Cardiopulmonary Exercise Testing and Exercise Stress Echocardiography in Degenerative Mitral Regurgitation: An Exploratory Analysis of Functional and Left Ventricular Outcomes After Surgery

Background: Surgical correction of severe degenerative Mitral Regurgitation (DMR) is indicated in the presence of symptoms and signs of left ventricular (LV) dysfunction. However, conventional clinical and resting echocardiographic parameters may underestimate myocardial impairment. Cardiopulmonary exercise testing (CPET) and exercise stress echocardiography (ESE) may provide a more complete functional and haemodynamic assessment. Objectives: To characterize preoperative CPET and ESE findings in patients with severe DMR and to explore, in a hypothesis-generating analysis, their association with early functional and left ventricular outcomes after surgery. Methods: We included patients with severe DMR who underwent CPET and ESE before surgery. Functional improvement was defined as an improvement of at least one NYHA class from the preoperative baseline to early follow-up. LV function was evaluated as the continuous change in LVEF from discharge to early follow-up (Delta LVEF = follow-up LVEF − discharge LVEF). Baseline parameters were compared between patients who did and did not improve functionally. Random forest analyses were used only as an exploratory secondary analysis to assess whether baseline variables showed any non-linear signal of association with the outcomes and to document the instability of variable-importance rankings. Results and Conclusions: We included 60 patients, of whom 72% were in NYHA class II and all had preserved LV function. At CPET, rest and peak oxygen uptake were 6 +/− 1.5 and 17.2 +/− 5 mL/kg/min, respectively; the VE/VCO2 slope was 33 +/− 8.9 and the Oxygen Uptake Efficiency Slope was 1.6 (1.3–1.9). At ESE, LVOT-VTI increased from 18.3 +/− 3.9 cm at rest to 24.5 +/− 4.9 cm at peak; stroke volume from 51.0 (43.0–60.0) mL to 72.5 +/− 21.6 mL; and cardiac output from 3.8 (3.2–5.1) L/min to 9.0 +/− 3.2 L/min. No baseline clinical, CPET or ESE parameter significantly distinguished patients who improved functionally from those who did not, and early Delta LVEF was negligible. Random forest analyses did not discriminate above chance and variable-importance rankings were unstable. Patients with severe DMR and preserved LVEF showed objectively abnormal exercise responses despite mild symptoms, supporting the use of CPET and ESE for preoperative functional and haemodynamic characterization; larger prospective studies are required before any predictive or decision-support use can be proposed.