Regional Right Ventricular Wall Stress and Thickness in Pulmonary Hypertension

Background: Right ventricular (RV) dysfunction in pulmonary hypertension (PH), characterized by chamber dilation and hypertrophy, is theorized to result from increased wall stress (σ). We characterized regional RV σ from ECG-gated multislice computed tomography (MSCT) using ellipsoidal modeling in PH patients with compensated (PH-C) and decompensated (PH-D) RV function. Methods: A total of 18 patients (age 51 ± 11, 8 males, mean pulmonary artery pressure [MPAP] range 13-79 mmHg) underwent right heart catheterization and ECG-gated MSCT of the chest. Patients were divided into 3 groups: Normal (MPAP≤25 mmHg), PH-C (MPAP>25 mmHg and right atrial pressure [RAP]<10 mmHg) and PH-D (MPAP>25 mmHg and RAP≥10 mmHg). CT images were analyzed in both short axis and modified four-chamber views, and best-fit ellipses were determined. Wall thickness (h), measured from the CT images, was applied to formulas derived from Laplace's law and simple force-balance considerations, yielding radial RV σ at the free wall, inferior wall, and infundibulum. Results: Regional σ (table 1), as calculated by the ellipsoid model, was highest in the mid-RV free wall. There was a significant difference in h between normal (N=5) and PH-D patients (N=7; p<0.01). However, there was no difference between normal and PH-C subjects (N=6; p>0.01). Although h was not significantly different between normal and PH-C patients, the end-systolic σ was different between these groups in all regions (p<0.05). Both h and σ were significantly increased in the PH-D group vs. normal (p<0.01). Conclusion: In PH, regional RV σ increases even without changes in h, indicating that it may be a stimulus for hypertrophy. Thus, elevated regional σ without a change in h should be explored as a marker of progressive RV failure and an indication for aggressive treatment.Table 1Patient data in end-systoleNormalPH-CPH-DN567RVP(mm Hg)29.4 ± 2.358 ± 23.391.1 ± 19.1Infudibulumh(mm)5.4 ± 0.65.5 ± 0.88.2 ± 2.7∗σ(kPa)11.7 ± 4.030.3 ± 9.1∗44.3 ± 17.3∗Free Wallh(mm)4.5 ± 1.05.8 ± 2.48.6 ± 3.3∗σ(kPa)20.3 ± 6.440.0 ± 22.8∗55.7 ± 22.9∗Inferior Wallh(mm)4.4 ± 1.34.4 ± 1.17.4 ± 1.3∗σ(kPa)14.3 ± 4.633.2 ± 14.0∗40.8 ± 9.3∗Mean values±SD are shown. ∗P<0.05 compared with Normal. N, subjects; RVP, right ventricular pressure. Open table in a new tab Mean values±SD are shown. ∗P<0.05 compared with Normal. N, subjects; RVP, right ventricular pressure.