Objective assessment
CPET: Pre-operative CPET was conducted using an electromagnetically braked cycle ergometer (Lode, Gronigen, The Netherlands) and a Medgraphics Ultima metabolic cart (MedGraphicsTM, Gloucester, UK) as previously outlined by our group7, 12, 13. Briefly, calibration was undertaken in accordance with the manufacturer’s guidelines using a 3-L volume syringe (Hans Rudolph, Kansas City, USA) and reference calibration gases. During data collection, the middle five of seven breaths were averaged. An exercise protocol was employed requiring patients to cycle at 60 revolutions per minute for three minutes in an unloaded freewheeling state followed by a progressively ramped period of exercise (5 to 15 W/min based on mass, stature, age, and sex) to volitional or symptom limited termination, followed by three minutes recovery14. Medgraphics BreezeTMsoftware automatically determined peak oxygen uptake ( O2PEAK) (defined as the highest O2 during the final 30 seconds of exercise reported), the slope of the relationship between pulmonary ventilation and carbon dioxide output ( E/ CO2) and oxygen uptake efficiency slope (OUES). Pulmonary oxygen uptake at the anaerobic threshold ( O2-AT) was manually interpreted by an experienced clinician using the V-slope method15, supported by E/ CO2-AT, and E/ O2-AT.
Risk classification: Each patient was classified with a O2-AT below (<) or above (>) 11mL O2/kg/min) based on the seminal works of Weber and Janicki16 and Older et al.17 We further differentiated between low, intermediate and high risk according to the following criteria:Low risk : O2-AT ≥11 mL/kg/min;Intermediate risk : One of: O2-AT 8-10.9 mL/kg/min, E/ CO2-AT >34, history of ischaemic heart disease (IHD); High risk : O2-AT <8 mL/kg/min or ≥two of: E/ CO2-AT >34, O2-AT <11 mL/kg/min, history of IHD.