Predictors of Impaired Exercise Performance in Patients Qualified for Cardiac Rehabilitation: The Impact of Sex and Comorbidities

<b>Background/Objectives:</b> Exercise capacity and patient prognosis are heavily influenced by comorbidities. However, the specific impact of individual comorbid conditions on objective measures of exercise performance remains insufficiently characterized. The study aimed to identify predictors of reduced physical capacity in patients qualified for cardiac rehabilitation. <b>Methods:</b> A single-center retrospective analysis was conducted on 518 patients qualified for cardiac rehabilitation. After excluding 51 post-cardiac surgery patients, cardiopulmonary exercise testing data from 425 patients (316 men, median age 63 years) were analyzed. Comorbidities data, peak oxygen uptake (peak VO₂), and the ventilation-to-carbon dioxide output slope (VE/VCO₂ slope) were evaluated. <b>Results:</b> A significantly reduced exercise capacity (peak VO₂ < 70% of the predicted value) was observed in 29.4% of patients, while an increased VE/VCO₂ slope (≥36) was noted in 20.8% of patients. Univariate logistic regression identified sex, heart failure, valvular disease, peripheral artery disease, diabetes mellitus (T2DM), chronic kidney disease (CKD), Charlson Comorbidity Index (CCI), left ventricular ejection fraction <50%, diastolic dysfunction, and anemia as predictors of both reduced peak VO₂ and a steeper VE/VCO₂ slope. Multivariate regression analysis further identified T2DM and CKD as independent predictors of reduced peak VO₂, while sex, CKD, and CCI were independent predictors of a steeper VE/VCO₂ slope. <b>Conclusions:</b> Among patients qualified for cardiac rehabilitation, patient's sex, T2DM, CKD, and the CCI emerged as key predictors of reduced exercise capacity. Reduced peak VO₂ was more commonly observed in men, while women more frequently exhibited a steeper VE/VCO₂ slope, indicating potential sex-related physiological mechanisms influencing exercise performance.