Determinants of exercise intolerance in breast cancer patients prior to anthracycline chemotherapy

Women with early‐stage breast cancer have reduced peak exercise oxygen uptake (peak V O2). The purpose of this study was to evaluate peak V O2 and right (RV ) and left (LV ) ventricular function prior to adjuvant chemotherapy. Twenty‐nine early‐stage breast cancer patients (mean age: 48 years) and 10 age‐matched healthy women were studied. Participants performed an upright cycle exercise test with expired gas analysis to measure peak V O2. RV and LV volumes and function were measured at rest, submaximal and peak supine cycle exercise using cardiac magnetic resonance imaging. Peak V O2 was significantly lower in breast cancer patients versus controls (1.7 ± 0.4 vs. 2.3 ± 0.5 L/min, P = 0.0013; 25 ± 6 vs. 35 ± 6 mL/kg/min, P = 0.00009). No significant difference was found between groups for peak upright exercise heart rate (174 ± 13 vs. 169 ± 16 bpm, P = 0.39). Rest, submaximal and peak exercise RV and LV end‐diastolic and end‐systolic volume index, stroke index, and cardiac index were significantly lower in breast cancer patients versus controls (P < 0.05 for all). No significant difference was found between groups for rest and exercise RV and LV ejection fraction. Despite preserved RV and LV ejection fraction, the decreased peak V O2 in early‐stage breast cancer patients prior to adjuvant chemotherapy is due in part to decreased peak cardiac index secondary to reductions in RV and LV end‐diastolic volumes.