis were obtained using second-harmonic imaging, with frequency, depth, and sector width adjusted for frame-rate optimization (between 60 and 100 frames/sec). For strain and strain rate (SR) analysis of the RV free wall and interventricular septum, an apical four-chamber view was acquired, ensuring that the RV free wall and interventricular septum had an optimal delineation that would allow a proper tracking. All acquired images were stored digitally for later offline analysis using dedicated software (EchoPAC BT08; GE Vingmed Ultrasound AS). All parameters were averaged over three consecutive beats.
Hemodynamic Assessment
In patients with PAH and controls, RV systolic pressure (RVSP) was estimated from peak tricuspid regurgitant velocity, taken as the maximal value measured using several views and estimates of right atrial pressure. Right atrial pressure was estimated on the basis of the diameter of the inferior vena cava and its change with inspiration (using cutoffs of 17 mm and 50% change with inspiration). In the PS group, RVSP was approximated as the peak pressure gradient between the right ventricle and the pulmonary artery measured with continuous-wave Doppler in the parasternal short-axis view at the base of the heart. Because the patients included in our study had no distal PS, we considered the patients with PS to have normal pulmonary pressures, approximated at a value of 20 mm Hg. The severity of tricuspid regurgitation was assessed qualitatively using color Doppler imaging of the tricuspid regurgitation jet and graded as mild, moderate, or severe.
Parameters of Cardiac Morphology
RV and left ventricular (LV) dimensions (RV end-diastolic diameter [RVEDD], RV end-diastolic and end-systolic areas, RV outflow tract end-diastolic diameter, RV outflow tract end-systolic diameter, and LV eccentricity index) were measured according to American Society of Echocardiography and European Association of Echocardiography recommendations. RV free wall thickness was measured at end-diastole from the subcostal four-chamber view.
Parameters of Cardiac Function
RV longitudinal function was quantified using tricuspid annular plane systolic excursion (TAPSE) and peak systolic pulsewave velocity of the tricuspid ring (S′t) at the level of the lateral RV wall.
A parameter of global function, RV fractional area change (RVFAC), was computed from the apical four-chamber view as follows:
RVFAC ( % ) = RV end – diastolic area − RV end – systolic area RV end – diastolic area × 100.
RV outflow tract fractional shortening ( % ) = RV end – diastolic diameter − RV end – systolic diameter RV end – diastolic diameter × 100.
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