Right Ventricular End-Diastolic Wall Stress: Does It Impact on Right Atrial Size, and Does It Differ in Right Ventricular Pressure vs Volume Loading Conditions?

Right Ventricular Diastolic Performance in Patients With Chronic Thromboembolic Pulmonary Hypertension Assessed by Echocardiography

Background: There have been no systemic studies about right heart filling pressure and right ventricular (RV) distensibility in patients with chronic thromboembolic pulmonary hypertension (CTEPH). Therefore, we aimed to explore combinations of echocardiographic indices to assess the stages of RV diastolic dysfunction.

Methods and Results: We recruited 32 healthy volunteers and 71 patients with CTEPH. All participants underwent echocardiography, cardiac catheterization (in patients with CTEPH), and a 6-min walk test (6MWT). The right atrial (RA) end-systolic area was adjusted for body surface area (BSA) (indexed RA area). RV global longitudinal diastolic strain rates (SRs) and RV ejection fraction (EF) were measured by speckle tracking and three-dimensional echocardiography (3D echo), respectively. All 71 patients with CTEPH underwent pulmonary endarterectomy. Of the 71 patients, 52 (73%) had decreased RV systolic function; 12 (16.9%), 26 (36.6%), and 33 (46.5%) patients had normal RV diastolic pattern, abnormal relaxation (stage 1), and pseudo-normal patterns (stage 2), respectively. The receiver operating characteristic curve analysis showed that the optimal cut-off values of early diastolic SR <0.8 s⁻¹ and indexed RA area > 8.8 cm²/BSA had the best accuracy in identifying patients with RV diastolic dysfunction, with 87% sensitivity and 82% specificity. During a mean follow-up of 25.2 months after pulmonary endarterectomy, the preoperative indexed RA area was shown as an independent risk factor of the decreased 6MWT distance.

Conclusions: Measuring early diastolic SR and indexed RA area would be useful in stratifying RV diastolic function.

The clinical significance and prognostic value of right ventricular wall tension in moderate or severe tricuspid regurgitation

Background: We aim to explore the determinants of right ventricular wall tension (RV WT [RV base-to-apex length multiplied by systolic pulmonary artery pressure] and association with all-cause mortality in patients with moderate-to-severe tricuspid regurgitation. Materials & methods: Of total, 180 patients (71 ± 15years, 54% females) were included. An increased RV WT was defined as >3300 mmHgxmm. Results: Patients with increased RV WT (n = 85, 47%) were more likely to be male and taller than patients with normal RV WT. In a multivariable-adjusted model, increased RV WT was associated with a 2.6-fold higher risk of all-cause mortality (HR: 2.59, 95% CI: 1.65-4.06). Conclusion: In patients with significant tricuspid regurgitation, an increased RV WT was common, and associated with a 2.6-fold higher risk of all-cause mortality. Male sex was the only independent determinant.

Early return of reflected waves increases right ventricular wall stress in chronic thromboembolic pulmonary hypertension

Pulmonary vascular resistance (PVR) and compliance are comparable in proximal and distal chronic thromboembolic pulmonary hypertension (CTEPH). However, proximal CTEPH is associated with inferior right ventricular (RV) adaptation. Early wave reflection in proximal CTEPH may be responsible for altered RV function. The aims of the study are as follows: 1) to investigate whether reflected pressure returns sooner in proximal than in distal CTEPH and 2) to elucidate whether the timing of reflected pressure is related to RV dimensions, ejection fraction (RVEF), hypertrophy, and wall stress. Right heart catheterization and cardiac MRI were performed in 17 patients with proximal CTEPH and 17 patients with distal CTEPH. In addition to the determination of PVR, compliance, and characteristic impedance, wave separation analysis was performed to determine the magnitude and timing of the peak reflected pressure (as %systole). Findings were related to RV dimensions and time-resolved RV wall stress. Proximal CTEPH was characterized by higher RV volumes, mass, and wall stress, and lower RVEF. While PVR, compliance, and characteristic impedance were similar, proximal CTEPH was related to an earlier return of reflected pressure than distal CTEPH (proximal 53 ± 8% vs. distal 63 ± 15%, P < 0.05). The magnitude of the reflected pressure waves did not differ. RV volumes, RVEF, RV mass, and wall stress were all related to the timing of peak reflected pressure. Poor RV function in patients with proximal CTEPH is related to an early return of reflected pressure wave. PVR, compliance, and characteristic impedance do not explain the differences in RV function between proximal and distal CTEPH.NEW & NOTEWORTHY In chronic thromboembolic pulmonary hypertension (CTEPH), proximal localization of vessel obstructions is associated with poor right ventricular (RV) function compared with distal localization, though pulmonary vascular resistance, vascular compliance, characteristic impedance, and the magnitude of wave reflection are similar. In proximal CTEPH, the RV is exposed to an earlier return of the reflected wave. Early wave reflection may increase RV wall stress and compromise RV function.

