Chronic thromboembolic disease (CTED) is suboptimally defined by a mean\ud pulmonary artery pressure (mPAP)\ud <\ud 25 mmHg at rest in patients that remain\ud symptomatic from chronic pulmonary artery thrombi. To improve identifica-\ud tion of right ventricular (RV) pathology in patients with thromboembolic\ud obstruction, we hypothesized that the RV ventriculo-arterial (Ees/Ea) coupling\ud ratio at maximal stroke work (Ees/Ea\ud max sw\ud ) derived from an animal model of\ud pulmonary obstruction may be used to identify occult RV dysfunction (low\ud Ees/Ea) or residual RV energetic reserve (high Ees/Ea). Eighteen open chested\ud pigs had conductance catheter RV pressure-volume (PV)-loops recorded dur-\ud ing PA snare to determine Ees/Ea\ud max sw\ud . This was then applied to 10 patients\ud with chronic thromboembolic pulmonary hypertension (CTEPH) and ten\ud patients with CTED, also assessed by RV conductance catheter and cardiopul-\ud monary exercise testing. All patients were then restratified by Ees/Ea. The ani-\ud mal model determined an Ees/Ea\ud max sw\ud =\ud 0.68\ud �\ud 0.23 threshold, either side of\ud which cardiac output and RV stroke work fell. Two patients with CTED were\ud identified with an Ees/Ea well below 0.68 suggesting occult RV dysfunction\ud whilst three patients with CTEPH demonstrated Ees/Ea\ud ≥\ud 0.68 suggesting\ud residual RV energetic reserve. Ees/Ea\ud >\ud 0.68 and Ees/Ea\ud <\ud 0.68 subgroups\ud demonstrated constant RV stroke work but lower stroke volume (87.7\ud �\ud 22.1\ud vs. 60.1\ud �\ud 16.3 mL respectively,\ud P\ud =\ud 0.006) and higher end-systolic pressure\ud (36.7\ud �\ud 11.6 vs. 68.1\ud �\ud 16.7 mmHg respectively,\ud P\ud <\ud 0.001). Lower Ees/Ea in\ud CTED also correlated with reduced exercise ventilatory efficiency. Low Ees/Ea\ud aligns with features of RV maladaptation in CTED both at rest and on exer-\ud cise. Characterization of Ees/Ea in CTED may allow for better identification\ud of occult RV dysfunctio
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