Altered Right Ventricular Kinetic Energy Work Density and Viscous Energy Dissipation in Patients with Pulmonary Arterial Hypertension: A Pilot Study Using 4D Flow MRI

<div><p>Introduction</p><p>Right ventricular (RV) function has increasingly being recognized as an important predictor for morbidity and mortality in patients with pulmonary arterial hypertension (PAH). The increased RV after-load increase RV work in PAH. We used time-resolved 3D phase contrast MRI (4D flow MRI) to derive RV kinetic energy (KE) work density and energy loss in the pulmonary artery (PA) to better characterize RV work in PAH patients.</p><p>Methods</p><p>4D flow and standard cardiac cine images were obtained in ten functional class I/II patients with PAH and nine healthy subjects. For each individual, we calculated the RV KE work density and the amount of viscous dissipation in the PA.</p><p>Results</p><p>PAH patients had alterations in flow patterns in both the RV and the PA compared to healthy subjects. PAH subjects had significantly higher RV KE work density than healthy subjects (94.7±33.7 mJ/mL vs. 61.7±14.8 mJ/mL, p = 0.007) as well as a much greater percent PA energy loss (21.1±6.4% vs. 2.2±1.3%, p = 0.0001) throughout the cardiac cycle. RV KE work density and percent PA energy loss had mild and moderate correlations with RV ejection fraction.</p><p>Conclusion</p><p>This study has quantified two kinetic energy metrics to assess RV function using 4D flow. RV KE work density and PA viscous energy loss not only distinguished healthy subjects from patients, but also provided distinction amongst PAH patients. These metrics hold promise as imaging markers for RV function.</p></div

RV KE density and percent viscous energy loss together separated the PAH subjects from the healthy controls.

<p>In addition, PAH patients within the same functional classes had a wide distribution.</p

Comparing viscous energy loss in healthy subjects and patients with pulmonary arterial hypertension.

<p>(A) The amount of viscous energy loss is higher in patients throughout the cardiac cycle. (B) The percent viscous energy loss is significantly greater in PAH patients than in healthy subjects (21.1±6.4% vs. 2.2±1.3%, p = 0.0001).</p

Comparison of kinetic energy density and viscous energy loss in PAH and healthy subjects.

<p>A. Healthy subjects showed significantly lower RV KE density than PAH patients (61.7±14.8 mJ/mL vs. 94.7±33.7 mJ/mL, p = 0.007). Linear regression of RV KE density against RVEF for both populations gives result: y = -1.47x + 152.00, R² = 0.11. B. Healthy subjects showed significantly lower percent viscous energy loss than PAH patients (2.2±1.3% vs. 21.1±6.4%, p = 0.0001). Linear regression of percent viscous energy loss against RVEF for both populations gives result: y = -1.05x + 63.82, R² = 0.41.</p

Subject RV Functional Characteristics.

<p>Abbreviations: BSA = body surface area. RVEDV = right ventricular end-diastolic volume. RVEDVI = right ventricular end-diastolic volume indexed to BSA. RVESV = right ventricular end-systolic volume. RVSV = right ventricular stroke volume. RVEF = right ventricular ejection fraction. RVM = right ventricular mass. RVMI = right ventricular mass indexed to BSA.</p><p>Subject RV Functional Characteristics.</p

PAH subject clinical characteristics and RV function.

<p>Abbreviations: ERA = Endothelin receptor antagonists. PDE-5 = Phosphodiesterase Type 5 inhibitor. CCB = Calcium channel blocker. PGI₂ = prostacyclin. All medications are taken in the usual dosing schedule. PAH09 was not on pulmonary hypertension specific medication due to chronic thromboembolic pulmonary hypertension before surgery.</p><p>PAH subject clinical characteristics and RV function.</p

Comparison of the in flow kinetic energy and outflow kinetic energy in healthy subjects and PAH subjects.

<p>(A). Normalized KE_in through the tricupsid valve. (B). Normalized KE_out through the pulmonic valve.</p