Relation between right ventricular wall stress, fibrosis, and function in right ventricular pressure loading

Right ventricle (RV) pressure loading can lead to RV fibrosis and dysfunction. We previously found increased RV, septal hinge-point and left ventricle (LV) fibrosis in experimental RV pressure loading. However, the relation of RV wall stress to biventricular fibrosis and dysfunction is incompletely defined. Rabbits underwent progressive pulmonary artery banding (PAB) over 3 wk with hemodynamics, echocardiography, and myocardial samples obtained at a terminal experiment at 6 wk. An additional group received PAB and treatment with an endothelin receptor antagonist. The endocardial and epicardial borders of short-axis echo images were traced and analyzed with invasive pressures to yield regional end-diastolic (ED) and end-systolic (ES) wall stress. To increase clinical translation, computer model-derived wall stress was compared with Laplace wall stress. The relation of wall stress with fibrosis (picrosirius red staining) and ventricular function was analyzed. ED wall stress in all regions and RV and LV free-wall ES wall stress were increased in PAB rabbits versus sham animals. Laplace wall stress correlated well with computational models. In PAB, fibrosis was highest in the RV free wall, then septal hinge regions, and lowest in the septum and LV free wall. Fibrosis was moderately related to ED (r = 0.47, P = 0.0011), but not ES wall stress. RV ED wall stress was strongly related to echo indexes of function (strain rate: r = 0.71, P = 0.048; E', r = -0.75, P = 0.0077; tricuspid annular plane systolic excursion: r = 0.85, P = 0.0038) and RV fractional area change (r = 0.77, P = 0.027). ED, more than ES, wall stress is related moderately to fibrosis and strongly to function in experimental RV pressure loading, especially at the septal hinge-point regions, where fibrosis is prominent. This suggests that wall stress partially links RV pressure loading, fibrosis, and dysfunction and may be useful to follow clinically.NEW & NOTEWORTHY Biventricular fibrosis and dysfunction impact outcomes in RV pressure loading, but their relation to wall stress is poorly defined. Using a pulmonary artery band rabbit model, we entered echocardiography and catheter data into a computer model to yield regional end-diastolic (EDWS) and end-systolic (ESWS) wall stress. EDWS, more than ESWS, correlated with fibrosis and dysfunction, especially at the fibrosis-intense septal hinge-point regions. Thus, wall stress may be clinically useful in linking RV pressure loading to regional fibrosis and dysfunction.

Biomechanical and Hemodynamic Measures of Right Ventricular Diastolic Function: Translating Tissue Biomechanics to Clinical Relevance

Background

Right ventricular (RV) diastolic function has been associated with outcomes for patients with pulmonary hypertension; however, the relationship between biomechanics and hemodynamics in the right ventricle has not been studied.

Methods and Results

Rat models of RV pressure overload were obtained via pulmonary artery banding (PAB; control, n=7; PAB, n=5). At 3 weeks after banding, RV hemodynamics were measured using a conductance catheter. Biaxial mechanical properties of the RV free wall myocardium were obtained to extrapolate longitudinal and circumferential elastic modulus in low and high strain regions (E₁ and E₂, respectively). Hemodynamic analysis revealed significantly increased end‐diastolic elastance (E_ed) in PAB (control: 55.1 mm Hg/mL [interquartile range: 44.7–85.4 mm Hg/mL]; PAB: 146.6 mm Hg/mL [interquartile range: 105.8–155.0 mm Hg/mL]; P=0.010). Longitudinal E₁ was increased in PAB (control: 7.2 kPa [interquartile range: 6.7–18.1 kPa]; PAB: 34.2 kPa [interquartile range: 18.1–44.6 kPa]; P=0.018), whereas there were no significant changes in longitudinal E₂ or circumferential E₁ and E₂. Last, wall stress was calculated from hemodynamic data by modeling the right ventricle as a sphere: stress=Pressure×radius2×thickness.

Conclusions

RV pressure overload in PAB rats resulted in an increase in diastolic myocardial stiffness reflected both hemodynamically, by an increase in E_ed, and biomechanically, by an increase in longitudinal E₁. Modest increases in tissue biomechanical stiffness are associated with large increases in E_ed. Hemodynamic measurements of RV diastolic function can be used to predict biomechanical changes in the myocardium.

The right atrium, a forgotten cardiac chamber: An updated review of multimodality imaging

Despite several limitations, two-dimensional echocardiography (2DE) is the standard method for assessing the right atrium (RA) in everyday clinical routine. Cardiac magnetic resonance remains the current "gold standard" for RA visualization and volume quantification. The development of 2DE-derived strain imaging has enabled assessing RA deformation and phasic function in various pathologic conditions. Three-dimensional echocardiography was demonstrated to be more accurate and reproducible than 2DE for cardiac chamber quantification, while also allowing the evaluation of RA phasic function without geometric assumption. The purpose of this review is to summarize currently available data about RA anatomy, phasic function, and mechanics acquired by different imaging modalities.